Group Title: 7th International Conference on Multiphase Flow - ICMF 2010 Proceedings
Title: 15.6.2 - The Effect of Flow Structure in the Narrow Gap of the Rotational Disk on the Photoresist Stripping Rate
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Permanent Link: http://ufdc.ufl.edu/UF00102023/00385
 Material Information
Title: 15.6.2 - The Effect of Flow Structure in the Narrow Gap of the Rotational Disk on the Photoresist Stripping Rate Reactive Multiphase Flows
Series Title: 7th International Conference on Multiphase Flow - ICMF 2010 Proceedings
Physical Description: Conference Papers
Creator: Hamada, H.
Kaneko, A.
Abe, Y.
Ike, M.
Fujimori, K.
Kato, T.
Asano, T.
Publisher: International Conference on Multiphase Flow (ICMF)
Publication Date: June 4, 2010
 Subjects
Subject: aqueous ozone
photoresist stripping
rotating disk
narrow gap
 Notes
Abstract: In recent years, photoresist stripping techniques of lithography by high concentrated aqueous ozone are proposed. Photoresist stripping rate with aqueous ozone is slower than a existing method using hot concentrated sulfuric acid. Therefore the photoresist stripping rate with the aqueous ozone is necessary to be improved. The authors' previous study proposed the following technique with the disk-shaped nozzle. That is, aqueous ozone is supplied between the rotational silicon wafer coated with photoresist and the stationary disk nozzle, and improvement of the stripping rate was partly succeeded. However, the mechanism for the improvement of the stripping rate is not identified circumstantially. The purpose of the present study is to obtain the knowledge of the relation between flow structure and photoresist stripping rate in the narrow gap. In order to examine the flow structure in the narrow gap, visualized measurement between the rotational disk and the disk-shaped nozzle is conducted with high speed video camera. The flow structure is compared with remaining film thickness of photoresist removed with high concentrated aqueous ozone. The correlation between the local flow structure and the photoresist stripping rate is discussed.
General Note: The International Conference on Multiphase Flow (ICMF) first was held in Tsukuba, Japan in 1991 and the second ICMF took place in Kyoto, Japan in 1995. During this conference, it was decided to establish an International Governing Board which oversees the major aspects of the conference and makes decisions about future conference locations. Due to the great importance of the field, it was furthermore decided to hold the conference every three years successively in Asia including Australia, Europe including Africa, Russia and the Near East and America. Hence, ICMF 1998 was held in Lyon, France, ICMF 2001 in New Orleans, USA, ICMF 2004 in Yokohama, Japan, and ICMF 2007 in Leipzig, Germany. ICMF-2010 is devoted to all aspects of Multiphase Flow. Researchers from all over the world gathered in order to introduce their recent advances in the field and thereby promote the exchange of new ideas, results and techniques. The conference is a key event in Multiphase Flow and supports the advancement of science in this very important field. The major research topics relevant for the conference are as follows: Bio-Fluid Dynamics; Boiling; Bubbly Flows; Cavitation; Colloidal and Suspension Dynamics; Collision, Agglomeration and Breakup; Computational Techniques for Multiphase Flows; Droplet Flows; Environmental and Geophysical Flows; Experimental Methods for Multiphase Flows; Fluidized and Circulating Fluidized Beds; Fluid Structure Interactions; Granular Media; Industrial Applications; Instabilities; Interfacial Flows; Micro and Nano-Scale Multiphase Flows; Microgravity in Two-Phase Flow; Multiphase Flows with Heat and Mass Transfer; Non-Newtonian Multiphase Flows; Particle-Laden Flows; Particle, Bubble and Drop Dynamics; Reactive Multiphase Flows
 Record Information
Bibliographic ID: UF00102023
Volume ID: VID00385
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: 1562-Hamada-ICMF2010.pdf

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7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010


Paper No


Introduction

In the process of lithography in semiconductor
manufacture, photoresist which is photosensitive polymer
material is used and necessary to strip eventually. In
recent years, hot concentrated sulfuric acid is more
commonly used in the photoresist stripping process,
although it causes high environmental road due to
desulfuration. In order to reduce environmental load,
photoresist stripping techniques of lithography by high
concentrated aqueous ozone are proposed (Kurokawa, et al.,
1999, Inoue, et al., 2005). Photoresist stripping rate with
aqueous ozone is slower than an existing method by the
sulfuric acid. Therefore the photoresist stripping rate with
the aqueous ozone is necessary, to be improved.
The authors' previous study proposed the following
technique with the disk-shaped nozzle (Abe et al., 2008).
That is, aqueous ozone is supplied between the rotational


silicon wafer coated with photoresist and a stationary disk
shaped nozzle. It was reported that photoresist stripping
rate is improved by using the disk-shaped nozzle partly, and
the results supposed that the flow structure between the
disks plays an important roles in the stripping. However,
the mechanism of the improvement of the stripping rate is
not identified circumstantially.
Several studies have been made on the flow structure
between disks. Those studies mostly reported a
hermetically closed condition (Schouveiler, et al., 1999).
In the closed condition, it is identified that the flow structure
is changed as aspect ratio 7= h/R and the Reynolds number
ReR e ry where h is distance between disks, R is radius
of a disk, D is angular velocity and v is kinematic viscosity
coefficient. And a large circulation is existed between
disks. In present study, the condition is open to the
atmosphere at the edge of disk-shaped nozzle. Thus it is
necessary to clarify the difference of the flow structure


The Effect of Flow Structure in the Narrow Gap of the Rotational Disk
on the Photoresist Stripping Rate


Hiroyuki Hamadal, Akiko Kanekol, Yutaka Abel, Masatoshi Ike2, Ken Fujimori3,
Takeshi Kato4 and Toshiyuki Asano4


i Department of Engineering Mechanics and Energy, University of Tsukuba
1-1-1 Tennodai, Tsukuba, Ibaraki, 305-8573, Japan
E-mail: hhamadartedu.esys.tsukuba.ac~jp

2 Apptex LLC
2-16G Nagakunidai, Tsuchiura, Ibaraki, 300-0810, Japan

STsukuba Industrial Liaison and Cooperative Research Center
1-1-1 Tennodai, Tsukuba, Ibaraki, 305-8573, Japan

4 Ibaraki Prefectural Industrial Technology Institute
3781-1 Nagaoka, Ibaraki-machi, Higashiibaraki-gun, Ibaraki, 311-3195, Japan


Keywords: Aqueous ozone, Photoresist stripping, Rotating disk, Narrow gap




Abstract

In recent years, photoresist stripping techniques of lithography by high concentrated aqueous ozone are proposed.
Photoresist stripping rate with aqueous ozone is slower than a existing method using hot concentrated sulfuric acid.
Therefore the photoresist stripping rate with the aqueous ozone is necessary to be improved. The authors' previous study
proposed the following technique with the disk-shaped nozzle. That is, aqueous ozone is supplied between the rotational
silicon wafer coated with photoresist and the stationary disk nozzle, and improvement of the stripping rate was partly
succeeded. However, the mechanism for the improvement of the stripping rate is not identified circumstantially.
The purpose of the present study is to obtain the knowledge of the relation between flow structure and photoresist
stripping rate in the narrow gap. In order to examine the flow structure in the narrow gap, visualized measurement between
the rotational disk and the disk-shaped nozzle is conducted with high speed video camera. The flow structure is compared
with remaining film thickness of photoresist removed with high concentrated aqueous ozone. The correlation between the
local flow structure and the photoresist stripping rate is discussed.







































-L


structure in the narrow gap between disks. A metal halide
light (HVC-SL, Photron, Ltd.) is used as the light source for
visualizing the flow field. The flow fields in the narrow
gap are visualized with illuminated a small amount of flake
particles (Mearlmaid AA, BASF Japan, Ltd.) which are
added in the working fluid. The tracer particle flows
following on shear structure to be flattened. High speed
video camera (FASTCAM-MAX, Photron, Ltd.) is placed
above the disk shaped nozzle. The experimental
conditions of whole disk visualization are listed in table 1.
Flow rate, rotational rate, diameter of disk shaped nozzle,
and distance between disks are assumed to be parameters.
Because it is supposed that these parameters influence the
flow between disks.

Table 1: Experimental conditions for observation of
overall flow structure in the gap
Flow rate O 0.75 2.0 L/min
Rotational rate N 100 400 rpm
Diameter of disk shaped nozzle D 100 175 mm
Distance between disks Z 2.0 4.0 mm

Figure 3 shows a measurement setup for flow structure
in the narrow gap between disks. A YAG laser
(excel+mpc6000, Laser Quantum, Ltd.) is used as the light
source for illuminating the tracer particles and visualizing
the flow fields. The working fluid is, seeded with nylon
spherical microparticles (Nylon particle, KANOMAX Japan,


7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010


Paper No


speed video
a


:tal halide light


f r
Rotating disk N
Figure 2: Observation setup for overall flow structure
in the narrow gap


between the open and closed conditions. And few attempts
have been made at conditions which have a through-flow
(Kurokawa and Sakuma, 1988) and be open to the
atmosphere at the edge of disk (Soong et al., 2003). There
are several numbers of the studies on the flow structure in a
narrow gap between two disks, although the relation
between the flow structure in the gap and the photoresist
stripping is not cleared yet. It is required necessary to
clarify the relation between the flow structure between disks
and the photoresist stripping rate.
The purpose of the present study is to obtain the
knowledge of the relation between flow structure and
photoresist stripping rate in the narrow gap. In order to
examine the flow structure in the narrow gap, visualization
observation and PTV measurement between the rotational
disk and the disk shaped nozzle are conducted with high
speed video camera. Flow structure is compared with a
photoresist stripping rate with high concentrated aqueous
ozone. The correlation between the local flow structure
and the photoresist stripping rate is discussed.



Nomenclature

D Diameter of disk shaped nozzle (mm)
N Rotational rate (rpm)
Q Flow rate (Lmnun)
Z Axial distance between two parallel disks (mm)
Do Inner diameter of disk shaped nozzle (mm)
u Radial flow velocity (mms')
v Rotational flow velocity (mms')

Greek letters
p Density of fluid (kgm')
r Shear stress (Nm )
vKinematic viscosity coefficient (m~s')
D Angular velocity (rad)



Experimental Setup and Experimental Conditions

A schematic diagram of the present experimental
apparatus is shown in Fig. 1. It is consisted of a tank, a
pump, a flow control valve and test section. The test
section is consisted a rotating disk and a disk shaped nozzle
which is fixed above the rotating disk. Tap water used as
working fluid flows into the test section with the pump.
Flow rate is controlled with the flow control valve located
between the pump and the test section. Flow rate is
measured with a Karman vortex flowmeter. In order to
satisfy photoresist stripping condition mn an actual
equipment, 8 inch silicon wafer is fixed on the rotating disk.
Rotation of the disk is provided with a speed control motor
(US590-001C, ORIENTAL MOTOR Co., Ltd.) in variable
speed. The disk shaped nozzle is consisted of a
disk-shaped glass and a cylindrical nozzle. The
disk-shaped glass is made of Pyrex glass to allow flow
visualization. An inter diameter of cylindrical nozzle Do is
6.3 mm. The distance of the gap between the rotating disk
and the nozzle is adjustable.
Figure 2 shows an observation setup for overall flow


camer




Nozzle M

Z De


C\





Inc.) having a mean diameter of 4.1 Cpm and a density of
1.02 g/cm3, respectively. High speed video camera is
placed above the nozzle and it can be traversed 10 mm with
in accuracy less than 0.01 mm on z axis. A 5-times
magnification objective lens (M Plan Apo 5x, Mitutoyo Co.),
with NA of 0.14 and a depth of field of +14 Cpm, is attached
to the camera providing a filed of view of 0.8 x 1.7 nun2
Thus two-dimensional flow field (r-B plane) layers are
measured due to the narrow depth of field. The origin is
defined as the center of the rotating disk. The positive xis
radial direction and the positive y is z direction. Images
were recorded every 0.1 mm in z direction and every 2 mm
in r direction from 30 to 62 mm. The experimental
condition of the measurement of flow field layer is listed in
table 2.

Table 2: Experimental condition for measurement of
flow structure in the narrow a
Flow rate Q 1.0 L/min
Rotational rate N 100 rpm
Diameter of disk shaped nozzle D 125 mm
Distance between disks Z 2.0 mm

The experimental conditions of photoresist stripping
using high concentrated aqueous ozone is listed in table 3.
In the experiment of photoresist stripping, two types of
nozzle, disk shaped nozzle and cylindrical nozzle, are used
for comparing the effect of nozzles. 8 inch silicon wafer
coated photoresist film is used for the stripping experiment.
Photoresist is administered on the silicon wafer using spin
coating and coated uniformly with film thicknesses of about
10300 Ai. Initial thickness of photoresist is measured by a
film thickness measurement instrument (F20, Filmetrics
Japan, Inc.). After the measurement of initial thickness of
photoresist on the wafer, aqueous ozone is provided on it
according as the experimental condition in table 3. Then
the silicon wafer is rinsed with ultrapure water and rotated
at 1500 rpm for drying the surface of it. After that process,
thickness of remained photoresist is measured.

Table 3: Experimental condition for photoresist stripping
(a) Experimental condition of disk shaped nozzle
Flow rate of aqueous ozone Q 1.0 L/min
Concentration of aqueous ozone C 143 mg/L
Processing time 90 sec
Rotational rate N 100 rpm
Diameter of disk shaped nozzle D 125 nun
Distance between disks Z 2 mm
Initial thickness of photoresist 10370 A

(b) Experimental condition of cylindrical nozzle
Flow rate of aqueous ozone Q 1.6 L/min
Concentration of aqueous ozone C 1 08 mg/L
Processing time 60 sec
Rotational rate N 100 rpm
Distance between disks Z 2 mm
Initial thickness of photoresist 10280 A


7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010


Paper No


High speed video
camera



z-axis traverse



Microscopical lens
YAG laser

r


Do


Nozzle


ational disk N

Figure 3: Measurement setup for flow structure
in the narrow gap


Nozzle


D/2 [mm] D/2 [mm]
(a) Original image (b) Image composition
Figure 4: Image processing technique


+ 100


-200


-300


0


10 20 30 40 50 60 rIm
Figure 5: Composite image


St [ms]


Results and Discussions

Visualization of the overall flow structure in the narrow gap
One of the snapshots of the flow between two disks is
shown in Fig. 4(a). It can be seen white plots which is
illuminated the flake particles under the stationary glass disk.
It is too difficult to examine the flow structure from the snap
shots, thus image processing is performed for each image.
An image which surrounded by yellow line in Fig. 4(a)
is extracted from raw images. It consists 1 pixel in height
and some pixel in width which is from center of the disk
shaped nozzle to the edge of the nozzle. A composite
image which shown in Fig. 4(b) is made with combining the
image in time series from the top to the bottom. One of the













-~~L


- 4

- 1

a 0


- ~


~1 Oos









Figure 9: Motion of the particles in the two
dimensional flow field layers


7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010


Paper No


70

c 60

0 50 -

40 -4


20 -2
3;10


0 10 20 30 40 :
Distance from wafer center r [mm]
Figure 6: Standard deviation of a brightness value
mn ime axis


50


S45






S35


1000 1500 2000 2500 3000 3500
Rotational Reynolds number Ren
Figure 8: Relation between the transition radius and
rotational Reynolds number (Res = 2000)

deviation has large value. And in the area of the rotational
direction flow, the standard deviation has small value. It
considerably changes in the vicinity of the transition radius.
In Fig. 7, two lines are drawn with the least-square method
in the vicinity of the radial direction where the gradient of
standard deviation widely changing. One of the line is
drawn decreasing sharply and the other is drawn almost
flattened. And an intersection of the two lines is defined as
the transition radius.
Figure 8 shows the relation between the transition radius
and rotational Reynolds number. X-axis is rotational
Reynolds number and v-axis is the transition radius. A line
is drawn with the least-square method. Reynolds number
Res and Rotational Reynolds number Ren are expressed as
(1) and (2), respectively.

Re, = (1)

Re, =ZRoQ (2)

where, O is flow rate, Z is distance between disks, v is
kinematic viscosity coefficient, Ro is a radius of disk shaped
nozzle, and Dis an angular velocity.
According to Fig. 8, the transition radius is decreased as
increasing rotational Reynolds number linearly. There is a
possibility that the transition radius can be moved with
controlling rotational Reynolds number.


20


a 38 15
10



5 g


25 30 35 40 45
Distance from wafer center r [mm]
Figure 7: Method of definition of the transition radius

composite image which condition is Q = 1.0 L/min, K= 100
rpm, D = 125 mm and Z = 2 mm is shown in Fig. 5.
According to Fig. 5, white lines are identified from center of
the nozzle to radius of about 35 mm. Near the center of
the nozzle, white lines are appeared parallel to the radial
direction. Toward the outside of the radial direction, white
lines are obliquely and become perpendicularly to the radial
direction at a certain particular position. It is indicated that
working fluid flows to the radial direction at the center of
the nozzle and radial direction flow is become slow
gradually toward the outside due to a flow passage area is
increasing toward the radial direction. Then the flow
direction is changed from the radial direction to the
rotational direction. There is a particular position that flow
direction is changed. Here, this position is tentatively
named as a "transition radius".
In order to estimate the transition radius, standard
deviation of brightness changing at each pixel in time scale
is employed. Figure 6 shows an example of the standard
deviation profile with a reconstructed particle image. In
Fig. 6, it is found that the standard deviation has large value
bth esnmtherdalb nt druatl r t oonto ound 3 m n
and 45 mm. Because of a reflecting at edge of the nozzle,
nt Oalarge valle ibewen te r diala decioenc of bout u
working fluid flows radial direction. And outside of the
radial direction of about 32 mm, it flows rotational direction.
So in the area of the radial direction flow, the standard


30 30 85 49.15


50 50.85


r
[mm]

1.0 mm




0.5 mm




0.2 mm






7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010


Paper No


2.0



1.5









0 5







2.0



1.5



. 1.0



0.5



0


1.7
1.5


,1.1
0.9
S0.7
0.5


0.1




1.9
1.7
1-5
1.3
S1.1


.~0.7

0.5

0.1


1 ,


-20
mm s


30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60
Radial direction [mm]
Figure 11: Radial flow velocity map


0 100 200 300 400
Flow velocity [mm/s]
(a) r =30 mm


30 3234 36 3840 4244 4648 50 5254 56 5860 62
Radial direction [mm]
Figure 12: Rotational flow velocity map


working fluid flows toward radial direction at the center of
the two parallel disks (z = 1.0 mm) and gradually changes
toward rotational direction as approaching toward the
rotating disk. Near the rotating disk, working fluids
follows the rotational direction. At radius of 50 mm,
working fluid flows as same as that at radius of 30 mm near
the rotating disk (z = 0.2 mm), and it also flows toward the
rotational direction at the center of the disks. Moreover,
flow direction marks toward the radial direction rather than
rotational direction at := 0.5 mm. It is found that the flow
direction is changed from the radial direction to the
rotational direction at : = 1.0 mm in a short distance of 20
mm.
Figure 10 shows radial and rotational flow velocity
profiles between disks in the gap of 2.0 mm at radii of 30,
40 and 46 mm. In Fig. 10, x-axis is flow velocity and
v-axis is z direction of the gap between disks. Radial and
rotational flow velocity show blue square and red circle
plots, respectively. Radial and rotational flow velocity was
measured every 0.1 mm in direction. In Fig. 10(a), radial
flow velocity is constant between 0.6 and 1.4 mm in :
direction and decreases toward the rotating disk and the
stationary disk. The rotational velocity is fast near the
rotational disk and gradually decreases toward z direction.
And it is constant in the upper side of the disks. In the
region where : > 0.6 mm, radial flow velocity is faster than
rotational flow velocity. In Fig. 10(b), radial and rotational
flow velocities are almost same in the region where : is
larger than 0.7 mm. In Fig. 10(c), radial flow velocity is
faster in lower side between disks and become negative in
the region where : > 1.4 mm. The rotational velocity is
fast near the rotational disk and drastically decreases above
0.5 mm in z direction. The rotational flow velocity is
faster than radial flow velocity anywhere in z direction. It


0 100 200 300 400
Flow velocity [mm/s]
(b) r =40 mm


09 1.0
t


0 100 200 300 400
Flow velocity [mm/s]
(c) r =46 mm
Figure 10: Flow velocity profiles between disks

Visualization measurement of flow structure in layers
Figure 9 shows scattering particle images between two
disks. In Fig. 9, white doted lines which are multiply
exposed tracer particles are shown the trajectories of the
particles in r-B planes at each : direction. Arrowed lines
indicate a direction of particle motion. X-axis is radial
direction and v-axis is rotational direction of the disk.
These images are observed in z direction of 0.2, 0.5, 1.0 mm
at the radii of 30 and 50 mm, respectively. At 30 mm, the


MS






7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010


Nr1 l10 -





S7-

6 -e-~ Experiment
s T R estimated with results
sb Kurokawa and Sakuma

430 35 40 45 50 55 60 65
Distance from wafer center r [mm]
Figure 13: Shear stress on the rotating disk

Initial thickness
"610000-

S8000-

S6000-
E I ~I Disk shaped nozzle
S4000~ - Cylindrical nozzle

S2000


0 20 40 60 80 100
Distance from wafer center [mm]
Figure 14: Thickness profile of remained photoresist


Paper No


is indicated that momentum of radial and rotational flow
drastically change toward radial direction due to the drastic
changing of radial and rotational flow velocity near the
rotating disk. It is assumed that z directional flow between
disks is existed and it drastically changes toward radial
direction due to the moment of radial and rotational flow
drastically change. And it is thought that it greatly
influences the photoresist stripping.
From the velocity profiles as shown in Fig. 10, the maps
of components of radial and rotational flow are
reconstructed in Fig. 11 and 12. In Fig. 11, radial flow
velocity map is shown with x-axis as radial direction and
y-axis as z direction of the gap between disks. Flow
velocity is shown in a color contour beside the map. In Fig.
11, radial flow velocity is fast near the center of the disk.
In the area near the rotating disk, radial flow velocity
decreases as increasing of r to the radius of 42 mm and
increases toward the radial direction which is larger than the
radius of 42 mm. In the upper side region of the gap,
radial flow velocity decreases as increasing of r and
becomes negative. It indicates the fluid flows inward from
the edge of disk toward the nozzle center. And it suggests
that a large circulation is existed between disks. In Fig. 12,
the rotational velocity is shown and it becomes fast near the
rotational disk due to the viscous force and drastically
decreases above 0.5 mm. And also it increases as
increasing of r due to the centrifugal force induced by the
disk rotation.


Shear stress on the rotating disk
A shear stress on the rotating disk TR iS estimated with a
numerical calculation. It is expressed as follows, referring
to Daily, et al. (1964).
TR = cp[Ur,,(/UI Urez)1/4 ]z 0 (3)
where, c = 0.0256 is constant number (Kurokawa and
Sakuma, 1988), Urel ( v2 + 2, p iS density of fluid,
and v is kinematic viscosity coefficient of fluid. Fig. 13
shows the shear stress on the rotating disk. In Fig. 13,
x-axis is distance from wafer center r and y-axis is shear
stress on the rotating disk. In order to estimate TR ffOm the
present experiment, Urez is estimated from radial and
rotational velocity at 0.1 mm in z direction which shown in
Fig. 11 and 12. In Fig. 13, Redplots are shown the shear
stress which estimated from the experimental result. And
the shear stress estimated from the previous study by
Kurokawa and Sakuma (1988) is lined in Fig. 13. In Fig.
13, the shear stress increases toward the radial direction. It
is indicated that the shear stress has large value at the edge
of the nozzle (r = 62.5 mm). The shear stresses which
estimated with experimental result and numerical
calculation become same tendency and these are
corresponding by the order.


Correlation between photoresist stripping and the flow
structure in the gap
Figure 14 shows thickness profile of remained photoreist
in the condition in table 3. In Fig. 14, x-axis is distance
from wafer center and y-axis is remained photoresist film
thickness. It is indicated that the photoresist stripping rate
is fast when remained photoresist film thickness is small.


10000


8000-


6000-


4000-


2000-


OlI
0 20 40 60 80 100
Distance from wafer center [mm]
Figure 15: Relation between remained photoresist
thickness and flow structure between disks

The remained photoresist film thickness increases as
increasing r between the center of the silicon wafer and r =
30 mm when disk shaped nozzle is used. Then it decreases
as increasing r toward the edge of the disk shaped nozzle.
In the outside of the disk shaped nozzle (r > 62.5 mm), the
remained photoresist film thickness increases as increasing r
again. The profile of the remained photoresist film
thickness has a peak under the disk shaped nozzle. On the
other hand, the removed photoresist film thickness with a
cylindrical nozzle decreases as increasing of r. Thus it is
suggested that the flow structure between two disks widely






7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010

OMRON TECHNICS, Vol. 46, No. 1, 2005 (in Japanese)

Kurokawa, J. and Sakuma, M., Flow in a Narrow Gap
Along an Enclosed Rotating Disk with Through-Flow,
JSME Intemnational Joumnal, Series II, Vol. 31, No. 2, pp.
243-251, 1988

Kurokawa, Y., Hirose. H., Moriya. T. and Kimura, C.,
Cleaning by Brush-Scrubbing of Chemical Mechanical
Polished Silicon Surfaces Using Ozonized Water and
Diluted HF, Japanese Joumnal of Applied Physics, Vol. 38,
pp. 5040-5043, 1999

Schouveiler, L., Le Gal, P., Chauve, P. and Takeda, Y.,
Spiral and circular waves in the flow between a rotating and
a stationary disk, Experiments in Fluids, Vol. 26, pp.
179-187, 1999

Soong, CY., Wu, CC., Liu, TP. and Liu, TP., Flow structure
between two co-axial disks rotating independently,
Experimental Thermal and Fluid Science 27, pp.295-311,
2003


Paper No


effects on the photoresist stripping. At the center of the
silicon wafer, the large amount of photoresist is removed
due to the high concentration of aqueous ozone and an
impinging jet. The concentration of aqueous ozone is
expected to decrease toward radial direction of silicon wafer
because of chemical reaction to the photoresist on the wafer,
reduction and diffusion at air-liquid surface.
The relation between remained photoresist thickness and
flow structure between disks is shown in Fig. 15. A dashed
line indicates the transition radius. It is found that the
remained photoresist thickness tumns from an increase to a
decrease near the transition radius. And photoresist
stripping rate is increasing toward the radial direction
between outside of the transition radius and the edge of the
disk shaped nozzle. It is suggested that the photoresist
stripping rate is able to increase by moving the transition
radius on the wafer.



Conclusions

In order to clarify the relation between flow structure in the
narrow gap and photoresist stripping rate, the visualization
measurement of the flow between disks and the experiment
of photoresist stripping with high concentrated aqueous
ozone are performed.
1) It is confirmed that the flow direction between disks are
changed radial direction to rotational direction and a
particular position where flow direction is changed
named as a "transition radius" is decreased as
increasing rotational Reynolds number.
2) It is assumed that z directional flow between disks is
drastically changes toward radial direction and greatly
influences the photoresist stripping.
3) It is found that the remained photoresist thickness tumns
from an increase to a decrease near the transition radius.
And it is suggested that the photoresist stripping rate is
able to increase by moving the transition radius on the
wafer.



Acknowledgements

This work was partly supported through a grant-in-aid of
Ibaraki research and development promotion business by
Ibaraki prefecture, Japan.



References

Abe, Y., Fujimori, K. and Ike, M., Equipment of photoresist
stripping, Japanese Patent Disclosure 2008-311256, 2008
(in Japanese)

Daily, JW., Emnst, WD. and Asbedian, W., Enclosed rotating
disks with superposed through flow, MIT Hydrodynamics
Lab., Dep. of Civil Engineering, Rep 64, 1964

Inoue, K., Asakino, S. and Nishio. H, Development of resist
stripping technique with high concentrated aqueous ozone,




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