U.S. patent application number 11/043945 was filed with the patent office on 2005-06-16 for coating film forming method and coating film forming apparatus.
This patent application is currently assigned to TOKYO ELECTRON LIMITED. Invention is credited to Terashita, Yuichi, Yoshihara, Kousuke.
Application Number | 20050126474 11/043945 |
Document ID | / |
Family ID | 19014653 |
Filed Date | 2005-06-16 |
United States Patent
Application |
20050126474 |
Kind Code |
A1 |
Yoshihara, Kousuke ; et
al. |
June 16, 2005 |
Coating film forming method and coating film forming apparatus
Abstract
A coating film is formed by the steps of supplying a mixture of
a solvent for dissolving a coating liquid and a volatilization
suppressing substance for suppressing the volatilization of the
solvent onto the surface of the target substrate W, expanding the
mixture onto the entire surface of the target substrate W, and
supplying a coating liquid onto substantially the central portion
of the target substrate W that has received the mixture while
rotating the target substrate W thereby expanding the coating
liquid outward in the radial direction of the target substrate W
thereby forming a coating film.
Inventors: |
Yoshihara, Kousuke;
(Kikuchi-gun, JP) ; Terashita, Yuichi;
(Kikuchi-gun, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
TOKYO ELECTRON LIMITED
Tokyo
JP
|
Family ID: |
19014653 |
Appl. No.: |
11/043945 |
Filed: |
January 28, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11043945 |
Jan 28, 2005 |
|
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10162606 |
Jun 6, 2002 |
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6869640 |
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Current U.S.
Class: |
118/52 |
Current CPC
Class: |
H01L 21/6715 20130101;
B05D 3/104 20130101; G03F 7/162 20130101; B05D 1/005 20130101 |
Class at
Publication: |
118/052 |
International
Class: |
B05C 011/02; B05C
013/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 7, 2001 |
JP |
2001-173137 |
Claims
What is claimed is:
1. A coating film forming apparatus for forming a coating film by
supplying a coating liquid onto a rotating target substrate,
comprising: a substrate holding member for holding a target
substrate substantially horizontal; a rotating mechanism for
rotating said substrate holding member; a mixture supply mechanism
for supplying a mixture of a solvent dissolving a coating liquid
and a volatilization suppressing substance for suppressing the
volatilization of the solvent onto the target substrate held by
said substrate holding member; and a coating liquid supply
mechanism for supplying a coating liquid onto substantially the
central portion of the target substrate held by said substrate
holding member, wherein said mixture is supplied from said mixture
supply mechanism onto the target substrate before formation of said
coating film, and the target substrate is rotated by said rotating
mechanism thereby permitting the mixture to be diffused onto the
entire surface of the target substrate.
2. The apparatus according to claim 1, wherein said mixture supply
mechanism comprises a container in which said solvent and said
volatilization suppressing substance are mixed in advance thereby
forming said mixture and the formed mixture is stored therein, a
mixture supply nozzle for supplying said mixture onto said target
substrate, and a pipe connecting said container to said mixture
supply nozzle.
3. The apparatus according to claim 1, wherein said mixture supply
mechanism comprises a mixture supply nozzle for supplying said
mixture onto said target substrate and a static mixer arranged in
the vicinity of and upstream of said mixture supply nozzle for
mixing said solvent and said volatilization suppressing substance,
said mixture being supplied from said static mixer into said
mixture supply nozzle thereby being spurted from said mixture
supply nozzle.
4. The apparatus according to claim 1, wherein said mixture supply
mechanism includes a mixture supply nozzle provided with a mixing
section for mixing said solvent and said volatilization suppressing
substance thereby forming said mixture.
5. The apparatus according to claim 1, wherein said mixture supply
mechanism includes a solvent supply nozzle for supplying said
solvent onto said target substrate and a volatilization suppressing
substance supply nozzle for supplying said volatilization
suppressing substance onto said target substrate, said solvent and
said volatilization suppressing substance being supplied separately
from said solvent supply nozzle and said volatilization suppressing
substance supply nozzle onto said target substrate so as to be
mixed on said target substrate and, thus, to form a mixture.
6. The apparatus according to claim 1, further comprising a
temperature adjusting mechanism for adjusting the temperature of
the mixture supplied onto said target substrate.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a coating film forming
method and a coating film forming apparatus for forming a coating
film by coating a target substrate such as a semiconductor wafer
with coating liquid such as a resist solution.
[0003] 2. Description of the Related Art
[0004] In the manufacturing process of, for example, a
semiconductor device, a resist pattern is formed as a mask for
forming a prescribed pattern by a so-called photolithography
technology in which a resist film is formed by supplying a resist
solution onto the surface of a semiconductor wafer (hereinafter
referred to simply as "wafer"), followed by applying a light
exposure treatment to the wafer after the resist coating in
conformity with a prescribed pattern and subsequently developing
the exposed pattern formed in the resist film on the wafer. In the
resist coating process included in the photolithography technology
noted above, a spin coating method is employed in many cases as a
method for uniformly coating the wafer surface with the resist
solution.
[0005] In the spin coating method, a wafer fixed on, for example, a
spin chuck by the vacuum suction is rotated together with the spin
chuck, and a resist solution is allowed to drip from a resist
nozzle arranged above the wafer onto substantially the central
portion of the wafer. The resist solution dripping onto the wafer
surface is centrifugally expanded outward in the radial direction
of the wafer, with the result that a resist film is formed on the
entire surface of the wafer. Then, the dripping of the resist
solution is stopped, and the wafer is kept rotated so as to remove
the excess resist solution on the surface of the wafer W so as to
control the thickness of the resist film and to dry the resist
film.
[0006] It should be noted that, in the conventional spin coating
method, a resist solution is allowed to drip onto substantially the
central portion of the wafer, and the resist solution is expanded
by the centrifugal force generated by the rotation of the wafer, as
described above. What should be noted is that the peripheral speed
in the outer peripheral portion of the wafer is markedly higher
than that in the central portion, with the result that a
considerably large amount of the resist solution is scattered from
the outer peripheral portion of the wafer. It follows that only
about 10 to 20% of the supplied resist solution is actually used
for forming the resist film, leading to a markedly large
consumption of the resist solution required for forming the resist
film. Under the circumstances, it is of high importance nowadays to
decrease the amount of the resist consumption for the resist
coating step, i.e., to decrease the dripping amount of the resist
solution onto the wafer, in view of the saving of the manufacturing
cost.
[0007] As a method for decreasing the resist solution consumption
for forming the resist film, proposed in, for example, JP 7-320999
A is a method (pre-wet system) of allowing a solvent such as a
thinner to drip onto the substrate prior to the dripping of the
resist solution so as to facilitate the diffusion of the resist
solution and, thus, to decrease the supply amount of the resist
solution.
[0008] However, the effect produced by the prior art quoted above
differs depending on the kind of the solvent. In other words, a
sufficient effect is not necessarily obtained depending on the
solvent used. It is certainly possible to overcome this difficulty
by selecting an effective solvent. However, the solvent used by the
user is limited and, thus, required is a coating film forming
method that permits stably decreasing the amount of the coating
liquid used such as a resist solution regardless of the kind of the
solvent used.
BRIEF SUMMARY OF THE INVENTION
[0009] An object of the present invention is to provide a coating
film forming method and a coating film forming apparatus that are
based on a pre-wet system and permit stably decreasing the
consumption of the coating liquid regardless of the kind of the
solvent used.
[0010] According to a first aspect of the present invention, there
is provided a coating film forming method for forming a coating
film by coating the surface of a target substrate to be processed
with a coating liquid, comprising the steps of supplying a mixture
of a solvent for dissolving said coating liquid and a
volatilization suppressing substance for suppressing the
volatilization of the solvent onto the surface of said target
substrate; expanding said mixture onto the entire surface of said
target substrate; and supplying a coating liquid onto substantially
the central portion of said target substrate while rotating said
target substrate that has supplied said mixture thereby expanding
the coating liquid outward in the radial direction of the target
substrate thereby forming a coating film.
[0011] According to a second aspect of the present invention, there
is provided a coating film forming method for forming a coating
film by coating the surface of a target substrate with a coating
liquid, comprising the steps of supplying a mixture of a solvent
dissolving a resist solution and water onto the surface of said
target substrate; rotating said target substrate thereby expanding
said mixture onto the entire surface of the target substrate;
supplying a coating liquid onto substantially the central portion
of said target substrate that has supplied said mixture while
rotating the target substrate thereby expanding the coating liquid
outward in the radial direction of the target substrate, thereby
forming a coating film; and centrifugally removing the excess
coating liquid after formation of said coating film thereby
controlling the thickness of the coating film.
[0012] Further, according to a third aspect of the present
invention, there is provided a coating film forming apparatus for
forming a coating film by supplying a coating liquid onto a
rotating target substrate, comprising a substrate holding member
for holding a target substrate substantially horizontal; a rotating
mechanism for rotating said substrate holding member; a mixture
supply mechanism for supplying a mixture of a solvent dissolving a
coating liquid and a volatilization suppressing substance for
suppressing the volatilization of the solvent onto the target
substrate held by said substrate holding member; and a coating
liquid supply mechanism for supplying a coating liquid onto
substantially the central portion of the target substrate held by
said substrate holding member, wherein said mixture is supplied
from said mixture supply mechanism onto the target substrate before
formation of said coating film, and the target substrate is rotated
by said rotating mechanism thereby permitting the mixture to be
diffused onto the entire surface of the target substrate.
[0013] In the present invention, the pre-wetting is performed by
using a mixture of a solvent and a volatilization suppressing
substance suppressing the volatilization of the solvent. Therefore,
the volatilization of the solvent is suppressed even if the solvent
used is highly volatile so as to make it possible to obtain a
sufficient pre-wetting effect. It follows that the amount of the
coating liquid used can be decreased stably regardless of the kind
of the solvent used.
[0014] As a result of an extensive research, the present inventors
have found that:
[0015] (1) In the case of employing the pre-wet system, the
resist-saving effect differs depending on the kind of the solvent
used because, in the case of using a solvent having a high
volatility, the solvent is volatilized before the solvent exhibits
a sufficient pre-wetting effect; and
[0016] (2) The difficulty can be prevented by using a substance
capable of suppressing the volatilization of the solvent together
with the solvent.
[0017] The present invention is based on the two findings pointed
out above.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0018] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate presently
preferred embodiments of the invention, and together with the
general description given above and the detail description of the
preferred embodiments given below, serve to explain the principles
of the invention.
[0019] FIG. 1 is a plan view showing the entire construction of a
resist coating-developing process system of a semiconductor wafer
including a resist coating unit for working the coating film
forming method of the present invention;
[0020] FIG. 2 is a front view of the coating-developing process
system shown in FIG. 1;
[0021] FIG. 3 is a back view of the coating-developing process
system shown in FIG. 1;
[0022] FIG. 4 is a cross sectional view showing the entire
construction of the resist coating unit mounted to the resist
coating-developing process system shown in FIGS. 1 to 3;
[0023] FIG. 5 is a plan view of the resist coating unit shown in
FIG. 4;
[0024] FIG. 6 is a flow chart showing the process steps in the
resist coating unit;
[0025] FIG. 7 is a cross sectional view showing another example of
a mixture supply means used in the resist coating unit;
[0026] FIG. 8 is a cross sectional view showing another example of
a mixture supply means used in the resist coating unit; and
[0027] FIG. 9 is a cross sectional view showing still another
example of a mixture supply means used in the resist coating
unit.
DETAILED DESCRIPTION OF THE INVENTION
[0028] Some embodiments of the present invention will now be
described in detail with reference to the accompanying
drawings.
[0029] FIG. 1 is a plan view showing the entire construction of a
resist coating-developing process system 1 including a resist
coating unit for working the coating film forming method of the
present invention, and FIGS. 2 and 3 are a front view and a back
view, respectively, of the resist coating-developing process system
shown in FIG. 1.
[0030] As shown in the drawings, the resist coating-developing
process system 1 comprises a cassette station 10, which is a
transfer station, a process station 11 including a plurality of
process units, and an interface section 12 arranged adjacent to the
process station 11 for the delivery of a wafer W between the
process station 11 and a light exposure device (not shown).
[0031] The cassette station 10 is for transferring a wafer cassette
CR housing a plurality of wafers W used as a target object to be
processed, e.g., 25 wafers W, from another system to this system,
for transferring the particular wafer cassette CR from this system
to said another system, or for transferring the wafer W between the
wafer cassette CR and the process station 11.
[0032] As shown in FIG. 1, in the cassette station 10, a plurality
of positioning projections 20a, i.e., four positioning projections
20a in the drawing, are arranged in the X-direction in the drawing
on a table 20 on which the cassette CR is disposed. It is possible
for the wafer cassettes CR to be disposed on the positions of the
projections 20a in a manner to form a row such that the wafer
entrances (exits at same time) of the wafer cassettes CR are
allowed to face the process station 11. In the wafer cassette CR,
the wafers W are arranged in the vertical direction (Z-direction).
Further, the cassette station 10 includes a wafer transfer
mechanism 21 that is positioned between the table 20 and the
process station 11. The wafer transfer mechanism 21 includes a
wafer transfer arm 21a movable in the cassette arranging direction
(X-direction) and in the arranging direction of the wafers within
the wafer cassette CR (Z-direction) such that the transfer arm 21a
is capable of selectively gaining access to any of the wafer
cassettes CR. Further, the wafer transfer arm 21a is swingable in
the 0 direction so as to be capable of gaining access to the
alignment unit (ALIM) and the extension unit (EXT) referred to
herein later, which belong to a third process unit group G.sub.3 on
the side of the process station 11.
[0033] The process station 11 includes a plurality of process units
for a series of processes for coating and developing the resist to
the wafer W. These process units are arranged in prescribed
positions to form a multi-stage structure, and the wafers W are
processed one by one in these process units. As shown in FIG. 1, a
transfer path 22a is formed in the central portion of the process
station 11. A main wafer transfer mechanism 22 is arranged in the
transfer path 22a and all the process units are arranged around the
transfer path 22a. These plural process units are divided into a
plurality of process unit groups each consisting of a plurality of
process units arranged in the vertical direction to form a
multi-stage structure.
[0034] As shown in FIG. 3, the main wafer transfer mechanism 22
comprises a cylindrical support body 49 and a wafer transfer device
46 arranged movable in the vertical direction (Z-direction) inside
the cylindrical support body 49. The cylindrical support body 49
can be rotated by a not shown motor, and the wafer transfer device
46 can also be rotated integrally in accordance with the rotation
of the cylindrical support body 49.
[0035] The wafer transfer device 46 includes a plurality of holding
members 48 movable back and forth along a transfer base 47 so as to
achieve the wafer delivery among the process units.
[0036] In this embodiment, first to fourth process unit groups
G.sub.1, G.sub.2, G.sub.3 and G.sub.4 are arranged around the
transfer path 22a, as shown in FIG. 1. Further, a fifth process
unit group G.sub.5 can be arranged, as required.
[0037] The first and second process unit groups G.sub.1 and G.sub.2
are arranged in a line on the front side of the system (lower side
in FIG. 1). The third process unit group G.sub.3 is arranged
adjacent to the cassette station 10, and the fourth process unit
group G.sub.4 is arranged adjacent to the interface section 12.
Further, the fifth process unit group G.sub.5 can be arranged in
the back portion.
[0038] Arranged in the first process unit group G.sub.1 is a resist
coating process unit (COT) for coating a resist on the wafer W
disposed on a not shown spin chuck within a cup CP. Further,
stacked on the resist coating process unit (COT) is a developing
process unit (DEV) for developing a pattern of the resist within
the cup CP. Likewise, arranged in the second process unit group
G.sub.2 is a resist coating process unit (COT) as two spinner type
process units, and a developing process unit (DEV) is stacked on
the resist coating process unit (COT).
[0039] In the third process unit group G.sub.3, a plurality of oven
type process units for applying a prescribed process to the wafer W
disposed on a table SP are stacked one upon the other, as shown in
FIG. 3. To be more specific, the third process unit group G.sub.3
includes an adhesion unit (AD) for applying a so-called
"hydrophobic processing" for improving the fixing properties of the
resist, an alignment unit (ALIM) for aligning the position of the
wafer W, an extension unit (EXT) for transferring the wafer W, a
cooling unit (COL) for a cooling processing, and four hot plate
units (HP) for a heat processing before or after the light exposure
process and after the developing processing. These process units
are stacked one upon the other in the order mentioned to form an
eight-stage structure. Incidentally, the alignment unit (ALIM) may
be replaced by the cooling unit (COL) which works also as an
alignment unit.
[0040] The fourth process unit group G.sub.4 also includes a
plurality of oven type process units stacked one upon the other. To
be more specific, the fourth process unit group G.sub.4 includes a
cooling unit (COL), an extension-cooling unit (EXTCOL) constituting
a wafer delivery section equipped with a cooling plate, another
cooling unit (COL), and four hot plate units (HP), which are
stacked one upon the other in the order mentioned so as to form an
eight-stage structure.
[0041] Where the fifth process unit group G.sub.5 is installed at
the back side of the main wafer transfer mechanism 22, the fifth
process unit group G.sub.5 is movable sideward along a guide rail
25 as viewed from the main wafer transfer mechanism 22. It follows
that, even where the fifth process unit group G.sub.5 is installed,
the fifth process unit group G.sub.5 can be slid along the guide
rail 25 so as to ensure a free space behind the main wafer transfer
mechanism 22. As a result, a maintenance operation for the main
wafer transfer mechanism 22 can be executed easily from behind the
main wafer transfer mechanism 22.
[0042] The interface section 12 is equal to the process station 11
in the length in the X-direction. As shown in FIGS. 1 and 2, a
flexible pick-up cassette CR and a stationary buffer cassette BR
are stacked one upon the other in a front portion of the interface
section 12. A peripheral light exposure device 23 is arranged in a
back portion of the interface section 12. Further, a wafer transfer
mechanism 24 is arranged in the central portion of the interface
section 12. The wafer transfer mechanism 24 includes a wafer
transfer arm 24a, which is movable both in the X-direction and the
Z-direction so as to gain access to the cassettes CR, BR and the
peripheral light exposure device 23. Also, the wafer transfer arm
24a is swingable in the .theta. direction so as to gain access to
the extension unit (EXT) in the fourth process unit group G.sub.4
of the process station 11 and to a not shown wafer delivery table
adjacent to the light exposure device.
[0043] In the resist coating-developing process system 1 of the
construction described above, unprocessed wafers W are taken out
one by one from the wafer cassette CR so as to be transferred into
the alignment unit (ALIM) of the process station 11. Then, the
wafer W whose position has been aligned is taken out by the main
wafer transfer mechanism 22 so as to be transferred into the
adhesion unit (AD) for the adhesion processing. After completion of
the adhesion processing, the wafer W is taken out by the main wafer
transfer mechanism 22 so as to be transferred into the cooling unit
(COL) for the cooling processing. Further, the wafer W is
transferred into the resist coating unit (COT) for the resist
coating processing and, then, into the hot plate unit (HP) for the
pre-bake treatment. Still further, the wafer W is transferred into
the interface section 12 through the extension-cooling unit
(EXTCOL) and, then, the wafer W is further transferred by the wafer
transfer mechanism 24 into the adjacent light exposure device. The
exposed wafer W is transferred by the wafer transfer mechanism 24
into the process station 11 through the interface section 12 and
the extension unit (EXT). In the process station 11, the wafer W is
transferred by the main wafer transfer mechanism 22 into the hot
plate unit (HP) for the post exposure processing and, then,
transferred into the developing unit (DEV) for the developing
processing. After the developing, the wafer W is post-baked in the
hot plate unit (HP) and, then, cooled in the cooling unit (COL),
followed by transferring the wafer W into the cassette station 10
through the extension unit (EXT). After completing a series of
these processings, the wafer W is transferred by the wafer transfer
mechanism 22 into the wafer cassette CR so as to be housed in the
wafer cassette CR.
[0044] The resist coating unit (COT) for working the coating film
forming method of the present invention will now be described with
reference to FIGS. 4 and 5.
[0045] The resist coating unit (COT) includes a casing 50 provided
with an opening 50a through which the holding member 48 of the main
wafer transfer mechanism 22 is inserted into the casing 50. A cup
CP, which is a container for housing the wafer W, is arranged
within the casing 50, and a spin chuck 51 for holding the wafer W
horizontal by vacuum suction is arranged inside the cup CP. The
spin chuck 51 can be rotated by a driving motor 52 such as a pulse
motor arranged below the cup CP, and the rotating speed of the spin
chuck 51 can be controlled optionally. An exhaust pipe 53 is
connected to that portion of the bottom of the cup CP which is
positioned close to the central portion of the bottom of the cup
CP, and a drain pipe 54 is connected to that portion of the bottom
of the cup CP which is positioned close to the outer portion of the
bottom of the cup CP. The gaseous material within the cup CP is
discharged to the outside through the exhaust pipe 53, and the
resist solution and the solvent scattered during the coating
processing are discharged to the outside through the drain pipe 54.
Incidentally, the spin chuck 51 can be vertically moved by a not
shown lift mechanism such as an air cylinder.
[0046] A spurting head 60 movable between the position right above
the spin chuck 51 and a retreat position is arranged above the spin
chuck 51. The spurting head 60 is connected to a driving mechanism
70 with an arm 61 interposed therebetween. The spurting head 60 can
be moved in the X-direction by the driving mechanism 70, the
Y-direction and the Z-direction shown in FIGS. 4 and 5.
Incidentally, the spurting head 60 is detachable from the arm
61.
[0047] The spurting head 60 includes a base member 62, a mixture
supply nozzle 80 for supplying a mixture of a solvent capable of
dissolving a coating liquid and a volatilization suppressing
substance suppressing the volatilization of the solvent, and a
resist solution supply nozzle 90 positioned close to the mixture
supply nozzle 80 for supplying a resist solution, which is a
coating liquid. As shown in the drawing, the spurting head 60 is
constructed such that the mixture supply nozzle 80 and the resist
solution supply nozzle 90 are mounted to the base member 61. It
should be noted that it is possible for the solvent capable of
dissolving the coating liquid to be a solvent of the coating
liquid. In addition, it is possible to use any solvent as far as
the solvent is capable of dissolving the coating liquid.
[0048] The spurting head 60 is provided with tubes 65a, 65b for
circulating a temperature adjusting fluid for the temperature
adjustment such that the temperature of the resist solution spurted
from the resist solution supply nozzle 90 is rendered constant and
with tubes 66a, 66b for circulating a temperature adjusting fluid
for the temperature adjustment such that the temperature of the
solvent spurted from the mixture supply nozzle 80 is rendered
constant. The tube 65a is arranged around a pipe contiguous to the
resist solution supply nozzle 90 so as to constitute a forward
passageway, and the tube 65b constitutes a return passageway. Also,
the tube 66a is arranged around a pipe contiguous to the mixture
supply nozzle 80 so as to constitute a forward passageway, and the
tube 66b constitutes a return passageway.
[0049] The mixture supply nozzle 80 is connected to an intermediate
tank 83 via a mixture supply pipe 81, and a valve 82 is mounted to
the mixture supply pipe 81. A solvent supply pipe 84 for supplying
a solvent into the intermediate tank 83 and a volatilization
suppressing substance supply pipe 86 for supplying a volatilization
suppressing substance into the intermediate tank 83 are connected
to the intermediate tank 83. Valves 85 and 87 are mounted to these
pipes 84 and 86, respectively. The solvent and the volatilization
suppressing substance supplied into the intermediate tank 83
through the pipes 84 and 86, respectively, are stirred by a not
shown stirring mechanism so as to form a mixture, and the mixture
thus formed is stored in the intermediate tank 83. A compressed gas
such as a compressed nitrogen gas (N.sub.2) is supplied into the
intermediate tank 83 so as to permit the mixture to be supplied
onto the wafer W through the mixture supply pipe 81 and the mixture
supply nozzle 80. In this case, the flow rate of the mixture is
controlled by controlling the pressurizing force of the N.sub.2
gas.
[0050] The resist solution supply nozzle 90 communicates via a
resist solution supply pipe 91 with a resist solution tank 92
housing a resist solution. Mounted to the resist solution supply
pipe 91 are a suck back valve 93, an air operation valve 94, a
bubble removing mechanism 95 for separating and removing the
bubbles within the resist solution, a filter 96 and a bellows pump
97 in the order mentioned as viewed from the downstream side. The
bellows pump 97 is shrinkable. By controlling the shrinkage of the
bellows pump 97, a prescribed amount of the resist solution is
supplied onto the surface of the wafer W through the resist
solution supply nozzle 90. The bellows pump 97 makes it possible to
control a very small supply amount of the resist solution. The
driving section of the bellows pump 97 comprises a ball screw
mechanism 98 including a screw 98a having one end mounted to one
end of the bellows pump 97 and a nut 98b engaged with the screw
98a, and a stepping motor 99 that rotates the nut 98b so as to
permit the screw 98a to make a linear motion.
[0051] The suck back valve 93 mounted to the resist solution supply
system noted above serves to bring the resist solution remaining by
surface tension on the inner wall in the tip portion of the resist
solution supply nozzle 90 after spurting of the resist solution
from the resist solution supply nozzle 90 back into the resist
solution supply nozzle 90. As a result, the residual resist
solution is prevented from being solidified.
[0052] As shown in FIG. 5, a holding section 55 capable of holding
four spurting heads 60, which are basically equal to each other in
construction, is arranged in the outside portion of the cup CP
within the casing 50. In order to prevent the nozzle port of each
nozzle from being dried and solidified, an not shown inserting
section for placing the nozzle port of each nozzle under a solvent
atmosphere is mounted to the holding section 55. Each spurting head
60 can be mounted to the tip portion of the arm 61 by a mounting
section 63 so as to permit the four spurting heads 60 to supply
different kinds of resist solutions onto the surfaces of the wafers
W. A selected one of the spurting heads 60 is mounted to the arm 61
so as to be taken out of the holding section 55. As described
previously, the arm 61 can be moved by the driving mechanism 70 in
three dimensional directions, i.e., in the X-, Y- and Z directions,
such that the spurting head 60 taken out of the holding section 55
and mounted to the arm 61 is moved to a prescribed position right
above the wafer W in a coating processing. Incidentally, in this
embodiment, the mixture supply nozzle 80 and the resist solution
supply nozzle 90 are mounted to the spurting head 60, and four
spurting heads 60 of the particular construction are arranged in
the holding section 55. Alternatively, it is possible to fix a
single or a plurality of mixture supply nozzles 80 directly to the
arm 61 and to mount the resist solution supply nozzle 90 alone to
the spurting head 60.
[0053] The processing carried out in the resist coating unit (COT)
of the particular construction described above will now be
described in detail with reference to the flow chart shown in FIG.
6.
[0054] If the wafer W is transferred through the opening 50a of the
casing 50 by the holding member 48 of the main wafer transfer
mechanism 22 onto a position right above the cup CP within the
resist coating unit (COT), the wafer W is held by vacuum suction by
the spin chuck 51 moved upward by the not shown lift mechanism.
After the wafer W is held by the spin chuck 51 by vacuum suction,
the main wafer transfer mechanism 22 brings back the holding member
48 from within the resist coating unit (COT) so as to finish
delivery of the wafer W into the resist coating unit (COT) (step ST
1).
[0055] Then, the spin chuck 51 is moved downward until the wafer W
reaches a prescribed position within the cup CP, followed by
allowing the driving motor 52 to rotate the spin chuck 51 at a
rotating speed of about 1,000 rpm so as to make the temperature of
the wafer W uniform (step ST 2).
[0056] In the next step, the rotation of the spin chuck 51 is
stopped, and the spurting head 60 is moved by the driving mechanism
70 in the Y-direction so as to reach a position right above the
wafer W. When spurting port of the mixture supply nozzle 80
included in the spurting head 60 has been moved to reach a position
right above the center of the spin chuck 51, i.e., above the center
of the wafer W, the mixture of a prescribed solvent capable of
dissolving the resist and a volatilization suppressing substance
suppressing the volatilization of the solvent is supplied onto
substantially the center on the surface of the stationary wafer W
(step ST 3). In this step, the solvent and the volatilization
suppressing substance are supplied at a prescribed mixing ratio
into the intermediate tank 83 through the solvent supply pipe 84
and the volatilization suppressing substance supply pipe 86,
respectively. Further, the solvent and the volatilization
suppressing substance are stirred by a not shown stirring mechanism
within the intermediate tank 83, with the valves 85 and 87 closed,
so as to form a prescribed amount of the mixture. Further, the
mixture formed and stored within the intermediate tank 83 is
pressurized by a pressurizing gas such as a N.sub.2 gas so as to be
supplied onto the wafer W through the mixture supply pipe 81 and
the mixture supply nozzle 80. In this case, the flow rate of the
mixture is controlled by controlling the pressurizing force of the
N.sub.2 gas.
[0057] After the mixture has been supplied onto the wafer W, the
wafer W is rotated at a prescribed rotating speed, preferably at a
rotating speed not higher than 1,000 rpm (step ST 4). As a result,
the mixture supplied onto the surface of the wafer W is
centrifugally diffused from the central portion toward the
peripheral portion of the wafer W such that the mixture is
uniformly spread over the entire surface of the wafer W.
Incidentally, the mixture can be supplied onto the wafer W while
rotating the wafer W. In other words, it is possible to carry out
simultaneously the steps ST 3 and ST 4 described above. It is also
possible to employ a spraying method for coating the entire surface
of the wafer W with the mixture. In this case, the wafer W can be
rotated or stopped during the spraying operation.
[0058] In the next step, the spurting head 60 is moved in the
Y-direction by the driving mechanism 70 until the spurting port of
the resist solution supply nozzle 90 is moved to reach a position
right above the center of the spin chuck 51, i.e., right above the
center of the wafer W, and the rotating speed of the wafer W is
increased to a prescribed level. Under this state, the resist
solution is supplied from the spurting port of the resist solution
supply nozzle 90 onto substantially the center on the surface of
the rotating wafer W so as to permit the resist solution to be
centrifugally diffused outward, thereby coating the surface of the
wafer W with the resist solution (step ST 5). Where the wafer has a
diameter of 200 mm, it is desirable to set the rotating speed of
the wafer W at 2,000 to 6,000 rpm. Also, where the wafer has a
diameter of 300 mm, it is desirable to set the rotating speed of
the wafer W at 1,000 to 4,000 rpm.
[0059] After the resist solution has been supplied while rotating
the wafer W, the supply of the resist solution is stopped, and the
rotating speed of the wafer W is lowered (step ST 6). As a result,
the function of adjusting the thickness of the resist solution film
is produced so as to make the thickness of the resist solution film
uniform over the entire region of the wafer W. The particular
effect can be produced because, when the rotating speed of the
wafer W is lowered, the force toward the center is exerted on the
resist solution on the semiconductor wafer W by the deceleration.
In addition, the resist solution is dried slowly because the target
substrate is rotated at a low speed. It follows that the function
of controlling the thickness of the resist film is produced. What
should be noted is that the scattering of the resist from the wafer
W is suppressed by the inward force produced by the deceleration so
as to permit the resist to be retained in the outer peripheral
portion as in the central portion of the wafer W, thereby making
uniform the thickness of the resist film formed on the wafer W. In
this case, it is desirable for the rotating speed of the wafer W to
be 50 to 1,000 rpm. Particularly, if the rotating speed of the
wafer W is not higher than 500 rpm, the drying of the resist
scarcely proceeds, leading to a high degree of freedom in the
thickness control. The holding time in this step is set
appropriately so as not to exceed, for example, 3 seconds.
Incidentally, the process in step ST 6 is not absolutely necessary
and is carried out as required.
[0060] Then, the rotating speed of the wafer W is increased so as
to centrifugally remove the residual resist solution (step ST 7).
It is desirable for the rotating speed of the wafer W in this step
to be 1,500 to 4,000 rpm in the case where the wafer W has a
diameter of 200 mm and to be 1,000 to 3,000 rpm in the case where
the wafer W has a diameter of 300 rpm.
[0061] After removal of the residual resist solution in step ST 7,
the rotation of the wafer W is continued so as to dry the resist
film (step ST 8). It is desirable for the rotating speed of the
wafer W in this step to be 1,000 to 2,000 rpm in the case where the
wafer W has a diameter of 200 mm and to be 500 to 1,500 rpm in the
case where the wafer W has a diameter of 300 rpm. The resist
coating step is finished after the drying step is performed for a
prescribed period of time in step ST 8.
[0062] As described above, in the present invention, the entire
surface of the wafer W is coated with a mixture of a solvent
capable of dissolving the resist and a volatilization suppressing
substance suppressing the volatilization of the solvent prior to
the coating of the resist solution. Therefore, even if the solvent
used is highly volatile, the volatilization of the solvent is
suppressed by the volatilization suppressing substance so as to
produce the effect of sufficiently diffusing the resist solution in
the subsequent coating step of the resist solution. It follows that
the amount of the resist solution used can be stably decreased
regardless of the kind of the solvent used.
[0063] The solvent contained in the mixture should be capable of
dissolving the resist. Typically, a thinner is contained as the
solvent in the mixture. To be more specific, it is possible for the
mixture to contain at least one kind of the solvent selected from
the group consisting of, for example, propylene glycol monomethyl
ether, propylene glycol monomethyl ether acetate, butyl acetate,
ethyl lactate, ethyl cellosolve acetate, and methyl methoxy
propionate. Particularly, the effect of the present invention is
improved in the case of using at least one kind of the solvent
selected from the group consisting of propylene glycol monomethyl
ether and propylene glycol monomethyl ether acetate as the solvent.
Of course, it is also possible to use another solvent as far as the
solvent is capable of dissolving the resist.
[0064] It is desirable for the volatilization suppressing substance
used in the present invention to have a hydrogen bond. At least one
kind of the substance selected from the group consisting of water,
methyl alcohol, ethyl alcohol and isopropyl alcohol (IPA) is
suitably used as the substance having a hydrogen bond. Among these
substances, it is desirable to use water, particularly pure water,
as the volatilization suppressing substance. Of course, it is also
possible to use another substance as far as the substance is
capable of effectively suppressing the volatilization of the
solvent used.
[0065] It is desirable for the amount of the volatilization
suppressing substance to be not smaller than 5% by mass and smaller
than 50% by mass of the entire mixture. If the amount of the
volatilization suppressing substance is smaller than 5% by mass,
the volatilization suppressing effect tends to be rendered
insufficient. On the other hand, if the amount of the
volatilization suppressing substance is not smaller than 50% by
mass, the resist solution diffusing effect produced by the solvent
tends to be rendered insufficient. The supply amount of the mixture
is, for example, 2 ml in the case where the wafer W has a diameter
of 200 mm, and 3 ml in the case where the wafer W has a diameter of
300 mm.
[0066] The temperature control of the mixture is carried out at a
suitable temperature falling within a range of between, for
example, 18.degree. C. and 24.degree. C. Within this temperature
range, the mixture is allowed to wet the wafer surface uniformly so
as to make it possible to render uniform the thickness of the
resist film. It should be noted that it is necessary to eliminate
the temperature difference between the central portion and the
outer peripheral portion of the wafer W as much as possible.
Because of the particular requirement, the appropriate temperature
is changed depending on the size of the wafer. For example, the
appropriate temperature is 22 to 24.degree. C. in the case of the
wafer W having a diameter of 200 mm. However, where the diameter of
the wafer W is increased to 300 mm, the peripheral speed in the
outer peripheral portion of the wafer W is increased. As a result,
the temperature difference tends to be generated between the
central portion and the outer peripheral portion of the wafer W
and, thus, the solvent contained in the mixture tends to be
volatilized in the outer peripheral portion of the wafer W. Such
being the situation, the temperature of the mixture is set a
somewhat low level of 18 to 19.degree. C. in order to eliminate the
temperature difference between the central portion and the outer
peripheral portion of the wafer W as much as possible.
[0067] Some experiments for actually confirming the effect of the
present invention will now be described.
[0068] In the first experiment, the minimum amount of the resist
that can be coated on the entire wafer surface was measured by
using a wafer having a diameter of 200 mm. The experiment covered
the case where butyl acetate, propylene glycol monomethyl ether
(PGME), or ethyl lactate was used as a solvent for the pre-wetting
and the case where the pre-wetting was not performed. A solution
having a viscosity of about 7 CP, which was prepared by dissolving
a KrF resist in an EL solvent, was used as the resist solution. The
wafer was rotated at a speed of 3,000 to 6,000 rpm during dripping
of the resist solution, and the supply amount of the solvent was 2
ml. It has been found that the minimum amount of the resist
solution that can be coated on the entire wafer surface can be
markedly decreased by applying the pre-wetting, as shown in Table
1, though the degree of reduction in the amount of the required
resist solution differs depending on the kind of the solvent used.
It is considered reasonable to understand that the difference in
the degree of reduction noted above is caused by the difference in
the volatilizing rate of the solvent. To be more specific, it is
considered reasonable to understand that, if the solvent has a low
volatilizing rate, a greater amount of the solvent remains on the
wafer surface during dripping of the resist solution so as to
improve the resist diffusion effect.
1TABLE 1 Minimum amount of resist solution on 200 mm wafer no
pre-wetting 0.85 ml butyl acetate 0.6 ml PGME 0.45 ml ethyl lactate
0.25 ml
[0069] Then, a second resist coating experiment was conducted
similarly by using a wafer having a diameter of 300 mm. In the
second experiment, the pre-wetting was performed by using the three
kinds of the solvents equal to those used in the first experiment.
The rotating speed of the wafer was set at 2,000 to 4,000 rpm
during dripping of the resist solution, and the supply amount of
the solvent was 3 ml. It has been found that the difference in the
minimum amount of the resist solution required for the coating on
the entire surface of the wafer depending on the kind of the
solvent used is rendered greater than that in the case of using the
wafer having a diameter of 200 mm, as shown in Table 2. Table 2
also shows that PGME constituting the main component of the PGME
series thinner, which is most frequently used nowadays, is
incapable of producing a sufficient resist saving effect.
2TABLE 2 Minimum amount of resist solution on 300 mm wafer butyl
acetate 2.0 ml or more PGME 1.7 ml ethyl lactate 0.65 ml
[0070] Further, a third experiment was conducted for measuring the
minimum amount of the resist solution that can be coated on the
entire surface of each of the wafer having a diameter of 200 mm and
the wafer having a diameter of 300 mm, covering the cases where the
pre-wetting was performed by using PGME and where the pre-wetting
was performed by using a mixture specified in the present
invention, i.e., a mixture of PGME and a pure water used as the
volatilization suppressing substance. The mixing ratio of PGME to
the pure water in the mixture was set at 5:1 (16.7% by mass of the
pure water). The resist solution and the coating conditions were
equal to those in the first and second experiments given above. As
a result, it has been confirmed that, in the case of performing the
pre-wetting by using a mixture of PGME and a pure water, the
minimum amount of the resist solution required for the coating on
the entire wafer surface is rendered smaller than half the amount
in the case where the pre-wetting is performed by using PGME alone
in any of the wafer having a diameter of 200 mm and the wafer
having a diameter of 300 mm. It is considered reasonable to
understand that, by the addition of a pure water, a hydrogen bond
is formed between the solvent molecule and the water molecule so as
to suppress the volatilization of the solvent, with the result that
the amount of the solvent remaining on the wafer surface is
increased in the resist dripping step. A similar result was
exhibited in the case of using a mixture prepared by adding a pure
water to a general purpose thinner of OK 73 (PGME:PGMEA (propylene
glycol monomethyl ether acetate)=7:3) in the same mixing ratio. In
conclusion, it has been confirmed that a prominent resist saving
effect can be produced in the case of performing the pre-wetting by
using a mixture specified in the present invention of a solvent and
a pure water.
3 TABLE 3 Minimum amount of PGME 0.45 ml resist solution on PGME +
pure water 0.2 ml 200 mm wafer Minimum amount of PGME 1.7 ml resist
solution on PGME + pure water 0.7 ml or less 300 mm wafer
[0071] Other examples of the supply means of the mixture of a
solvent and a volatilization suppressing substance will now be
described. In the embodiment described above, a mixture is formed
in the intermediate tank 83, and the mixture formed is supplied
from the intermediate tank 83 by utilizing a pressurizing gas.
Alternatively, it is also possible to use a system shown in FIG. 7.
In the system shown in FIG. 7, a solvent supplied through a solvent
supply pipe 101 extending from a not shown intermediate tank and a
volatilization suppressing substance supplied at a prescribed flow
rate through a volatilization suppressing substance supply pipe 102
extending from a not shown intermediate tank are mixed in a static
mixer 103 arranged in the vicinity of the mixture supply nozzle 80,
and the mixture is supplied from the static mixer 103 into the
mixture supply nozzle 80 through the mixture supply pipe 81.
[0072] FIG. 8 shows another example of the mixture supply means. As
shown in the drawing, arranged is a mixture supply nozzle 110
provided with a mixing section 111. In this case, a solvent supply
pipe 112 extending from a not shown intermediate tank and a
volatilization suppressing substance pipe 113 extending from a not
shown intermediate tank are connected to the mixing section 111 so
as to permit the solvent and the volatilization suppressing
substance supplied through the pipes 112 and 113, respectively, are
mixed in the mixing section 111.
[0073] FIG. 9 shows still another example of the mixture supply
means. As shown in the drawing, arranged are a solvent supply
nozzle 121 and a volatilization suppressing substance supply nozzle
122. In this case, a solvent supply pipe 123 extending from a not
shown intermediate tank and a volatilization suppressing substance
supply pipe 124 extending from a not shown intermediate tank are
connected to the solvent supply nozzle 121 and the volatilization
suppressing substance supply nozzle 122, respectively. What should
be noted is that the solvent and the volatilization suppressing
substance spurted from the solvent supply nozzle 121 and the
volatilization suppressing substance supply nozzle 122,
respectively, are mixed on the wafer surface so as to form a
mixture.
[0074] It should be noted that the embodiments described above are
simply intended to clarify the technical idea of the present
invention. Naturally, the technical scope of the present invention
should not be construed solely on the basis of the specific
embodiments described above. In other words, the present invention
can be worked in variously modified fashions on the basis of the
spirit of the present invention and within the scope defined in the
accompanying claims.
[0075] For example, each of the embodiments described above covers
the case where a resist solution is used as a coating liquid.
However, the coating liquid is not limited to a resist solution. It
is also possible to use another coating liquid such as a coating
liquid for forming an antireflection film or an interlayer
dielectric film by the rotary coating processing. Also, each of the
embodiments described above covers the case where a semiconductor
wafer is used as the target substrate. However, the target
substrate used in the present invention is not limited to the
semiconductor wafer. It is also possible to use another target
substrate such as an LCD substrate or a reticle substrate for a
mask.
* * * * *