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New Single Source Precursors for MOCVD of Tungsten Carbonitride Thin Films

Permanent Link: http://ufdc.ufl.edu/UFE0022115/00001

Material Information

Title: New Single Source Precursors for MOCVD of Tungsten Carbonitride Thin Films
Physical Description: 1 online resource (130 p.)
Language: english
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2008

Subjects

Subjects / Keywords: amidinate, barrier, carbonitride, circuits, crystallography, diffusion, films, guanidinato, hydride, imido, integrated, kinetics, metal, mocvd, nmr, thin, tungsten
Chemistry -- Dissertations, Academic -- UF
Genre: Chemistry thesis, Ph.D.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Tungsten carbonitride (WN_x_C_y_) thin films were produced from the single-source precursors Cl_4_(L)W(NCH_2_CH=CH_2_) (L = PhCN or MeCN). The compound Cl_4_(NCMe)W(NCH_2_CH=CH_2_) was characterized by ^1^H and ^13^C NMR spectroscopy, and X-ray crystallography. Mass spectrometry was performed to determine possible fragmentation pathways of the precursors. Deposited films were characterized by X-ray diffraction and Auger electron spectroscopy. This allowed for comparison of the film growth properties to those using the previous precursors (Cl_4_(L)W(NR), R = ^i^Pr or Ph). Comparison of the three precursors provided a strong correlation between the imido N?C bond dissociation energy and the activation energy of film deposition. MOCVD growth of tungsten nitride (WN_x_) and WN_x_C_y_ thin films has been reported from the complex Cl_4_(CH_3_CN)W(N^i^Pr). NMR kinetics of acetonitrile exchange in solution verified that dissociation of the acetonitrile ligand should be facile for the family of precursors Cl_4_(CH_3_CN)W(NR), R = ^i^Pr, CH_2_CH=CH_2_, or Ph in the temperature range used for film growth ( > 450 ?C). These data are compared to computational studies of the compounds. A solution of the tungsten imido guanidinato complex W(N^i^Pr)Cl_3_^i^PrNC(NMe_2_)N^i^Pr in benzonitrile was used to deposit WN_x_C_y_ thin films by chemical vapor deposition (CVD) in the temperature range 400 to 750 ?C. The resulting films were composed of tungsten, nitrogen, carbon and oxygen as determined by Auger electron spectroscopy (AES). X-ray photoelectron spectroscopy (XPS) results indicated that no chlorine impurity was present in the film. The properties of thin films deposited were compared to those from the isopropyl imido complex, Cl_4_(RCN)W(N^i^Pr) (2a, R = CH_3_, 2b, R = Ph), to provide insight into the effect of imido and guanidinato ligands on film properties. New WN_x_C_y_ precursors incorporating imido, guanidinato, and hydride moieties were synthesized. Compounds were characterized by ^1^H and ^13^C NMR spectroscopy, X-ray crystallography, mass spectrometry, and thermogravimetric analysis (TGA). The characterization data were used to predict possible fragmentation pathways in film deposition. Variable temperature NMR studies were done on bridging hydride complexes to demonstrate fluxionality of hydrogens.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Thesis: Thesis (Ph.D.)--University of Florida, 2008.
Local: Adviser: McElwee-White, Lisa A.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2010-05-31

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2008
System ID: UFE0022115:00001

Permanent Link: http://ufdc.ufl.edu/UFE0022115/00001

Material Information

Title: New Single Source Precursors for MOCVD of Tungsten Carbonitride Thin Films
Physical Description: 1 online resource (130 p.)
Language: english
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2008

Subjects

Subjects / Keywords: amidinate, barrier, carbonitride, circuits, crystallography, diffusion, films, guanidinato, hydride, imido, integrated, kinetics, metal, mocvd, nmr, thin, tungsten
Chemistry -- Dissertations, Academic -- UF
Genre: Chemistry thesis, Ph.D.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Tungsten carbonitride (WN_x_C_y_) thin films were produced from the single-source precursors Cl_4_(L)W(NCH_2_CH=CH_2_) (L = PhCN or MeCN). The compound Cl_4_(NCMe)W(NCH_2_CH=CH_2_) was characterized by ^1^H and ^13^C NMR spectroscopy, and X-ray crystallography. Mass spectrometry was performed to determine possible fragmentation pathways of the precursors. Deposited films were characterized by X-ray diffraction and Auger electron spectroscopy. This allowed for comparison of the film growth properties to those using the previous precursors (Cl_4_(L)W(NR), R = ^i^Pr or Ph). Comparison of the three precursors provided a strong correlation between the imido N?C bond dissociation energy and the activation energy of film deposition. MOCVD growth of tungsten nitride (WN_x_) and WN_x_C_y_ thin films has been reported from the complex Cl_4_(CH_3_CN)W(N^i^Pr). NMR kinetics of acetonitrile exchange in solution verified that dissociation of the acetonitrile ligand should be facile for the family of precursors Cl_4_(CH_3_CN)W(NR), R = ^i^Pr, CH_2_CH=CH_2_, or Ph in the temperature range used for film growth ( > 450 ?C). These data are compared to computational studies of the compounds. A solution of the tungsten imido guanidinato complex W(N^i^Pr)Cl_3_^i^PrNC(NMe_2_)N^i^Pr in benzonitrile was used to deposit WN_x_C_y_ thin films by chemical vapor deposition (CVD) in the temperature range 400 to 750 ?C. The resulting films were composed of tungsten, nitrogen, carbon and oxygen as determined by Auger electron spectroscopy (AES). X-ray photoelectron spectroscopy (XPS) results indicated that no chlorine impurity was present in the film. The properties of thin films deposited were compared to those from the isopropyl imido complex, Cl_4_(RCN)W(N^i^Pr) (2a, R = CH_3_, 2b, R = Ph), to provide insight into the effect of imido and guanidinato ligands on film properties. New WN_x_C_y_ precursors incorporating imido, guanidinato, and hydride moieties were synthesized. Compounds were characterized by ^1^H and ^13^C NMR spectroscopy, X-ray crystallography, mass spectrometry, and thermogravimetric analysis (TGA). The characterization data were used to predict possible fragmentation pathways in film deposition. Variable temperature NMR studies were done on bridging hydride complexes to demonstrate fluxionality of hydrogens.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Thesis: Thesis (Ph.D.)--University of Florida, 2008.
Local: Adviser: McElwee-White, Lisa A.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2010-05-31

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2008
System ID: UFE0022115:00001


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1 NEW SINGLE SOURCE PRECURSORS FOR MOCVD OF TUNGSTEN CARBONITRIDE THIN FILMS By LAUREL LEIGH REITFORT A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2008

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2 To my mom and dad

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3 ACKNOWLEDGMENTS First, I thank m y advisor, Professor Lisa McEl wee-White. She is always an inspiration and has been a pleasure to work for. Her patience, support and encouragement have meant so much to me and will never be forgotten. I would also like to thank Dr. Khalil Abboud. He has been a wonderful mentor and support system during my graduate studies. There are not enough words to thank my parents and family for all of their love, support, patience, and understanding. For this I will ever be grateful. I also acknowledge Ahmet Baysal, Delmy Diaz, Ewa Hughes, Karen Lyle, Shannon Skoog, Ece Unur, and Marie Correia for their love, friendship, and never ending encouragement. I thank Dr. Sylvia Montesinos, Dr. Barbara Welsch, and Dr. Beree Darby for the countless conversations and time they put forth to help me endure graduate school. The McElwee-White group members, present and past, have been a pleasure to work with and learn from. I also thank Professor Joe Te mpleton and Dr. Jeff Cross for introducing me to research and encouraging me to pursue graduate school.

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4 TABLE OF CONTENTS page ACKNOWLEDGMENTS...............................................................................................................3LIST OF TABLES................................................................................................................. ..........7LIST OF FIGURES.........................................................................................................................9ABSTRACT...................................................................................................................................11 CHAP TER 1 INTRODUCTION..................................................................................................................13Thin Films..................................................................................................................... ..........13Thin Film Deposition Techniques.......................................................................................... 13Physical Vapor Deposition..............................................................................................13Chemical Vapor Deposition............................................................................................ 14Film Characterization.......................................................................................................... ...16X-ray Diffraction (XRD)................................................................................................. 16X-Ray Photoelectron Spectroscopy (XPS) a nd Auger Electron Spectroscopy (AES).... 16Four Point Probe.............................................................................................................. 17Use of Thin Films in Microelectronics................................................................................... 19Materials Used in Microelectronics................................................................................. 19Interconnect metal.................................................................................................... 19Interlayer dielectrics (ILD).......................................................................................20Diffusion barriers.....................................................................................................21Metal Nitride Precursor Design....................................................................................... 23Co-reactant precursors.............................................................................................. 24Amido/imido precursors........................................................................................... 25Azolate precursors.................................................................................................... 28Guanidinate and amidinate precursors..................................................................... 28Hydrazido precursors...............................................................................................29Precursor Screening................................................................................................................302 SYNTHESIS AND CHARACTERIZATION OF Cl4(RCN)W(NCH2CH=CH2) (R = Me or Ph) AS A PRECURSOR FOR MOCVD OF WNXCY.......................................................31Metal Imido Compounds........................................................................................................ 31Synthesis of the W(VI) Allylimido Precursor........................................................................ 32Characterization of 3a .............................................................................................................33X-ray Crystallographic Study of Cl4(CH3CN)W(NCH2CH=CH2) (3a)..........................33Mass Spectrometry.......................................................................................................... 36Film Growth....................................................................................................................38Film Composition............................................................................................................ 39X-ray diffraction....................................................................................................... 39

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5 Auger electron spectroscopy....................................................................................42Effect of the Imido N-C BDE on Film Growth...................................................................... 44Conclusions.............................................................................................................................47Experimental Procedure......................................................................................................... .47General (Precursor Synthesis)......................................................................................... 47Synthesis of WOCl4.................................................................................................48Synthesis of Cl4(CH3CN)W(NCH2CH=CH2) (3a)..................................................48Mass Spectrometry.......................................................................................................... 49Crystallographic Structur al Determination of 3a ............................................................49Film Growth Studies........................................................................................................ 503 EXPERIMENTAL AND COMPUTATIONAL COMPARISON OF PRECURSOR DECOMPOSITION ................................................................................................................52CVD Precursor Decomposition Pathways..............................................................................52NMR Line Shape Analysis.....................................................................................................52Dissociation of Acetonitrile in Cl4W(NiPr)(NCCH3).............................................................53Loss of Chlorine During Deposition....................................................................................... 55Dissociation of the W-N(imido) and N(imido)-C Bonds in 1a3a .........................................57Conclusions.............................................................................................................................60Experimental Procedure for NMR Kine tics of Acetonitrile Exchange in 2 ...........................614 SYNTHESIS, CHARACTERIZATION, AND FILM DEP OSITION OF AN ISOPROPYL GUANIDINATO MOCVD PRECURSOR..................................................... 62Metal Guanidinate Compounds..............................................................................................62Use of Guanidinates in Thin Film Deposition........................................................................ 63Results and Discussion......................................................................................................... ..63Precursor Synthesis......................................................................................................... 63Precursor Screening.........................................................................................................66Thermogravimetric analysis..................................................................................... 66Mass spectrometry.................................................................................................... 68Film Deposition from 4 ...................................................................................................70Film growth.............................................................................................................. 70Film comp osition......................................................................................................70XRD of films............................................................................................................ 72Film growth rate (X-SEM).......................................................................................73Film resi stivity.......................................................................................................... 74Diffusion barrier testing...........................................................................................75Conclusions..............................................................................................................77Experimental Procedure......................................................................................................... .78General Procedure........................................................................................................... 78Synthesis of W(NiPr)Cl3[iPrNC(NMe2)NiPr] ( 4).....................................................78Crystallographic Struct ure Determination of 4...............................................................79Mass Spectrometry.......................................................................................................... 80Thermogravimetric Analysis........................................................................................... 80Film Growth Studies........................................................................................................ 80

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6 5 SYNTHESIS OF TUNGSTEN IMIDO GUANIDINATO HYDRIDE COMPLEXES ......... 82Transition Metal Hydrides...................................................................................................... 82Synthesis and Characterization of Tran sition Metal Hydride MOCVD Precursors............... 82Synthesis..........................................................................................................................82Characterization...............................................................................................................83NMR spectroscopy...................................................................................................83X-ray crystallography...............................................................................................86Thermogravimetric analysis..................................................................................... 88Mass spectrometry data............................................................................................ 90Conclusion..............................................................................................................................91Experimental Procedures........................................................................................................ 92General Procedures.......................................................................................................... 92Synthesis of {W2(NiPr)2[iPrNC(NMe2)NiPr]2(H2)(-H)2} ( 5)................................. 92Synthesis of {W2(NCy)2[iPrNC(NMe2)NiPr]2(H2)(-H)2} ( 6)................................ 93Synthesis of {W2(NPh)2[iPrNC(NMe2)NiPr]2(H2)(-H)2} ( 7)................................. 93X-ray Crystallography.....................................................................................................94Mass Spectrometry.......................................................................................................... 95Thermogravimetric Analysis........................................................................................... 95 APPENDIX A CRYSTALLOGRAPHY DATA FOR 3a ..............................................................................96B KINETICS DATA FOR 1 ......................................................................................................99C STRUCTURAL CHARACTERIZATION FOR 5 ...............................................................100LIST OF REFERENCES.............................................................................................................117BIOGRAPHICAL SKETCH.......................................................................................................130

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7 LIST OF TABLES Table page 2-1 Crystal data and st ructure refinement for Cl4(CH3CN)W(NCH2CH=CH2) (3a).................. 352-2 Selected bond distances () and angles (degrees) for Cl4(CH3CN)W(NCH2CH=CH2) ( 3a )....................................................................................................................................362-3 Summary of relative abundances for posi tive ion EI and negative ion NCI mass spectra of tungsten imido complexes Cl4(CH3CN)W(NCH2CH=CH2) (3a)................................ 372-4 Comparison of deposition behavior for 1a,b-3a,b ................................................................453-1 Calculated bond lengths () and bond angles ( ) for complexes 1-3 ....................................583-2 Calculated bond dissociation enth alpy for the N1-C and W-N1 bonds in 1a-3a and 1a 3a ......................................................................................................................................594-1 Crystal data and st ructure refinement for 4...........................................................................644-2 Selected bond distances () and angles () for compound 4 .................................................664-3 Molar flow rates of r eactants in the CVD reactor.................................................................. 805-1 Selected bond distances () and angles () for compound 5.................................................88A-1 Atomic coordinates ( x 10 4 ) and equivalent isotropi c displacement parameters ( 2 x 10 3 ) for 3a.........................................................................................................................96A-2 Bond lengths [] and angles [] for 3a...............................................................................97A-3 Anisotropic displacement parameters ( 2 x 10 3 ) for 3a. ..................................................98A-4 Hydrogen coordinates ( x 10 4 ) and isotropic displacement parameters ( 2 x 10 3 ) for 3a.......................................................................................................................................98B-1 Rates for the acetonitr ile exchange of complex 1. ................................................................99C-1 Crystal data and structure refinement for 5.........................................................................101C-2 Atomic coordinates ( x 10 4 ) and equivalent isotropi c displacement parameters ( 2 x 10 3 ) for 5..........................................................................................................................102C-4 Anisotropic displacement parameters ( 2 x 10 3 ) for 5.....................................................113

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8 C-5 Hydrogen coordinates ( x 10 4 ) and isotropic displacement parameters ( 2x 10 3 ) for 5 ........................................................................................................................................114

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9 LIST OF FIGURES Figure page 1-1 Electronic transitions involved in XPS and AES..................................................................171-2 Four point probe....................................................................................................................181-4 Device layers in an integrated circuit................................................................................... .201-5 Early precursors for TiNx deposition developed by Gordon and co-workers....................... 262-1 Bonding in metal imido complexes....................................................................................... 322-2 Synthesis of tungsten imido precursors................................................................................. 332-3 Thermal ellipsoids diagram of the molecular structure of Cl4(CH3CN)W(NCH2CH=CH2) (3a). .............................................................................. 342-4 Schematic diagram of CVD system.161,162.............................................................................392-5 XRD spectra for films grown with 3a,b on Si (100) in a H2 atmosphere............................. 412-6 Change in XRD pattern with deposition temperature for films grown from 3a,b on Si (100) in a H2 atmosphere................................................................................................... 422-7 Comparison of W, N, C and O content in the films grown from 1a,b, 2a,b and 3a,b Data are from AES measuremen ts after 2.0 minutes sputter............................................. 442-8 Variation of apparent activation energy (Ea) for film growth from Cl4(R'CN)W(NR) ( 1a,b R = iPr; 2a,b R = Ph; 3a,b R = allyl) with the N C bond energies of the corresponding amines R-NH2 as models for the imido N-C bonds. ................................. 463-1 Effect of exchange rates on NMR line shapes.......................................................................533-2 Complexes 1-3 .......................................................................................................................583-3 Comparison of nitrogen conten t in the films grown from 1-3 (AES)...................................604-1 Resonance forms of the guanidinate anion............................................................................ 624-2 Thermal ellipsoids diagram of the molecular structure of 4..................................................654-3 TGA curves of compound 4 ..................................................................................................684-4 PCI mass spectra of compound 4..........................................................................................694-5 Composition of films deposited from 4 and 1 on Si (100) substrate at different deposition tem perature as determined by AES after 0.5 min of sputtering.......................71

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10 4-6 XRD patterns for films deposited on Si (100) substrate from 4. ............................................724-7 X-SEM images for films grown from 4 .................................................................................744-8 Arrhenius plot of log of fi lm growth rate vs. inverse temperature for deposition from 1 and 4 on a Si(100) substrate............................................................................................... 744-9 Change in film resistivity with depositi on temperature for films grown on Si (100) from 4 and 1a,b ..................................................................................................................754-10 AES depth profiles of Cu (100 nm)/ WNxCy (50 nm)/Si (100) stack for WNxCy film deposited at 450 C and anneal ed in vacuum for 30 min.................................................. 765-1 Synthesis of tungsten imi do/guanidinato/hydride complexes 57.........................................835-2 1H NMR spectrum of 5 in THFd8.........................................................................................855-3 Thermal ellipsoid diagram of the molecular structure of 5 .................................................875-4 TGA data for 5. Weight % and Derivative (Weight %) vs. Temperature............................ 895-5 Comparison of TGA data for complexes 4 and 5..................................................................905-6 PCI mass spectrum of compound 5.......................................................................................91C-1 Heteronuclear Multiple Bond Coheren ce (gHMBC) NMR spectru m of Hydride Dimer 5 ........................................................................................................................................100

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11 Abstract of Dissertation Pres ented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy NEW SINGLE SOURCE PRECURSORS FOR MOCVD OF TUNGSTEN CARBONITRIDE THIN FILMS By Laurel L. Reitfort May 2008 Chair: Lisa McElwee-White Major: Chemistry Tungsten carbonitride (WNxCy) thin films were produced from the single-source precursors Cl4(L)W(NCH2CH=CH2) (L = PhCN or MeCN). The compound Cl4(NCMe)W(NCH2CH=CH2) was characterized by 1H and 13C NMR spectroscopy, and X-ray crystallography. Mass spectrometry was perfor med to determine possible fragmentation pathways of the precursors. Deposited films were characterized by X-ray diffraction and Auger electron spectroscopy. This allowed for comparison of the film growth pr operties to those using the previous precursors (Cl4(L)W(NR), R = iPr or Ph). Comparison of the three precursors provided a strong correlation between the imido N C bond dissociation energy and the activation energy of film deposition. MOCVD growth of tungsten nitride (WNx) and WNxCy thin films has been reported from the complex Cl4(CH3CN)W(N iPr). NMR kinetics of acetonitrile exchange in solution verified that dissociation of the acetoni trile ligand should be facile for the family of precursors [Cl4(CH3CN)W(NR), R = iPr, CH2CH=CH2, or Ph] in the temperature range used for film growth (>450 C). These data are compared to computational studies of the compounds. A solution of the tungsten im ido guanidinato complex W(NiPr)Cl3[iPrNC(NMe2)NiPr] in benzonitrile was used to deposit WNxCy thin films by chemical vapor deposition (CVD) in the

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12 temperature range 400 to 750 C. The resulting films were composed of tungsten, nitrogen, carbon and oxygen as determined by Auger electron spectroscopy (AES). X-ray photoelectron spectroscopy (XPS) results indica ted that no chlorine impurity wa s present in the film. The properties of thin films deposited were compar ed to those from the isopropyl imido complex, Cl4(RCN)W(NiPr) (R= CH3, Ph), to provide insight into th e effect of imido and guanidinato ligands on film properties. New WNxCy precursors incorporating imido, guanidinato, and hydride moieties were synthesized. Compounds were characterized by 1H and 13C NMR spectroscopy, X-ray crystallography, mass spectrometry, and th ermogravimetric analysis (TGA). The characterization data were used to predict possible fragmentation pathways in film deposition. Variable temperature NMR studi es were done on bridging hydr ide complexes to demonstrate fluxionality of hydrogens.

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13 CHAPTER 1 INTRODUCTION Thin Films Thin films are deposited layers with high surface to volume ratio, which vary from the bulk material of the substrate on which they lie. They typically vary in thickness from a few atomic layers to several micrometers. Thin film deposition is used in a wide variety of applications, including semiconductor devices, indu strial coatings, flat panel displays, disk drives, and inks. The growth in this area of scie nce has lead to an increase in the development of new thin film deposition and processing techniques. In addition to new thin film technologies, development of new materials is a rapidly growing area of research.1,2 Thin Film Deposition Techniques Physical Vapor Deposition Physical vapor deposition (PVD) is a film de position process where atoms or molecules of a material are vaporized from a solid or liqui d source, transported through a vacuum or low pressure gaseous environment, and condensed on a substrate. In PVD the source material does not undergo a chemical reaction to form the film only a phase change. Methods of PVD include vacuum deposition or vacuum evaporation, sputter deposition, and ion plating. In vacuum deposition the source is vaporized by boiling or sublimation, tr ansported, and condensed to a solid film on the substrate surface. Ion plating involves ionizing the material to be deposited and applying an electric field to accelerate the im pingement energy on the substrate, modifying the deposition process and the properties of the deposite d film. The source material can be deposited using various methods such as evaporation, sputtering, or other vaporization sources.2 The most widely utilized method of PVD is sputter deposition. In this method thin films are formed when atoms or molecules are physically ejected fr om a source by energetic particle bombardment,

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14 leading to the ejected atoms or molecules conde nsing on a substrate as a thin film. Some advantages to sputter deposition include easily controllable film thickness, compatibility with most inorganic materials, less hazardous by-pro ducts, and utilization in large scale deposition applications. PVD also has disadvantages such as line-of-sight deposition leading to poor conformality in small device features, low rates of deposition, and introduction of impurities into the substrate.2-5 Chemical Vapor Deposition Chem ical vapor deposition (CVD) is the form ation of a film on a surface from a volatile precursor (vapor or gas), as a consequence of one or more chemical reactions. The precursor can break down by thermal decomposition in order to deposit the desired film. This form of deposition can be useful in a va riety of applications including electronics, optoelectronics, and optical and protective coatings. The advantages of CVD include the ability to uniformly coat complex components, high purity and variety of chemical compositions of deposited films, relatively high deposition rates, and potential selective area deposition.6 A number of chemical reactions can o ccur under CVD conditions including thermal decomposition, oxidation, reduction, hydrolysis, carbidization and ammonol ysis. In thermal decomposition a precursor breaks down into its el ements and uses only one precursor gas. A reduction reaction occurs when the desired elemen t gains one or more el ectrons and lowers its oxidation state. This reaction is used in reduc tion of metal halides to deposit pure metals; coreduction reactions where more than one element is reduced to deposit binary materials; as well as use of metals such as zinc, cadmium, magne sium, sodium, and potassium as reducing agents for metal halides. Oxidation and hydrolysis reactions are used in CVD for metal oxide deposition. In these reactions O2, CO2, or O3 is used as an oxygen source along with a metal halide. Carbidization and ammonolysis allow fo r deposition of metal carbides and nitrides.

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15 Typical precursors for these reactions again u tilize metal halides and either hydrocarbons or ammonia respectively. In th e ammonolysis reactions N2 and H2 can be used in place of ammonia. CVD has the capability of synthesizing simple to complex materials with ease at low temperatures.7 There are several variations of CVD such as metal-or ganic CVD (MOCVD), plasmaenhanced CVD (PECVD), low pressure CVD (L PCVD), and aerosol as sisted CVD (AACVD). MOCVD incorporates the use of an organomet allic precursor, PECVD utilizes plasma to enhance decomposition and reaction, and in LPC VD the reaction chamber is below atmospheric pressure. To avoid the necessity of using a hi ghly volatile precursor AACVD can be used. In this method of deposition a liquid or dissolved solid precursor is transported to the substrate as an aerosol generated by a nebuli zer. Another variation of CV D is Atomic Layer Deposition (ALD). ALD is a surface cont rolled reaction process that wo rks by subsequent, self-limiting surface reactions to attain cont rolled atomic-level deposition. A growth cycle in ALD proceeds in the following manner: 1. Introduction of the first precursor that will react with the surface until all reac tive sites are consumed. This step involves chemisor ption of the precursor or formation of relatively strong chemical bonds. 2. Purge of the reaction chambe r with a nonreactive gas to re move excess of the first precursor. The physisorbed molecules, which have weak van der Waals interactions, are removed. 3. Introduction of the second precursor which r eacts with the initia l deposited layer. 4. A final purge of the reaction chamber.8 Due to the cyclic nature of this process, control of film thickness is extremely accurate. Also, since the introduction of precursors is separate, gas phase reactions are avoided. Some other advantages to ALD include ease of scale-up, good conformality, and reproducibility.3,4,7,9

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16 Film Characterization Characterization of deposited film s is an important aspect of thin film deposition. It allows for quantitative analysis of the composition, th ickness, and performance. Some common thin film characterization techniques include X-ray diffraction (XRD) for structure determination; Auger electron spectrosc opy (AES) and X-ray photoelectron spectroscopy (XPS) to determine elemental composition, impurities, and chemical states; and four point probe to determine resistance. X-ray Diffraction (XRD) XRD utilize s an incident beam of X-rays focused on a sample; the atomic planes of a crystal cause the beam of X-rays to interfere as they exit the crys tal. The beam is diffracted by the crystalline phases acc ording to Braggs law: = 2d sin (where = wavelength of X-rays, d is the spacing between planes in the atomic lattice, and is the angle between the incident ra y and the scattering planes). Diffraction occurs only when the conditions of Braggs Law are sati sfied. From the diffraction patte rn the crystalline phases can be identified and structural propert ies of the film can be measured.10 X-Ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectro scopy (AES) XPS and AES are both based on the photoelectric effect. The photoelectric effect is when incident light causes the emission or ejection of electrons from a surface of a metal. In XPS a sample is irradiated with X-ray photons and if of sufficient energy, electrons are emitted from the inner-shell orbitals of the sample. The kinetic energy of the ejected photoelectrons is measured and allows direct identification of the elements present in the thin film by calculating the binding energy with the following equation: KE = h BE

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17 (where KE is the kinetic energy of emitted photoelectron, h is the X-ray photon energy, BE is the binding energy of the ejected photoelectron, and is the spectrophotometer work function). Small variations in the kinetic energy of the ej ected photoelectrons also allow determination of the chemical state of the elem ents present in the sample.4 Once a photoelectron has been emitted, an outer shell electron can fill the vacant site. In order to maintain an energy bala nce, a photon (or Auger electron) can be expelled from an outer shell. In AES the kinetic energy of the Auger electron is measured in a similar manner to XPS. Information gathered from AES can allow dete rmination of the elemental composition and the chemistry of the surfaces of samples. Figure 1-1 illustrates the diffe rence between XPS and AES.4,10 Figure 1-1. Electronic transitions involved in XPS and AES. Four Point Probe The four point probe is used to determ ine th e sheet resistivity and bulk resistance of thin films. In this technique four thin collinear tungsten wires are us ed to contact a sample. Current is applied through the two outer probes, and the voltage between the two inner probes is measured (Figure 1-2). When the probes are pla ced with equivalent spacing then the following equation is applicable:

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18 (where is resistivity, s is the distance between each probe, t is the thickness of the thin film, V is the voltage measured, and I is the current flowing through the two outer probes). These equations give the bulk resistivity. Figure 1-2. Four point probe. To determine the sheet resistance of a thin f ilm the latter of the two equations would be used and both sides would be divided by t giving the following equation: The sheet resistance is the preferred measurement for thin films since it disregards the geometry of the material and is purely a repr esentation of the deposited material.4,10

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19 Use of Thin Films in Microelectronics Gordon Moore, co-founder of In tel corporation, m ade the pr ediction on April 19, 1965 that component density and performance of inte grated circuits would double every year.11 Ten years later, in 1975, Moore gave a speech at the In ternational Electron Devices Meeting where he revised this prediction to doubling every two years.12 In order to compensate for extreme downsizing of electronic devices, ne w materials are being investigated to increase signal speed and provide more diverse functions. Thin films play an important role in integrated circuits as interlayer dielectric material (ILD), diffusion barriers, metal interconnects and semiconductors. Materials Used in Microelectronics Many m aterials can be used for the various device layers in multi-layered structures of integrated circuits. New materials are constantly being developed and rese arched to improve the ever changing technologies. Some of these ma terials include metal oxi des, transition metal nitrides and carbides, and pure transition metal thin films. Interconnect metal A m ajor development in this field is the re placement of aluminum by copper in integrated circuits.1,13 The use of copper metallization has allo wed for a decrease in interconnect size due to its lower resistivity an d higher melting point (1.7-2.0 -cm, 1084 C) compared to aluminum (2.7-3.0 -cm, 660 C).5 While copper metallization allows for greater performance and reliability, it also introduces several challenges for integra tion purposes, such as limited processing methods, high diffusivity in to silicon, and low adhesion to SiO2. A solution to the latter two challenges is the use of a diffusion ba rrier layer that will prevent the diffusion of the copper into the silicon and promote adhesion of copper (Figure 1-4).

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20 Figure 1-4. Device layers in an integrated circuit. a) Without diffusion barrier, b) With diffusion barrier Interlayer dielectrics (ILD) Lowdielectrics are used to elect rically insulate conducting me tal lines. Requirements of this material include a low dielectric constant (or low, where is a reference value for silicon dioxide, SiO2 of 3.9 eV); good adhesion to silicon, metals and silicides; thermal stability; and lack of moisture and metallic impurities. Another role that the ILD material must play is either as a getter or a barrier to mobile ions such as Na+. Due to the widespread use of copper as the metallization material of choice, finding a compatible lowdielectric material to lower the signal delay in a device is of great importanc e. Lowering the density of the ILD films by introducing pores helps to greatly reduce the dielectr ic constant of these films. The main types of ILD materials are silsesquioxa ne (SSQ) based, silica based, organic polymers, and amorphous carbon.4,5,14,15 Highdielectric materials are used in metaloxide-semiconductor field effect transistor (MOSFET) as gate dielectrics. In the past SiO2 was used due to the thermodynamically stable

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21 Si-SiO2 interface; it also has good electrical insulation and interfacial bonding properties. However, as the thickness of this layer continues to decrease the SiO2 will be unable to act as an insulator. Electrical current will leak acro ss the dielectric material and the capacitor will discharge. In order to circumvent th is problem, new materials with a highvalue are being investigated to replace SiO2. Important properties of a replacement material include permittivity, thermodynamic stability, film morphology, interface quality, compatibility with current or new materials used in devices and their processi ng, and reliability. Other oxides such as ZrO2, HfO2, and La2O3 are being considered for this appl ication. These materials have high values (between 25-30 eV) and high Eg (band gap) values (4.3-5.8 eV) co mpared to the values of SiO2 where = 3.9 eV and Eg = 8.9 eV. The main focus for the replacement of SiO2 is on Hf-based dielectrics such as HfO2 and HfSiO4.14,16,17 Diffusion barriers A m aterial must meet several requirements to be considered for use in a diffusion barrier layer. The material should prevent diffusion of copper into silicon, ha ve low resistivity, and allow for low temperature deposition to prevent damage to previously deposited device layers (Figure 1-4). Transition metal nitrides such as TiNx,18-22 TaNx,18,19,23-26 and WNx 27-34 have been used extensively as barrier materials.35 In the past, TiNx has been used as a diffusion barrier for aluminum.1,36 This poses a problem when it comes to diffusion barrier applications with copper metallization. TiNx has a columnar type structure, a llowing for ease of copper diffusion along the grain boundaries into the silicon layer.37-39 Another issue that is presented with the use of TiNx barriers and copper is the diffusivity of copper in TiN.38 Tantalum nitride has been shown to provide a good barrier, but has some general problems. There are several phases of tantalum nitride including Ta2N, TaN, Ta5N6, Ta4N5, and Ta3N5.40 In CVD the nitrogen source is usually either NH3 or N2, which is used in excess. Due

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22 to the excess nitrogen atmosphere the favored phases are those rich in nitrogen (TaN and Ta3N5). While resistivities of most of the TaxNy phases range from 100 cm to 800 cm; Ta3N5 has a resistivity of 6 cm, an attribute ideal for an insu lator instead of a diffusion barrier.40,41 Most depositions obtaining TaxNy films ideal for diffusion barr ier applications require high temperatures, leading to damage to previously deposited device layers. However, deposition at the lower temperatures results in Ta3N5 films. In order to avoid deposition of Ta3N5 a strong reducing agent is required to obtain the Ta+3 oxidation state.42 Another issue with tantalum nitride is the low adherence to coppe r, making a Ta/TaN bilayer necessary.1 Typically tantalum nitride is deposited by sputtering, resu lting in amorphous and conductive films.43 As mentioned previously, the line-of-sight deposition leads to unsatisfactory coverage of detailed device features. Some tantalum nitr ide films have been deposited using CVD giving more conformal films, but resulting in films with higher resistance.44 Tungsten nitride films have also demonstrated excellent growth and barrier characteristics. 45-48 Advantages of this material incl ude migration of nitrogen to the grain boundaries preventing diffusion of c opper, increased adhesion to copper, and facile chemical mechanical polishing after deposition. As WNx was being studied as a suitable diffusion barrier material, it was discovered that WNxCy, with resistivities of about 350 cm, could be deposited by ALD and the precursor system of WF6, NH3, and triethyl boron at temperatures as low as 350 C.46,47,49-52 This was an important discove ry because while thin films of WNx have been deposited at low temperatures, usually the resistivity is higher at the lower deposition temperatures.53 Therefore, WNxCy is a good candidate as a ternar y material for diffusion barrier applications.

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23 Metal Nitride Precursor Design A useful precursor for C VD must possess a few characteristics such as a low vapor pressure in order to be transferred to the substr ate, facile decomposition at low temperatures, and should not be reactive in the gas phase.54 There are two types of pr ecursor systems that can be used in CVD: a co-reactant precursor system and a single source precursor. A co-reactant precursor system consists of multiple precursors each containing one element of the desired film. A single source precursor incorporates multiple elements of the desired film in one compound. Use of organometallic compounds for single so urce precursors has become a popular choice. These precursors can be synthesized to possess desi red characteristics such as increased volatility and clean decomposition pathways. Some ligands of interest for use in organometallic precursors include amides,55,56 imides,57 azolates,58,59 amidinates,60 and guanidinates.61-66 Each of these ligands has a specific advantage; all take advantage of direct metal nitrogen bonds. This is especially implicit with imides, which possess a strong M-N double bond. Azolates, a nitrogen analogue to the highly utilized cycl opentadienyl (Cp) ligand, were us ed in an effort to increase volatility of the compounds. Amidinates and guanidinates are used to enhance thermal stability of the precursors while the R groups increase vol atility. Use of organometallic precursors also allows for compounds with predetermined stoichio metries to be assembled prior to deposition. While synthesis of organometallic compounds is a well established field, precursor design forces one to examine possible decomposition pathways of the designed molecule. Previously co-reactant systems were utilized for deposition of metal nitride thin films. Precursors such as metal halides and metal carbonyls along with NH3 or N2 were the systems of choice. As deposition chemistry has evolved, us e of single source metalorganic precursors has developed into a major area of research.

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24 Co-reactant precursors Exam ples of co-reactant precursor systems used to deposit metal nitride or metal carbonitride thin films are shown in the list below. WCl6 + NH3 67,68 W(CO)6 + NH3 68-71 WF6 + NH3 29,72-75 WF6 + N2 + H2 76-79 WF6 + NH3 + Et3B46,47,49-52 TaCl5 + N2 + H2 + Ar25,40 Initial attempts at deposition of WNx using the WF6/NH3 precursor system produced WF6 4NH3 and never deposited the desired fi lm even at high temperatures.29 In attempts at lowering the activation energy, H2 gas was added to this system to react with fluorine from WF6, producing an activated intermediate, which would in turn react with NH3. While incorporation of the H2 gas allowed for successful deposition of tungsten nitr ide, it was necessary to closely monitor the molar ratios of the precursors. If too much hydrogen was used then WF6 was reduced too quickly and pure tungsten metal film s were produced. However, if too little hydrogen was used deposition of WNx films was very slow. Another issue with the WF6 + NH3 precursor system is the production of HF as a byproduc t. HF can react with NH3 to form the solid byproducts, NH4F and/or NH4HF, providing a source of unwan ted particles in the deposited films as well as etching the silicon substrate.29 In order to avoid issues that arose with the WF6 + NH3 system, several groups began looking at the N2/ H2/WF6 precursor system.76-79 The N2 gas was used as a source of nitrogen, while the H2 gas was used as a method to remove fluorine from WF6. These deposition methods utilized PECVD systems in attempts at lowering the deposition temperatures. While thin films

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25 of WNx can be deposited by this method, residual fluorine in the films could cause issues with a device. Tsai and co-workers showed that most of the residual fluorine can be removed using rapid thermal annealing (RTA).76 While this provides a mean s of producing thin films of WNx the high temperature required durin g RTA could damage previously de posited layers in a device. Amido/imido precursors Developm ent of organometallic precursors for metal nitride deposition began as an effort to circumvent problems associated with the meta l halide co-reactant precursor systems. Early organometallic precursors for deposition of metal nitride thin films utilized homoleptic alkyl amide metal complexes, Ti(NR2)4 (R = alkyl or aryl).56,80-85 Sugiyama and co-workers first used Ti(NR2)4 (R = Me, Et) with N2, H2, or Ar atmosphere to investigate metal nitride deposition in 1975.80 While these precursors deposited TiNx, the films also contained carbon and oxygen contamination. In 1990, Gordon and co-workers re investigated the use of these precursors to deposit TiNx films. Not only did they ta ke a second look at the Ti(NR2)4 (R = Me, Et) precursors, they developed a new set of precursor s for comparison (Figure 1-5). Films deposited from the precursors with dialkylamido ligands contained carbon contam ination that was both organic and Ti-bound in nature, while films deposited with cy clic amido ligands contained exclusively organic carbon. Th is finding led implied that in the dialkylamido precursors hydrogen activation leads the decomposition pathwa y; while in the cyclic amido precursors, homolytic Ti-N bond cleavage gives way to decomposition.82,84 Also investigated was deposition of TaNx using Ta(NMe2)5 26 and ammonia. Films deposited from this precursor system were the nitrogen-rich dielectric, Ta3N5. Several studies have claimed to use Ta(NEt2)5 as a precursor for TaNx films.43,80,86 However, it has been shown that Ta(NEt2)5 is not stable at moderate te mperatures and decomposes into Ta(EtNCHCH3)(NEt2)3 and (Et2N)3Ta=NEt.87 Most likely the repor ts of deposition with

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26 Ta(NEt2)5, described results from using a mixture of Ta(EtNCHCH3)(NEt2)3 and (Et2N) 3Ta=NEt to deposit TaNx. Nonetheless, this mixture ha s been successful at depositing TaNx thin films.23,88 The films deposited from this system showed evidence of Ta3N5, and had high carbon contamination. Taking advantage of the imido bond in (Et2N) 3Ta=NEt, Chiu and co-workers developed the precursor (Et2N) 3Ta=NtBu.89 Development of the more stable tBu analogue takes advantage of the strong imido bond strength and he lps to eliminate lack of reproducibility from the previous mixture. TaNx thin films were deposited from (Et2N) 3Ta=NtBu at temperatures ranging from 450 C to 650 C, with resistivities as low as 920 cm at 650 C. Films deposited at 600 C had low carbon and oxygen contamination. Figure 1-5. Early precursors for TiNx deposition developed by Gordon and co-workers.82 Continuing to take advantage of the str ong metal-nitrogen imido bond strength, several WNx precursors were developed.90-92 Chiu and co-workers did ex tensive deposition studies using the precursor bis( tert-butylimido)bis( tert -butylamido)tungsten.53,90,93-95 Taking into

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27 consideration the high car bon content resulting from -hydrogen decomposition pathways in the dialkylamido complexes, the ligands in this precursor were chosen to elim inate this option. Films with resistivities of 620-8000 cm were grown at deposition temperatures ranging from 450 to 650 C.53 Volatile by-products were identified as isobutylene (Me2C=CH2) and MeCN, when using argon; and under hydrogen carrier gas tBuNH2, NH3, and HCN were also detected. Gas evolution was evident, although unidentifiable. H2, N2, and methane are all possible gases that could be released from the system. Possible decomposition pathways le ading to these products include -H activation yielding isobutylene and -methyl eliminations leading to MeCN and methane generation. Under H2 conditions a methyl group could be stripped from acetonitrile, then react with surface hydrogen to form HCN. The remaining -NH2 and =NH groups from isobutylene elimination could react with surface hydrogen to generate NH3, N2, and H2. Due to these decomposition pathways a significant amount of carbon is left in the deposited films.90,94 Similar studies were also performed with a molybdenum analogue of this precursor.96 Other precursors investigated in this family include W(NtBu)2(NEt2)2 and W(NtBu)2(NMe2)2.91,92,97,98 In the W(NtBu)2(NEt2)2 precursor, an extra species was detected in thermal decomposition studies. -Hydrogen elimination of the diethylamido group leads to formation of EtN=CHMe, an inaccessible pathway in the -NHtBu analogue.91,98 These studies gave great insight to the chemistry involved in organometalli c precursor decomposition. Another class of imido precursors is Cl4W(NR)(NCR) (R = iPr, Ph or CH2CH=CH2; R = Me or Ph).33,57,99 This series of studies demonstrated deposition of WNxCy thin films and illustrated a strong correlation between the bond dissociation energy of the N-C bond of the imido ligand and the activation energy for deposition.57 This will be discussed in more detail in later chapters.

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28 In a similar fashion several tit anium imido precursors, [TiCl2(NR)(L)n] (R = alkyl or aryl group and L = various N bound ligands) have been synthesized.100 Of these precursors, [TiCl2(NtBu)(py)3] seemed to be the best single source precursor. Comparison of films from [TiCl2(NR)(L)n] showed that the presence of bulky imido substituents and chelating ligands allowed for high oxygen and carbon cont ent in the films. Taking a dvantage of an all nitrogen coordination sphere, TiNx films were deposited using precursors of [Ti(NMe2)2(N3)2]n and [Ti(NMe2)2(N3)2(py)2].101 The silyl imido complexes [NbCl3(NSiMe2Ph)(NH2SiMe2Ph)]2 and [TaCl3(NSiMe3)(NC5H3Me2-3,5)2]2 were also successful precur sors for deposition of niobium and tantalum nitride thin films respectively.102 Analysis of the films showed little to no silicon, carbon, or chlorine contamination, indi cating that the elimination of R3SiCl is a facile process. Azolate precursors The -diketonate and cyclopentadienyl (Cp) ligan ds are prevalent in MOCVD precursors.103-109 It has been shown that early transition metal complexes with 2-pyrazolate ligands have similar structural and chemical characteristics to metal-diketonate and Cp complexes.110,111 The structural and chemical similaritie s, along with elimination of oxygen from the ligand, make metal azolate compounds interes ting as MOCVD precursors. Winter and coworkers have synthesized pyrazolato, triazolato, and tetrazolato as single source precursors.112-119 The structural and thermal properties of these compounds have been investigated, but few have been used for actual film deposition. Some of the precursors synthesized include Mo(NtBu)2(tBu2pz)2, W(NtBu)2(tBu2pz)2, Ti(tBu2pz)3(PhCN4) and Nb(tBu2pz)3(PhCN4)2, which appear to have optimal volat ility and thermal stability n ecessary for MOCVD precursors.115,118 Guanidinate and amidinate precursors In recent years, there has been great interest in g uanidinate and amidinate ligands for use in organometallic precursors. The tunability of th e organic groups of these compounds can enhance

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29 the volatility of the precursors. More about the speci fic ligand structure will be discussed in Chapter 4. A number of transi tion metal and lanthanide amid inate compounds of the form [M(RNC(R)NR)n]x (R = iPr, tBu, R = Me, tBu) using Ti, V, Mn, Fe, Co, Ni, Cu, Ag, and La have been investigated structurally and thermally for use as MOCVD precursors.120 Using the [Cu(sBu-amidinate)]2 precursor, copper thin films with low carbon and oxygen contamination and low resistivities were successfully deposited.121 Several transition metal guanidinato complexes have been synthesized and investigated as single source MOCVD precursors.122-125 The tungsten guanidinato complexes, [W(NtBu)2(NMe){(iPrN)2CNMe2}] and [W(NtBu)2(H){(iPrN)2CNMe2}] with ammonia as a co-reactant, were used to deposit WNx thin films.63 Lack of ammonia in the deposition atmosphere produced low nitrogen content films, while use of ammonia reduced carbon contamination. Films grown from the dimethyl amide precursor had lower carbon contamination than the hydride precursor. TaNx thin films were successfully deposited with a similar compound, [Ta(NtBu)(NMeEt){(NiPr)2C(NMeEt)}], in the absence of ammonia.126 Use of W(NiPr)Cl3[iPrNC(NMe2)NiPr] in deposition of WNxCy will be discussed in Chapter 4. Hydrazido precursors In co-reactant precursor syst em s, hydrazine was used as a nitrogen source and a strong reducing agent in deposi tion of metal nitride th in films. Using hydrazi ne as a co-reactant allowed for a significant depos ition temperature decrease.127 In efforts to increase the nitrogen content in metal nitride thin films and take adva ntage of the strong reduci ng nature of hydrazine, a series of metal hydrazido compounds have be en synthesized for MOCVD precursors. This ligand has been utilized fo r several different transition metals such as Ga,128 In,128 Ta,129-131 Ti,132,133 Nb,130,131 Hf,129,133 Zr,129,133 Mo,130 and W.130,134 The compounds [Ta(N-

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30 tBu)(NMe2)2(tdmh)] and Cl4W(NNMe2)(NCCH3) were successfully used to deposit TaNx and WNxCy, respectively.129,134 Precursor Screening Screening of MOCVD precursors is necessary in determining the suitability of a compound for use in deposition. X-ray crystallogr aphy can be used to examine the bonding in a complex. Identifying the strong and weak bonds can give insight to possible decomposition that may occur during deposition. Mass spectrometr y has been used as a means of precursor screening to identify the most favorable fragmentation pathways.135,136 Care has to be taken in the comparison between the ionic mass spectrometry fragmentations versus thermal decomposition during CVD. Thermogravimetri c analysis (TGA) can also give useful information for precursor selection. Vapor pressure, temperatures of sublimation, and decomposition characteristics can be interpreted from the TGA data.60,124,125,137 Isothermal studies can also help predict the stability of precursors. This work presents the synthesis of various WNxCy precursors. The precursors are screened by several analytical methods to determ ine applicability for deposition. The precursors are used for depositing WNxCy thin films, which are characteri zed and tested as use for diffusion barriers in integrated circuits. NMR kinetics experiments were also studied to gain insight into decomposition pathways.

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31 CHAPTER 2 SYNTHESIS AND CHARACTERIZATION OF Cl4(RCN)W(NCH2CH=CH2) (R = Me OR Ph) AS A PRECURSOR FOR MOCVD OF WNXCY Metal Imido Compounds There are two limiting types of metal-imido (NR2-) bonds, which are characterized by the M-N-C bond angle. The hybridization of the nitrogen and the M-N bond order affect the structure of the imido ligand. Figure 2-1 A shows an sp2 hybridized nitrogen which forms a M-N double bond consisting of one -bond and one -bond. The lone pair in the N( sp2) orbital contributes to a bent M-N-R configuration. This type of imido bond is considered a 4edonor and is identified by a M-N-R bond angle 140 C. Most imido bonds have an sp hybridized nitrogen where the nitrogen lone pair is in a p orbital. (Figure 2-1 B) If the environment around the metal does not allow for back donation from th e nitrogen lone pair then the M-N bond order is two with a nearly linear M-N-R bond angle, and the imi do ligand is considered a 4edonor. When back donation into a metal d orbital is possible then an M-N triple bond is formed and contributes greatly to the lin ear M-N-R bond angle. This st ructure is considered a 6edonor.138,139 (Figure 2-1 C) Transition metal complexes that incorporate imido moieties (NR2-) have multiple applications. Some uses of transition me tal imido compounds where the imido ligand is involved in the reaction include amination,140 hydroamination,141 and transfer of imido groups onto tertiary phosphines and isocyanides.142-144 Examples in which the imido ligand is simply a spectator ligand used to st abilize the compound include ol efin metathesis catalysts,145 alkene dimerization and polymerization,146,147 C-H bond activation,148 and alkene cyclopropanation.149 More recently many transition metal imido comple xes have been utilized in MOCVD of metal nitride thin films, making use of the strong metal nitrogen bo nd to remain intact during the deposition process.

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32 Figure 2-1. Bonding in metal imido complexe s. A) Bent, B) Linear, C) Linear.139 Synthesis of the W(VI) Allylimido Precursor Synthesis of new single source precursors for deposition of WNxCy has recently become an area of significant intere st. Specifically, tungste n imido complexes are of interest due to the strong W-N multiple bonds that are predicted to st ay intact during deposition which in turn will aid in incorporating nitrogen in the deposited fi lms. The previously synthesized precursors Cl4(RCN)W(NiPr) (1a, R = CH3; 1b R = Ph)33,150 and Cl4(RCN)W(NPh) ( 2a, R = CH3; 2b R = Ph)151 (Figure 2-2) were developed to investigate the effect of varying the bond dissociation energy of the alkyl/ary l-imido bond on the deposited films. In a continuation of this study, Cl4(RCN)W(NCH3H5) (3a, R = CH3; 3b R = Ph) was synthesized, characterized, and used to deposit thin films of WNxCy.57 In designing these precursors it was propos ed that the strong tungsten imido bond would withstand the CVD process while the loosely coordinate d acetonitrile fragment would dissociate easily, use of the H2 carrier gas would eliminate the chlori ne as HCl, and the alkyl group would dissociate from the imido s ubstituent to deposit WNx films.33 In addition by varying the imido R-group the optimal properties for WNx deposition could be determined. Varying the N-C(alkyl) or N-C(aryl) bond dissociation energy is important because this bond must be cleaved during the CVD process.57

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33 Figure 2-2. Synthesis of tungsten imido precursors. Precursor 3 was synthesized by a metathesis react ion, in which tungsten oxychloride is refluxed with allyl isocyanate in heptanes to form the dimer [Cl4W(NCH2CH=CH2)]2. The target complexes 3a,b are formed by addition of a coordina ting solvent, either acetonitrile or benzonitrile. Allyl imido complex 3a can be synthesized in relative ly high yields of 60-70%. The compound is a bright orange crystalline powder that is extremely air and moisture sensitive. Characterization of 3a X-ray Crystallographic Study of Cl4(CH3CN)W(NCH2CH=CH2) (3a) The results of single crystal stru cture determination of complex 3a appear in Figure 2-3 and Tables 2-1 and 2-2. As has been previously reported for analogous tungsten imido complexes,152,153 the overall geometry at the tungsten center is octahedral with the imido and acetonitrile ligands located in a tr ans orientation with respect to each other. The alkene carbons of the allyl moiety are disordered and for brevity, only one set of positions [C(2)' and C(3)'] will be discussed.

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34 Figure 2-3. Thermal ellipsoids diag ram of the molecular structure of Cl4(CH3CN)W(NCH2CH=CH2) (3a). Thermal ellipsoids are plotted at 50% probability. The disordered carbon positions C(2) and C(3) of the allyl moiety are omitted for clarity. The W N bond length of the related chloroimido complex Cl4(CH3CN)W(NCl) has been reported as 1.72(1) .152 This value is somewhat longer th an the W-N(1) distance of 1.687(9) observed for 3a, reflecting the electronic differences in the chloroimido vs. alkylimido ligands. The W N bond length of Cl4(THF)W(NC6H4CH3p)153 (1.711(7) ) compares more favorably with that of 3a, as expected for an alkylimido complex. The W-N distance for the nitrile ligand (2.28(1) ) as well as the W-Cl bond le ngths (2.350(3) and 2.316(3) ) of Cl4(CH3CN)W(NCl) are consistent with the analogous distances for 3a To my knowledge, only one other allylimi do tungsten compound, as well as several molybdenum complexes containing the NCH2CH=CH2 ligand have been reported, including the W(IV) compound, [WCl2(PMePh2)2(CO)(NCH2CH=CH2)],154 and the Mo(V) compound

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35 Cl3(OPPh3)2Mo(NCH2CH=CH2).155 Much like [WCl2(PMePh2)2(CO)(NCH2CH=CH2)] and Cl3(OPPh3)2Mo(NCH2CH=CH2), 3a has a C(2)'-C(3)' distance (1.36(3) ) which is consistent with the presence of a double bond between these atoms. Furthermore, the C(3)'-C(2)'-C(1) angle of 120(2) confirms the presence of sp2 hybridized carbons at C(2) and C(3). Table 2-1. Crystal data and structure refinement for Cl4(CH3CN)W(NCH2CH=CH2) (3a). Empirical formula C5 H8 Cl4 N2 W Formula weight 421.78 Temperature 173(2) K Wavelength 0.71073 Crystal system Monoclinic Space group P21 Unit cell dimensions a = 6.1482(7) = 90. b = 7.4742(8) = 95.089(2). c = 12.3697(13) = 90. Volume 566.18(11) 3 Z 2 Density (calculated) 2.474 Mg/m 3 Absorption coefficient 11.097 mm -1 F(000) 388 Crystal size 0.12 x 0.09 x 0.04 mm 3 Theta range for data collection 1.65 to 27.50. Index ranges -6 h 7, -8 k 9, -15 l 15 Reflections collected 3692 Independent reflections 2287 [R(int) = 0.0442] Completeness to theta = 27.50 98.6 % Absorption correction Integration Max. and min. transmission 0.6624 and 0.3050 Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 2287 / 1 / 112 Goodness-of-fit on F 2 1.047 Final R indices [I>2sigma(I)] R1 = 0.0372, wR2 = 0.0883 [1939] R indices (all data) R1 = 0.0469, wR2 = 0.0936 Absolute structure parameter 0.44(4) Largest diff. peak and hole 1.818 and -1.413 e. -3 R1 = (||F o | |F c ||) / |F o | wR2 = [ w(F o 2 F c 2 ) 2 ] / w F o 2 2 ]] 1/2 S = [ w(F o 2 F c 2 ) 2 ] / (n-p)] 1/2 w = 1/[ 2 (F o 2 )+(m*p)2+n*p], p = [max(F o 2 ,0)+ 2* F c 2 ]/3, m & n are constants.

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36 Table 2-2. Selected bond distances () and angles (degrees) for Cl4(CH3CN)W(NCH2CH=CH2) ( 3a)a W-N(1) 1.687(9) W-Cl(4) 2.351(9) W-N(2) 2.308(8) N(1)-C(1) 1.508(17) W-Cl(1) 2.339(10) C(1)-C(2)' 1.51(2) W-Cl(2) 2.317(8) C(2)'-C(3)' 1.36(3) W-Cl(3) 2.324(9) N(2)-C(4) 1.130(12) C(1)-N(1)-W 167(2) N(1)-W-N(2) 175.8(15) N(1)-W-Cl(2) 90.6(8) N(2)-W-Cl(2) 86.0(7) N(1)-W-Cl(3) 93.6(7) N(2)-W-Cl(3) 84.0(6) Cl(2)-W-Cl(3) 88.7(4) C(4)-N(2)-W 175(3) N(1)-W-Cl(1) 102.4(8) N(2)-W-Cl(1) 81.1(7) C(2)'-C(1)-N(1) 114.2(21) C( 3)'-C(2)'-C(1) 120(2) Cl(3)-W-Cl(1) 90.18(13) N(2)-C(4)-C(5) 178(2) aThe structure of 3a exhibits disorder in the carbon atoms C(2) and C(3) of the allyl moiety. Data for one set of olefinic carbon atoms [C(2)' and C(3)'] are included. Data for the alternative set [C(2) and C(3)]can be found in Appendix A. Mass Spectrometry Previously mass spectrometric fragmenta tion patterns of CVD precursors and their probable decomposition pathways ha ve shown a strong association.156,157 Realizing that gas phase ionization and thermal deco mposition are different processes, there seems to be a strong correlation between the fragmentation patterns in mass spectrometry and the resulting film deposition properties. Previous studies have shown that mass spectrometry of the tungsten imido precursors Cl4(CH3CN)W(NiPr) (1a) and Cl4(CH3CN)W(NPh) ( 2a) affords qualitative insights into their CVD behavior.33,151,158 Therefore mass spectrometry of the precursor complexes was used as a preliminary screening technique to pos tulate possible fragmentation pathways before beginning CVD experiments. Results of a mass spectrometric study of the allylimido complex 3a follow (Table 2-3). Table 2-3 summarizes the major fragment ions observed in the positive ion electron-impact (EI) and negative ion electron-capture ch emical ionization (NCI) spectra of 3a. As with the isopropyl and phenyl imido complexes 1a and 2a no molecular ion was detected with either

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37 method. Instead the highest mass envelopes in the EI and NCI spectra occurred at m/z 346 and 381, corresponding to [Cl3W(NCH2CH=CH2)]+ and [Cl4W(NCH2CH=CH2)]respectively. The [Cl3W(NCH2CH=CH2)]+ fragment was also the base peak of the EI spectrum. A high abundance (95%) peak at m/z 41 corresponds to bot h acetonitrile [CH3CN]+ and the allyl fragment [CH2CH=CH2]+ from the imido moiety. Table 2-3. Summary of relative abundances for positive ion EI and negative ion NCI mass spectra of tungsten imido complexes Cl4(CH3CN)W(NCH2CH=CH2) (3a). EI Fragments NCI Fragments m/z Abundancea [Cl3W(NCH2CH=CH2)]+ 346 100 [Cl4W]+ 326 34 [Cl3WNH]+ 306 12 [Cl3W]+ 291 58 [Cl2W]+ 256 27 [CH3CN]+ or [CH2CH=CH2]+ 41 95 [Cl4W(N CH2CH=CH2)]381 5 [Cl4WN]340 100 aRelative abundances were adjusted by summing the observed intensities for the predicted peaks of each mass envelope and normalizing the largest sum to 100% Importantly, the base peak of the NCI spectrum corresponds to the mass envelope of the nitrido fragment [Cl4WN]( m/z = 340). A small amount of the protonated nitrido complex fragment [Cl3WNH]+ was detected in the EI spectrum, but at low relative abundance (~12%). The observation of the fragments [Cl3WNH]+ and [Cl4WN]indicates that the critical imido N-C bond is broken under ionization conditions. The lack of any molecular ion in either mass spectrum is consistent with the nitrile liga nd being labile. As observed with precursors 1a and 2a, the EI spectrum of the allylimido complex 3a also exhibited fragments corresponding to loss of the imido nitrogen. A ccordingly, mass envelopes at m/z 256 (27% abundance) and 291 (58% abundance) are assigned to the fragments [Cl2W]+ and [Cl3W]+ respectively. Relative to the isopropyl and phenyl imido precursors 1a and 2a, the allyl complex 3a shows some similarities and important differenc es. In each case, the base peak of the EI

PAGE 38

38 spectrum corresponds to the loss of CH3CN and one chloride ligand (i.e., [Cl3W(NR)]+). The abundance of the protonated nitrido fragment [Cl3WNH]+ in the EI spectrum of the allylimido complex 3a was only about 12% as compared to th e 78% relative abundance of the same mass envelope in the spectrum of the isopropyl imido precursor 1a. Strikingly, this fragment is not observed at all in the EI spectrum of the phenyl precursor. Additionally, the fragment corresponding to the loss of the nitrile ligand (i.e., [Cl4W(NR)]-) was observed in the NCI spectra of all three precursors. Interestingly, this frag ment was the base peak for the NCI spectrum of the phenyl precursor 2a. In contrast, the nitrido fragment [Cl4WN]was the base peak in the NCI spectra of the isopropy l and allyl complexes 1a and 3a, while this mass envelope only accounted for 4% relative abundanc e in the spectrum of 2a. To the extent that the facile cleavages under mass spectrometric conditions are also facile under CVD conditions, one would expect higher nitrogen content in films from 1a and 3a. The greater abundance of the nitrido fragment [Cl4WN]in the NCI spectra of 1a and 3a relative to 2a indicates that the N-C bond of the imido ligand is more easily broken for the allyl and isopropyl imido precursors than for their phenyl imido analogue. This conclusion is supported by the absence of [Cl3WNH]+ in the EI spectrum of 2a and its presence in the spectra of 1a and 3a. These data correlate well with the homolytic C-N bond dissociation energies reported for the corresponding amines ( cf CH2=CHCH2NH2 = 73 kcal/mol, iPrNH2 = 84 kcal/mol, and PhNH2 = 105 kcal/mol).159,160 Film Growth1 To overcome the low vola tility of precursors 1-3 a nebulizer was incorporated into the delivery system to for deposition of WNxCy.33 The precursors were disso lved in benzonitrile (7.5 1 Film growth and film characterization were done by Omar Bchir.

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39 mg/mL) and injected into the nebulizer via sy ringe. A vibrating quartz plate converts the dissolved precursor into an aeros ol that is carried through the system with a hydrogen carrier gas to the heated impinging jet. The precursor is then deposited on a silicon substrate that rests on a heated graphite susceptor (Fi gure 2-4). After deposition was complete, the films typically had a smooth, shiny metallic surface, with colors ra nging from gold to black, depending on deposition temperature. Figure 2-4. Schematic diagram of CVD system.161,162 Film Composition X-ray diffraction The X ray diffraction (X RD) spectra in Figure 25 indicate amorphous and polycrystalline film deposition from complexes 3a,b at 450 and 650 C, respectively. The polycrystalline film has peak locations consiste nt with polycrystalline WNxCy. Four characteristic peaks are evident, indicating that no pref erred crystal orientation was pr esent in the films. Primary Graphite Susceptor Note: Not to Scale Dissolved Precursor from Syringe Pump Precursor Aerosol Thermocouple Gate Valve (for sample loading) Sight Glass Water Cooled Flange To Vacuum Pump RF Coils Quartz Tube Impinging Jet Cable to Power Supply Vibrating Quartz Plate Carrier Gas to Nebulizer 1/16 Plastic Tubing Cold Trap Heated Transfer Tube

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40 reflections at 37.18 and 43.33 2 degrees are consistent with (111) and (200) WNxCy growth planes, while additional re flections at 62.88 and 74.88 2 degrees indicate (220) and (311) planes, respectively. Figure 2-6 shows the evolution of film cr ystallinity with de position temperature. For deposition at and below 525 C, the characteristic WNx peaks are not observed. At 550 C, a broad peak appears near 37.63 2 degrees, indicating polycrystalline WNxCy (111) growth. As the deposition temperature increases to 575 C this peak sharpens and a broad peak at 44.08 2 degrees appears, indicating WNxCy (200) growth. The peaks sharpen further as the temperature approaches 650C, indicating polycrystalline grain growth. Some of the films displayed two additional peaks at 32.98 and 61.63 2 degrees, representing Si (200) K and Si (400) K radiation, respectively. Broad peaks emerge at 63.33 and 75.43 2 degrees for growth at 650 C, indicating WNxCy (220) and (311) growth. Since the formation of polycrystalline films is highly undesirable for diffusion barrier app lications, the ability to grow amorphous films by deposition with this precursor below 550 C is significant. The film crystallization fo r growth at 550 C with 3a,b can be compared to samples grown at 500 and 525 C from 1a,b and 2a,b respectively. The maximum deposition temperature for films deposited from 3a,b was 650 C, as compared to 700 and 750 C for 1a,b and 2a,b respectively. For all three precursors, deposition above the respective maximum growth temperature resulted in formation of unchara cterized black particle s on the substrate and susceptor, which subsequently compromised film quality.

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41 Figure 2-5. XRD spectra for films grown with 3a,b on Si (100) in a H2 atmosphere. a) 450 C b) 650 C c) Standard powder diffraction plots for WN0.5 and WC0.6

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42 Figure 2-6. Change in XRD pattern with deposition temperature for films grown from 3a,b on Si (100) in a H2 atmosphere. Auger electron spectroscopy Auger results in Figure 2-7 indicate that tungsten, nitrogen, carbon and oxygen were present in th e films deposited from 3a,b while chlorine was not detected. The lowest carbon level, 6 at.%, occurs at the lowest depos ition temperature of 450 C. The carbon content increases with deposition temperature from 6 to 38 at.% between 450 and 600 C and then levels off. As in the case for films grown from 1a,b and 2a,b the overall trend in carbon content for films grown from the allylimido complexes 3a,b reflects the increas ing tendency of the hydrocarbon groups present in th e precursor ligands and the solvent to decompose with increasing deposition temperature.163 Carbon levels in the films from 3a,b were slightly higher than those from 1a,b for most deposition temperatures, and significantly higher than those from 2a,b (Figure 2-7). The fact that films from 2a,b contained lower levels of both nitrogen and carbon than those from 1a,b or

PAGE 43

43 3a,b suggests that the phenylimido moiety is more likely to dissociate intact than the isopropylimido or allylimido fragment s, consistent with the higher N C bond strength in the phenylimido group. The nitrogen content in films grown at 450 C was 4 at.%, and this rose to a maximum of 11 at.% for deposition at 500 C. Above 500 C, th e nitrogen levels decreas e, dipping to 2 at.% at 650 C. The higher nitrogen levels at lowe r temperature reflect th e stability of the W N multiple bond in the precursor molecule, which likely endures at deposition temperatures up to 500 C, inhibiting release of nitrogen into the gas phase during deposition. The drop in nitrogen above 500 C may indicate decomposition of the W N multiple bond in the gas phase and/or increased nitrogen desorption from the film (to form N2 gas) at higher temperature.164 Oxygen contamination resulted from post growth exposure of the film samples to air, as demonstrated by incremental AES sputtering, whic h showed a steady decr ease in oxygen levels with increasing depth into the films. The oxyge n concentration was highest at 450 C, reaching 16 at.%, and decreased slightly to 11 at.% at 525 C. Amorphous films deposited below 550 C had low density and high porosity, which allo wed substantial amounts of oxygen to penetrate into the film lattice. As th e deposition temperature was incr eased to 550 C, the oxygen content dropped sharply to 4 at.%. This obs ervation is consistent with crysta llization of the film in this temperature range. As the film crystallizes, its microstructure becomes denser, thereby inhibiting post growth oxygen diffusi on into the lattice.165,166 As the deposition temperature increased above 550 C, the oxygen concentration dr opped further, reaching a steady level near 3 at.% at the highest deposition temp eratures. This resulted from further film densification (by polycrystal grain growth) and in creased carbon levels at higher deposition temperature, which stuff the grain boundaries and block diffusion of oxygen into the films.

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44 Figure 2-7. Comparison of W, N, C and O c ontent in the films grown from 1a,b, 2a,b and 3a,b Data are from AES measurements after 2.0 minutes sputter. Effect of the Imido N-C BDE on Film Growth. In term s of their expected decomposition chemistry, the most significant difference between the isopropylimido complexes 1a,b the phenylimido complexes 2a,b and the allylimido complexes 3a,b is the respective dissociation energies of the N C bond in the imido ligand. Using the corresponding primary amines as organic model compounds, the N C bond of complex 3a,b should be approximately 11 kcal/mol weaker than the analogous bond in 1a,b and 32 kcal/mol weaker than that in 2a,b .159 Since cleavage of this bond is necessary for deposition

PAGE 45

45 of WNx, one would expect there to be differences in deposition behavior (Table 2-4) for the three precursors. Table 2-4. Comparison of deposition behavior for 1a,b-3a,b Precursor Deposition Temp. Range (C) Deposition Rate (/min) Ea (eV) Ref. Cl4(PhCN)W(NCH2CH=CH2), 3a,b 450 650 5 10 0.15 0.13 57 Cl4(PhCN)W(NiPr), 1a,b 450 700 10 27 0.84 0.23 33 Cl4(PhCN)W(NPh), 2a,b 475 750 2 21 1.41 0.28 99 The Ea for film deposition varied significantly for the three precursors, following a trend consistent with the strength of the imido N C bond. Film deposition from 2a,b which possesses the strongest imido N C bond, yielded the highest value for Ea (1.41 eV), while that from 1a,b yielded an intermediate value (0.84 eV). Deposition from 3a,b which has the weakest N C bond, yielded the lowest Ea (0.15 eV), which is well below the typical activation energy range for CVD growth in the kinetic regime (0.5 to 1 eV).167 A plot of the Ea values for deposition with the three precursors against the N C bond strengths for the analogous amines is linear (Figure 2-8), with a goodness of fit (R2) of 0.96. The linear relations hip suggests that cleavage of the N C imido bond is the rate-determining step in film growth from the 1a,b, 2a,b and 3a,b complexes. The strength of the bond in 3a,b is so low, though, that film growth borders on being mass-transfer controlled. While the typi cal film growth temperature dependence168 in the masstransfer controlled region is ~T1.71.8, the temperature dependence for film growth from 3a,b was slightly higher (~T2.1), indicating that the rate-determi ning step for film growth from 3a,b has a very weak kinetic barrier. Imido moieties with higher N C bond energies, such as those in 1a,b and 2a,b present a substantial kinetic constraint on film growth at lower temperature.

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46 Figure 2-8. Variation of a pparent activation energy (Ea) for film growth from Cl4(R'CN)W(NR) ( 1a,b R = iPr; 2a,b R = Ph; 3a,b R = allyl) with the N C bond energies of the corresponding amines R-NH2 as models for the imido NC bonds. Error bars reflect the uncertainty in film thickness measurement from XSEM images The strength of the N C imido bond also has a strong effect on the amount of nitrogen incorporated into the film. If the N C imido bond strength is relatively high, as with the phenylimido complexes 2a,b the imido group has a greater tende ncy to dissociate as an intact ligand via cleavage of the W N bond, which leaves the films defi cient in nitrogen. If the bond strength is relatively low, as with 1a,b and 3a,b the alkyl group cleaves from the nitrogen more easily, leading to higher n itrogen levels in the film. It is interesting to note that unlike compounds 1a,b and 2a, allylimido complex 3a gives conflicting inform ation on the facility of N-C bond cleavage in its mass spectra. The [Cl4WN]ion is the base peak in the NCI spectrum of 3a while the ion corresponding to loss of the allyl moiety in the EI spectrum, [Cl3WNH]+, is

PAGE 47

47 present in only 12% abundance. Although the reason for this behavior is not clear, it may be an indicator of unanticipated difficulty in clean N-C cleavage under CVD c onditions as well. Conclusions Com parison of the film growth properties of 3a,b to those of 1a,b and 2a,b allowed evaluation of the effect of the imido N C bond dissociation energy on film growth and properties. Films deposited from 2a,b were deficient in nitrogen compared to those from 1a,b and 3a,b consistent with a tendenc y of the stronger imido N C bond of 2a,b to result in dissociation of intact NPh fr agments during deposition. Acco rdingly, an optimal window for N C imido bond energy appears to ex ist in these precursors. If the energy of this bond is too high (as in 2a,b ), the W N bond cleaves, leaving the films very deficient in nitrogen. If the bond energy is too low (as in 3a,b ), N C bond cleavage may occur in the gas phase, leading to side reactions that consume precursor before it reaches the substrate surface. A moderate N C imido bond energy (as in 1a,b ) combines a substantial growth rate and better nitrogen retention during low temperature growth w ith greater likelihood of N C imido bond cleavage (relative to 2a,b ). In practical terms, films grow n from isopropylimido complexes 1a,b are superior to those from phenylimido complexes 2a,b for barrier applications because material produced from 1a,b can be deposited at a lower minimum temperatur e (450 C), contains more nitrogen, and has a lower sheet resistance.151 Moreover, the isop ropylimido precursor 1a,b appears to be preferable to the allylimido precursor 3a,b due to higher growth rate and n itrogen content at their mutual lowest deposition temperature (450 C). Experimental Procedure General (Precursor Synthesis). Standard Schlenk and glovebox techniques were em ployed in the synthesis of Cl4(CH3CN)W(NCH2CH=CH2) (3a). Allyl isocyanate was purchased from Aldrich and used

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48 without further purification. Anhydrous heptan e was purchased from Aldrich in a Sure-SealTM bottle and used as received. A ll other solvents were purchased from Fisher and passed through an M. Braun MB-SP solvent purification system prior to use. Th e benzonitrile complex Cl4(PhCN)W(NCH2CH=CH2) (3b ) was not isolated, but was produced in situ by the substitution of the acetonitrile ligand of 3a with benzonitrile, which was utilized as the solvent for the deposition experiments ( vide infra ). NMR solvents were dega ssed by three freezepumpthaw cycles and stored over 3 molecular siev es in an inert at mosphere glove box. 1H and 13C NMR spectra were recorded on VXR 300, or Inova 500 spectrometers. In cases where assignments of 1H or 13C NMR resonances were ambiguous, 13C-1H HMQC experiments were used. Elemental analyses were performed by Robertson Microlit (Madison, NJ). Synthesis of WOCl4 WOCl4 was prepared by the following modification of a literature procedure.169 Inside the glovebox, 26.17 g of WCl6 (0.06598 mol) was suspended in a 500 mL Schlenk flask in excess methylene chloride (approx. 350 mL). Freshly distilled Me3SiOSiMe3 (10.71 g, 0.06598 mol) was added dropwise to the vigorously stirring susp ension. The reaction mixture continued to stir vigorously for 1 hour during which the color changed from a deep red to a bright orange color. The flask was then removed from the box and the solvent was removed in vacuo on a Schlenk line. The orange solid was then washed seve ral times with dry hexa ne to yield clean WOCl4 (21.00 g, 93%). Synthesis of Cl4(CH3CN)W(NCH2CH=CH2) (3a) In a glove box, tungsten oxychloride (1.229 g, 3.597 mmol) was slurried in a solution of allyl isocyanate (0.366 g, 4.41 mmol) in heptane (60 mL) in a sealed Chemglass 350 mL heavy wall pressure vessel with a Teflon bushing. Th e vessel was removed from the glovebox and the mixture was heated for 36 h at 110 C. The solvent was removed from the resulting dark red

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49 solution on a vacuum line. The reddish brown residue was dissolved in a minimal amount of CH3CN (approximately 10 mL). The resulting so lution was stirred for two hours and the solvent removed under reduced pressure. The resulting brown residue was washed with 5 x 10 mL of toluene and the extracts concentrated to approx imately 5 mL. Hexane was added to precipitate the product. The orange-brown solid was filtere d and washed with hexane to afford 0.974 g (64 % yield) of the imido complex. 1H NMR (CDCl3) 7.55 (ddd, J = 1.5, 1.4, 5.6 Hz, 2H, NCH2CHCH2); 6.07 (tdd, J = 5.6, 10.2, 17.1 Hz, 1H, NCH2C H CH2); 5.73 (dtd, J = 0.6, 1.5, 17.1 Hz, 1H, NCH2CHC H2); 5.60 (dtd, J = 0.6, 1.4, 10.2 Hz, 1H, NCH2CHCH2); 2.50 (s, 3H, C H3CN). 13C NMR (CDCl3, ): 129.7 (CH2C HCH2N); 121.9 (C H2CHCH2N); 118.9 (CH3C N); 68.3 (CH2CHC H2N); 3.5 (C H3CN). mp 148-152 C (dec.). Anal. Calcd for C5H8N2Cl4W: C, 14.24%, H, 1.91%, N, 6.64%. Found: C, 14.51%, H, 1.86%, N, 6.43%. Mass Spectrometry All m ass spectral analyses were performed us ing a Finnigan MAT95Q hybrid sector mass spectrometer (Thermo Finnigan, San Jose, CA). Electron ionization (EI) was carried out in positive ion mode using electrons of 70 eV potential and a so urce temperature of 200 C. Negative ion electron capture chemical ionization (NCI) used methane as the bath gas at an indicate pressure of 2 x 10-5 Torr, an electron energy of 100 vo lts and a source temperature of 120 C. All samples were introduced via a cont rolled temperature prob e with heating and cooling enabling temperature control down to 35 C. The mass resolving power (m/ m) was 5000 full width-half maximum (FWHM). Crystallographic Structural Determination of 3a Data were collected at 173 K on a Siem ens SMART PLATFORM equipped with A CCD area detector and a graphite monochromator utilizing MoK radiation ( = 0.71073 ). Cell

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50 parameters were refined using up to 8192 reflections. A full sphe re of data (1850 frames) was collected using the -scan method (0.3 frame width). The first 50 frames were remeasured at the end of data collection to monitor instrument and crystal stability (maximum correction on I was < 1 %). Absorption corrections by integrat ion were applied based on measured indexed crystal faces. The structure was solved by the Direct Methods in SHELXTL6,170 and refined using fullmatrix least squares. The non-H atoms were tr eated anisotropically, wh ereas the hydrogen atoms were calculated in ideal positions and were ridi ng on their respective ca rbon atoms. The C2-C3 moiety is disordered and was refi ned in two parts (the other part being C2'-C3' with their site occupation factors dependently refi ned. Atom C1 is apparently al so disordered but to a lesser extent than the C2-C3 moiety. It could not be resolved and was re fined in the final model as not disordered. A total of 112 parameters were re fined in the final cycle of refinement using 1939 reflections with I > 2 (I) to yield R1 and wR2 of 3.72% and 8.83%, resp ectively. Refinement was done using F2. Film Growth Studies2 The solid precursor 3a was dissolved in benzonitrile at a concentration of 7.5 mg/mL, loaded into a syringe and pumped into a nebulizer. Operation of the nebulizer was described previously.158 Experiments were conducted in a cust om-built vertical quartz cold wall CVD reactor system. P-type boron doped Si (100) substrates with resistivity of 1-2 -cm were used for the film growths. Growths were conduc ted for a fixed time period of 150 minutes at temperatures ranging from 425-675 C. The system was maintained at vacuum by a mechanical 2 Film growth and characterization was done by Omar Bchir.

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51 roughing pump, with the operating pressure fixed at 350 Torr. Hydrogen (H2) carrier gas was used for the depositions. Film structure was examined by X-ray diffraction (XRD) on a Philips APD 3720, operating from 5-85 2 degrees with Cu K radiation. Film composition was determined by Auger electron spectroscopy (AES) using a Perk in-Elmer PHI 660 Scanning Auger Multiprobe, while film sheet resistance was measured with an Alessi Industries fou r-point probe. Film thickness was estimated by cross-sectional scanning electron microscopy (X-SEM) on a JEOL JSM-6400, with growth rate calculated by dividing film thickness by deposition time.

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52 CHAPTER 3 EXPERIMENTAL AND COMPUTATIONAL COMPARISON OF PRECURSOR DECOMP OSITION CVD Precursor Decomposition Pathways In CVD, understanding decom position pathways fr om precursor to deposited material is of vital importance. Many parameters have to be considered when deconvoluting these pathways. Not only are solution phase reactions possible, but due to the high temperatures new reactions should also be considered. While it has been sh own that mass spectrometry data can give some insight into decomposition pathways, they are not conclusive since th e mass spectrometry does not involve thermal degradation of the neutral compound.156,157 Other methods to investigate the decomposition of metal imido precursors during f ilm deposition have been employed, such as thermal desorption spectroscopy and temperature programmed reaction spectroscopy.94,98 After determination of the deposition byproducts, possible decomposition pathways can be inferred. Experimental and computational studie s can help confirm these studies. NMR Line Shape Analysis Dynam ic chemical processes have a large e ffect on NMR spectra. Analysis of these spectra can lead to determination of rate cons tants (k) and activation parameters. The rate constant of a reaction has a strong effect on NM R spectra. For example, in the exchange of NCCH3 in Cl4W(NiPr)(NCCH3), the bound and free NCCH3 will have different chemical shifts depending on the experimental parame ters. If the exchange of NCCH3 is slow then two sets of resonances with moderately sharp peaks will be apparent. For fast exchange of the NCCH3, a single sharp peak will be evident at the weighted average of the chemical shifts from the peaks evident at slow exchange. Intermediate exchange leads to coalescence of the peaks, forming a single broad peak that can di sappear into the baseline.171 (Figure 3-1)

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53 Figure 3-1. Effect of exchange rates on NMR line shapes. Dissociation of Acetonitrile in Cl4W(NiPr)(NCCH3) In design of the Cl4W(=NR)(NCCH3) (R = iPr, Ph, CH2CH=CH2) precursors, it was proposed that the NCCH3 ligand would dissociate readily under CVD conditions due to the strong trans effect of the imido ligand. The trans influence of a ligand is its effect on the strength of the bond trans to it in a coordination compound.172 In turn the strong tr ans influence is often connected to a strong trans effect, which is the effect of a ligand on the rate of substitution for the trans ligand. Therefore the NCCH3 ligand should readily dissociate based on these considerations. Previously mass spectrometry was used to illustrate facile dissociation by the lack of an m/z value of the molecular ion for complexes 1-3 .33,57,99 Use of solution phase NMR kinetics to determine the activation energy for NCCH3 dissociation confirms the ease of this step in the precursor decomposition. The experimental results are then compared to DFT calculations for further insight. To obtain experimental values for the activation energy of CH3CN dissociation from complex 1, 1H NMR kinetics were used to study the exch ange of the acetonitr ile ligand with free CH3CN in CDCl3 solution. Upon lowering the temperature to -20 C, both bound and free acetonitrile could be detected in the 1H NMR spectra. As the temperature was raised, the bound and free acetonitrile signals coalesced. The ex change rate, k, was de termined by line shape

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54 analysis in the temperature range -6 to 34 C The value of k at each temperature can be calculated from the following equations based on the line shape: Fast Exchange: Coalescence: Intermediate Exchange: Slow Exchange: (k = exchange rate, = peak frequency, h = peak-width at half-height, e = w ith exchange, o = without exchange).173-177 Both the Arrhenius and Eyring equations define the relationship between temperature and reaction rate. Since th e Arrhenius equation applies strictly to gas reactions, the Eyring equation is used to calculate the activatio n energy of the exchange. The linear form of the Eyring equation is as follows: (where k = rate constant, T = temper ature, R = universal gas constant, H = activation enthalpy, S = activation entropy, kB = Boltzmanns constant, and h = Plancks constant).178-180 Using the slope of the plot of ln(k/T) vs. 1/T, H is calculated to be 18.52 0.14 kcal/mol and from the yintercept S is 15.8 0.5 cal/molK for the exchange of acetonitrile in 3a (Figure 3-1). Calculating G from: The value of G at temperatures within the film growth range indicate a loss of acetonitrile is kinetically accessible. Since the first order kinetics of the process are consistent with a

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55 dissociative mechanism for the exchange process, those values correspond to H and S for loss of CH3CN from isopropylimido complex 1. The calculated value for H is 10.2 kcal/mol.181 Given that the experiment al values were obtained in solution while the calculated values are for a gas phase process, the agreement between them is reasonable. 1/T 0.00320.00330.00340.00350.00360.00370.0038 ln(k/T) -4 -3 -2 -1 0 1 2 1/T vs ln(k/T) regression line Figure 3-1. Plot of ln(k/T) vs. 1/T for acetonitrile exchange in complex 1. Loss of Chlorine During Deposition Based on previous RGA (residual gas analyz er) data, during deposition of the im ido precursor 1 with H2 carrier gas, the only detected deco mposition product containing chlorine was HCl.99,163 When using N2 as the carrier gas, H2 and HCl are still det ected, leading to the conclusion that H2 produced during deposition or surface bound H2 still reacts with chlorine present.163 Another interesting observa tion is the lack of the reductive elimination product, Cl2, a process that has been observed in a solution reactions of dichlorotellurium(IV) complexes, which reductively eliminate chlorine to yiel d the corresponding tellurium(II) complexes.182 It has also been shown that thermolysis of cis-PtL2Cl4 (L = pyridine, -picoline) can reductively eliminate

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56 Cl2 to yield trans-PtL2Cl2.183 There was also no evidence of chlorine in the deposited films within the detection limits of AES (ca. 1 at%). These data lead us to believe the removal of Cl from the precursor as HCl is an efficient process and piqued curiosity about the mechanistic pathways from the imido compounds 1a-3a to HCl. For assessment of the chemistry of 1-3 following loss of the labile acet onitrile ligand, their coordinati vely unsaturated derivatives Cl4W(NiPr) (1a), Cl4W(NPh) ( 2a), and Cl4W(NCH2CH=CH2) (3a ) were used for DFT calculations.181 In order to produce HCl during deposition, involvement of H2 is probable. Mechanistic pathways to react H2 with organometallic compounds includ e oxidative additi on, coordination of H2 followed by transfer of an acidic proton, and -bond metathesis. The d0 electron count eliminates oxidative addition from consideration. DFT calculations have shown coordination of H2 through a -bond in early electron poor transition metals,184 however, no such transition state was found for complexes 1a-3a.181 This leaves the -bond metathesis pathway, which is favorable for d0 transition metal complexes reacting with H2.185 This reaction takes place by ligand exchange through a four-cen tered transition state forming a metal hydride and HCl. DFT calculations of this intermediate were performe d and showed the formation of the metal hydride and HCl to be endothermic with an activa tion energy of approximately 37 kcal/mol.181 Under normal conditions this value may seem high, but under CVD reaction conditions using high temperatures (450 to 750 C) and high flux of H2, this endothermic process appears to be a viable pathway. This appears to be the first reported -bond metathesis of a me tal chloride with H2 to form a metal hydride and HCl. Calculations for further removal of chlorines showed the activation energy for -bond metathesis was consiste ntly less than that fo r reductive elimination.

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57 Dissociation of the W-N(imido) and N(imido)-C Bonds in 1a-3a Loss of the alkyl or aryl fragm ents in complexes 1-3 is also necessary for deposition of WNxCy. A strong correlation between the bond di ssociation energy of the N-C bond in the corresponding amine and the activation energy of deposition for compounds 1-3 has been demonstrated previously.57 Based on this a conclusion coul d be drawn that cleavage of the N(imido)-C bond is before or during the rate de termining step. A computational study was done to further understand the bonding in the imido moiety a nd its effect on precursor decomposition under CVD conditions. As seen in Figure 3-2 and Table 3-1, bonding in the phenylimido moiety shows conjugation between th e phenyl and imido nitrogen, while the longer C-N(imido) bonds in the iPr and allylimido moieties reflect th e saturated carbon. This also has an effect on the W-N(imido) bond distance, wher e the W-N(Ph) is longer as a result of the stronger C( sp2)-N bond, but the W-N(iPr) and W-N(allyl) have shorter W-N(imido) bonds. (Table 3-1) The Wiberg bond indices were also calculated for complexes 1-3 As expected the N-C(phenyl) bond index in 2 (1.1243) is higher than those of N-C(alkyl) for 1 and 3 (0.9763 and 1.0090 respectively). Also the Wiberg bond index for the W-N(imido) bond in 2 (1.8864) is lower than those of 1 and 3 (2.0412 and 2.0079 respectively).181

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58 Figure 3-2. Complexes 1-3 Table 3-1. Calculated bond le ngths () and bond angles ( ) for complexes 1-3 1 (iPr) 2 (Ph) 3 (CH2CH=CH2) Calc.c Calc.c Calc.c Exp.b W-Cla 2.377 2.380 2.375 2.333 W-N1 1.715 1.738 1.716 1.687(9) W-N2 2.347 2.262 2.342 2.308(8) C-N1 1.428 1.363 1.425 1.508(17) Cl-W-N1a 98.1 95.9 98.1 97.4 W-N1-C 179.6 180.0 177.7 167(2) aAverage value for the four equivalent chlorides. bExperimental values from the X-ray crystal structure of 3 .57 cCalculations done by Yong Sun Won. The bond dissociation energy of W-NCCH3 was calculated using both the acetonitrile free Cl4WNR ( 1a-3a) and the previously mentioned Cl3HW(NR) (1a-3a ) intermediates (Table 3-2). While the calculated bond lengths of the N-C(iPr) and N-C(CH2CH=CH2) were similar, the corresponding calculated bond dissociation energies reflect the stability of the organic radical formed upon homolysis. Hence, the general tr end for N-C(alkyl, aryl) cleavage is parallel to

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59 that of the bond dissociati on energy of the corresponding amine. In using the hydride intermediate the W-N(imido) bond strength incr eases, while the N-C weakens making cleavage of the alkyl or aryl groups more favorable. Table 3-2. Calculated bond dissociation en thalpy for the N1-C and W-N1 bonds in 1a-3a and 1a -3a .a Compound BDE (N1-C) (kcal/mol) BDE (W-N1) (kcal/mol) 1a (iPr) 98.4 88.2 2a (Ph) 121.3 80.0 3a (CH2CH=CH2) 82.7 86.4 1a (iPr) 90.2 94.5 2a (Ph) 107.5 85.6 3a (CH2CH=CH2) 70.4 93.1 aCalculations done by Yong Sun Won. The computational data indicate a str ong correlation between the W-N(imido) and N(imido)-C bond strengths to the nitrogen cont ent in the films (Figure 3-3). At lower temperatures, films deposited from complexes 1a and 2a, with the stronger W-N(imido) bonds have higher nitrogen content in the film than the films deposited from 3a with a weaker WN(imido) bond, leading to the conclusion that th e W-N(imido) multiple bond can withstand the lower deposition temperatures. At temperatures above 500 C, the nitrogen content in the films decreases despite the precursor used for deposition indicating possible decomposition of the WN(imido) multiple bond. As mentioned pr eviously the weaker W-N(imido) bond in 3a is also reflected in mass spectrometry data from the lack of the [Cl4WN]ion. Comparison of computational results and experiment al data illustrates that computa tional work can be utilized as a means of precursor screening.

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60 Figure 3-3. Comparison of nitrogen content in the films grown from 1-3 (AES).57 Conclusions Experim ental kinetics, DFT calculations and statistical thermodynamics were compared to evaluate reaction pathways for precur sor decomposition during growth of WNx films from the isopropylimido complex Cl4(CH3CN)W(NiPr) (1), the phenylimido complex Cl4(CH3CN)W(NPh) ( 2), and the allylimido complex Cl4(CH3CN)W(NCH2CH=CH2) (3). The computational results and experime ntally determined activation pa rameters are consistent with facile dissociation of the acetonitrile ligand (CH3CN) from 1-3 in the temperature range used for CVD. Computational study of reaction of the coordinativ ely unsaturated complexes 1a-3a with H2 located possible transition states for chloride loss via -bond metathesis with hydrogen to yield HCl, the experimentally observed chlori ne-containing product in th e reactor effluent. Finally, through qualitative and quantitative theoretical analys es for N(imido)-C and W-

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61 N(imido) bonds, nitrogen conten t in the films grown from 1-3 is linked to calculated bond dissociation energies. Experimental Procedure for NMR Kinetics of Acetonitrile Exchange in 2 Com pound 1 was prepared as previously described.186 The sample for the exchange study was prepared in the dry box, by dissolving complex 1 and an equivalent amount of acetonitrile in CDCl3. The 1H NMR spectrum of this sample at -20 oC displayed the signals for 1 [ (ppm) 7.14 (hp, 1H), 2.58 (s, 3H) 1.70 (d, 6H)] together with free acetonitrile (2.11 ppm) in a ratio of 1:3. The exchange of 1 with acetonitrile in the solution was monitored by 1H NMR in the temperature range -54 to 34 oC. The exchange rate k (see Appendix A) was determined by lineshape analysis in the temperature range -6 to 34 oC. A plot of ln(k/T) vs. 1/T afforded the activation enthalpy (18.52 0.14 kcal/mol) and entropy (15.8 0.5 cal/m olK) for the exchange of acetonitrile by 1. (Figure 3-1) The NMR spectra were recorded on a Vari an Inova at 500 MHz for proton, equipped with a 5 mm indirect detection probe, with z-axis gradients. The variable temperature spectra were recorded on automation. To achieve temper ature stability, for each temperature step of 2 C, a preacquisition delay of 1500 s was followed by shimming on the lock level. The spectra were collected in 16 tran sients, with an acquisi tion time of 5 seconds. No relaxation delay and no apodization were used. The actua l temperature was measured by r unning a standard of methanol under the same conditions. The simulation of the spectra with exchange was done using gNMR.187

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62 CHAPTER 4 SYNTHESIS, CHARACTERIZATION, AND FILM DEP OSITION OF AN ISOPROPYL GUANIDINATO MOCVD PRECURSOR Metal Guanidinate Compounds In the pas t decade, use of the guanidinato ligand in organometallic chemistry has developed greatly.188,189 Metal guanidinate compounds have been used in a variety of applications including catalysts for polymerization reactions and as nitrogen rich precursors for MOCVD of metal nitride thin films.63,65,137,190-193 There are two resonance forms of the guanidinate ligand. (Figure 4-1) The electronic flexibility of this ligand makes it compatible with a range of transition metals and la nthanides in various oxidation states.194-197 Resonance form A of the guanidinate ligand is essentially considered an amidinate ligand with an amino substituent. (Figure 4-1) Wher eas, contribution from the diamide resonance form B increases the ligands compatibility with electron defi cient metal ions due to the increased -donor ability. Guanidinates are stronger donors than amidinates and therefore increase the electron density on the metal and reduce its ability to be oxidized, an advantage for CVD precursors. Evaluation of bond lengths in the crystal structures of coor dination compounds bearing guanidinate moieties can help determine which resonance form is the major contributor. Figure 4-1. Resonance forms of the guanidinate anion. The first metal guanidinate compounds were synthesized by Lappert et al. in 1970 by insertion of a carbodiimide into a zirconium or titanium amide bond.198 Since then several other

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63 metal guanidinate complexes have been synthesized by this method.124,125,199 Another route to synthesize metal guanidinates is th e use of the lithium guanidinate salt in a salt metathesis reaction.62,63,123,196,200 One of the advantages of this route is the ability to isolate the guanidinate salt for characterization before further use. Use of Guanidinates in Thin Film Deposition Transition m etal guanidinate and amidinate comp lexes have been used to deposit materials such as TiCxNy, Fe, Co, Ni, Cu, and TaN by CVD and/or ALD.61,125,201 The volatility of metal guanidinate complexes makes them ideal precursors for MOCVD. Also, the bidentate ligand makes these compounds more stable over time. We recently synthesized a series of guanidinate and amidinate derivatives of precursors 1-3 .62 Thermogravimetric analysis and mass spectrometry were used as a means of screening the new precursors. WNxCy thin films were deposited using W(NiPr)Cl3[iPrNC(NMe2)NiPr], 4, the guanidinato derivative of 1. The film properties obtained from 4 are compared to those from Cl4(RCN)W(NiPr) (R = CH3, Ph) (1a,b ) to assess the effect of the guanidinato ligand. The WNxCy films were also evaluated as diffusion barriers by coating them with P VD Cu and annealing the Cu/WNxCy/Si stack in vacuum at different temperatures. Results and Discussion Precursor Synthesis The tungsten guanidinate com plex 4 was synthesized by reacting the imido complex W(NiPr)Cl4(OEt2) with the lithium guanidinate salt, Li[iPrNC(NMe2)NiPr]. In attempts to improve the synthesis of the guanidinate complexe s, an alternate solvent system was used. The lithium guanidinate was synthesized in hexane at 0 C and used in situ .62,192,202 The W(NiPr)Cl4(OEt2) complex was dissolved in toluene, cooled to -78 C, and the lithium guanidinate salt was added dropwis e. The reaction mixture was warmed to room temperature,

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64 and stirred overnight to afford compound 4 as an amber solid in 37% yield without the need for recrystallization. The 1H and 13C NMR spectra of complex 4 display an inequivalence between the substituents of the chelat ing guanidinate nitrogens, lead ing to the assignment as the mer isomer. Table 4-1. Crystal data a nd structure refinement for 4. Complex 4 Empirical formula C12H27Cl3N4W Formula weight 517.58 Temperature (K) 173(2) Wavelength () 0.71073 Crystal system Triclinic Space group P-1 Unit cell dimensions a = 8.4844(7) = 93.063(2) b = 8.8717(8) = 101.094(2) c = 14.8556(13) = 116.862(2) Volume ( 3 ) 966.23(15) Z 2 Density (Mg/m 3 ) 1.779 Absorption coefficient (mm -1 ) 6.389 F(000) 504 Crystal size (mm 3 ) 0.06 x 0.05 x 0.01 Theta range for data collection () 1.42 to 24.60 Index ranges -9 h 9 -9 k 9 -16 l 16 Reflections collected 6201 Independent reflections (Rint) 2732 (0.0465) Completeness to = 24.60 (%) 83.6 Absorption correction Integration Max. and min. transmission 0.9390 and 0.6490 Data / restraints / parameters 2732 / 1 / 189 Goodness-of-fit on F 2 0.935 R1a 0.0361 wR2b 0.0502 Largest diff. peak and hole/e. 3 0.757 and -0.694 aR1 = (||F o | |F c ||) / |F o | bwR2 = [ w(F o 2 F c 2 ) 2 ] / w F o 2 2 ]] 1/2 S = [ w(F o 2 F c 2 ) 2 ] / (n-p)] 1/2 w= 1/[ 2 (F o 2 )+(m*p)2+n*p], p = [max(F o 2 ,0)+ 2* F c 2 ]/3.

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65 Figure 4-2. Thermal ellipsoids diag ram of the molecular structure of 4. Thermal ellipsoids are drawn at 40% probability and hydrogens have been omitted for clarity. Single crystals suitable for X-ra y diffraction were obtained from 4, and the structure was determined. Crystal data and structure refineme nt for this complex can be found in Table 4-1. Compound 4 adopts a distorted octahedral geometry as shown in the ORTEP representation of 4 (Figure 4-2). The tungsten-chlo rine bond distances are on the orde r of 2.38 which is within the expected range for tungsten(VI)-c hlorine bonds.203 The W-N(3) bond length of 1.702(4) and the W-N(3)-C(10) bond angle of 168.4(8) are consistent with th e values previously reported for other W(VI) imido complexes that are expect ed to have strong conjugation of the N lone pairs into empty metal d orbitals.153,204 The W-N(2) bond length is 1.961(4) while the WN(1) bond length is 2.247(4) The elongated bond length of the latter is consistent with the strong trans influence of the imido ligand.172 The C(1)-N(4), C(1 )-N(1) and C(1)-N(2) bond distances in the guanidinate li gand are 1.373(6), 1.294(6), and 1.399(6) respectively. All of these bond distances are roughl y in the range for C(sp2)-N(sp2) bonds (ca. 1.36 ).205 This is an

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66 indication of lone pair donation fr om N(4) to C(1) and electron delocalization involving all three nitrogens of the chelatin g ligand. A sum of 357.6 for the three bond angles about N(4) is consistent with the sp2 hybridization necessary for conjugation. A list of selected bond lengths and angles for 4 is given in Table 4-2. Table 4-2. Selected bond distances () and angles () for compound 4 Bond Bond Length () Bond Bond Angle () W-N1 2.247(4) N1-W-N3 163.23(18) W-N2 1.961(4) N2-W-Cl3 155.81(13) W-N3 1.702(4) Cl1-W-Cl2 167.30(5) W-Cl1 2.3752(15) N2-W-N3 101.44(19) W-Cl2 2.3819(16) N1-W-N2 61.88(16) W-Cl3 2.3833(14) W-N1-C1 90.3(3) C1-N2 1.399(6) N1-C1-N2 107.8(4) C1-N1 1.294(6) W-N2-C1 100.0(3) C1-N4 1.373(6) W-N3-C10 168.4(8) Precursor Screening Thermogravimetric analysis TGA experim ents run with a heating rate of 10 C/min from 25 C to 900 C resulted in a residual mass of 43% which was constant above 400 C (Figure 4-3a). Examination of the derivative plot (Figure 4-3b) reveals an inflection point corres ponding to onset of a decomposition process around 237 C. At 237 C the residual ma ss is 77% corresponding to loss of an isopropyl group and two chlorines or comp lete loss of the guanidi nato ligand. A second inflection point appears at 315 C and 49% residual weight %, after which additional weight loss is slow. Loss of an isopropyl group, three chlori ne atoms, and fragmentation of the guanidinato ligand, leaving a bisimido complex, correspond to 49% residual mass. Isothermal studies of 4 at 120 C for 180 minutes are depicted in Figur e 4-2c. The thermal behavior of 4 strongly resembles that of the tantalum guanidinato complexes [Ta(NR1R2){iPrNC(NR1R2)NiPr}2(NtBu)] (R1, R2 = methyl, ethyl), which have been demo nstrated to be CVD precursors to TaN.125

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67 a. b.

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68 c. Figure 4-3. (a) TGA curve of compound 4 recorded at a heating rate of 10 C/min under nitrogen; (b) First deriva tive of TGA curve a.; (c) Isothermal study of compound 4 at 120 C under nitrogen. Mass spectrometry A relationship has previously been esta blished b etween the mass spectrometric fragmentation of precursors and the deco mposition pathways during the CVD process.157,206 In comparing these two processes, one must be careful, since mass spectrometry involves a gas phase ionization process while the precursor undergoes a thermal degradation process during CVD.157 However, previous research has shown that mass spectral data are useful for screening CVD precursors.57,99,207

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69 Figure 4-4. PCI mass spectra of compound 4. Mass spectra were obtained for 4 using positive ion electron-capture chemical ionization (PCI). In contrast to precursors 1-3 ,57,99,207 the molecular ion for 4 could be observed ( m/z 518). The base peak of the PCI spectrum corresponds to loss of a chlorine ( m/z = 481). Also present is a peak at m/z 446 (37% abundance) which corresponds to the molecular ion w ith loss of two chlorines. Facile elimination of the chlorines in the PCI spectrum is consistent with the lack of chlorine in the films deposited by these precursors. (Figure 4-4)

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70 Film Deposition from 43 Film growth Film s were deposited from precursor 4 at temperatures as lo w as 400 C. Films grown with precursor 4 were generally smooth and had a shiny metallic surface with film color varying from golden at low deposition temperature to shiny black at high depos ition temperature. Film composition Figure 4-5 shows AES r esults for films deposited with precursors 4 and 1a,b using H2 as co-reactant. The AES spectra indicated the presence of tungsten, nitrogen, carbon, and oxygen for films deposited with precursor 4. Even though precursor 4 bears chloride ligands, no chlorine was detected in the film by X-ray phot oelectron spectroscopy (s pectra not shown). For films deposited with 4 above 450 C, the tungsten concentration gradually decreases until 700 C, reflecting an increase in carbon cont ent as the deposition temperature rises. The nitrogen content of films deposited with precursor 4 has a higher nitrogen content than 1 for films deposited at 400 C and 450 C. Then the nitrogen content of th e film decreases as deposition temperature is increased from 450 to 650 C. The variation of nitrogen content in the films is likely influenced by several factor s, including nitrogen volatilization, competition between carbon and oxygen for bonding with tung sten sites, and precursor decomposition pathways and rates. Both carbon and oxygen were detected in sign ificant amounts in all films. The carbon content of film deposited with precursor 4 decreases from 400 C to 450 C and then continuously until 700 C. In a previous study using Cl4(CH3CN)W(NiPr) (1 ), it was demonstrated that the extent of carbon incorporation depended upon the solvent (1,2 3 Film growth and film characterization were done by Hiral Ajmera.

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71 dichlorobenzene or benzonitrile).163 Ligand decomposition and possi ble precursor reactions with the solvent could also contribu te to increased carbon content. The oxygen content of film deposited with 4 decreases as the temp erature increases. Poss ible sources of oxygen incorporation include an oxygen be aring impurity in the reactants, post growth exposure of the film to air, residual oxygen in the reactor and a leak in th e system. While both precursor impurities and reactor residual gas can result in o xygen incorporation in the film, the bulk of the oxygen is believed to diffuse into the film upon po st growth exposure to the atmosphere. The change in film density with deposition temperatur e is believed to affect the oxygen diffusion and resultant change in oxygen conten t with deposition temperature. Figure 4-5. Composition of films deposited from 4 and 1 on Si (100) substrate at different deposition temperature as determined by AES after 0.5 min of sputtering

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72 XRD of films Figure 4-6. XRD patterns for films depos ited on Si (100) substrate from 4. Figure 4-6 shows the XRD patte rns for films deposited with 4 between 400 and 750 C deposition temperature. XRD spectra for film s deposited at 400 and 450 C show no peaks attributable to the film. The absence of WNxCy peaks in these two spec tra suggests that films deposited at 400 and 450 C are X-ray amorphous. The XRD pattern for the film deposited at 500 C shows onset of crystallinity as evid enced by the two broad peaks at 37.74 and 44.40. These peaks lie between the standard peak position of -W2N [37.74 2 for (111) phase and 43.85 2 for (200) phase and -W2C [37.74 2 for (111) phase and 43.85 2 for (200) phase, indicating the presence of either the solid solution -WNxCy or a physical mixture of -W2N and -W2C.208 Films deposited at 550, 600, and 650 C show evidence of increased crystallinity with

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73 four peaks observed at approximately 37.50, 43.70, 63.55 and 75.05, corresponding to (111), (200), (220) and (311) phases of -WNxCy respectively. The (111) peaks become sharper at higher deposition temperature, sugges ting an increase in grain size. Film growth rate (X-SEM) The growth rate for film s grown from 4 was determined from the measured film thickness (X-SEM) divided by deposition time. Figure 4-7 shows X SEM images for films grown at 450 and 650 C. The growth rate varied from 3 / min to 24 /min, with the lowest growth rate observed at 400 C and highest gr owth rate observed at 700 C Figure 4-8 shows Arrhenius plots of growth rate for deposition from 4 and 1a,b in the presence of hydrogen. The growth rate for films deposited with 4 is lower than that for films deposited with 1a,b between 400 and 650 C. The Arrhenius plot for 4 shows that film growth between 400 and 600 C is surface reaction limited with a change to mass tran sfer limited between 600 and 750 C. While the mass transfer limited growth regime usually exhibits a small positive slope in an Arrhenius plot, 4 shows a small negative slope between 600 and 750 C. This is consistent with homogenous decomposition of the precursor above 600 C, resulting in a slight decrease in growth rate in the mass transfer limited growth regime for 4. While the transition from surface reaction limited growth to mass transf er limited growth occurs between 550 and 600 C for 1a,b 4 shows the same transition at 600 C. An activation energy for film growth using 4 of 0.54 eV was calculated from th e Arrhenius equation, which is si gnificantly lower than 0.84 eV activation energy reported for 1a,b .33 The value of activation energy for 4 is within the typical values between 0.5 and 1.0 eV observed for CVD growth in the surface reaction limited regime.167

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74 Figure 4-7. X-SEM images for films grown from 4 at a) 450 C b) 650 C Figure 4-8. Arrhenius plot of log of film growth rate vs. inverse temperature for deposition from 1 and 4 on a Si(100) substrate Film resistivity Film resistivity was calculated using: tRs where is film resistivity in cm, Rs is sheet resistance in / (measured by 4 point probe) and t is film thickness in cm (measured from X SEM). Figure 4-9 shows film resistivity at different deposition temperature fo r films grown w ith precursors 4 and 1a,b For depositions with 4 the resistivity ranges from 980 cm to 6857 cm. The film with the lowest resistivity of 980 cm was grown at 450 C. The low resistivity at this temperature is thought

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75 to be due to higher tungsten cont ent and lower carbon and nitrogen content of the film. Between 450 and 600 C deposition temperature, the film resistivity gradually increases, which is attributed to a decrease in tungs ten content of the film and an increase in amorphous nitrogen and carbon in the film as observed by AES. Comparison of resistivity for films deposited with 4 and 1a,b reveals that while the lowest resistivity obtained with 1a,b is 750 cm at 450 C, the lowest resistivity obtained with 4 is 980 cm at 450 C. The resistiv ity of films deposited with 1a,b increases throughout the deposition temperature, whereas the resistivity of films deposited with 4 shows a steep increase between 450 and 600 C followed by a decrease in resistivity between 600 and 750 C. Figure 4-9. Change in film resistivity with deposition temperature for films grown on Si (100) from 4 and 1a,b Diffusion barrier testing To determ ine the effectiveness of diffusion barrier deposited with 4, barrier films deposited at 450 and 500 C were coated with 100 nm PV D Cu. The thickness of films deposited at 450 was 45 nm. The Cu/barrier/Si stack was annealed in vacuum at temperatures ranging from 200

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76 to 600 C for 30 min to determine the temperatur e at which Cu diffuses through the barrier film into the Si substrate. After annealing, three-point AES depth pr ofile was used to detect copper diffusion. Figure 4-10. AES depth profiles of Cu (100 nm)/ WNxCy (50 nm)/Si (100) stack for WNxCy film deposited at 450 C and annealed in v acuum for 30 min at (a) 200 (b) 400 (c) 500 and (d) 600 C. Figure 4-10 shows the depth pr ofile for post-anneal Cu/WNxCy/Si stack for WNxCy films deposited from 4 at 450 C. For an anneal at 200 C for 30 min, the Cu-WNxCy interface is similar to that for films with no anneal, suggesting that no bulk copper diffusion occurred. As the anneal temperature is increased to 400 C, there is slight mixing of the Cu/WNxCy interface,

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77 however the copper has not diffused through the barri er film. For 500 C anneal, there is further diffusion of Cu in the WNxCy film, but the barrier film is able to prevent complete diffusion of Cu through it. At 600 C annealing temperature, there is complete di ffusion of copper through the barrier film. Intermixing is also observed for the WNxCy/Si interface. The depth profiling shows that 45 nm barrier film of WNxCy deposited with 4 at 450 C is able to prevent bulk Cu diffusion when annealed at 500 C for 30 min. Conclusions It has been dem onstrated that th e mixed imido guanidinato complex W(NiPr)Cl3[iPrNC(NMe2)NiPr] ( 4) can be used in an aerosol assisted CVD system to deposit WNxCy thin films. A comparison of the effects of imido and guanidinato ligands on film properties is presented by comparing the film composition, crystallinity, growth rate and resistivity of films deposited with 4 and Cl4(RCN)W(NiPr) (R = CH3, Ph) (1a,b ). For 4, the lowest growth temperature at which films could be obtained is 400 C. AES spectra showed presence of tungsten, nitrog en, carbon and oxygen in this material. When compared with films grown with 1a,b the films grown with 4 have a higher C/W ratio and almost similar N/W ratio. The oxygen content of films deposited with 4 is also significantly lower than that for films deposited with 1a,b especially at lower deposition temperature. The lowest growth temperature for 4 is 50 C lower than that for 1a,b For both 4 and 1a,b films grown are crystalline at and above 500 C depos ition temperature. From the diffusion barrier application standpoint, films deposited with 4 at 450 were able to pr event copper diffusion after annealing at 500 C for 30 min in vacuum. Since the film deposited from 4 at 450 C is amorphous, has lowest resistivity of 980 cm and can prevent Cu di ffusion after annealing at 500 C, films deposited from 4 at 450 C might be the best candidate for diffusion barrier application.

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78 Experimental Procedure General Procedure Unless otherwise stated, reac tions and m anipulations were performed in an inert atmosphere (N2) glovebox or using standard Schlenk te chniques. All reaction solvents were purified using an MBraun MB-SP solvent purification system prior to use. NMR solvents were degassed by three freezepumpthaw cycles and st ored over 3 molecular sieves in an inertatmosphere glove box. 1H and 13C NMR spectra were recorded on Mercury 300, Gemini 300 or VXR 300 spectrometers using residual protons of deuterated solvents for reference. Infrared spectra were recorded as mineral oil mulls on NaCl plates on a Perkin Elmer Spectrum One FTIR spectrometer. UV/Visible spectra were recorded on a Shimadzu UV-1650 UV-Visible spectrophotometer. TGA analysis was car ried out using a Perkin-Elmer TGA7 thermogravimetric analyzer under nitrogen with a heating rate of 10 C/min (Sample size 2 mg). Lithium dimethylamide and 1,3-diisopr opylcarbodiimide were used as purchased from Aldrich. W(NiPr)Cl4(OEt2) complexes were prepared by the method of Schrock.209 Synthesis of W(NiPr)Cl3[iPrNC(NMe2)NiPr] (4) W(NiPr)Cl3[iPrNC(NMe2)NiPr] ( 4) was prepared by modification of a literature procedure.62 Lithium dimethylamide was dissolved in 40 ml of hexane. The solution was cooled to 0 C, after which diisopropylcarbodiimide was added dropwise. The solution was stirred for 2 hours while warming to room temperature forming the Li[iPrNC(NMe2)NiPr] salt. The ligand was added dropwise to a solution of Cl4W(NiPr)(OEt2) dissolved in 30 ml of toluene at -78 C. This stirred and allowed to warm to room temper ature overnight with excl usion of light. Solvent was removed in vacuo and the product was extracted with diethylether. The ether was removed in vacuo to yield clean 4 as a dark amber powder. 1H NMR (300 MHz, C6D6): 1.23 (d, 6H, J = 6 Hz, CH(C H3)2), 1.38 (d, 6H, J = 7 Hz, CH(CH3)2), 1.70 (d, 6H, J = 6 Hz, CH(C H3)2), 2.14 (s,

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79 6H, N(C H3)2), 4.08 (septet, 1H, C H (CH3)2), 4.39 (septet, 1H, C H (CH3)2), 5.31 (septet, 1H, WNC H (CH3)2). 13C NMR (C6D6): 23.3, 23.4, 25.4, 40.1 (N( C H3)2), 50.4 ( C H(CH3)2), 53.8 ( C H(CH3)2), 66.8 (WN C H(CH3)2), 164.7 (N3C ). IR (cm-1): 2925 (s), 2854 (s), 1607 (w), 1461 (m), 1377 (m), 1278 (w). UV/Vis [Ether, max/nm ( /M-1cm-1)]: 251 (1800), 309 (2800), 392 (1500). Anal. Calcd. for WC12H27N4Cl: C, 27.85; H, 5.26; N, 10.83. Found: C, 28.14; H, 5.52; N, 10.52. Crystallographic Structure Determination of 4. Data were collected at 173 K on a Siem ens SMART PLATFORM equipped with A CCD area detector and a graphite monochromator utilizing MoK radiation ( = 0.71073 ). Cell parameters were refined using up to 8192 reflections. A full sphe re of data (1850 frames) was collected using the -scan method (0.3 frame width). The first 50 frames were re-measured at the end of data collection to monitor instrument and crystal stability (maximum correction on I was < 1 %). Absorption corrections by integrat ion were applied based on measured indexed crystal faces. The structure was solved by the Direct Methods in SHELXTL6,170 and refined using fullmatrix least squares. The non-H atoms were tr eated anisotropically, wh ereas the hydrogen atoms were calculated in ideal positions and were riding on their respectiv e carbon atoms. The isopropyl moiety on N1 is disordered and is refine d in two parts with their site occupation factors dependently refined. A total of 189 parameters we re refined in the final cycle of refinement using 2299 reflections with I > 2 (I) to yield R1 and wR2 of 2.64% and 4.87%, respectively. Refinement was done using F2.

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80 Mass Spectrometry Mass spectral analyses were perform ed usi ng a ThermoScientific DSQ mass spectrometer equipped with a direct insertion probe (DIP) that was held at 50 C for 1 minute and then heated up to 280 C at 30 /min during the sample analysis. Ion source temperature was 150 C with methane gas at 0.5 mL/min. Thermogravimetric Analysis TGA analysis was carried out using a Perkin-E lmer TGA7 thermogravimetric analyzer under nitrogen with a heating rate of 10 C/min (Sample size 2 mg). Film Growth Studies4 Film deposition was done in a vertical cold-wa ll CVD (chemical vapor de position) reactor. The reactor configuration has been described previously.99 The solid precursor 4 was dissolved in benzonitrile at a concentration of 9.0 mg/mL. The deposition was carried out at atmospheric pressure for a period of 150 min and the growth temperature was varied from 400 to 750 C. Table 4-3 provides the molar flow rate of reactants used in the MOCVD reactor. Table 4-3. Molar flow rates of reactants in the CVD reactor Reactant Molar flow rate (mol/min) H2 24.0910 W(NiPr)Cl3[iPrNC(NMe2)NiPr] 51.1610 Benzonitrile (solvent) 46.4710 Film crystallinity was exam ined by X-ray diffraction (XRD) using a Phillips APD 3720 system. Cu K radiation, generated at 40 kV and 40 mA (1.6 kW), was used for the XRD analysis. The XRD patterns were taken between 5 and 85 degrees 2 with step size of 0.05 degree/step. Film composition was determined by Auger electron spectroscopy (AES) using a Perkin-Elmer PHI 660 Scanning Auger Multipro be. A 5 kV accelerati on voltage and 50 nA 4 Film growth and film characterization were done by Hiral Ajmera.

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81 beam current was used for the Auger analysis with a beam diameter of 1 m. The sample surface was cleaned by sputter etching for 30 sec using Ar+ ions. The etch ra te for the sputtering was calibrated at 100 /min using ta ntalum oxide standard. No WNxCy standard, however, was available. XPS spectra were taken using monochromatic Mg K radiation with the X-ray source operating at 300 W (15 kV and 20 mA). The sample surface was sputter et ched for 15 min using Ar ions to remove surface contaminants. The et ch rate for the XPS system was calibrated at 10 /min using a tantalum oxide standard. The pass energy used for XPS multiplex measurement was 35.75 eV and the step size of scans was 0.1 eV per step. The film thickness was measured by cross-s ectional scanning electron microscopy (XSEM) on a JEOL JSM-6400. The sheet resistance of the deposited films was measured using an Alessi Industries four-point probe. To test diffusion barrier quality, the WNxCy films were transferred in air to a multi-tar get sputter deposition system (K urt J. Lesker CMS-18) where 100 nm thick Cu films were deposited. The base pressure of the system was 10-6 Torr and deposition was done at 5 mTorr with Ar used as sputter de position gas. The forward sputtering power for Cu target was 250 W and the film growth ra te was 240 /min. Annealing of the Cu/WNxCy/Si stacks was also done in the sputter system at base pressure of 10-6 Torr.

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82 CHAPTER 5 SYNTHESIS OF TUNGSTEN IMIDO GUANIDINATO HYDRIDE C OMPLEXES Transition Metal Hydrides Transition m etal hydrides have played an important part in the development of organometallic chemistry.210-212 The first transition metal hydride, H2Fe(CO)4, was reported in 1931.213 Since then the area of transition metal hydr ides has grown extensively. Metal hydrides are typically very reactive complexes that can ta ke part in various transformations such as deprotonation,214 hydride transfer and insertion,215,216 and hydrogen atom transfer.217 Along with these various transformations, metal hydrides play an important role in catalytic cycles and as olefin polymerization intermediates.218-220 In addition to these applications, transition metal hydrides, such as [(Me2NCH2CH2)C5H4]GaH2,221 [(Me2NCH2CH2)C5H4]AlH2,221 and [W(NtBu)2(H){(iPrN)2CNMe2}],63 have been of interest for us e as single source precursors for MOCVD. Hydrogen can bond to a metal as a terminal hydride, bridging hydride (2-H), capping hydride (3-H), or as a dihydrogen ligand ( 2-H2).171,222 The most common metal hydride complexes include a terminal hydride, while many complexes of the other types are known. Metal hydrides can be synthesized using a variety of pathways including protonation,223 hydriding,224,225 hydrogen atom transfer,226,227 oxidative addition of H2,228 and ligand decomposition.229,230 This chapter will discuss the synt hesis and characterization of metal hydride complexes to be used as si ngle source precursors for MOCVD. Synthesis and Characterization of Tr ansition Metal Hydride MOCVD Precursors Synthesis Recently, m etal imido and guanidinato complexes have been of interest for use as single source precursors in MOCVD.61,63,123-125 Advantages of these liga nds include strong nitrogen

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83 interactions with the metal cen ter and tunable alkyl groups to adjust the vola tility of the compounds. In attempts at producing a WNxCy precursor lacking chlo rine, several tungsten precursors with an imido/guanidinato/ hydride ligand set were synthesized. To a solution of W(NiPr)Cl3[iPrNC(NMe2)NiPr] ( 4) dissolved in THF, two equivalents of LiBEt3H was added drop-wise at room temperature.62 Effervescence was observed and upon completion the solvent was removed in vacuo. The product was extracted with hexane and upon removal of solvent a bright yellow solid of the dimer {W2(NiPr)2[iPrNC(NMe2)NiPr]2H2(-H)2} (5) remained in 66% yield. Bright yellow crystals were easily grown from a concentrated solution of 5 in pentane at -30 C. A similar proce dure was used to synthesize the cyclohexyl ( 6) and phenyl ( 7) imido adducts of 5 ( Figure 5-1). However, attempts at obtaining crystals of these complexes were unsuccessful. Figure 5-1. Synthesis of tungsten im ido/guanidinato/hydride complexes 57. Characterization NMR spectroscopy Investigation of 5 by 1H NMR shows one septet at 4.04 ppm for the imido isopropyl group and one septet at 3.84 ppm for the guanidinato isopropyl groups integrating in a 2:4 ratio, respectively. The doublets for the isopropyl groups are displayed at 1.12 and 1.23 ppm

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84 integrating to 12 and 6 protons, respectively. The methyl groups for the guanidinato ligands are present as a singlet at 2.81 pp m integrating to 6 protons. Ab sence of any observable hydride peaks in the NMR at room temperature led to the measurement of variable temperature NMR spectra. Lowering the temperature to -53 C revealed peaks at 11.43 and 3.18 ppm. The hydride peaks were identifiable by their tungsten satellites with a c oupling constant of 1JW-H = 61.2 Hz for the peak at 11.43 ppm. This downfield shif t represents the termin al hydrogens in compound 5, while the peak at 3.18 ppm is from the bridging hydride. These peaks are not visible at room temperature because they are exchanging too fast on the NMR time scale to be detected. The IR spectrum shows an absorption band at 1871 cm-1, which is in the range for terminal W-H stretching frequencies.63,171,231 (Figure 5-2) a)

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85 b) Figure 5-2. 1H NMR spectrum of 5 in THFd8. a) Room temperature, b) -53 C. Compound 6 shows four overlapping doublets from 1.11 ppm to 1.22 ppm. This indicates that compound 6 does not contain the sa me symmetry as compound 5. Protons from the cyclohexyl group show up as a series of broad multiplets from 2.20-1.75 ppm and 1.68-1.41. The methyl groups from the NMe2 group in the guanidinato b ackbone are at 2.85 and 2.81 ppm while the methine protons from the isopropyl an d cyclohexyl group show up as two septets at 3.84 and 4.06 ppm. The hydride peak is visibl e at room temperature at 12.71 ppm with a average coupling constant of 1JW-H = 52.5 Hz. In compound 7 the hydride peak is appare nt at 14.81 ppm in benzened6 with a coupling constant of 51.5 Hz. The phenyl group is seen as several multiplets at 6.92-7.00, 7.16-7.23, and 7.48-7.60 ppm. The methine protons from the isopropyl groups appear as a septet at 3.79 ppm, while the methyl protons from NMe2 are seen at 2.29 and 2.32 ppm. Again for compound 7, the terminal protons from the isopropyl groups appe ar as two overlapping doublets at 1.33 and 1.37

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86 ppm. The low temperature 1H NMR spectrum of 7 in THFd8 shows hydride peaks at 12.31 ppm with a coupling constant of 61.3 Hz and at 14.17 ppm with a coupling constant of 53.1 Hz. A crystal structure will be n ecessary to elucid ate the structures of compounds 6 and 7, but attempts to crystallize these co mpounds have not been successful thus far. X-ray crystallography The m olecular structure of 5 in the solid state as obtained from single-crystal X-ray diffraction studies is shown in Figure 5-3. The hydrides were found in the difference Fourier maps and refined without constraint s. The X-ray structure of compound 5 shows two bridging hydrides and two terminal hydrides and adopts a highly distorted octa hedral geometry around tungsten. A list of select bond lengt hs and angles is given in Ta ble 5-1. The imido ligand in compound 5 has less triple bond character than that of compound 4, evident by the longer W-N bond lengths (W1-N1, 1.733(4) ; W2-N5, 1.746(4) ) as compared to 1.720(3) for compound 4.62 Also supporting the lo wer bond order in compound 5 is the less linear angle of W1-N1-C2 (162.7(3)) and W2-N5-C14 (166.1( 3) deg) than that of th e imido ligand in compound 4 (174.0(3)). The guanidina to ligands in compound 5 demonstrate more electron delocalization between the chelating nitrogens than in compound 4. This is apparent by the more equivalent N3-C1 (1.317(6) ), N4-C1 (1.384(6) ), N7-C13 (1.335(5) ), and N8-C13 (1.384(6) ) in the guanidinato ligands in compound 5. These values show bond lengths between that of a C-N single bond ( ca. 1.47 ) and a C-N double bond ( ca. 1.25 ), demonstrating a partial double bond character across the chelati ng nitrogen atoms. This is in contrast to compound 4 where the corresponding guanidinato bond lengths of 1.399( 6) and 1.294(6) show less electron delocalization. Another structural characteristic that supports th e electron deloca lization present in the guanidinato ligand of 5 is the W-N bond lengths which s how more symmetric coordination

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87 of the tungsten with bond lengths of 2.147(3), 2.127(4), 2.157(3), and 2.118(4) compared to those in compound 5 (2.247(4) and 1.961(4) ). Figure 5-3. Thermal ellipsoid diagra m of the molecular structure of 5. Thermal ellipsoids are drawn at 40% probability, and the hydrogens not attached to the metal have been omitted for clarity. When comparing compound 5 to compound 4, we know that the guanidinato ligand has an overall charge of -1. If the guanidinato ligand in compound 5 has a -1 charge in its binding to the metal then tungsten would be in the W5+ oxidation state with a d1 electron configuration, causing the compound to be paramagnetic. However, analysis of the NMR spectra indicated that 5 is a diamagnetic complex. An explan ation for the diamagnetic character of 5 is that the guanidinato ligand has its major resonance form s represented in Figure 4-1b, where there is a -2 charge at the metal as opposed to the -1 charge in complex 4. Taking into consideration the difference in bond lengths in the gu anidinato ligand between complex 4 and 5, a -2 charge on the guanidinato ligand at the metal in complex 5 is a reasonable assumption. If the resonance

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88 structure is the guanidinato(2-), then the tungsten in complex 5 would be in a W6+ oxidation state with a d0 electron configuration yielding a diamagnetic complex. A dianionic guanidinato ligand can function as a diamido ligand, with delocalization or Y-conjugation throughout the CN3 backbone. The average W-N(guanidinato) bond le ngth is 2.14 which is longer than typical tungsten dimethyl amide bond lengths of 2.05-2.07 indicating single bonds between the WN(guanidinato) in complex 5.232 The guanidinato ligand binds to the tungsten in complex 5 through the two nitrogens forming a planar f our-membered metallacycle (N3-C1-N2, N3-W1-N2 dihedral angle = 1.1). The average C1-N4-(C11, C11, C12, C12) bond angle is 121.9 indicating an sp2 hybridized nitrogen (N4). This is ve ry interesting due to the lack of guanidinato (2-) ligands in the literature compared to guanidinato(1-) and neutral ligands.189 A complete listing of bond angles and bond lengths is shown in Appendix C. Table 5-1. Selected bond distances () and angles () for compound 5. Thermogravimetric analysis Therm ogravimetric analysis of 5 was also carried out (Figure 5-4). Compared to TGA data of 4, decomposition seems to be a mu ch cleaner process for compound 5. Compound 5 starts to lose mass around 125 C as compared to about 165 C for compound 4. A comparison of the Bond Length () Bond Length () Bond Angle () W1-H1 1.71(5) N2-C1 1.324(6) N2-C1-N4 124.7(5) W1-H3 1.71(6) N3-C1 1.317(6) N3-C1-N4 126.1(5) W1-H4 1.96(5) N4-C1 1.384(6) N3-C1-N2 109.2(4) W1-N1 1.733(4) W1-H3-W2 42(2) W1-N2 2.147(3) W1-H4-W2 38.9(14) W1-N3 2.127(4) W1-W2 2.6332(3) W2-H2 1.58(4) N6-C13 1.330(6) N6-C13-N7 109.3(4) W2-H3 1.78(6) N7-C13 1.335(5) N6-C13-N8 128.2(4) W2-H4 1.66(5) N8-C13 1.384(6) N7-C13-N8 122.4(4) W2-N5 1.746(4) W2-N6 2.157(3) W2-N7 2.118(4)

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89 TGA data from compounds 4 and 5 is shown in Figure 5-5. The first inflection point is at 169 C at 84% which corresponds to lo ss of several isopropyl and me thyl fragments. The second inflection point occurs at 328 C and 60% corresponding to furthe r loss of isopropyl and methyl groups and possible guanidinato fragmentation. The mass loss seems to be complete around 52% which could correspond to W2N (380 g/mol) with 12% carbon incorporation. Figure 5-4. TGA data for 5. Weight % and Derivative (Weight %) vs. Temperature.

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90 Figure 5-5. Comparison of TGA data for complexes 4 and 5. Mass spectrometry data Fragm entation patterns in mass spectrometric data of CVD precursors have shown a strong relationship with likely decompositi on pathways during the CVD process.156,157 Acknowledging the difference between gas phase ionization and th ermal decomposition processes, there seems to be a strong correlation between the fragmentation pa tterns in mass spectrometry and the resulting film deposition properties. Previous studies ha ve shown that mass spectrometry of the tungsten imido precursors Cl4(CH3CN)W(NiPr) (1a) and Cl4(CH3CN)W(NPh) ( 2a) affords qualitative insights into thei r CVD behavior.33,151,158 Therefore mass spectrometry of the precursor 5 was used as a preliminary screening technique. Mass spectral data were obtained for 5 using positive ion elec tron-capture chemical ionization (PCI). In co ntrast to precursors 1-3 ,57,99,207 but similar to complex 4,62 a mass envelope for the molecular ion for 5 could be observed ( m/z 826), which was overlapping the

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91 mass envelope for loss of H2 ( m/z 824). These were the base peak of the PCI spectrum. Also evident is a peak at m/z 698 with 32% abundance, correspondi ng to loss of a methyl group and fragmentation of one of the guanidinato ligands to form a bisimido coordination sphere on one of the tungstens. The guanidinato fr agment that was lost to give m/z of 698 is seen at m/z 113, [C6H13N2]+ with a 6% abundance. (Figure 5-6) Figure 5-6. PCI mass spectrum of compound 5. Conclusion New potential single source precurso rs for MOCVD of WNxCy have been synthesized. The compounds synthesized incorporate strongly bound nitrogen ligands and eliminate chlorine through the use of hydride ligands, a significant advantage in a C VD precursor. TGA data shows an onset of decomposition for complex 5 at a lower temperature than 4. X-ray crystallography and NMR spectroscopy allowed for detailed analysis of bonding in compound 5.

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92 Experimental Procedures General Procedures Unless otherwise stated, reac tions and m anipulations were performed in an inert atmosphere (N2) glovebox or using standard Schlenk te chniques. All reaction solvents were purified using an M. Braun MB-SP solvent purification system prior to use. NMR solvents were degassed by three freezepumpthaw cycles and st ored over 3 molecular sieves in an inertatmosphere glove box. 1H and 13C NMR spectra were recorded on Mercury 300, Gemini 300 or VXR 300 spectrometers using residual protons of deuterated solvents for reference. Infrared spectra were recorded as pure compound on a Pe rkin Elmer Spectrum One FT-IR spectrometer. LiBEt3H (1 M in THF) was used as purchased from Aldrich. W(NiPr)(iPrNC(NMe2)NiPr)Cl3, W(NCy)(iPrNC(NMe2)NiPr)Cl3, and W(NPh)(iPrNC(NMe2)NiPr)Cl3 were prepared by the method used to synthesize 4 in Chapter 4 of this work.62 Synthesis of {W2(NiPr)2[iPrNC(NMe2)NiPr]2H2(-H)2} (5). W(NiPr)(iPrNC(NMe2)NiPr)Cl3 was dissolved in 20 mL of THF. A 1 M solution of LiBEt3H in THF was added dropwise at room temperature. Upon addition of LiBEt3H, effervescence was observed; when addition was co mplete the solution had turned emerald green. When effervescence was complete, the solvent was removed in vacuo As solvent was removed the color changed from green to brown. The pr oduct was extracted with hexane giving a yellow solution. The hexane was removed in vacuo to give {W2(NiPr)2[iPrNC(NMe2)NiPr]2H2(-H)2} (5) in a 66 percent yield. Recrystalliza tion from a concentrated solution of 5 in pentane at -30 C yielded pure 5 as yellow crystals. Where assignments of 1H or 13C NMR resonances were ambiguous, 13C-1H HMBC experiments were used to elucidate them (Appendix C). 1H NMR (300 MHz, room temperature, THFd8): ppm 1.12 (24 H, d, J = 6.41 Hz), 1.23 (12 H, d, J = 6.41 Hz), 2.81 (12 H, s), 3.84 (4 H, septet, J = 6.31 Hz), 4.04 (2 H, septet, J = 6.38 Hz). 1H

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93 NMR (300 MHz, -53 C, THFd8): ppm 1.01 (6 H, d, J = 5.5 Hz), 1.11 (12 H, q, J = 5.8 Hz), 1.22 (18 H, t, J = 5.8 Hz), 2.83 (6 H, s), 3.18 (t, W H, 1JW-H = 55.3 Hz 1JH-H = 6.7 Hz), 3.84 (4 H, septet, J = 5.8 Hz), 4.04 (2 H, septet, J = 6.2 Hz), 11.43 (s, W H, 1JW-H = 61.2 Hz 1JH-H = 6.7 Hz). 13C NMR (300 MHz, THF d8): ppm 25.45 (NCHC H3), 27.46 (NCH C H3, imido), 39.91 (N( C H3)2), 46.64 (N C HCH3), 61.96 (N C HCH3, imido), 172.91 (N C N). IR (cm-1): 3392 (s), 2965 (s), 2928 (m), 2861 (m), 1871 (w), 1627 (m), 1536 (m), 1452 (m), 1413 (m), 1300 (m), 1198 (m), 1063 (m), 750 (s). Synthesis of {W2(NCy)2[iPrNC(NMe2)NiPr]2H2(-H)2} (6). W(NCy)(iPrNC(NMe2)NiPr)Cl3 was dissolved in 20 mL of THF. A 1M solution of LiBEt3H in THF was added dropwise at room temperature. Upon addition of LiBEt3H effervescence was observed; when addition was co mplete the solution had turned emerald green. When effervescence was complete, the solvent was removed in vacuo The product was extracted with hexane giving a bright emer ald green solution. The hexane was removed in vacuo to give {W2(NCy)2[iPrNC(NMe2)NiPr]2H2(-H)2} (6) in a 61 percent yield. Attempted recrystallization of 6 was unsuccessful. 1H NMR (300 MHz, THFd8): 1.10-1.23 (multiple d, 28H, CH(C H3)2, C H2) 1.41-1.64 (br, 8H C H2), 1.75-2.01 (br, 8H, C H2), 2.81 (s, 6H, N(C H3)2), 2.85 (s, 6H, N(C H3)2), 3.84 (septet, 2H, WNC H ), 4.06 (septet, 2H, WNC H ), 12.71 (s, W H, 1JW-H = 52.5 Hz). 13C NMR (300 MHz, THFd8): 24.5, 25.1, 25.37, 25.41, 25.64, 25.66 ( C H2), 26.6, 26.3, 27.00, 27.3 (N( C H3)2), 35.5, 35.7, 37.7, 40.1, 40.5 (CH( C H3)2), 46.8, 48.9, 49.0( C H(CH3)2), 69.3, 71.5 (WN C ), 170.3, 172.9 (N3C). Synthesis of {W2(NPh)2[iPrNC(NMe2)NiPr]2H2(-H)2} (7). W(NPh)(iPrNC(NMe2)NiPr)Cl3 was dissolved in 20 mL of THF. A 1M solution of LiBEt3H in THF was added drop wise at room temperature. Upon addition of LiBEt3H

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94 effervescence was observed, when addition was co mplete the solution had turned brown. When effervescence was complete, the solvent was removed in vacuo The product was extracted with hexane giving an orange solu tion. The hexane was removed in vacuo to give {W2(NPh)2[iPrNC(NMe2)NiPr]2H2(-H)2} (7) in a 55 percent yield. Attempted recrystallization of 7 was unsuccessful. 1H NMR (300 MHz, C6D6): 1.33, 1.37 (two d, 24H, CH(C H3)2), 2.29, 2.32 (two s, 12H, N(C H3)2), 3.79 (septets, 4H, WNC H ), 6.92-7.00 (m, 2H, C H ), 7.16-7.23 (m, 4H, C H ) 7.48-7.60 (m, 4H, C H ), 14.81 (s, W H ). 1JW-H = 51.5 Hz). 1H NMR (300 MHz, -56 C, THFd8): 12.31 (t, W H, 1JW-H = 61.3 Hz, 1JH-H = 6.8 Hz), 14.17 (s, W H, 1JW-H = 53.1 Hz). 13C NMR (300 MHz, THFd8): 39.95, 40.43, 42.24, (CH( C H3)2, C H(CH3)2, N( C H3)2), 122.54, 125.74, 128.40, 128.82, 129.65, 129.83, ( C H, WN C ), 191.10, (N3C ). X-ray Crystallography Data were collected at 173 K on a Siem ens SMART PLATFORM equipped with A CCD area detector and a graphite monochromator utilizing MoK radiation ( = 0.71073 ). Cell parameters were refined using up to 8192 reflections. A full sphe re of data (1850 frames) was collected using the -scan method (0.3 frame width). The first 50 frames were re-measured at the end of data collection to monitor instrument and crystal stability (maximum correction on I was < 1 %). Absorption corrections by integrat ion were applied based on measured indexed crystal faces. The structure was solved by the Direct Methods in SHELXTL6,170 and refined using fullmatrix least squares. The non-H atoms were tr eated anisotropically, wh ereas the hydrogen atoms were calculated in ideal positions and were riding on their respective car bon atoms. A total of 324 parameters were refined in the final cycle of refinement using 22106 reflections with I > 2 (I) to yield R1 and wR2 of 2.69% and 6.67%, respectively. Refinement was done using F2.

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95 The toluene molecule was disordered and could not be modeled properly, thus program SQUEEZE,233 a part of the PLATON233 package of crystallographic software, was used to calculate the solvent disorder area and remove its contribution to the ove rall intensity data. Mass Spectrometry Mass spectral analyses were perform ed usi ng a ThermoScientific DSQ mass spectrometer equipped with a direct insertion probe (DIP) that was held at 50 C for 1 minute and then heated up to 280 C at 30 /min during the sample analysis. Ion source temperature was 150 C with methane gas at 0.5 mL/min. Thermogravimetric Analysis TGA analysis was carried out using a TA Instrum ents TGA Q5000 V3.3 Build 250 thermogravimetric analyzer. The sample wa s run under nitrogen using the hi-res dynamic method with a heating rate of 40 C/min from 25 C to 700 C (Sample size = 6.353 mg).

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96 APPENDIX A CRYSTALLOGRAPHY DATA FOR 3a Table A-1. Atom ic coordinates ( x 104) and equivalent isotropic displacement parameters (2x 103) for 3a. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor. x y z U(eq) W 3673(1) 8599(10) 2535(1) 49(1) N1 5066(15) 8370(40) 1429(7) 70(6) N2 1708(12) 8700(50) 4039(6) 44(2) Cl1 5703(14) 10782(10) 3533(7) 76(3) Cl2 1187(11) 6445(7) 1876(6) 59(2) Cl3 5635(13) 6364(9) 3495(7) 68(3) Cl4 1046(15) 10783(8) 1997(7) 79(3) C1 6430(20) 8580(40) 484(10) 93(5) C2 5470(60) 9880(60) -410(30) 66(9) C3 3800(60) 8730(120) -1180(30) 80(10) C2' 5130(30) 8860(50) -592(16) 65(7) C3' 3020(30) 8270(30) -748(16) 53(5) C4 665(13) 8640(50) 4747(7) 44(3) C5 -633(17) 8530(50) 5692(8) 52(3)

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97 Table A-2. Bond lengths [] and angles [] for 3a. Bond Length () or Angle () W-N1 1.687(9) W-N2 2.308(8) W-Cl2 2.317(8) W-Cl3 2.324(9) W-Cl1 2.339(10) W-Cl4 2.351(9) N1-C1 1.508(17) N2-C4 1.130(12) C1-C2' 1.51(2) C1-C2 1.55(4) C2-C3 1.59(6) C2'-C3' 1.36(3) C4-C5 1.476(14) N1-W-N2 175.8(15) N1-W-Cl2 90.6(8) N2-W-Cl2 86.0(7) N1-W-Cl3 93.6(7) N2-W-Cl3 84.0(6) Cl2-W-Cl3 88.7(4) N1-W-Cl1 102.4(8) N2-W-Cl1 81.1(7) Cl2-W-Cl1 167.0(3) Cl3-W-Cl1 90.18(13) N1-W-Cl4 103.1(7) N2-W-Cl4 79.1(6) Cl2-W-Cl4 88.14(11) Cl3-W-Cl4 163.0(3) Cl1-W-Cl4 89.2(4) C1-N1-W 167(2) C4-N2-W 175(3) C2'-C1-N1 114.2(12) C2'-C1-C2 30.9(16) N1-C1-C2 114.8(17) C1-C2-C3 106(4) C3'-C2'-C1 120(2) N2-C4-C5 178(2) Symmetry transformations used to generate equivalent atoms.

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98 Table A-3. Anisotropic di splacement parameters (2x 103) for 3a. The anisotropic displacement factor exponent takes the form: -2 2[ h2 a*2U11 + ... + 2 h k a* b* U12 U 11 U 22 U 33 U 23 U 13 U 12 W 31(1) 79(1) 38(1) -1(1) 2(1) -1(1) N1 53(5) 115(16) 41(4) 1(8) 1(4) 51(11) N2 35(3) 51(7) 47(4) 13(12) 3(3) 8(10) Cl1 58(5) 101(7) 65(5) 18(5) -10(4) -30(5) Cl2 40(3) 86(5) 51(3) -8(3) 9(2) -14(3) Cl3 52(4) 94(7) 58(5) 2(5) -4(3) 22(4) Cl4 87(5) 69(5) 73(4) 7(3) -30(4) 0(4) C1 69(8) 146(13) 67(7) -6(16) 17(7) 75(13) C4 35(4) 53(6) 45(5) -21(12) 1(4) 14(12) C5 52(5) 58(7) 48(5) -8(15) 13(4) 19(14) Table A-4. Hydrogen coordinates ( x 104) and isotropic displacement parameters (2x 10 3) for 3a. x y z U(eq) H1B 6628 7394 154 112 H1A 7896 9024 761 112 H1B' 7403 9632 623 112 H1A' 7373 7516 438 112 H2 5816 11109 -492 80 H3B 3577 7498 -1024 96 H3A 3011 9267 -1789 96 H2' 5774 9445 -1165 78 H3B' 2371 7687 -177 63 H3A' 2207 8450 -1429 63 H5A -750 7281 5915 78 H5B -2097 9017 5497 78 H5C 85 9229 6294 78

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99 APPENDIX B KINETICS DATA FOR 1 Table B-1. Rates for the aceton itrile exchange of complex 1. T (C) k (sec-1) 1/T ln(k/T) -5.6 11.2 0.00374 -3.17343 -3.4 15.0 0.00371 -2.88948 -1.9 20.2 0.00369 -2.59740 0.4 25.5 0.00366 -2.37284 2.6 33.3 0.00363 -2.11397 4.8 43.8 0.00360 -1.84784 6.9 57.6 0.00357 -1.58148 8.9 73.7 0.00355 -1.34212 10.8 93.3 0.00352 -1.11301 12.8 119.0 0.00350 -0.87673 14.8 151.0 0.00347 -0.64554 16.8 191.0 0.00345 -0.41747 18.7 241.0 0.00343 -0.19148 20.7 305.0 0.00340 0.03721 22.7 382.0 0.00338 0.25553 24.6 474.0 0.00336 0.46492 26.5 544.0 0.00334 0.59630 28.5 684.0 0.00331 0.81866 30.4 854.0 0.00329 1.03435 32.4 943.0 0.00327 1.12692 34.3 1100.0 0.00325 1.27472

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100 APPENDIX C STRUCTURAL CHARACTERIZATION FOR 5 Figure C-1. Heteronuclear Mu ltiple Bond Coherence (gHMBC) NMR spectrum of Hydride Dimer 5.

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101 Table C-1. Crystal data a nd structure refinement for 5. Identification code llr8 Empirical formula C24 H58 N8 W2 Formula weight 826.48 Temperature 173(2) K Wavelength 0.71073 Crystal system Monoclinic Space group P2(1)/n Unit cell dimensions a = 9.2735(9) = 90. b = 24.545(2) = 98.950(2). c = 14.7551(2) = 90. Volume 3317.6(6) 3 Z 4 Density (calculated) 1.655 Mg/m 3 Absorption coefficient 6.953 mm -1 F(000) 1624 Crystal size 0.17 x 0.09 x 0.09 mm 3 Theta range for data collection 1.62 to 27.50. Index ranges -9 h 12, -27 k 31, -19 l 19 Reflections collected 22106 Independent reflections 7583 [R(int) = 0.0563] Completeness to theta = 27.50 99.8 % Absorption correction Integration Max. and min. transmission 0.6063 and 0.2981 Refinement method Full-matrix least-squares on F 2 Data / restraints / parameters 7583 / 12 / 324 Goodness-of-fit on F 2 1.028 Final R indices [I>2sigma(I)] R1 = 0.0269, wR2 = 0.0667 R indices (all data) R1 = 0.0340, wR2 = 0.0694 Largest diff. peak and hole 1.550 and -0.921 e. -3 R1 = (||F o | |F c ||) / |F o | wR2 = [ w(F o 2 F c 2 ) 2 ] / w F o 2 2 ]] 1/2 S = [ w(F o 2 F c 2 ) 2 ] / (n-p)] 1/2 w= 1/[ 2 (F o 2 )+(m*p)2+n*p], p = [max(F o 2 ,0)+ 2* F c 2 ]/3, m & n are constants.

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102 Table C-2. Atomic coordinates ( x 104) and equivalent isotropic displacement parameters (2x 103) for 5. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor. x y z U(eq) W(1) 1425(1) 992(1) 7347(1) 29(1) W(2) 2585(1) 1791(1) 8408(1) 31(1) N(1) 701(5) 472(2) 7930(3) 50(1) N(2) 452(4) 998(1) 5928(2) 34(1) N(3) 2619(4) 680(2) 6341(3) 60(1) N(4) 1686(6) 668(2) 4724(3) 70(1) N(5) 1449(5) 2356(1) 8448(2) 45(1) N(6) 4127(4) 1690(1) 9650(2) 35(1) N(7) 4803(4) 1993(2) 8396(2) 44(1) N(8) 6737(4) 1739(2) 9580(3) 50(1) C(1) 1597(5) 777(2) 5634(3) 45(1) C(2) 221(8) 148(2) 8646(3) 82(2) C(3) -1198(19) -47(5) 8449(9) 68(3) C(4) 1395(18) -378(5) 8733(8) 68(3) C(3') -1630(30) 108(8) 8336(13) 68(3) C(4') 700(20) -344(7) 8940(11) 68(3) C(5) 3811(6) 291(3) 6373(6) 96(3) C(6) 5147(13) 617(6) 6590(11) 101(3) C(7) 3589(12) -175(5) 7103(10) 101(3) C(6') 5075(18) 332(8) 7156(15) 101(3) C(7') 3330(17) -222(7) 6030(13) 101(3) C(8) -632(7) 1342(2) 5377(3) 63(2) C(9) 499(7) 1949(2) 5504(3) 58(1) C(10) -1784(19) 1439(6) 5624(11) 58(1) C(9') -600(10) 1932(3) 5562(5) 58(1) C(10') -2242(9) 1101(3) 5593(6) 58(1) C(11) 314(15) 481(6) 4095(10) 56(2) C(12) 2863(13) 774(4) 4244(7) 56(2) C(11') 810(20) 458(10) 4083(17) 56(2) C(12') 3380(20) 663(6) 4615(12) 56(2) C(13) 5270(5) 1806(2) 9241(3) 39(1) C(14) 247(6) 2740(2) 8348(3) 61(2) C(15) 807(10) 3290(2) 8045(4) 97(3) C(16) -381(7) 2799(3) 9244(5) 78(2) C(17) 4171(5) 1314(2) 10433(3) 43(1) C(18) 4266(6) 723(2) 10147(4) 59(1) C(19) 2858(6) 1424(3) 10907(4) 66(2) C(20) 5637(6) 2347(2) 7862(3) 54(1) C(21) 5085(9) 2924(3) 7869(5) 88(2) C(22) 5508(7) 2144(3) 6887(4) 71(2) C(23) 7671(6) 1438(3) 9030(4) 77(2) C(24) 7308(6) 1797(2) 10550(3) 61(2)

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103 Table C-3. Bond lengths [] and angles [] for 5 Bond Length () or Angle () W(1)-N(1) 1.733(4) W(1)-N(3) 2.128(4) W(1)-N(2) 2.147(3) W(1)-C(1) 2.611(4) W(1)-W(2) 2.6332(3) W(1)-H(1) 1.70(5) W(1)-H(3) 1.71(6) W(1)-H(4) 1.96(5) W(2)-N(5) 1.746(4) W(2)-N(7) 2.118(4) W(2)-N(6) 2.156(3) W(2)-C(13) 2.600(4) W(2)-H(2) 1.58(4) W(2)-H(3) 1.78(6) W(2)-H(4) 1.66(5) N(1)-C(2) 1.446(6) N(2)-C(1) 1.325(6) N(2)-C(8) 1.460(6) N(3)-C(1) 1.317(6) N(3)-C(5) 1.456(7) N(4)-C(11') 1.26(2) N(4)-C(1) 1.384(6) N(4)-C(12) 1.414(10) N(4)-C(11) 1.524(16) N(4)-C(12') 1.607(19) N(5)-C(14) 1.451(6) N(6)-C(13) 1.330(6) N(6)-C(17) 1.474(5) N(7)-C(13) 1.336(5) N(7)-C(20) 1.471(6) N(8)-C(13) 1.384(6) N(8)-C(24) 1.454(6) N(8)-C(23) 1.473(7) C(2)-C(4') 1.336(18) C(2)-C(3) 1.388(17) C(2)-C(4) 1.681(17) C(2)-C(3') 1.71(2) C(2)-H(2A) 1.0000 C(2)-H(2B) 1.0000 C(3)-H(3A) 0.9800 C(3)-H(3B) 0.9800 C(3)-H(3C) 0.9800 C(4)-H(4A) 0.9800

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104 Table C-3. Continued. C(4)-H(4B) 0.9800 C(4)-H(4C) 0.9800 C(3')-H(3'A) 0.9800 C(3')-H(3'B) 0.9800 C(3')-H(3'C) 0.9800 C(4')-H(4'A) 0.9800 C(4')-H(4'B) 0.9800 C(4')-H(4'C) 0.9800 C(5)-C(7') 1.404(16) C(5)-C(6) 1.467(14) C(5)-C(6') 1.516(17) C(5)-C(7) 1.606(17) C(5)-H(5A) 1.0000 C(5)-H(5B) 1.0000 C(6)-H(6A) 0.9800 C(6)-H(6B) 0.9800 C(6)-H(6C) 0.9800 C(7)-H(7A) 0.9800 C(7)-H(7B) 0.9800 C(7)-H(7C) 0.9800 C(6')-H(6'A) 0.9800 C(6')-H(6'B) 0.9800 C(6')-H(6'C) 0.9800 C(7')-H(7'A) 0.9800 C(7')-H(7'B) 0.9800 C(7')-H(7'C) 0.9800 C(8)-C(10) 1.205(17) C(8)-C(9') 1.473(9) C(8)-C(10') 1.682(11) C(8)-C(9) 1.8139 C(8)-H(8A) 1.0000 C(8)-H(8B) 1.0000 C(9)-H(9A) 0.9800 C(9)-H(9B) 0.9800 C(9)-H(9C) 0.9800 C(10)-H(10A) 0.9800 C(10)-H(10B) 0.9800 C(10)-H(10C) 0.9800 C(9')-H(9'A) 0.9800 C(9')-H(9'B) 0.9800 C(9')-H(9'C) 0.9800 C(10')-H(10D) 0.9800 C(10')-H(10E) 0.9800 C(10')-H(10F) 0.9800 C(11)-H(11A) 0.9800

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105 Table C-3. Continued. C(11)-H(11B) 0.9800 C(11)-H(11C) 0.9800 C(12)-H(12A) 0.9800 C(12)-H(12B) 0.9800 C(12)-H(12C) 0.9800 C(11')-H(11D) 0.9800 C(11')-H(11E) 0.9800 C(11')-H(11F) 0.9800 C(12')-H(12D) 0.9800 C(12')-H(12E) 0.9800 C(12')-H(12F) 0.9800 C(14)-C(16) 1.532(8) C(14)-C(15) 1.536(9) C(14)-H(14A) 1.0000 C(15)-H(15A) 0.9800 C(15)-H(15B) 0.9800 C(15)-H(15C) 0.9800 C(16)-H(16A) 0.9800 C(16)-H(16B) 0.9800 C(16)-H(16C) 0.9800 C(17)-C(18) 1.515(7) C(17)-C(19) 1.521(7) C(17)-H(17A) 1.0000 C(18)-H(18A) 0.9800 C(18)-H(18B) 0.9800 C(18)-H(18C) 0.9800 C(19)-H(19A) 0.9800 C(19)-H(19B) 0.9800 C(19)-H(19C) 0.9800 C(20)-C(21) 1.508(8) C(20)-C(22) 1.510(7) C(20)-H(20A) 1.0000 C(21)-H(21A) 0.9800 C(21)-H(21B) 0.9800 C(21)-H(21C) 0.9800 C(22)-H(22A) 0.9800 C(22)-H(22B) 0.9800 C(22)-H(22C) 0.9800 C(23)-H(23A) 0.9800 C(23)-H(23B) 0.9800 C(23)-H(23C) 0.9800 C(24)-H(24A) 0.9800 C(24)-H(24B) 0.9800 C(24)-H(24C) 0.9800 N(1)-W(1)-N(3) 111.4(2)

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106 Table C-3. Continued. N(1)-W(1)-N(2) 110.63(14) N(3)-W(1)-N(2) 60.50(15) N(1)-W(1)-C(1) 114.70(16) N(3)-W(1)-C(1) 30.13(15) N(2)-W(1)-C(1) 30.37(14) N(1)-W(1)-W(2) 114.08(12) N(3)-W(1)-W(2) 118.33(12) N(2)-W(1)-W(2) 130.21(8) C(1)-W(1)-W(2) 130.22(9) N(1)-W(1)-H(1) 93.8(16) N(3)-W(1)-H(1) 137.9(15) N(2)-W(1)-H(1) 79.6(15) C(1)-W(1)-H(1) 109.0(15) W(2)-W(1)-H(1) 76.8(16) N(1)-W(1)-H(3) 102(2) N(3)-W(1)-H(3) 90(2) N(2)-W(1)-H(3) 142(2) C(1)-W(1)-H(3) 117(2) W(2)-W(1)-H(3) 42(2) H(1)-W(1)-H(3) 118(3) N(1)-W(1)-H(4) 153.0(14) N(3)-W(1)-H(4) 88.5(14) N(2)-W(1)-H(4) 94.8(14) C(1)-W(1)-H(4) 91.8(14) W(2)-W(1)-H(4) 38.9(14) H(1)-W(1)-H(4) 82(2) H(3)-W(1)-H(4) 59(2) N(5)-W(2)-N(7) 114.01(17) N(5)-W(2)-N(6) 112.72(14) N(7)-W(2)-N(6) 61.15(13) N(5)-W(2)-C(13) 120.76(15) N(7)-W(2)-C(13) 30.77(14) N(6)-W(2)-C(13) 30.70(13) N(5)-W(2)-W(1) 114.73(12) N(7)-W(2)-W(1) 118.43(10) N(6)-W(2)-W(1) 125.10(9) C(13)-W(2)-W(1) 124.32(9) N(5)-W(2)-H(2) 94.9(15) N(7)-W(2)-H(2) 140.5(14) N(6)-W(2)-H(2) 83.6(14) C(13)-W(2)-H(2) 111.3(14) W(1)-W(2)-H(2) 66.7(14) N(5)-W(2)-H(3) 155(2) N(7)-W(2)-H(3) 87(2) N(6)-W(2)-H(3) 89(2)

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107 Table C-3. Continued. C(13)-W(2)-H(3) 84(2) W(1)-W(2)-H(3) 40(2) H(2)-W(2)-H(3) 75(2) N(5)-W(2)-H(4) 101.7(17) N(7)-W(2)-H(4) 87.2(17) N(6)-W(2)-H(4) 140.1(17) C(13)-W(2)-H(4) 113.1(17) W(1)-W(2)-H(4) 48.1(16) H(2)-W(2)-H(4) 114(2) H(3)-W(2)-H(4) 64(2) C(2)-N(1)-W(1) 162.7(3) C(1)-N(2)-C(8) 124.9(4) C(1)-N(2)-W(1) 94.6(3) C(8)-N(2)-W(1) 134.1(3) C(1)-N(3)-C(5) 126.4(4) C(1)-N(3)-W(1) 95.7(3) C(5)-N(3)-W(1) 133.5(5) C(11')-N(4)-C(1) 132.7(10) C(11')-N(4)-C(12) 99.2(10) C(1)-N(4)-C(12) 128.1(6) C(11')-N(4)-C(11) 15.8(11) C(1)-N(4)-C(11) 118.6(6) C(12)-N(4)-C(11) 112.8(6) C(11')-N(4)-C(12') 116.9(10) C(1)-N(4)-C(12') 107.8(7) C(12)-N(4)-C(12') 26.7(5) C(11)-N(4)-C(12') 132.5(7) C(14)-N(5)-W(2) 166.1(3) C(13)-N(6)-C(17) 124.2(4) C(13)-N(6)-W(2) 93.4(2) C(17)-N(6)-W(2) 132.2(3) C(13)-N(7)-C(20) 125.5(4) C(13)-N(7)-W(2) 95.0(3) C(20)-N(7)-W(2) 137.2(3) C(13)-N(8)-C(24) 122.1(4) C(13)-N(8)-C(23) 119.3(4) C(24)-N(8)-C(23) 115.8(4) N(3)-C(1)-N(2) 109.2(4) N(3)-C(1)-N(4) 126.1(5) N(2)-C(1)-N(4) 124.7(5) N(3)-C(1)-W(1) 54.2(2) N(2)-C(1)-W(1) 55.0(2) N(4)-C(1)-W(1) 179.4(4) C(4')-C(2)-C(3) 90.8(9) C(4')-C(2)-N(1) 127.5(12)

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108 Table C-3. Continued. C(3)-C(2)-N(1) 115.2(6) C(4')-C(2)-C(4) 26.1(8) C(3)-C(2)-C(4) 109.4(7) N(1)-C(2)-C(4) 102.0(7) C(4')-C(2)-C(3') 107.7(10) C(3)-C(2)-C(3') 17.0(7) N(1)-C(2)-C(3') 104.3(7) C(4)-C(2)-C(3') 126.0(8) C(4')-C(2)-H(2A) 101.3 C(3)-C(2)-H(2A) 110.0 N(1)-C(2)-H(2A) 110.0 C(4)-C(2)-H(2A) 110.0 C(3')-C(2)-H(2A) 104.0 C(4')-C(2)-H(2B) 105.2 C(3)-C(2)-H(2B) 112.4 N(1)-C(2)-H(2B) 105.2 C(4)-C(2)-H(2B) 112.1 C(3')-C(2)-H(2B) 105.2 H(2A)-C(2)-H(2B) 4.8 C(2)-C(3)-H(3A) 109.5 C(2)-C(3)-H(3B) 109.5 H(3A)-C(3)-H(3B) 109.5 C(2)-C(3)-H(3C) 109.5 H(3A)-C(3)-H(3C) 109.5 H(3B)-C(3)-H(3C) 109.5 C(2)-C(4)-H(4A) 109.5 C(2)-C(4)-H(4B) 109.5 H(4A)-C(4)-H(4B) 109.5 C(2)-C(4)-H(4C) 109.5 H(4A)-C(4)-H(4C) 109.5 H(4B)-C(4)-H(4C) 109.5 C(2)-C(3')-H(3'A) 109.5 C(2)-C(3')-H(3'B) 109.5 H(3'A)-C(3')-H(3'B) 109.5 C(2)-C(3')-H(3'C) 109.5 H(3'A)-C(3')-H(3'C) 109.5 H(3'B)-C(3')-H(3'C) 109.5 C(2)-C(4')-H(4'A) 109.5 C(2)-C(4')-H(4'B) 109.5 H(4'A)-C(4')-H(4'B) 109.5 C(2)-C(4')-H(4'C) 109.5 H(4'A)-C(4')-H(4'C) 109.5 H(4'B)-C(4')-H(4'C) 109.5 C(7')-C(5)-N(3) 112.3(7) C(7')-C(5)-C(6) 141.0(9)

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109 Table C-3. Continued. N(3)-C(5)-C(6) 105.2(7) C(7')-C(5)-C(6') 119.9(12) N(3)-C(5)-C(6') 118.4(7) C(6)-C(5)-C(6') 43.2(10) C(7')-C(5)-C(7) 62.3(10) N(3)-C(5)-C(7) 108.2(7) C(6)-C(5)-C(7) 115.7(10) C(6')-C(5)-C(7) 72.6(11) C(7')-C(5)-H(5A) 48.4 N(3)-C(5)-H(5A) 109.2 C(6)-C(5)-H(5A) 109.2 C(6')-C(5)-H(5A) 129.2 C(7)-C(5)-H(5A) 109.2 C(7')-C(5)-H(5B) 100.3 N(3)-C(5)-H(5B) 100.3 C(6)-C(5)-H(5B) 61.6 C(6')-C(5)-H(5B) 100.3 C(7)-C(5)-H(5B) 150.5 H(5A)-C(5)-H(5B) 52.6 C(5)-C(6)-H(6A) 109.5 C(5)-C(6)-H(6B) 109.5 H(6A)-C(6)-H(6B) 109.5 C(5)-C(6)-H(6C) 109.5 H(6A)-C(6)-H(6C) 109.5 H(6B)-C(6)-H(6C) 109.5 C(5)-C(7)-H(7A) 109.5 C(5)-C(7)-H(7B) 109.5 H(7A)-C(7)-H(7B) 109.5 C(5)-C(7)-H(7C) 109.5 H(7A)-C(7)-H(7C) 109.5 H(7B)-C(7)-H(7C) 109.5 C(5)-C(6')-H(6'A) 109.5 C(5)-C(6')-H(6'B) 109.5 H(6'A)-C(6')-H(6'B) 109.5 C(5)-C(6')-H(6'C) 109.5 H(6'A)-C(6')-H(6'C) 109.5 H(6'B)-C(6')-H(6'C) 109.5 C(5)-C(7')-H(7'A) 109.5 C(5)-C(7')-H(7'B) 109.5 H(7'A)-C(7')-H(7'B) 109.5 C(5)-C(7')-H(7'C) 109.5 H(7'A)-C(7')-H(7'C) 109.5 H(7'B)-C(7')-H(7'C) 109.5 C(10)-C(8)-N(2) 120.8(8) C(10)-C(8)-C(9') 75.1(9)

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110 Table C-3. Continued. N(2)-C(8)-C(9') 118.3(5) C(10)-C(8)-C(10') 32.6(8) N(2)-C(8)-C(10') 104.2(4) C(9')-C(8)-C(10') 107.7(5) C(10)-C(8)-C(9) 109.4(9) N(2)-C(8)-C(9) 94.6(3) C(9')-C(8)-C(9) 34.9(4) C(10')-C(8)-C(9) 141.8(3) C(10)-C(8)-H(8A) 120.9 N(2)-C(8)-H(8A) 108.8 C(9')-C(8)-H(8A) 108.8 C(10')-C(8)-H(8A) 108.8 C(9)-C(8)-H(8A) 95.8 C(10)-C(8)-H(8B) 110.3 N(2)-C(8)-H(8B) 110.3 C(9')-C(8)-H(8B) 118.3 C(10')-C(8)-H(8B) 94.2 C(9)-C(8)-H(8B) 110.3 H(8A)-C(8)-H(8B) 15.0 C(8)-C(9)-H(9A) 109.5 C(8)-C(9)-H(9B) 109.5 H(9A)-C(9)-H(9B) 109.5 C(8)-C(9)-H(9C) 109.5 H(9A)-C(9)-H(9C) 109.5 H(9B)-C(9)-H(9C) 109.5 C(8)-C(10)-H(10A) 109.5 C(8)-C(10)-H(10B) 109.5 H(10A)-C(10)-H(10B) 109.5 C(8)-C(10)-H(10C) 109.5 H(10A)-C(10)-H(10C) 109.5 H(10B)-C(10)-H(10C) 109.5 C(8)-C(9')-H(9'A) 109.5 C(8)-C(9')-H(9'B) 109.5 H(9'A)-C(9')-H(9'B) 109.5 C(8)-C(9')-H(9'C) 109.5 H(9'A)-C(9')-H(9'C) 109.5 H(9'B)-C(9')-H(9'C) 109.5 C(8)-C(10')-H(10D) 109.5 C(8)-C(10')-H(10E) 109.5 H(10D)-C(10')-H(10E) 109.5 C(8)-C(10')-H(10F) 109.5 H(10D)-C(10')-H(10F) 109.5 H(10E)-C(10')-H(10F) 109.5 N(4)-C(11)-H(11A) 109.5 N(4)-C(11)-H(11B) 109.5

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111 Table C-3. Continued. H(11A)-C(11)-H(11B) 109.5 N(4)-C(11)-H(11C) 109.5 H(11A)-C(11)-H(11C) 109.5 H(11B)-C(11)-H(11C) 109.5 N(4)-C(12)-H(12A) 109.5 N(4)-C(12)-H(12B) 109.5 H(12A)-C(12)-H(12B) 109.5 N(4)-C(12)-H(12C) 109.5 H(12A)-C(12)-H(12C) 109.5 H(12B)-C(12)-H(12C) 109.5 N(4)-C(11')-H(11D) 109.5 N(4)-C(11')-H(11E) 109.5 H(11D)-C(11')-H(11E) 109.5 N(4)-C(11')-H(11F) 109.5 H(11D)-C(11')-H(11F) 109.5 H(11E)-C(11')-H(11F) 109.5 N(4)-C(12')-H(12D) 109.5 N(4)-C(12')-H(12E) 109.5 H(12D)-C(12')-H(12E) 109.5 N(4)-C(12')-H(12F) 109.5 H(12D)-C(12')-H(12F) 109.5 H(12E)-C(12')-H(12F) 109.5 N(6)-C(13)-N(7) 109.3(4) N(6)-C(13)-N(8) 128.2(4) N(7)-C(13)-N(8) 122.4(4) N(6)-C(13)-W(2) 55.9(2) N(7)-C(13)-W(2) 54.2(2) N(8)-C(13)-W(2) 169.8(3) N(5)-C(14)-C(16) 111.2(5) N(5)-C(14)-C(15) 108.2(5) C(16)-C(14)-C(15) 111.0(4) N(5)-C(14)-H(14A) 108.8 C(16)-C(14)-H(14A) 108.8 C(15)-C(14)-H(14A) 108.8 C(14)-C(15)-H(15A) 109.5 C(14)-C(15)-H(15B) 109.5 H(15A)-C(15)-H(15B) 109.5 C(14)-C(15)-H(15C) 109.5 H(15A)-C(15)-H(15C) 109.5 H(15B)-C(15)-H(15C) 109.5 C(14)-C(16)-H(16A) 109.5 C(14)-C(16)-H(16B) 109.5 H(16A)-C(16)-H(16B) 109.5 C(14)-C(16)-H(16C) 109.5 H(16A)-C(16)-H(16C) 109.5

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112 Table C-3. Continued. H(16B)-C(16)-H(16C) 109.5 N(6)-C(17)-C(18) 112.2(4) N(6)-C(17)-C(19) 108.8(4) C(18)-C(17)-C(19) 112.5(4) N(6)-C(17)-H(17A) 107.7 C(18)-C(17)-H(17A) 107.7 C(19)-C(17)-H(17A) 107.7 C(17)-C(18)-H(18A) 109.5 C(17)-C(18)-H(18B) 109.5 H(18A)-C(18)-H(18B) 109.5 C(17)-C(18)-H(18C) 109.5 H(18A)-C(18)-H(18C) 109.5 H(18B)-C(18)-H(18C) 109.5 C(17)-C(19)-H(19A) 109.5 C(17)-C(19)-H(19B) 109.5 H(19A)-C(19)-H(19B) 109.5 C(17)-C(19)-H(19C) 109.5 H(19A)-C(19)-H(19C) 109.5 H(19B)-C(19)-H(19C) 109.5 N(7)-C(20)-C(21) 110.1(4) N(7)-C(20)-C(22) 110.2(4) C(21)-C(20)-C(22) 109.9(5) N(7)-C(20)-H(20A) 108.9 C(21)-C(20)-H(20A) 108.9 C(22)-C(20)-H(20A) 108.9 C(20)-C(21)-H(21A) 109.5 C(20)-C(21)-H(21B) 109.5 H(21A)-C(21)-H(21B) 109.5 C(20)-C(21)-H(21C) 109.5 H(21A)-C(21)-H(21C) 109.5 H(21B)-C(21)-H(21C) 109.5 C(20)-C(22)-H(22A) 109.5 C(20)-C(22)-H(22B) 109.5 H(22A)-C(22)-H(22B) 109.5 C(20)-C(22)-H(22C) 109.5 H(22A)-C(22)-H(22C) 109.5 H(22B)-C(22)-H(22C) 109.5 N(8)-C(23)-H(23A) 109.5 N(8)-C(23)-H(23B) 109.5 H(23A)-C(23)-H(23B) 109.5 N(8)-C(23)-H(23C) 109.5 H(23A)-C(23)-H(23C) 109.5 H(23B)-C(23)-H(23C) 109.5 N(8)-C(24)-H(24A) 109.5 N(8)-C(24)-H(24B) 109.5

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113 Table C-3. Continued. H(24A)-C(24)-H(24B) 109.5 N(8)-C(24)-H(24C) 109.5 H(24A)-C(24)-H(24C) 109.5 H(24B)-C(24)-H(24C) 109.5 Symmetry transformations used to generate equivalent atoms: Table C-4. Anisotropic displacement parameters (2x 103) for 5. The anisotropic displacement factor exponent takes the form: -2 2[ h2 a*2U11 + ... + 2 h k a* b* U12 ] U 11 U 22 U 33 U 23 U 13 U 12 W(1) 31(1) 24(1) 31(1) -4(1) -2(1) 0(1) W(2) 33(1) 28(1) 31(1) -8(1) 1(1) 0(1) N(1) 64(3) 36(2) 40(2) 9(2) -20(2) -15(2) N(2) 46(2) 28(2) 26(2) -2(1) 3(1) -1(1) N(3) 43(2) 65(3) 69(3) -42(2) -1(2) 10(2) N(4) 97(4) 63(3) 58(3) -28(2) 40(3) -17(3) N(5) 59(2) 34(2) 38(2) -11(1) -3(2) 5(2) N(6) 38(2) 34(2) 31(2) -5(1) 3(1) -9(1) N(7) 45(2) 54(2) 32(2) -8(2) 2(2) -13(2) N(8) 31(2) 68(3) 50(2) -9(2) -1(2) -2(2) C(1) 51(3) 36(2) 51(3) -23(2) 20(2) -12(2) C(2) 147(6) 52(3) 35(2) 10(2) -24(3) -50(4) C(3) 98(8) 54(4) 49(3) 22(3) 6(3) -21(5) C(4) 98(8) 54(4) 49(3) 22(3) 6(3) -21(5) C(3') 98(8) 54(4) 49(3) 22(3) 6(3) -21(5) C(4') 98(8) 54(4) 49(3) 22(3) 6(3) -21(5) C(5) 36(3) 110(6) 139(6) -93(5) -1(3) 10(3) C(6) 58(3) 91(6) 138(8) -63(5) -34(5) 33(4) C(7) 58(3) 91(6) 138(8) -63(5) -34(5) 33(4) C(6') 58(3) 91(6) 138(8) -63(5) -34(5) 33(4) C(7') 58(3) 91(6) 138(8) -63(5) -34(5) 33(4) C(8) 115(5) 45(3) 26(2) 3(2) 1(3) 32(3) C(9) 70(3) 43(2) 55(3) 10(2) -5(3) 17(3) C(10) 70(3) 43(2) 55(3) 10(2) -5(3) 17(3) C(9') 70(3) 43(2) 55(3) 10(2) -5(3) 17(3) C(10') 70(3) 43(2) 55(3) 10(2) -5(3) 17(3) C(11) 86(6) 50(3) 34(2) -7(2) 18(4) -6(4) C(12) 86(6) 50(3) 34(2) -7(2) 18(4) -6(4) C(11') 86(6) 50(3) 34(2) -7(2) 18(4) -6(4) C(12') 86(6) 50(3) 34(2) -7(2) 18(4) -6(4) C(13) 40(2) 41(2) 34(2) -11(2) -1(2) -8(2) C(14) 66(3) 60(3) 51(3) -20(2) -15(2) 26(3) C(15) 171(8) 63(4) 61(4) 22(3) 33(4) 60(5) C(16) 68(4) 70(4) 101(5) -19(3) 25(4) -5(3)

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114 Table C-4. Continued. C(17) 44(2) 44(2) 38(2) 1(2) -1(2) -9(2) C(18) 72(4) 39(3) 62(3) 5(2) 1(3) 2(2) C(19) 73(4) 76(4) 54(3) 10(3) 23(3) -10(3) C(20) 50(3) 73(3) 38(2) -3(2) 5(2) -21(3) C(21) 134(7) 58(4) 82(4) -8(3) 46(4) -32(4) C(22) 92(5) 84(4) 43(3) -5(3) 28(3) -9(4) C(23) 50(3) 112(5) 71(4) -16(4) 13(3) 7(3) C(24) 44(3) 88(4) 48(3) 0(3) -7(2) -18(3) Table C-5. Hydrogen coordinates ( x 104) and isotropic displacement parameters (2x 10 3) for 5. x y z U(eq) H(1) -10(50) 1417(19) 7390(30) 51(13) H(2) 1610(40) 1393(17) 8900(30) 32(11) H(3) 3030(70) 1120(20) 8060(40) 100(20) H(4) 2450(50) 1687(19) 7290(30) 49(13) H(2A) 350 359 9233 98 H(2B) 373 385 9203 98 H(3A) -1884 259 8419 101 H(3B) -1382 -300 8931 101 H(3C) -1330 -236 7857 101 H(4A) 2389 -244 8933 101 H(4B) 1343 -556 8134 101 H(4C) 1137 -640 9182 101 H(3'A) -2062 471 8362 101 H(3'B) -2037 -136 8758 101 H(3'C) -1861 -35 7710 101 H(4'A) 160 -467 9422 101 H(4'B) 1743 -323 9186 101 H(4'C) 551 -602 8427 101 H(5A) 3780 122 5754 116 H(5B) 4289 428 5854 116 H(6A) 5181 888 6107 152 H(6B) 6000 377 6628 152 H(6C) 5152 801 7179 152 H(7A) 2692 -378 6884 152 H(7B) 3513 -7 7696 152 H(7C) 4424 -424 7173 152 H(6'A) 5725 628 7034 152 H(6'B) 5618 -13 7211 152 H(6'C) 4700 405 7729 152 H(7'A) 3208 -217 5358 152 H(7'B) 2394 -308 6227 152 H(7'C) 4053 -499 6266 152

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115 Table C-5. Continued. H(8A) -571 1283 4714 76 H(8B) -792 1218 4724 76 H(9A) 1401 1880 5254 86 H(9B) 739 2043 6156 86 H(9C) -31 2251 5171 86 H(10A) -2396 1112 5556 86 H(10B) -2279 1733 5248 86 H(10C) -1615 1551 6270 86 H(9'A) -1571 2054 5659 86 H(9'B) -317 2127 5037 86 H(9'C) 109 2009 6112 86 H(10D) -2363 723 5381 86 H(10E) -3037 1324 5271 86 H(10F) -2265 1115 6255 86 H(11A) -545 557 4386 84 H(11B) 375 89 3982 84 H(11C) 229 678 3510 84 H(12A) 2497 953 3660 84 H(12B) 3336 429 4125 84 H(12C) 3572 1011 4615 84 H(11D) -190 492 4219 84 H(11E) 1046 71 4025 84 H(11F) 882 646 3507 84 H(12D) 3962 821 5164 84 H(12E) 3524 878 4076 84 H(12F) 3699 287 4538 84 H(14A) -541 2606 7858 74 H(15A) 1210 3241 7475 145 H(15B) 1571 3428 8525 145 H(15C) -1 3551 7944 145 H(16A) -741 2445 9418 117 H(16B) -1187 3061 9157 117 H(16C) 384 2929 9730 117 H(17A) 5069 1399 10879 51 H(18A) 5120 674 9839 88 H(18B) 3381 625 9726 88 H(18C) 4359 490 10692 88 H(19A) 2841 1810 11075 99 H(19B) 2925 1200 11462 99 H(19C) 1961 1333 10491 99 H(20A) 6688 2340 8148 64 H(21A) 5173 3054 8504 132 H(21B) 4058 2936 7584 132 H(21C) 5663 3158 7526 132 H(22A) 5871 1769 6887 107

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116 Table C-5. Continued. H(22B) 6088 2377 6542 107 H(22C) 4483 2154 6598 107 H(23A) 7193 1424 8390 116 H(23B) 7827 1067 9270 116 H(23C) 8613 1624 9065 116 H(24A) 6614 2004 10852 92 H(24B) 8243 1991 10621 92 H(24C) 7453 1435 10831 92

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130 BIOGRAPHICAL SKETCH Laurel Reitfort was born in 1979 in Raleigh, North Carolina where she was raised. S he attended high school at Rave nscroft School and after gradua ted in 1997. She continued her studies at The University of North Carolina at Chapel Hill where she received her B.S. in Chemistry in December 2001. In her final year in Chapel Hill Laurel was introduced to the world of research in Professor Joe Templeton s group which motivated her to attend graduate school She worked at Research Triangle Instit ute from October 2001 until July 2002. In August 2002 Laurel moved to Gainesville, Fl to pursue her Ph.D. in chemistry at the University of Florida. She started research in Professor Lisa McElwee-Wh ites group in Spring of 2003 and graduated in the Spring of 2008.