Characterization of homoepitaxial diamond thin films grown by hot filament assisted chemical vapor deposition

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Title:
Characterization of homoepitaxial diamond thin films grown by hot filament assisted chemical vapor deposition
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vii, 256 leaves : ill. ; 29 cm.
Language:
English
Creator:
Alexander, William Brock, 1963-
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bibliography   ( marcgt )
theses   ( marcgt )
non-fiction   ( marcgt )

Notes

Thesis:
Thesis (Ph. D.)--University of Florida, 1995.
Bibliography:
Includes bibliographical references (leaves 247-255).
General Note:
Typescript.
General Note:
Vita.
Statement of Responsibility:
William Brock Alexander.

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University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
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notis - AKN3343
oclc - 33392962
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Full Text












CHARACTER IZATION


OF HOMOEPITAXIAL


DIAMOND


THIN


FILMS


GROWN


BY HOT


FILAMENT


ASSISTED


CHEMICAL


VAPOR


DEPOSITION


WILLIAM


BROCK


ALEXANDER


A DISSERTATION


PRESENTED


TO THE


GRADUATE


SCHOOL


OF THE


UNIVERSITY


OF THE


OF FLORIDA


REQUIREMENTS


IN PARTIAL


FOR


THE


FULFILLMENT


DEGREE


DOCTOR OF PHILOSOPHY















ACKNOWLEDGMENTS


would


advisor,


like


Paul


express


sincere


Holloway,


appreciation


guidance,


support,


encouragement.


Thanks


are


also


doctoral


committee


members


Robert


Park,


Robert


DeHoff


, Dr.


Rajiv


Singh,


and


.Tim


Anderson,


their


assistance


and


interest


work.


This


samples


work


and


would


assistance


have


provided


been


LMA,


possible


Inc.


without


am grateful


Robert


Linares


Patrick


Doering


their


endless


support


work.


would


also


like


thank


Romulo


Ochoa


and


Joseph


Simmons


discussions


Raman


scattering.


Additional


thanks


Tim


Anderson


providing


continual


use


of his


Raman


spectrometer.


Thanks


are


to Dr.


Maggie


Puga-Lambers


and


Balu


Pathangey


providing


SIMS


analysis


and


Tom


Joseph


r-nl1 1 F i nrr


FTTP


r9als


WPTrP


I nRt-nrlnrnntal.


this


Th .cs^









indebted


comradeship


friends


encouragement


coworkers


through


their


stay


Gainesville.


would


like


thank


Thompson


and


Wishy


Krishnamoorthy


entertaining


conversations


x-ray


diffraction.


Special


thanks


friend


Chris


Rouleau


numerous


discussions


and


good


times.


am also


indebted


Michelle


Somerday


constant


support


encouragement.















TABLE


OF CONTENTS


ACKNOWLEDGMENTS.


ABSTRACT


CHAPTER


INTRODUCTION


Moti


vation


and


ectives


Present


Work


CHAPTER


LITERATURE


REVIEW


HOMOEPITAXIAL


DIAMOND


FILM


GROWTH


AND


CHARACTERIZATION


Introduction


Phase


Chemi


stry


Diamond


Film


Growth


Homoepitaxial


Diamond


Film


Growth


Raman
Raman
X-Ray


Anal


ysis


ectrosco


Diffra


Stress


Bac


kgr


in Thin


Films


ound


action


Rocking
Lattice


Curves.


Parameter


and


M/26


king


Curves


3


saic


Structure


and


o Rocking


rves


CHAPTER


EXPERIMENTAL


APPROACH


Introduction


Filament


Assisted


Chemi


Vapor


Dep


position


Diamond


Growth


Chamber


and


Parameters.


Chara


cterization


Techniques


Raman
Stress
Control
Curve
X-Ray


ctrosc


opy


Measurement


lling


Raman


Exp


erimenta


Precision


Probing


Depth


Fitting.


Experimental


Proc


edures


Procedure


Meth


65
* 67
* 70


Analyzer


Crys


K-.n n ____ -


*n a n 4-. .


WA- i n;n


29


3


54
* 54









Secondary


Ion Mas


Spectrometry.


Quantitative Analysis with SIMS


CHAPTER


4 RESULTS


Surface Morphology
Raman Spectroscopy of


Graphite


Versus


Diamond


Deposition.


Raman Analysi
SIMS Analysis
FTIR Analysis


X-Ray


CHAPTER


Stress


109


Analysis


DISCUSSION


Surface Morphology
Raman Spectroscopy of


Depos


ited Films


Raman Analysis


Intrinsic


Stress


(110o)


Films


212
216


Stress


Classification


Natural


Diamond and SIMS


Analysis


of Diamond Films


FTIR Analysis.
X-Ray Diffraction


Cracking


of Films


CHAPTER


SUMMARY


AND CONCLUSIONS.


APPENDIX


CARBON PHASES


REFERENCE LIST


247


BIOGRAPHICAL SKETCH


256
















Abstract


of Dissertation


Presented


Graduate


School


:he University
Requirements fi


Florida


Degree


Partial


of Doctor


Fulfillment


Philosophy


CHARACTERIZATION


OF HOMOEPITAXIAL


DIAMOND


THIN


FILMS


GROWN


BY HOT


FILAMENT


ASSISTED


CHEMICAL


VAPOR


DEPOSITION


William


Brock


Alexander


May,


1995


Chairperson:


Paul


Holloway


Major


Department


Mate


rials


Science


Engineering


Diamond


films


were


grown


(100


(110


, and


(111)


oriented


natural


diamond


substrates


filament


assisted


chemical


vapor


deposition


(HFCVD)


thicknesses


100lm.


precursor


was


either


100%


methanol


balance

The


hydrogen,

accuracy


or 0

and


to 3% acetone


precision


balance

Raman sp


hydrogen.


ectroscopy


reflect


stress


versus


bonding


in thin


diamond


films


was


improved


calibration


significantly


line


(1320cm-1)


using


a pinhole


internal


aperture.


krypton


Tensile


atoa raoIaHr7


rnmo nr r


- (1 i n


,3r-l,


CT "VQ C? C3 C 3


Tt7QTrl


I f


r 1 I I r


IJ


I r









(1332cm-1)


and no graphitic


(1360,


1525,


1585cm-')


peaks.


The development


of stress during HFCVD growth of


diamond


was


attributed to


incorporation of


impurities


(Re,


and


influence


film


orientation


ability


diamond


plastically


deform.


Impurity


concentrations were greater at


interface


than


through


film


thickness


and


to -11%


and


~50ppm Re


were


measured


in the


films with secondary


ion mass


spectrometry


(SIMS)


The Griffith model


crack propagation


versus


slip was


used to predict


cracking of the


(110)


films.


Two of


(111}


cleavage


planes


are


perpendicular


(110)


surface


which


precludes


slip and results


in maximum tensile


stresses


plane of


film.


was


speculated


that


microflaws


film


created


stress


intensity


factors


which


under


tensile


stress


caused


cracks


to propagate along


cleavage


planes.


Homoepitaxial


diamond


films


were


further


characterized


using


seven


crystal


high


resolution


x-ray


diffraction


system.


This new characterization tool allowed the separation


effects


mosaicity


from


those


variations


lattice parameter.


Broadening of the x-ray rocking curves due















CHAPTER


INTRODUCTION


Motivation


Objectives


Diamond


possesses


many


attractive


properties


such


as high


hardness

optical


(104kg/mm2),

transparency,


high

low


thermal c

coefficient


onductivity


friction,


(22W/cmK)


chemical


inertness


wide


bandgap


.45eV)


[Ang91]


These


properties


sinks,


are


high


suitable


temperature


many


applications


semiconductors


and


such


wear


heat


resistant


coatings


mechanical,


chemical,


optical


applications.


More


specifically,


physical


properties


unique


makes


combination


diamond


desirable


mechanical

material


and

for


electronic


devices


applications.


Diamond-based


choice


electronic


high


devices


temperature


would


radiation


components


environments


such


those


encountered


outer


space.


Silicon


devices


require


cooling


to approximately


125C


proper


operation,


-a r i i r I -a


r'nnl 5nf


c3a7Ca+r( 3 mC


yrrn -1 r Tr


mar lt ln-ta-


t- b^ ;P s











unmanned


satellite.


Since


diamond


devices


can


operate


higher


temperatures


(400-5000C)


significant


reduction


cooling


systems and overall


volume could be achieved


[Gil91]


High


power


high


speed


diodes,


transistors,


switches


other devices


future


will


take


advantage


diamond's


high


thermal


breakdown


chemical


conductivity,


electric


inertness


field


and


electrical


strength,


superior


resistivity,


dielectric


charge-carrier


high


constant,


transport


properties


such


high


electron


mobility


and


velocity


[Rav93]


Optical device applications utilizing single crystal


diamond include optical detectors and emitters of radiation in


range


spectrum,


example,


metal-


semiconductor-metal


(MSM)


metal-insulator-semiconductor


(MIS)


radiation detectors.


The quantum efficiency,


transient


response,


and performance of these devices should improve with


higher quality material


[Mar94]


order


realize


diamond-based


electronic


devices,


growth processes


are required for


single crystal,


electronic-


grade


films.


hydrogen,


incorporation


development


impurities


secondary


defects


such


such


_ _


_












Scope


Present


Work


review


of the


literature


(Chap


shows


that


a range


diamond


film


quality


been


obtained


(100


, (111)


and


(110


diamond


substrates.


Evidence


stress


and


stress


relief


via


crack


formation


been


reported,


detailed


studies


origin


this


stress


been


reported.


One


objective


this


study


was


grow


homoepitaxial


diamond

diamond


films

were t


with


ised


HFCVD.


Natural


as substrates,


and


(100)


(110


precursor


and


gases


(111)

were


acetone o

discussed


?r methanol.


in Chapter


diamond growth

a diamond films


conditions

developed


will


smooth


rough


surface


morphologies,


penetration


twins,


pits,


graphitic


inclusions,


and relatively

strong function


renucleation


high

of the


sites,


quality

growth


cracking,


epilayers.


chemistry


mosaic


structure,


results


and


orientation


were a

of the


film


and


substrate.


Another


objective


study


was


define


magnitude


and


origin


stress


which


would


lead


crack


formation


some


of the


films.


To accompli


sh this


objective,










Raman spectroscopy was used extensively throughout


this study,


close evaluation of


analysis


stress


technique and its


transparent


materials


limitations

(diamond)


for

was


required.


The features and improvements implemented for using


Raman


spectroscopy


analyze


diamond


will


discussed


Chapter


High resolution and


triple-axis x-ray diffraction


was


also


employed


mosaic


structure


characterization.


Since


the x-ray techniques


used


this


study are


relatively


new,


the technique and appropriate literature is also reviewed


in Chapter


The experimental methods used for collecting


ray data


are discussed in


Chapter


The


results


characterization


are


given


Chapter


followed by a


discussion of


those


results


in Chapter


conclusions


study


are


given


Chapter


with


suggestions


future work


Chapter















CHAPTER


LITERATURE


REVIEW


ON HOMOEPITAXIAL


DIAMOND


FILM


GROWTH


AND


CHARACTERIZATION



Introduction


synthesis


of diamond


pressure


chemical


vapor


deposition


(CVD)


been


subject


of extensive


research


last


several


years


[Chu90,


Ang88,


Spi81,


Kob88]


Diamond


been


produced


filament


several


assisted


chemical


pressure


vapor


methods


deposition


including


(HFCVD


[Figure


[Cla89,


Ale92,


Kaw87,


Mat 82],


plasma


assisted


chemical

[Hir89]


vapor


deposition


In each


process


(PACVD)


[Ito91] ,


, hydrocarbon


and


and


acetylene


hydrogen


gases


orch

are


activated


plasmas


or hot


filaments,


creating


a mixture


species


which


include


atomic


hydrogen,


methane,


and


acetylene.


HFCVD


system


was


used


this


study


and


will


be discussed


further


Chapter


Various


vapor


deposition


diamond


growth


methods


have


been


discussed


[Zhu91]











chemical


physical


reactions


occurring


diamond


processes


are


complex


well


understood.


critical


role


of atomic


hydrogen


growth


of diamond


rather


than


graphite


been


recognized


[Spi81] ,


growth


species


growth


mechanisms


are


still


unclear.


Theoretical


predictions


quantum


mechanical


calculations


have


been


completed


which


show


that


most


probable


diamond


growth


species


are


radicals,


CH4,


C2H2 acting


through


gas/solid


reactions.


previous


Chemical

work


reaction


[Goo90,


models


Har89,


have


Fre88]


been

which.


proposed

h support


oased

the


importance


necessary


of particular


diamond


growth


growth


species


include


mechanisms.


adsorption


Steps


hydrogen


atoms


and


hydrocarbons;


dissociation


of H,


and


recombination


of H;


hydrogenation


formation


and


dehydrogenation


decomposition


diamond


of adsorbed con

, diamond-like


iplexes;

carbon


graphite


preferential


nuclei;


etching


desorption


of H2


graphitic


CiH,


carbon


molecules;


phases


atomic


hydrogen.


this


Chapter,


literature


pertaining


vapor


deposition


of diamond


and,


more


particularly,


homoepitaxial











literature


which


pertains


measurement


strain


homoepitaxial


diamond


films


other


epitaxial


layered


systems

stress


will b<

affects


Discussed.


Raman


fundamental


scattering


are


discussed


mechanism


by which


below.


Phase


Chemistry


Growth


Bachmann


et al.


[Bac91]


summarized


diamond


growth


phase


compositions


from


many


studies.


Bachmann


introduced


C/H/O


growth


ternary


studies


phase


which


diagram


used


relate


several


number


vapor


diamond


deposition


techniques.


feasible


was


a well


shown


defined


that

field


diamond


deposition


phase


was


diagram.


only

This


field


was


along


CO line.


Bachmann's


ternary


diagram


shown


Figures


b where


atom


fractions


are


represented


Xo/,=O/(O+H)


XH/=H/(H+C)


Xc/,=C/(C+O)


2-3


Diamond


C/H/O












equilateral


triangle


represents


composition


from


binary


system.


A C/H/O


ternary


phase


diagram


shown


again


in Chapter


illustrate


compositions


used


this


study.


this


dissertation,


mixture


1%CH4


and


99%H,


will


be referred


that


balance


as 1% CH4


consists


brevity


hydrogen.


It


will


Also,


be assumed


mixture


1%CH30H


99%H,


referred


1%CH3OH)


Researchers


continue


investigate


species


responsible


diamond


growth.


This


information


important


understand


growth


mechanisms,


increase


growth


rates,


and


improve


film


quality.


phase


analysis


modeling


diamond


growth


environment


have


revealed


most


probable


diamond


growth


species


to be


CH3,


CH4,


and


CH4


[Har88,


Cel91].


thermal


Calculated


equilibrium


concentrations


5%CH4


phase


shown


species


Figure


[Cel90]


The


curve


at a mole


fraction


was


shown.


A significant


fraction


of methane


was


converted


to acetylene


at higher


temperatures


>1500K=1227C)


relative


concentration


activated


species


are


-4-- S. I- 5-. I.- ~ --- --- - - 4- n -


- -.-


LCI


C2H2,


r. ..,


q .


- ~1J_ L-


I I*L.* IY)e~~


L










products


[Ale92,


versus


Som90,


methane


Som91,


and


Wu90,


cracking


Har88]


products


Since


[Fig.


filament


temperature


affects


concentrations


various


species,


was


important


hold


filament


temperature


constant


during


growth


this


study.


This


facilitated


mapping


growth


chemistries


versus


quality


diamond


grown.


Gas


films


composition


grown


greatly


vapor


affects


deposition


quality


diamond


measured


Raman


spectroscopy


and


scanning


electron


microscopy.


important


understand


influence


composition


diamond


growth


since


this


also


affects


film


quality


[Kaw87,


Kob88]


Raman


spectroscopy


of polycrystalline


diamond


films


grown


with


.7%,


are


shown


Figure


[Kaw87]


diamond


peak


1332


was


less


pronounced


and


graphite


peak


-1580cm-1


was


more


pronounced


higher


methane


concentrations.


peak


(1340-1360cm-1)


which


was


overwhelming


diamond


signal


on the


9%CH4


spectra


was


amorphous


carbon.


should


noted


that


these


samples


were


grown


hours


.5pm/hr)


on silicon


5cm-1


:











powder


grown


film


which


was


relatively


thin


Raman


analysis.


addition


oxygen


to the


precursor


composition


resulted


in improved


diamond


deposition


as measured


Raman


spectroscopy


[Figure


[Kaw87]


same


growth


conditions.


amorphous


carbon


increased


with


increased


methane


in the


oxygen/hydrogen


:50)


balance;


however,


amorphous


carbon


graphite


signals


are


less


pronounced


than


demonstrated


in the


previous


figure.


Scanning


electron


microscopy


(SEM)


been


used


to study


polycrystalline


film


texture


crystallite


geometry


[Ale92,


Cla91,


Cla89].


development


texture


result


competitive


growth


between


randomly


oriented


crystals.

to the su


Crystals


ibstrate


with


surface


fast


growth


outgrow


othe


directions

r crystals


perpendicular


, resulting


textured


film


with


columnar


structure.


texture


polycrystalline


films


was


important


dependence


mechanical


and


optical


properties


on the


film


orientation.


diamond


crystallite


geometry


was


result


relative


growth


rates


2 <100>


<111>


directions


which











was


ratio


that


<100>


that


<111>


directions.


This


parameter


was


first


used


Spitsyn


[Spi81],


been


used


extensively


Clausing


[Cla91]


ratio


a is equal


to the


ratio


distances


from


center


crystal


to the


center


{100oo}


and


{111}


facets.


growth


rate


ratio


1/3,


and


results


and


other


a cube


octahedral


words,


faster


bounded

bounded


a is greater


<100>


{(100}

{111}


planes,

planes,


than


direction


a cubo-octahedral,


respectively.


crystal


causing


(111}


grows


facets


increase


in size.


When


a is


less


than


VY/2


crystal


grows


faster


<111>


direction


causing


(100}


facets


increase


size.


geometric


features


are


used


correlate


growth


conditions


with


texture


polycrystalline


films.


are


Computer


shown


generated


Figure


cubo-octahedrons


Diamond


with


crystallites


grown


1.65

with


HFCVD


are


shown


in Figures


and


which


demonstrate


and


, respectively.


Note


smoother


{100}


faces


compared


{111}


faces


exhibited


diamond


V /2,


/3/2= 0


.6











It has been shown that


changes


in growth parameters,


e.g.


composition


Cla89],


[Kob88,


or filament


Spi81],


temperature


substrate


[Ale92],


temperature


affect


[Cla91,


shape


crystallites


texture


polycrystalline


films.


results are


not


always


similar.


For


example,


Kobashi


[Kob88]


concentrations


observed


and


{(111


(100}


faceting


faceting


lower


higher


methane


methane


concentrations,


while


Spitsyn


[Spi81]


observed


opposite relationship.


The reason for these discrepancies was


that


affect


other


film


growth


parameters,


texture.


addition


believed


that


chemistry,


chemistry


substrate


temperature


are


dominant


growth


parameters


affecting


film


texture.


Wild,


Koidl,


coworkers


[Wil94,


Koi94]


have


measured


texture with x-ray


diffraction


in a


four


circle x-ray powder


diffractometer on


(100)


oriented polycrystalline


films.


{400}


{220)}


pole


figures are


shown


in Figure


2.10.


This


diamond film is


highly oriented


for a


polycrystalline diamond


film.


This was achieved by a-mapping the growth parameters


1
n, -1r /-I ,I/ .-' r tT r a


I i II-- I I I r I Wn,,\ i i I .- niii-i \7 i I \ i ,,l i I r t *%,1 r-,i A


I I I lit


rornw


C* I


v\ I "" -* m ^


n nt/\ "


rr ~ t* rr Cn


I i r- I I 1 1I


i I I ,-











mapping


are


shown


Figure


2.11.


Using


conditions,


they


grew


a 120gm


thick


homoepitaxial


film


on a


(100


diamond


substrate


which


exhibited


"smooth"


surface


without


any


"maj or


defects"


[Wild94] )


However,


photograph


of this


film


showed


what


believe


{111}


growth


steps


and


penetration


twins.


HomoeDitaxial


Diamond


Film


Growth


Homoepitaxial


diamond


growth


refers


to a single


crystal


diamond


growing


with


same


orientation


single


crystal


diamond


conducted


substrate.


(100


This


, (111)


type


, and


of growth


(110)


oriented


generally


diamond


substrates


will


be discussed


in this


order.


Most


groups


report


that


diamond


growth


(100


surfaces


higher


quality


than


diamond


grown


(111)


and


(110


substrates


[Bad93,


Bad91,


Sut92,


Sna91,


Chu91,


Chu92,


Fuj 90]


measured


Raman


spectroscopy


and/or


SEM.


Evidently


only


exception


was


paper


Kamo


Kam8 8]


which


reported


that


(100)


oriented


growth


was


more


r-"i =ni "- r


(111\


1-ii n


p.- q -,


nrnrvrtj f


T 4 4p44 _,- -


+-h -i r-


=-ann


I- I










These


films were


reported


to exhibit


good,


stress


free


Raman


peaks


-1332cm-1


with


FWHM


<2.5cm-1


However,


microscopic


image


under


crossed


polarizers


60Om


thick


film


indicated


that


film


was


stressed


[Bad93]


magnitude


stress,


nor why


results


from


image


and Raman did not


agree,


were


not


discussed.


Films


have


been


grown


substrate


temperatures


ranging


from


1200C,


and it


was proposed by Badzian


[Bad93]


that


substrate


temperatures


>1100C


would


beneficial


(100)


homoepitaxial


substrate


diamond


temperature


film


and


growth.


chemistry


stated


are


earlier,


paramount


growth parameters,


and in


paper by Badzian et


[Bad93]


only the substrate temperature was varied;


was


the gas composition


1% methane.


Growth on


(100oo)


evidently proceeded by a


step growth


process


along


<110>


crystallization


fronts


[Bad93]


There


have been no reports of Raman peak shifts and therefore stress


measurements via Raman


A variety of


(100)


growth results


oriented


films.


have been achieved


(111)


oriented


diamond


substrates;


from


smooth


single


crystal


-a










thicker


than


a few


micrometers


typically


lost


their


epitaxial


structure


and became


polycrystalline


smooth


(111)


surfaces


have


only


been


reported


films


with


thicknesses


less


than


a few


micrometers.


Graphitic


appear


inclusions


more


have


common


been


films


reported


grown


diamond


(111)


and


oriented


substrates


[Chu91,


Chu92]


detected


graphite


amorphous


carbon


their


films


with


Raman


spectroscopy


and


also


reported


tensile


peak


shifts


approximately


1cm-1


from


13C diamond


Raman


mode.


Their


films


were


grown


with


isotopically


distinguished


labeled


from


methane


substrate


film


peak.


peak


could


observed


peak


shifts


are


rather


large,


though


FWHM


peak


was


given,


was


well


larger


than


10cm-l


visual


inspection


Raman


spectra.


After


a few


micrometers


of growth


film


cracked


and


relieved


stress


and


Raman


peak


shifted


toward


stress


free


value


diamond


Raman


frequency


(1280cm-i)


Growth


defect


propagation


(111)


[Bad93]


surface


appears


increase


to be


sensitive


in defect


density











polycrystalline


films grown


on silicon and


other non-diamond


substrates.


diamond


crystallites


shown


previously


Figures


exhibit


smoother


(100)


surfaces


compared


(111)


surfaces.


Diamond


films


grown


(110o)


diamond


surface


have


been


reported


have


rough


surface


morphologies


[Kon93,


Fuj90,


Sut92]


to grow faster then


(100)


(111)


surfaces


[Fuj 90,


Chu91,


Chu92,


Gei90].


(110)


homoepitaxial


surface


can


exhibit


a corrugated or microfaceted morphology revealing


(111)


and


(111)


surfaces


[Bad93,


Kon93].


This


surface


structure


may


result


three


dimensional


growth


suggested by RHEED patterns


[Kon93]


Badzian


et al.


[Bad93]


reported


that


after


several micrometers,


films can lose


their


epitaxial


relationship and become


polycrystalline


typical


substrate


temperatures.


However,


(110)


oriented film grown


substrate


temperature


1200C


thicknesses


1 .2mm,


remained


homoepitaxial.


This


thick


film


also


demonstrated good Raman


characteristics with a FWHM of


5cm-1


and


apparent


frequency


shift,


i.e.


peak


position


-1332cm-.












thick


homoepitaxial


film


[Chu91]


Films


were


grown


from


isotopically


labeled


methane


in order


ease


interpretation


Raman


spectra


Smaller


diamond


Raman


frequency


shifts


Fuj 90]


addition


cracking


films


thicknesses


only


a few


micrometers


[Kam8 8


have


been


reported.


Although


diamond


Raman


frequency


shifts


were


reported


tensile


stress,


origin


stress


was


not


investigated,


nor


were


vales


Raman


peak


position


versus


stress.


been


postulated


[Chu91]


that


stresses


could


be caused


graphitic


inclusions


or defects.


Raman


Analysis


Stress


Thin


Films


Raman


spectroscopy


was


used


extensively


in this


work


analysis


stress


in homoepitaxial


diamond,


thus


a brief


discussion


literature


is warranted.


Although


diamond


Raman


mode


peak


shifts


have


been


observed


for


homoepitaxial


films,


detailed


investigations


into


origin (s


these


frequency


shifts


have


been


reported.


Since


diamond


transparent


argon


laser


frequency


.5nm,


Crr


1-- 11 -


-.-- 1


. .. -- .


___ _


-- J-


_ -











signal


may overwhelm the


film signal.


There are no published


work


addressing


this


problem


homoepitaxial


diamond


thin


film characterization


have used isotopic


using


Raman spectroscopy.


labeling which allowed


Some groups


film peak


to be


resolved


from


substrate


peak.


insufficient


literature

spectroscopy


pertaining


homoepitaxial


strain

diamond


analysis


films,


Raman


other


material


systems


will


discussed


which


demonstrate


feasibility


and non-destructive


nature of


this


technique


to probe


strain.


Epitaxial


layers of GaAs grown by MBE on


(100)


(111)


silicon


exhibited


tensile


stress


which


was


revealed


decrease


Raman


frequency.


biaxial


stress


film resulted in a 2cm-1 shift


in the


longitudinal


optical


(LO)


phonon mode


for both


(100)


(111)


GaAs


layers


[Figures


2.12 and 2.13]


and the calculated stress was


350MPa and 490MPa


respectively


[Qua93]


A profile of


stress was


completed


etching


away


layers


film


which


revealed


greater


strain


stress


near


was


interface


from


than


differences


film


thermal


surface.


coefficients


expansion


(TCE)


and


lattice


mismatch,


since


layers











Silicon-germanium


alloys


have


been


characterized


with


Raman spectroscopy


[Mey91,


Die93]


The Raman frequency of the


Si-Ge


alloy


film


function


composition


and


stress


layer.


Compressive stresses


as large as


1.5GPa


were


measured


from


20%Ge


films


(grown


MBE)


after


misfit


dislocations had developed


[Die93]


Raman stress results were


compared with XRD and


TEM results


and were


in relatively good


agreement


with


respect


sign


and


magnitude.


Silicon-


germanium


films


prepared


ion-beam


sputter


deposition


resulted


in compressive


stresses


1.5GPa


also,


which


were


relieved


heating


800C


minutes


[Mey91]


Homoepitaxial


silicon


films


prepared


ion-beam


sputter


deposition


exhibited


compressive


stresses


1.8GPa


temperature growths.


Thus,


Raman spectroscopy has been proven


to be useful


stress


analysis


epitaxial


layers


semiconducting


materials


and is


a desirable characterization


tool


nondestructive nature of


technique.


Raman Spectroscopy Background











will


be followed


reasons


using


Raman


in this


study.


steps


used


gathering


Raman


data


are


discussed


Chapter


Absorption,


emission,


scattering


are


phenomena


which


occur


when


[Kit86]


electromagnetic


Absorption


occurs


radiation


when


interacts


molecular


with


a molecule


excited


state


separated


from


ground


state


energy


of a photon.


Emission


occurs


when


excited


molecule


decays


towards


ground


state,


energy


emitted


difference


between


photon


excited


energy


ground


equal


states


the molecule.

equal to the


Scattering


energy


occurs


difference


when


between


the

i th(


photon er

e excited


lergy

and


is not

ground


states.


Two

Scattering


types


scattering


without


change


events


can


energy


occur


[Kit86]


incident


photon


is termed Rayleigh


scattering;


scattering


with


a change


incident


Raman


scattering


photon


can


energy


explained


termed

quantum


Raman


scattering.


mechanically


when


momentum


we consider


conservation


e concept


considered,


of polarizability.


semiclassically


Both


when


explanations











incident


photon


will


increase


(anti-Stokes


scattering)


Raman


or decrease


scattering


[Kit86]


(Stokes


scattering)


processes


energy


can


during


be expressed


employing


Planck


formula:


E=hv


(2-4)


where


E is


photon


energy,


photon


frequency,


h is


Planck


s constant.


Raman


scattered


photon


an energy,


EsE= E Ephonon


where


phonon


crystal


energy


energy.


vibrational


of the


incident


definition,


energy


photon


phonon


[Sri90]


quantum


corresponding


frequency


, ~vs,


then:


i- i phonon


Rewriting


this


equation


considering


momentum


conservation


results


in:


hk_=hk +ha


1


Ephonon











wavevector of the incident and scattered photon,


respectively.


Stokes


scattering


(vi -vphonon)


generally


measured


most


Raman spectroscopy because


intensity is


stronger then


anti-Stokes


scattering


(vi+vphonon)


For the


concept


semiclassical approach,


of polarizability.


we need


Polarizability


introduce


extent


which


electron


cloud


nuclei


are


distorted


when


interacting with an electric field,


e.g.


the electric field of


photon.


The electrons


are


attracted


positive


end


and


nuclei


are


attracted


negative


electric


field.


polarization


is the


induced electric


dipole


moment


and is


related


to the electric


field


P=aE


(2-8)


where


polarizability.


Thus


measure


ease


which


oscillator


may


distorted.


For


electric


field given by:


E=E0cos (vit)


(2-9)


where E is


the maanitude and V2


the freanennv nf


s1 Pntri n












P=aE0cos (vit)


(2-10)


where


oscillator


electric


field


vibrates


same


can


frequency


source


radiation


(Rayleigh scattering)


The inherent


or natural


frequency


and


polarizability


oscillator


related


polarizability:


a=x0o+Eapcos (vpt)


(2-11)


where


static


polarizability


dipole.


Rewriting the


polarization by:


P=E0oocos (vit) +1/2E0caP [cos (vi-Vp) t+cos (vi+vp) t] ,


(2-12)


easy


second


associate


term with Stokes


first


(vi-vp)


term


, and the


with


third


Rayleigh,


term with anti-


Stokes


(vi+Vp)


scattering.


illustration


transverse


optical


(TO)


phonon


coupled


electric


field


shown


Figure


2.14.


positive and negative poles of the dipole vibrate against each











electric


field


transverse


wave.


dipole


oscillation


direction


electric


field


propagation


longitudinal


wave,


e.g.


longitudinal


optical


(LO)


phonon.


Raman


analysis


was


performed


with


unpolarized


radiation,


so our discussion will not


include consideration of


polarization


that


selection


is possible


rules.


to resolve


However,


should


three optical


noted


phonons


(one


longitudinal


transverse)


when


using


polarized


radiation [P

polarization


ol191]


A good


selection


explanation


rules


Raman


application


analysis


diamond-


cubic materials


is given by


Pollack


[Pol91]


Raman

scattering)


analysis


can


scattering


performed

geometry [


with


Figure


180

2.15] ,


(back

where


angle


refers


angle


between


propagation


direction


incident


scattered


light


[Bar87]


The back scattering geometry was used in this study.


back


scattering


geometry


results


electric


field


which is


parallel


to the sample


surface when


the direction of


Dropaaation


is oeroendicular to


,I .J


surface.











constant


their


between


vibration


atoms


[Pol91] .


and


Detailed


therefore


frequency


discussions


effects


stress


on the


atomic


force


constants


Raman


frequency


have


been


given


Cerdeira


et al.


[Cer72]


and


others


[Par77,


Gri78,


Ana70,


Gan70]


approach


used


here


to describe


dependence


phonon


frequency


with


stress


follows.


displacement


mass


atoms


elastic


atoms


vibrations


force


constant


related


between


neighboring


atoms


[Kit86]


Considering


only


neighboring


atoms


brevity,


force


acting


on an atom


point


us by


an atom


F,=C


(2-13


equation


of motion


atom


m (d2Us/dt2)


=C (Us+1


(2-14


dispersion


relation


lattice


vibration


[Kit86]


02= (4 C/m) sin2


1/2ka)


2-15


where C)


frequency,


k is


wavevector


magnitude,


and


(us+1


-us)


___ _


_











stress


affects


force


constant


thus


frequency


lattice


vibration.


Raman


spectroscopy


[Cah94,


Pol91,


Kit86]


was


used


two


purposes


in this


study


: 1)


to detect


both


characterized


peak


-1585cm-1)


characterized


peak


-133


2cm-1)


bonded


carbon,


measure


stress


in the


diamond


films


by measuring


frequency


shifts


of the


diamond


Raman


peak.


A typical


shown


Raman


in Figure


spectra


2.16.


from


a polycrystalline


Both


diamond


carbon


film


peaks


were


detected


at 1585


1334cm-1


, respectively


diamond


Raman


mode


peak


position


may


used


measure


stress


discussed


below.


stress-free


Raman


frequencies


of diamond


several


other


semiconducting


materials


are


shown


Table


Several


groups


have


used


Raman


spectroscopy


measure


shift

Par77


versus

Gri78.


pressure


Tar90


Wha76


, Sha85]


diamond

or the


Raman

Raman


mode

mode


[Bop85,

of other


materials


[Cer72,


Ana70,


Ven73,


Ona77,


Tek73]


Raman


frequency


increases


under


compressive


stress


and


decreases


with


tensile


stress.


-


hydrostatic


pressure


dependence of










average


value


.94cm1 /GPa


those


reported


literature


(Table


The


average


value


2 94cm-/GPa


was


used


determine


stress


homoepitaxial


diamond


films


described


below.


Table


Optical


phonon


frequencies


various


semiconductors


[Gan70


Cah94


Semiconductor


Structure


LO phonon


equency


(cm-1)


TO phonon
frequency


cm-'


diamond diamond 1332.5 1332.5

silicon diamond 520 520

germanium diamond 300.9 300.9

AlAs zincblende 404.1 360.9

GaP zincblende 403 367.3

GaAs zincblende 291.9 268.6

InP zincblende 345.0 303.7

InAs zincblende 238.6 217.3

ZnS zincblende 348.3 276.9

ZnSe zincblende 253.2 213.2

ZnTe zincblende 206.8 176.8

CdTe zincblende 169.5 140.1
















Table
order


Values


Raman mode


pressure


dependence


first


of diamond.


X-Ray Diffraction


X-ray


diffraction


[Cul78]


was


used


this


study


measure


strain


misorientation,


since


sensitive


both


lattice


constant


and


orientation


crystalline


material.


Ideally,


homoepitaxial


systems


should not


exhibit


strain


mosaicity


(relative


misorientation


mosaic


blocks)


However,


Raman


data


showed


that


some diamond


films


were


strained,


cracking


some


films


was


apparent


from


Reference (av/aP)T (cm-1/GPa) AP(GPa)

Bop85 2.87+0.10 0-27

Par77 3.6+0.3 0-2.4

Gri78 3.2+0.2 0-1

Tar90 2.64+0.10 0-15

Wha76 2.96+0.11 0-2.5

Sha85 2.37 0-25











films.


Background


information


experimental


approach


obtaining


lattice


parameters


(strain)


relative


tilts


of homoepitaxial


films


are


therefore


discussed.


Rocking


Curves


rocking


intensity


curve


around


crystallographic


plot


Bragg


reflection


[Phi93]


diffracted


angle


x-ray


particular


example,


to record


a rocking


curve


from


(220


reflection


(110


diamond


substrate,


(Bragg


angle


detector


and/or


sample


were


"rocked"


or moved


angularly


through


.6 )


schematic


shown


Figure


x-ray


configuration


used


to obtain


rocking


curves


[Phi93]


As shown


Figure


.17,


omega


angle


between


crystal


surface


plane


and


optical


axis


x-ray


source.


Two-


theta


(20)


is the


angular


position


of the


detector


relative


same


optical


axis.


Ideally,


co=Bragg


angle(8)


symmetric


reflections.


However,


to samples


being


miscut


or misoriented,


this


generally


not


case.


.g.,


I


.











reflects


the configuration geometry


sample,


detector,


and the optical axis of the x-ray source.


During recording of


an 0/26


rocking


curve


(also


known


as an c/28


scan)


both


detector


(26)


sample are


"rocked"


, with


detector


moving a


Q scan,


twice


only the


the angular velocity of the sample.


sample


During an


"rocked"


Lattice


Parameter Measurement


and co/2


Rocking Curves


0/28


rocking


curve


sensitive


differences


lattice


plane


spacing


[Few91a]


X-ray


diffraction


been


used


measure


lattice-mismatch


heteroepitaxial


systems


[Slu93,


Maz92,


Pes91,


Few91a,


Few91b,


Few87,


Bra90,


Rya87,


Bar83]


Consider


epitaxial


film


with


lattice


parameter


afilm,


substrate


with


smaller


lattice


parameter


[Figure


.18]


Through Bragg's


law,


nh=2dsin9,


film< esub


record


x-ray


rocking


curves


from


both


film


and


substrate,


detector


sample


are


"rocked"


through


Bragg


angle of


film and substrate.


The angular separation of


film and substrate


peaks,


A --- -. A- a 1 ~4-4- - 4- .-4 n


1 ,t-* -


, 4


n rr


L- -


L












(Aa/a)


=-Aocote/cos2


(2-16)


where


Bragg


asymmetric


angle,


angle


(Aa/a)


the s

1= (afiim


substrate,


- asub/asub)


perpendicular


lattice


mismatch


between


film


and


substrate


[Few87]


Bartels


[Bar83]


expressed


perpendicular


parallel


mismatch


asymmetric


reflections


to be:


(Aa/a)


=Adtanc-AOcotO


-17)


(Aa/a) 1i=-AIcotO-A~cot9


(2-18)


where


difference


in lattice


plane


orientation.


x-ray


beam


surface


anc


makes

d the


an angle

angular


(+0)


separation


(9-4) with

between the


sample


film


and


substrate


peaks


is either


(An+AO)


(Ae-AI)


, respectively


asymmetric


reflections.


In terms


x-ray


diffractometer


geometry:


2-19


u0 +d)











where co+


referred


to as


the positive m geometry and oe-


negative


o geometry.


should be noted


that


film


misoriented


from


substrate,


AV=0.O


This


causes


left side of equations 2-17


and 2-18


to go to 0,


therefore


they


are


valid


layers


which


are


tilted


substrates.


Mosaic Structure


Rocking


"ideal "


single


crystal


no defects,


and


atoms


are


their


appropriate


lattice


positions.


However,


real


single


crystalline materials consists of


varying size and orientation.


many small


Mosaic structure


[Cul78]


blocks


refers


distribution,


and can result


size,


from the


and


orientation


segregation


defects


these


which


blocks,


enclose


regions


of perfect


crystal


[Few91a]


mosaic


structure


film


will


affect


x-ray


rocking


curve


increasing


integrated


intensity


(area


under


curve)


angular


position


diffracted


beam


[Cul78]


A mosaic block which is misoriented relative


7 *n n *I n rI a


a-',


1. r7


-, .A- -


flr tre t o 1 t


Q ,S7'


and o


Curves


T*


T 1 E










spread)


, and


this


leads


increased


broadening


rocking


curve.


o rocking


curve


sensitive


to lattice


plane


tilt


mosaicity.


Fewster


[Few93


, Few92


, Few91a


, Few91b,


Few89]


others


[Hei94


, Ho193a,


Hol93b


, Kop94,


Slu93]


have


demonstrated


that


x-ray


analysis


can


used


characterize


crystal


mosaicity


of heteroepitaxial


layers.


Consider


"epitaxial"


film


which


misoriented


tilted


an angle


5 with


respect


substrate,


same


lattice


angle


film


parameter


[Figure


substrate


.19] .


are


same


Since


, only


Bragg


sample


is "rocked"

stationary.


through


angular


Bragg


angle;


separation


the

peaks


detector

(Amo):


Ao=5


therefore


equal


tilt


angle.


experimental


procedures


used


collecting


x-ray


data


are


discussed


Chapter


































MASS FLOW METER


THERMO COUPLE


VACUUM PUMP


SUBSTRATE


FURNACE


rxi
















c


diamond


non-diamond carbon


position of undiluted


enlarged
second l


0.9


Xo0&O/(O+H) 2


Figure


Atomic


C-H-O


diamond


deposition


phase


diagram


constructed
references


from


over


[Bac91]


deposition


numbers


experiments


diagram


and


indicated


f^ -try i-


~,r ar i, r~4- n ~ r n- --J A-1- ~ -


Thy n A/h~


T^ n |- -


i


1_1 1.


~rlCI n





























/diamond

" no growth

0 non-diamond carbon

D position of undiluted
compound


orientation line


limit of diamond
domain
I

set on connected on-diamond carbon
set of connected
experimental data / growth region

095


I -


*-- --- *- 57


no growth region


| 'r ) [ +* r -T T


r m'r


IIr 1I


^T-Plf-^r^^ r f i


X =O/(O+H)
Or S


* *'. ^ :


IT~"T^


















































1500 2000 2500 3000


TEMPERATURE (K

















0.010


) 008 r



0 006 K



0004



0 002




0 000 L


\
CH
4
C -1-~


\ ,^ ^'A" "-1


C M


----....--


--0-- ----I_


-- ----_ ---


2000


2100


Filam ntL Temperature (OC)


0 12 r------------------_-- ._

0 10 -


-) 004




0Q0
Y 0 O02


C211/


0 ----"" --S -
^^.^-*--'


C2 H
2 K


20 00


2100


2200


Filament Temperature (o C)


Figure 2.4


Relative


partial


pressures


versus


filament


1900


2200


.OJ
-- -""-_


I 900














































































1000


1200


1400


1600


WRVE


NUMBER


Figure


Raman


spectrum


from


polycrystalline


films


grown


-- q S --t


.i


A d


r


* 1


I


- *


1 _


II_ _I


I

































II 1
II
Pressure:560(Torr)

02: H2=0.2: 50








CH4;0.8 (scam)







CH4:1.4 (scorm)








CH4:2.0 (scom)


1000


1200


1400


1600


1800


WRVE


NUMBER


r, w rn a rn


C D m-n


C------


r2 ,---


anA -,l ,rnrol- 7 7 4 n r1 I I


1 m c


prr r .d t" v" I rv


.T'i tyr n T 7 ,"


~r yT^T


I


T~r


I



















I
I


I-li


0.87


1.15


1.65


I r I -





















D004


si (001)


(a)


D220


Si <110>


(b)


r'iSEtr -















^0


, xoo 0


.0.


1000


950


900


850


800


750
J

700
0


,a 30)


3.0 ( 0joo


1 2 3 4


METHANE


CONCENTRATION


%)















































-100


-400


Raman h ift ( on-l)


Figure


2.12


Raman spectrum showing the


longitudinal


optical


(LO)


phonon from:


Si substrate


wafer


(292cm-1)


(290cm-1)


4.1lm GaAs


film homoepitaxial


homoepitaxial


The GaAs peak


from


GaAs on a


was


to a
(100)


shifted 2cm-1


100)
GaAs
from


tensile


stress


calculated


from


1-hi


shift


was


\ r~ Jh Ir i r-A^ ^^c


Y





















































-100


-100


Raman


hiFtf


Cc-1 )




























o oscillating electric field



/2 /


'.--A--- J L^--



E



J2




transverse optical phonon
"!O


k=electric
q=phonon


field wavevector
wavevector


- -


_ ~~___


C---


I


i =


I


















sample


collecting
\ lens


rism


entrance
slit


focusing


ens


laser


source


sample


1800 scattering


collecting
\ lens


focusing


ens


laser


source


900


scattering


geometry


entrance
slit






geometry


Figure


I I IIf


r I -J


Schemati
nnmot-r ocQ


180


. -


II -


A fnr


Paman


scatte


1 \rc


ring)
Ffln r-Q


and


I i ra ia


; 1-


ar)i a


I


























1334


1200


1300


1400 1500 1600


1700


1800


Raman Shift (cm-1)




































































































Figure


S... -


Illustration


relationship


-


between


I-L'---


I













































































































9 1


T1 1 i.c t--r i nn


I


I I I.- I--


r1 at i nnh i n


bhPtWwen


STT11 T ,


J


1 1 .
















CHAPTER


EXPERIMENTAL APPROACH



Introduction


In this


study,


homoepitaxial


diamond


films were grown by


hot-filament


chemical


vapor


deposition


(HFCVD)


The


films


were characterized by various


techniques


including microRaman


spectroscopy,


high


resolution


X-ray


diffraction


(HRXRD)


optical


microscopy


(OM)


, secondary


electron microscopy


(SEM)


Fourier transform infrared spectroscopy


(FTIR)


, and secondary


ion mass spectrometry


(SIMS)


The HFCVD growth conditions and


details


characterization


techniques


are


discussed


following


chapter.


Filament


Chemical


Vapor Deposition


For hot


filament chemical


vapor deposition


[Kaw87,


Hir86,


Mat82,


Ang68] ,


a wire


filament


typically W,


or Re)


heated


to 1700-2500C


for the


purpose of


dissociating


m1ar 1 ar lni i 1 a 'ri


1Y\ n 1 n jn r I f^ r ^


' r TV1 / I


rhl/ i /^ ^/- ^T--


7 ^- J_- ,-,,-


*t- h ^ T i"-* -











precursor


hydrogen


diamond


95-99%)


deposition


hydrocarbon


generally


specie,


high


typically


methane


or acetylene,


balance.


The


dissociation


Table


Typical


filament


chemical


vapor


deposition


parameters


used


to deposit


diamond


(From


Spear [Spe89]


products


modeled


from


[Cel90


methane


Goo90]


acetylene


measured


hydrogen


[Har88 ]


have


several


been


groups,


and


consists


mainly


CH4,


CH3,


C2H,


and


atomic


hydrogen.


Calculated


concentrations


gas-phase


products


versus


dissociation


temperature


.e.


filament


temperature)


5%CHN4/H2


mixture


thermal


equilibrium


were


shown


Figure


2.3.


After


dissociation,


species


may


impinge


on the


substrate


which


heated


around


1000C.


Diamond


Variable Typical conditions Best crystals

Substrate Temp. (C) 700-1000 950-1050

Pressure (Torr) 10--100 40-100

CH4(in H2) (mol%) 0.1-5.0 0.1-1.0

Flow Rate (cc/min) 20-200 50-100

Filament Temp. (C) 1800-2500 2000-2500


CH2,


C2 H4,










diamond,


etc.)


have


been


used


[Lux91,


Bad93]


Non-


diamond


substrates


are


generally pretreated


with


diamond


seeds


or scratched


with


diamond


paste


to facilitate


nucleation


diamond


[Yar90


Diamond


Growth


Chamber


Parameters


The


HFCVD


diamond


growth


system


used


this


study


was


custom


built


LMA,


Incorporated


[Lin95]


cylindrical


chamber


was


made


quartz


, with


a diameter


inches


height


tungsten


inches


pancake


[Fig.


heating


3.1].


coil


encased


substrate


heater


in a molybdenum


was


block.


temperature


was


monitored


type


Pt: Pt/10%Rh)


thermocouple


which


was


input


Omega


CN2001


controller.


substrate


thermocouple


was


calibrated


observing


melting


point


silver


99%Ag)


which


9600C.


calibration


step


was


performed


under


run


conditions


with


flowing


in the


chamber.


thermocouple


was


recalibrated


filament


position


was


changed


or the


substrate


heater


coil


was


replaced.


substrates


homoepitaxial


growth


were


type


IIa












were


cleaned


with


acetone


and


methanol


prior


to growth.


cleaned


diamond


substrates


were


placed


molybdenum


block.


growth


chamber


was


evacuated


with


mechanical


pump


pressure


-10 2Torr.


Hydrogen


was


introduced,


raising


chamber pressure


to 40Torr.


pressure


was


held


constant


model


using


122A)


capacitance


measure


manometer


provide


gauge


a signal


(MKS


an MKS


baratron


type


pressure


controller


which


automatically


throttled


exhaust


valve.


wire


slowly


After


(dia.=0


to 2


the


02in,


000C;


chamber


pressure


.99%


filament


was


filament


temperature


stabilized,


temperature


was


the


was


monitored


rhenium


raised


using


an optical


pyrometer


with


no correction


emissivity.


substrate


temperature


was


also


raised


to 960C


as measured


thermocouple.


After


filament


and


substrate


temperatures


were


stabilized,


precursor


gas


was


introduced.


Precursor


gases


were


methanol


acetone


(Aldrich,


HPLC


Grade)


hydrogen


(Airco


.999%


addition,


a mixture


methane


and


oxygen


with


a balance


hydrogen


was


used


several


growths.


precursor


flow


- --4 I-. -. U)! t C 4. w.. n- -N N n % ~4~~ a 11 a-1 -


_--~-A4- .-- 1 --1


i nrn


C1 -


^^ I -


I~


I


I


tWirt ^""l *"f


I


I-- ,


*A n/ii MA


p C n












Table
times


3.2


chemistry,


diamond


samples


substrate


used


this


orientation,


and


growth


study.


Gas chemistry Substrate Growth time (hr)
orientation

3% methanol (110) 20,64
(111) 20,64

10% methanol (100) 3.5,5,21,93
(110) 3.5,5,20,93
(111) 93

20% methanol (100) 3.5
(110) 3.5,20

30% methanol (100) 5
(110) 5

50% methanol (100) 5,20
(110) 5,20
(111) 20

90% methanol (100) 24

100% methanol (110) 20

0.5% acetone (100) 19
(110) 19

1.0% acetone (100) 16
(110) 16,20
(111) 16

3% acetone (100 20
(110) 20


cc/min)


acetone


methanol


1-100


cc/min)


were


varied


to result


in different


precursor


concentrations.











shutting


carbon


precursor.


After


several


minutes


filament


temperature


was


reduced


followed


substrate


temperature.


Finally


hydrogen


flow


was


shut


off,


chamber


evacuated


(-10-2 Torr)


, and


chamber


opened


to air.


Characterization


Techniques


variety


techniques


were


used


characterize


diamond


films.


description


tool


and


important


attributes


technique


are


discussed


below.


Raman


Spectroscopy


Experimental


Procedure


In microRaman


spectroscopy,


a microscope


is used


to focus


laser


to a small


spot


(1-l100um


depending


on the


lens


and


excitation


wavelength)


scattered


light


collected


microscope


shown


Figure


small


probe


size


allows


data


to be acquired


from


different


regions


of a sample.


A schematic


Raman


spectrometer


used


this


study


shown


in Figure


Raman


data


were


collected


using


180


geometry


and


excitation


.5nm


radiation


from


a Coherent












10mW


sample.


focus


laser


Olympus


BH2


sample


microscope


spot


was


size


used


was


-5Mm,


which


resulted


power


density


-510W/mm2


magnification


aperture was


objective


0.95,


lens


and the depth of


was


focus


100X,


numerical


(DOF=A/4-NA2)


[Mel90]


was


calculated


to be


-143nm.


four


independent


slits


Ramanor U-1000 double monochromator were


either


100Mm


1200-1700cm-1


scans,


40Mm


1320-1340cm-1


scans.


procedure


used


acquiring


Raman


data


were


follows.


Water


flow to


laser power


supply was


turned on.


fault


water


switch


was


prevented


flowing.


laser


power


from


operating


switch


when


laser


was


turned


power


laser


was


increased


slowly


until


meter


laser


control


panel


read


100mW.


laser power was unstable


for approximately


10 minutes and


power


was


periodically


adjusted.


SPEX


1450


Tunable


Excitation


Filter


consisting


compact


grating


monochromator,


was adjusted with a micrometer for the selected


.7-3~Tr! 1 Q rTr An


f- I1t o


nl1 a Cam-3


I a I-.. nn A


Il e i n"


TA"!CI


am ?c ^nc


r ^












aluminized


guide


mirrors,


laser


with


into


reflectivities


microscope


92%,


were


align


used


excitation


beam


perpendicular


sample


surface.


A Type


IIa,


(110


oriented,


natural


diamond


substrate


was


used


to align


beam


to calibrate


monochromator.


A video


camera


mounted


microscope


laser


spot


and


connected


sample


monitor


was


surface.


used


laser


image


beam


was


aligned


perpendicular


(+_5)


sample


surface


changing


alignment


mirrors


until


laser


spot


defocused


symmetrically


(versus


asymmetrically


under-focus


and


over-focus


condition


of the


microscope)


There


was


one


mirror


between


microscope


monochromator


which


was


used


visually


align


laser


beam


on the


center


entrance


slit.


spectrometer


SpectraLink


IEEE


was


interface.


interfaced


A Prism


with


a computer


software


through


package


was


used


to control


spectrometer


collect


data.


step


sizes


between


data


points


was


varied


from


.02cm-1


1cm'1


time


per


step


was


typically


seconds,


although


counting


times


of 10 seconds


were


used


occasionally


better


-- r. r, -% I far


*m- r nV '


r'


1- Oflfl-rm-l


, I


,,,1


inin- y


___ ___


___1


* -'


'In Vr -T- TT^-


1


* E y\/











scan


range


1315cm-'


1345cm-'


was


generally


used


when


measuring


times


were


diamond


signal


minutes,


only


data


depending


acquisition


step


size


dwell


time.


Stress Measurement


Precision and Method


For


greater


precision


accuracy


measuring


diamond Raman


peaks,


their position


was generally referenced


position


5520A


krypton


line


(1322cm-')


[Ale94]


This


refinement


was


required


a mechanical


stepping motor


the monochromator which caused small


shifts


peak position


from run


run,


making


difficult


measure


small


stresses.


Shown


in Figure


are


the diamond


peak

ten


positions recorded

consecutive runs,


from a natural


with


diamond substrate


changes


instrumental


parameters or sample position.


Shifts to


lower wavenumbers of


0. lOcmr/scan


with


average


shift


.O53cm-r/scan


was


typical.


While


most


shifts


were


lower


wavenumbers,


sometimes


peak


would


shifted


higher


wavenumbers.


Attempts


to control


these effects


by unidirectional


scanning












using


possible


a krypton


to dramatically


line


as an internal


improve


precision


reference,


of the


was


measured


peak


position


to 0+


.03cm-1


Figure


.4 shows


peak


position


measured


sequential


runs


same


sample


Figure


while


using


same


spectrometer


parameters


and


krypton


reference


line.


This


precision


was


achieved


part


because


krypton


calibration


line


only


cm'-


from


diamond


Raman


line,


shown


Figure


Both


Raman


spectrum


from


a natural


diamond


krypton


line


which


was


used


reference


are


shown


in Figure


krypton


line


was


detected


placing


a krypton


lamp


near


optical


axis


in front


of the


monochromator


entrance


slit


[Figure


One


problems


with


using


krypton


internal


standard


was


that


light


(from


Kr lamp)


entering


monochromator


increased


background


or dark


counts.


This


decreased


our


ability


to observe


krypton


lamp


weak


position


Raman


could


signals.


be varied


To reduce


with


background,


respect


optical


However


axis


control


, movement


lamp


measured


during


krypton


course


intensity.


of recording


01f l 1 1 i'


mrvsrrTo i-


nnrt 1


n -at-


=31 r^- r ar


01 1/ri


TAT 3 0~


I


t rl 1 i f 11











light


diffraction


grating.


second


method


used


control


dark


counts


was


turn


lamp


after


monochromator


scanned


tol324cm-i


dark


through thi

counts were


krypton

minimized


peak


(1319


under


diamond


peak


(1325


to 1340cm-')


procedure


used


determine


average


shifts


(due


stress)


was


follows.


diamond

The r


Raman


)eak


peak


position


from


homoepitaxial


from


film


an unstressed,


single


crystal,


diamond


substrate


without


a film


was


measured


along


with


peak


position


krypton


line.


difference


peak


positions


diamond


and


krypton


resulted


Avsk= sub.


- )krypton


(3-2w)


where


Raman


Avsk


peak


was


wavenumber


and


krypton


difference


line


between


cm-1


diamond


Similarly,


homoepitaxial


diamond


film


on a substrate


was


measured:


Avfk=) film


- Vkrypton













AVsf=AVsk-Afk


(3-3


where


AVsf


was


difference


between


measured


diamond


substrate


position


film


position.


film


stress


was


calculated


-=Avsf/K


where


94cm-1/GPa,


as reported


above.


Controlling


Raman


Probing Depth


Raman


spectrum


(solid


line)


from


a 25Mm


thick


diamond


film


OO00m


thick


diamond


substrate


shown


Figure


Voight


curves


(shown


as dashed


lines)


, representing


Raman


scattering


generate


data


from


total


discussed


film


Raman


below.


peak.


total


substrate,


Curve


can


be summed


fitting


diamond


peak


Raman


Figure


solid


line)


exhibited


asymmetric


broadening


lower


wavenumbers.


contributions


from


peak


doublet


results


homoepitaxial


film


from


independent


and


diamond


. 1 r---.i


r-' -1 ..


S1_ ,


_1_ 1- -


I


Y


1











microscope.


Raman


spectrum


from


same


sample


Figure


was


recorded


with


a pinhole


(-400pm)


aperture


shown


increased


Figure


intensity


wavenumbers.


lower


relative


asymmetric


wavenumber


peak


broadening


peak


higher


Raman


peak


Figure


was


caused


microcrystalline


structures


[Pol91],


using


pinhole


aperture


would


not


have


changed


relative


intensities


peaks.


Diamond


is transparent


at 514


.5nm,


wavelength


used


excite


Raman


scattering,


therefore


Raman


signal


generated


bulk


transparent


media.


depth


focus


our


microscope


objective


was


calculated


to be


-143nm


see


was


above)

being r


so Raman


recorded .


scattering


was


from


possible


deep


to limit


within

It the


the s

signal


ample

from


substrate


with


pinhole,


however


substrate


signal


was


detected


through


homoepitaxial


films


which


were


less


than


-70 m


thick.


Although


natural


diamond


typically


colorless


[Fie92]


were


our


substrates,


homoepitaxial


films


ranged


from


black


nearly


colorless.


color


homoepitaxial


/


-*


V


. --











grown


with


<10%CH3OH


black


when


grown


with


>90%CH3OH.


color


films


affected


transparency


probing


laser


therefore


probed


depth


Raman


peak.


This


fact,


Raman


difficult.


addition to

scattered

Therefore


surface


scattering,


intensities


Raman


from


spectral


makes


various


intensities


comparison


samples


are


very


reported


below


only


in arbitrary


units.


Curve


Fitting


Peak


positions


and


linewidths


diamond


Raman


mode


peaks


were


obtained by non-linear


least


squares


curve


fitting.


Lorentzian,


Gaussian,


and


Voight


functions


[Arm67]


were


used


curve


Lorentzian


spectral


line


shape


lines


been


obtained


reported


with


to best


Raman.

represent


spectral


line


shape


produced


radiating


oscillator


[Arm67]


Gaussian


Doppler)


line


broadening


been


reported


result


from


statistical


distribution


radiation


frequency


influenced by


both


[Kle86]


Lorentz


and Doppler


spectral


line


broadening


shape


, the


were


profile


is represented


- 7 -.


Voirht


function


[Arm67] ,


which











Lorentzian


function


used


test


curve


fitting


this


study was:


(3-5)


(v-a)/b] 2


where


intensity,


frequency,


amplitude,


Lorentzian


a is


peak


function


can


center,


and b


evaluated


linewidth.


analytically.


A Raman


spectrum


from


(110)


diamond


substrate,


Lorentzian


using


PeakFit


software


[Pea92] ,


and


residuals


from


curve


are


resulted


shown


peak


Figure


position


Lorentzian


1332.55cm-'


linewidth


.13cm-1


, and


standard


deviation


19.1


cts/sec.


residuals


plotted


Figure


demonstrate


systematic


effects,


i.e. ,


regions


of mostly positive or mostly negative


residuals


indicate


over


that


range


wavenumbers.


a Lorentzian peak was


Systematic


not


most


effects


appropriate


function


to model


the Raman peak.


The Gaussian


function


used for


curve


fitting was:











where


variables


are


same


Lorentzian.


Fitting


same


Raman


spectra


with


Gaussian


function


[Figure


.13]


using


PeakFit


resulted


peak


position


1332


.55cm-1


linewidth


.43cm-1


a standard


deviation


cts/sec.


residuals


plotted


Figure


demonstrate


increased


systematic


variations


when


compared


Lorentzian


[Figure


Gaussian


therefore


even


a worse


function


to model


Raman


peak.


Pea92]


Voight f

However


unction,


can


cannot


evaluated


approximated


using


analytically


approach


developed


Puerta


Martin


[Pue81]


which


consists


four


generalized


Lorentzians.


Voight


function


used


curve


fitting


was


= {Aexp(


) / {z+ r


J{exp


where


proportional


Doppler


width


and


z is


ratio


collision


width


to the


Doppler


width.


same


Raman


spectrum


which


was


with


a Lorentzian


[Figure


and


Gaussian


[Figure


.10]


was


also


fitted


with


- i"d<:_


)}d(


-a2/












Voight


was equal


to the


value


(1332.55cm-')


obtained by the


Lorentzian


Voight


and


Gaussian


function


fit.


(2.21cm-')


linewidth


was


slightly


achieved


higher


from


.06cm-')


then


Lorentzian


-0.22cm-i


narrower


then


Guassian


fit.


Fitting


with


Voight


function


resulted


standard


deviation


15.6


cts/sec


which


was


improvement


over


both


Lorentzian


Gaussian


fits.


residuals


from the


Voight


show the


systematic


effects versus


wavenumbers


which


were observed from


Lorentzian and more


noticeably from the Gaussian fit residuals.


Although the peak


positions


were


same


linewidths


were


similar


both


Voight


and Lorentzian


fits,


curve


fitting with a


Voight


function was


chosen due


to the better


standard


deviation and


lack of


systematic patterns


in the


residuals.


X-Ray Experimental


Procedures


A Philips HR1 x-ray diffractometer was used


to perform


ray


analysis


homoepitaxial


diamond


films.


x-ray


tube


generator


was


operated


40kV


and


produced


(7iikrv r^iiainn


Swiv;1 enath


1 /\ 1


nf 1 4nflA.


Th^ r^rcintinn


1












and


AX/X=2


.3x10-5


wavelength


spread.


X-ray


analysis


preformed


with


4-crystal


monochromator


generally


referred


high-resolution


x-ray


diffraction


(HRXRD)


[Bar83


, He93,


Hei94,


Seg89


, Pet94]


To record


rocking


curve


peaks


which


were


representative


film


quality,


optimization


procedures


were


followed.


This


procedure


was


more


difficult


present


study


diamond


because


small


sizes


(=imm


2mm


2mm)


and


irregular


shapes


diamond


samples.


x-ray


beam


diameter


HRXRD


approximately


5mm,


i.e.


larger


than


some


samples


addition,


crystallographic


directions


sample


were


completely


unknown.


goniometer


diffractometer


arrangement


are


shown


Figure


.13.


samples


were


mounted


on glass


slides


with


double


sided


tape.


Care


was


taken


to minimize


any


stresses


sample.


glass


slide


sample


were


mounted


goniometer


with


tape


holding


glass


slide


on the


mounting


plate.

optical


The

axis


sample


surface


using


a dial


was


aligned


gauge


which


center


was


inserted


1'-' -, C, C'


Ctn C' fl N4 C' Y.Ar


*
r- iCl i -


n ?Imn Tf^ t n


m nt\ rti ^


-^ I /"ny n


r:4Ft -


TtT- e~


T- n ~











rotation


tilt


angles,


series


o rocking


curves


maximum


were


recorded


diffracted


were


intensity


adjusted


smallest


until


linewidth


was


achieved.


sample


was


re-aligned


in the


x and


directions


maximizing


diffracted


x-ray


intensity


while


changing


y slightly


2mm)


computer.


Analyzer


Crystal


Towards


this


study,


analyzer


crystal


was


added


respect


Figure


to the


.14.


HRXRD


system.


monochomator,


analyzer


geometry


sample,


crystal


crystal


detector


is a U-shaped


with


shown


(Bonse-Hart)


[Bon65]


crystal


which


was


mounted


directly


front


detector


direct


increase


result


resolution.


limiting


improved


acceptance


resolution


angle


-~14arcsec,


which


allows


separation


lattice


parameter


misorientation


contributions


diffraction


peak


broadening.


To record


rocking


curves


using


analyzer


crystal,


nfl I mnnrtnnf


n Pyr fnrm m r=A


nri nr


fn i-r-


1h .-'hf T ^


ot-p -n











crystal

critical.

equipment

receiving


with


respect


The

operator

slits.


crystal


the

may


touching


detector


beam

have


optics

become


detector


was


arm


rocked


was


extremely


misaligned


while


(28-scan)


from


changing

through


incident


beam


(without


diffraction


from


sample)


ensure


that


FWHM


intensity


profile


was


.00400


FWHM


was


.00400


, the


analyzer


crystal


required


re-


alignment)


illustrate


effect


limiting


acceptance


angle,


detector


was


rocked


through


x-ray


beam


under


three


conditions:


open-ended,


receiving


slit


(slit


width


5mm)


and


analyzer


crystal


[Figure


.15]


term


"open-


ended"


refers


diffracted


x-ray


beam


entering


detector


without


conditioning


slits


front


detector)


acceptance


angle


open-ended


detector


was


~7500arcsec.


receiving


slit


mode,


slit


was


placed

angle


in front


~920arcsec


detector


with


which


0.5mm


limited


slit.


When


acceptance


analyzer


crystal


was


used,


two


Bragg


reflections


from


analyzer










Scannina


Electron Microscopy


Scanning


Electron


Microscopy


(SEM)


[Bru92]


was


used


characterize


surface morphology


the diamond


films.


JEOL


JSM


operating


10-15kV


a working


distance


15-20mm was used to record SEM micrographs.


Occasionally,


sample


was


tilted


accentuate


imaging


surface


defects.


surface


morphology


diamond


films


were


strongly dependent on substrate orientation and gas chemistry.



Fourier Transform Infrared Spectroscopy


Fourier


Transform


Infrared


Spectroscopy


(FTIR)


[Bru92]


was used to characterize hydrogen and oxygen impurities in the


diamond


films.


Nicolet


Magna-IR


system


used


FTIR


analysis


homoepitaxial


diamond


films


includes an FT-IR


spectrometer,


Nic-Plan


IR Microscope,


and a


Spectra-Tech


Motorized


Micropositioning


Stage.


Nicolet


system


was


operated


via


486/66


computer


using


OMNIC


software.


microscope was used to


focus


IR beam to -250pm and collect


light.


More


precisely,


Nicolet


system


was


equipped











laser was


required


focusing


because


IR light


can not


seen with the naked eye.


The scan range was from 600


to 4000


cm-'


with


resolution


8 cm1-


total


data


acquisition


time


approximately


minutes.


Spectra


were


recorded


measuring the


percent


reflectance.


surface


roughness and


absorbance


varied


from


one


film


next,


therefore


spectra


were normalized for


intercomparison between different


samples.


Secondary


Ion Mass Spectrometry


Secondary


Mass


Spectrometry


(SIMS)


[Bru92]


was


performed


with


Perkin-Elmer


6600


system.


and


primary


current


beams


1.09


operated


1.12gA.


voltage


rastered


7keV


area


and


was


beam


150gm


150gm and


the analyzed area


was


37. 5gm


x 37. 5m.


Impurity analysis was performed using both


the mass


scan


and


depth


profiling


modes.


mass


scan


mode


impurities


(hydrogen


uranium)


film


are


surveyed.


depth


profile


mode


was


used


scan


preselected


i mmnn ri t I


S Fimfln nm nf


ti-mr












Ouantitative


Analysis


with


SIMS


Standards


quantifying


SIMS


data


were


available


this


study.


concentration


impurities


diamond


films


were


obtained


procedure


outlined


Wilson


et al.


[Wil89]


Relative


Sensitivity


Factor


(RSF)


defined


as:


p =RSF


li/Im)


where


impurity


isotope


impurity

secondary


atom

ion


density,


intensity,


cts/sec)


cts/sec)


matrix


isotope


secondary


intensity,


and


RSF


units


atoms/cm3


RSF


values


impurities


diamond


matrix


are


given


impurity


Table


element


These


in diamond


values


with


are


results


used


accurate


quantify an

to within a


factor


to 5.


Figures


shows


RSF


values


from


Table


plotted


versus


ionization


potential


primary


beam,


respectively.


id electron

RSF values


affinity


elements


a Cs4


not


primary


listed


beam,


in Table











was


drawn


perpendicular


x-axis


Figure


ionization


potential


value


or at


electron


affinity


value


in Figure


till


intersects


best-fit


line.


RSF


value


element


was


then


calculated.











Table


SIMS


Relative


Sensitivity


Factors


(RSF)


impurity atoms


in a


diamond matrix


(from[Wil89]


Element


(atoms/cm3 )


keV 02+


primary beam


RSF
14.5


primary


atoms/cm3)


keV


beam


H 6e23 4e23

Li 1.4e19

Be 4e20

B 3e21 2e24

C (matrix atom 1.8e23 1. 8e23
density)

0 2. 3e23

F 3.4e22 4.8e22

Na 7e18

Al 3.6e19

Si 2e21

P 3.6e22 2.2e23

Ca 2.2e19

Ti 6e19 9e25

As 5e22 3e23












Quartz
Chamber


exhaust
tube














microscope


monochromator











Ar-ion laser


sample


filter















10



8



6-



4



2



1331.9


I.





















I -


1332.1


1332.3


1332.5


1332.7


Raman Peak Position (cm"1)














10



8



6-



4



2



1331.9


1332.1


1332.3


1332.5


1332.7


Raman Peak Position (cm-1)

































1320


1325


1330


1335


1340


Raman Shift (cm-














microscope


pinhole


lens


monochromator


lamp


sample









































_ N


1315


1325


1335


1345


Raman Shift (cm-1)


Fiaure


Raman


spectrum


from


- -- ---


25um


thick.


g


(110)


-- _




























1315


1325


1335


1345


Raman Shift (cm-')










1600 -


1200 -


1320


1325


1330


1335


1340


1345


Raman Shift (cm-1)


1320


1325


1330


1335


1340


1345


Raman Shift (cm-1)


-- Lorentzian fit
o measured data


*
a
*
* a
a
a


S
S a


S S a -


c~~ia aaS


i t 1" il II I ., l i. ,"lt IIII1"lll









1600 -


1200


1320


1325


1330


1335


1340


1345


Raman Shift (cm-1)


140
120
100
80
60
40
20
0
-20
-40
-60
-80
-100


1320


1325


1330 1335


1340


1345


Raman Shift (cm-1)


---- Gaussian fit
m measured data


, .-


if










1600 -



1200 -



800 -



400 -


-- Voight fit


o measured data


S
a4
a


S S S a S S S ~ a *


a*

-


1320


1325


1330


1335


1340


1345


Raman Shift (cm-')


-40-

-60 -

-80


1320


1325


1330


1335


1340


1345


Raman Shift (cm-1)


''lilt. ''liii ''l*Jj '11111111 I'll III ij.tj~i
















x-ray
source


(110) Ge crystals
(220) reflection: d


livergence ~8arcsec


















Bartels


sample


monochromator


x-ray
source


analyzer
crystal
Ge(220)


detector












60000


40000








20000








0


-6000


-4000


-2000


2000


4000


6000


2Theta (arcsec.)


Ficrure


Rockincr


curves


obtained


from


passinac


detector


_ _


_J *


.L I