U.S. patent application number 11/305160 was filed with the patent office on 2006-05-11 for method for reducing pattern dimension in photoresist layer.
Invention is credited to Fumitake Kaneko, Yoshiki Sugeta, Toshikazu Tachikawa.
Application Number | 20060099347 11/305160 |
Document ID | / |
Family ID | 27567056 |
Filed Date | 2006-05-11 |
United States Patent
Application |
20060099347 |
Kind Code |
A1 |
Sugeta; Yoshiki ; et
al. |
May 11, 2006 |
Method for reducing pattern dimension in photoresist layer
Abstract
The invention discloses improvements in the so-called coated
thermal flow process for reducing the pattern dimension of a
patterned resist layer on a substrate to accomplish increased
fineness of resist patterning, in which a coating layer of a
water-soluble resin formed on the patterned resist layer is
heat-treated to effect thermal shrinkage of the coating layer with
simultaneous reduction of the pattern dimension followed by removal
of the coating layer by washing with water. The improvement of the
process is obtained by using an aqueous coating solution admixed
with a water-soluble amine compound such as triethanolamine in
addition to a water-soluble resin such as a polyacrylic acid-based
polymer. Further improvements can be obtained by selecting the
water-soluble resin from specific copolymers including copolymers
of (meth)acrylic acid and a nitrogen-containing monomer such as
N-vinylpyrrolidone, N-vinylimidazolidinone and
N-acryl-oylmorpholine as well as copolymers of N-vinylpyrrolidone
and N-vinylimidazolidinone in a specified copolymerization
ratio.
Inventors: |
Sugeta; Yoshiki;
(Yokohama-shi, JP) ; Kaneko; Fumitake;
(Kanagawa-ken, JP) ; Tachikawa; Toshikazu;
(Yokohama-shi, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
27567056 |
Appl. No.: |
11/305160 |
Filed: |
December 19, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10173880 |
Jun 19, 2002 |
|
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11305160 |
Dec 19, 2005 |
|
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Current U.S.
Class: |
427/372.2 ;
430/331; 524/555 |
Current CPC
Class: |
G03F 7/40 20130101 |
Class at
Publication: |
427/372.2 ;
524/555 |
International
Class: |
B05D 3/02 20060101
B05D003/02; C08F 8/30 20060101 C08F008/30 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 5, 2001 |
JP |
2001-205240 |
Jul 5, 2001 |
JP |
2001-205241 |
Jul 5, 2001 |
JP |
2001-205242 |
Sep 28, 2001 |
JP |
2001-302552 |
Sep 28, 2001 |
JP |
2001-302553 |
Sep 28, 2001 |
JP |
2001-302554 |
Sep 28, 2001 |
JP |
2001-302555 |
Claims
1. A method for reducing dimensions of a resist pattern on a
substrate which comprises the steps of: (a) coating a patterned
resist layer on a substrate surface with an aqueous coating
solution comprising a water-soluble resin and a water-soluble amine
compound to form a coating layer; (b) drying the coating layer of
the aqueous coating solution; (c) subjecting the dried coating
layer to a heat treatment to effect thermal shrinkage of the
coating layer and reduction of the distance between resist
patterns; and (d) removing the coating layer by washing with
water.
2. The method as claimed in claim 1 in which the water-soluble
resin is selected from the group consisting of alkyleneglycol-based
polymers, cellulose-based polymers, vinyl polymers, acrylic
polymers, urea-based polymers, epoxy-based polymers, melamine-based
polymers and polyamide-based polymers.
3. The method as claimed in claim 1 in which the aqueous coating
solution contains from 3 to 50% by weight of the water-soluble
resin.
4. The method as claimed in claim 1 in which the water-soluble
amine compound is selected from the amine compounds having a pKa
value in the range from 7.5 to 13 at 25.degree. C.
5. The method as claimed in claim 1 in which the amount of the
water-soluble amine compound contained in the aqueous coating
solution is in the range from 0.1 to 30% by weight based on the
amount of the water-soluble resin.
6. The method as claimed in claim 1 in which the temperature of the
heat treatment in step (c) is lower than the softening temperature
of the patterned resist layer.
7. The method as claimed in claim 4 in which the water-soluble
amine compound is monoethanolamine or triethanolamine.
8. A method for reducing dimensions of a resist pattern on a
substrate surface which comprises the steps of: (a2) coating a
patterned resist layer with an aqueous coating solution containing
a water-soluble resin, which is a copolymer of (meth)acrylic acid
and an ethylenically unsaturated monomeric compound selected from
the group consisting of N-vinylpyrrolidone, N-vinylimidazolidinone,
methyl acrylate, methyl methacrylate, N,N-dimethylacrylamide,
N,N-dimethylaminopropyl methacrylamide, N,N-dimethylaminopropyl
acrylamide, N-methhylacrylamide, diacetoneacrylamide,
N,N-dimethylaminoethyl methacrylate, N,N-diethylaminoethyl
methacrylate, N,N-dimethylaminoethyl acrylate and
N-acryloylmorpholine; (b2) drying the coating layer to form a dried
coating layer of the water-soluble resin; (c2) subjecting the dried
coating layer to a heat treatment to effect thermal shrinkage of
the coating layer and reduction of dimensions of the resist
pattern; and (d2) dissolving away the coating layer by washing with
water.
9. The method as claimed in claim 8 in which the water-soluble
resin is a copolymer of (meth)acrylic acid and the ethylenically
unsaturated monomeric compound in a copolymerization ratio in the
range from 4:1 to 1:1 by moles.
10. The method as claimed in claim 8 in which the heat treatment in
step (c2) is conducted at a temperature lower than the softening
temperature of the patterned resist layer.
11. A method for reducing dimensions of a resist pattern on a
substrate surface which comprises the steps of: (a2) coating the
patterned resist layer with an aqueous coating solution containing
a water-soluble resin which is a homopolymer of N-vinylpyrrolidone
or a copolymer of N-vinylpyrrolidone and a comonomer which is
N-vinylimidazolidinone, N-acryloylmorpholine or a combination
thereof to form a coating layer of the aqueous coating solution;
(b2) drying the coating layer to form a dried coating layer of the
water-soluble resin; (c2) subjecting the dried coating layer to a
heat treatment to effect thermal shrinkage of the coating layer and
reduction of the resist pattern dimension; and (d2) dissolving away
the coating layer by washing with water.
12. The method as claimed in claim 11 in which the water-soluble
resin is a copolymer of N-vinylpyrrolidone and
N-vinylimidazolidinone.
13. The method as claimed in claim 12 in which the water-soluble
resin is a copolymer of N-vinylpyrrolidone and
N-vinylimidazolidinone in a copolymerization ratio in the range
from 9:1 to 1:9 by moles.
14. The method as claimed in claim 11 in which the temperature of
the heat treatment in step (c2) is lower than the softening
temperature of the patterned resist layer.
15. An aqueous coating solution used in the coated thermal flow
process for reducing a resist pattern dimension of a patterned
resist layer on a substrate which comprises a water-soluble resin
and a water-soluble amine compound.
16. The aqueous coating solution as claimed in claim 15 in which
the water-soluble resin is selected from alkyleneglycol-based
polymers, cellulosic polymers, vinyl polymers, acrylic polymers,
urea-based polymers, epoxy polymers, melamine-based polymers and
polyamide polymers.
17. The aqueous coating solution as claimed in claim 15 in which
the water-soluble amine compound has a pK value in the range from
7.5 to 13.
18. The aqueous coating solution as claimed in claim 15 in which
the water-soluble amine compound is monoethanolamine or
triethanolamine.
19. The aqueous coating solution as claimed in claim 15 in which
the amount of the water-soluble amine compound is in the range from
0.1 to 30% by weight based on the amount of the water-soluble
resin.
20. An aqueous coating solution of a water-soluble resin used in
the coated thermal flow process for reducing a resist pattern
dimension of a patterned resist layer on a substrate in which the
water-soluble resin is a copolymer of (meth)acrylic acid and an
ethylenically unsaturated monomeric compound selected from the
group consisting of N-vinylpyrrolidone, N-vinylimidazolidinone,
methyl acrylate, methyl methacrylate, N,N-dimethylacrylamide,
N,N-dimethylaminopropyl methacrylamide, N,N-dimethylaminopropyl
acrylamide, N-methhylacrylamide, diacetoneacrylamide,
N,N-dimethylaminoethyl methacrylate, N,N-diethylaminoethyl
methacrylate, N,N-dimethylaminoethyl acrylate and
N-acryloylmorpholine.
21. The aqueous coating solution as claimed in claim 20 in which
the water-soluble resin is a copolymer of acrylic acid and
N-vinylpyrrolidone.
22. An aqueous coating solution of a water-soluble resin used in
the coated thermal flow process for reducing a resist pattern
dimension of a patterned resist layer on a substrate in which the
water-soluble resin is a copolymer of N-vinylpyrrolidone and
N-vinylimidazolidinone.
23. A method for selection of a water-soluble resin used in the
coated thermal flow process for reducing the pattern dimension of a
patterned resist layer formed on a substrate surface comprising the
steps of forming a coating layer of a water-soluble resin on a
patterned resist layer, subjecting the coating layer to a heat
treatment to effect thermal shrinkage of the coating layer and
reduction of the pattern dimensions and removing the coating layer
by washing with water, which comprises the steps of: (a3) forming a
coating layer of the water-soluble resin on the surface of an
unpatterned but photocured photoresist layer on a substrate
surface; (b3) subjecting the coating layer of the water-soluble
resin at 140.degree. C. for 60 seconds; and (c3) dissolving away
the coating layer of the water-soluble resin by washing with water
at 23.degree. C. to determine the dissolving time taken for
complete removal of the coating layer.
24. The method as claimed in claim 23 in which the water-soluble
resin is selected from the group consisting of acrylic polymers,
vinyl polymers, cellulose-based polymers and alkyleneglycol-based
polymers.
25. The method as claimed in claim 24 in which the water-soluble
resin is an acrylic polymer or a vinyl polymer.
26. The method as claimed in claim 25 in which the water-soluble
resin is an acrylic polymer.
27. The method as claimed in claim 23 in which the temperature of
the heat treatment in step (b) is lower than the softening point of
the photocured photoresist layer.
Description
[0001] This is a continuation of Ser. No. 10/173,880, filed Jun.
19, 2002, now abandoned.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to improvements in a method
for obtaining a patterned photoresist layer of which the resist
pattern has a reduced dimension by a post-patterning heat
treatment. More particularly, the invention relates to improvements
in the method for reducing the pattern dimension in a
photolithographically patterned resist layer by a post-patterning
procedure in which a patterned resist layer on a substrate is
provided thereon with a coating layer of a water-soluble resin and
then the thus coated patterned resist layer is subjected to a heat
treatment to effect thermal shrinkage of the resist layer resulting
in a reduced pattern dimension followed by complete removal of the
coating layer of the water-soluble resin by washing with water.
[0003] Along with the recent trend in the technology of
semiconductor devices toward higher and higher degrees of
integration and more and more compact sizes of the devices, the
photolithographic patterning technology of photoresist layers is
also required to accomplish finer and finer patterning of the
photoresist layer.
[0004] An approach for accomplishing the above mentioned
requirement in the photolithographic technology for a pattern
dimension of 0.20 .mu.m or finer is to use a patterning exposure
light of very short wavelengths such as KrF excimer laser beams,
ArF excimer laser beams and F.sub.2 excimer laser beams as well as
electron beams. This approach, however, cannot be successful
without development of a photoresist composition having
adaptability to these short-wavelength exposure radiations.
[0005] In this regard, so-called chemical-amplification photoresist
compositions are widely employed in the modern photolithographic
technology, in which the catalytic activity of an acid generated in
the light-exposed areas from a radiation-sensitive acid-generating
agent contained in the resist layer is utilized to effect a
solubility change of the resinous ingredient to give high
sensitivity and pattern resolution even with a small amount of the
acid-generating agent.
[0006] As a method for obtaining very finely patterned resist layer
on a substrate, there is a known method in which a photoresist
layer formed on a substrate is patterned in a conventional way
including patterning light-exposure and development and the thus
patterned resist layer is provided with a coating layer of a resin
by utilizing the activity of the acid diffused from the resist
layer followed by a heat treatment so as to effect reduction of the
pattern dimension to be finer than the resolution limit inherent in
the photoresist composition (Japanese Patent Kokai 5-166717 and
5-241348).
[0007] This method, however, has a problem in respect of the
relatively large temperature dependency amounting to more than 10
nm/.degree. C. within the substrate surface. This disadvantage can
hardly be overcome with the heating device currently employed in
the manufacture of semiconductor devices due to poor uniformity of
the temperature distribution. Accordingly, the above-described
method of post-patterning dimension-reducing method cannot be
practiced without substantial variations in the pattern
dimensions.
[0008] It is also known that the dimension of a patterned resist
layer can be reduced below the resolution limit of the photoresist
composition by subjecting the patterned resist layer to a heat
treatment or a radiation irradiation treatment to cause
mobilization of the patterned resist layer. Though advantageous in
respect of small temperature dependency of only a few nm/.degree.
C. within the plane of the substrate surface, this method has a
problem that, due to the difficulty in controlling mobilization of
the photoresist layer by the heat treatment, uniform reduction of
the dimension of the photoresist layer can hardly be expected
within the substrate surface.
[0009] Besides the above described photolithographic patterning
process by utilizing excimer laser beams for patterning light
exposure, proposals are made in Japanese Patent No. 2723260 for
reduction of the pattern dimension, according to which a layer of
an electron beam resist composition comprising a polymethyl
methacrylate resin is patterned to give a patterned resist layer
which is then provided thereon with a coating layer of a
positive-working resist composition followed by a heat treatment to
form a reacted layer at the interface between the patterned resist
layer and the positive-working resist layer and removal of the
positive-working resist layer from the unreacted areas. Japanese
Patent Kokai 6-250379 further discloses a method in which a reacted
layer is formed between the underlying patterned resist layer and
the upper resist layer by utilizing the acid generated from the
acid-generating agent or thermal crosslinking by the acid. Japanese
Patent Kokai 10-73927 discloses a method for the manufacture of
semiconductor devices by effecting reduction of the pattern
dimension in which the overcoating layer is formed by using, as the
coating solution, a composition prepared by dissolving a
water-soluble resin, water-soluble crosslinking agent or
combination thereof in a water-miscible solvent without addition of
any photosensitive ingredients. Japanese Patent Kokai 2000-347414
proposes a method in which a substrate surface is provided thereon
with a photosensitive layer of a chemical-amplification photoresist
composition which is subjected to patterning light-exposure and
development to form a patterned resist layer, a coating film is
formed on the patterned resist layer by using a coating composition
containing a water-soluble resin such as a polyvinyl acetal,
water-soluble crosslinking agent such as
tetra(hydroxymethyl)glycoluril, a water-soluble nitrogen-containing
compound such as amines and, optionally, a fluorine- and
silicon-containing surface active agent followed by a heat
treatment to form a water-insoluble reacted layer at the interface
between the patterned resist layer and the overcoating layer and
finally the overcoating layer in the unreacted areas is removed by
using a solvent.
[0010] Although each of the above-described methods is desirable
because reduction of the pattern dimension can be conveniently
accomplished to exceed the wavelength limitation of the photoresist
composition by forming an upper coating layer on the underlying
photoresist layer, several disadvantages are involved therein. For
example, the crosslinking reaction of the overcoating composition
may overly proceed to unnecessary portions such as the bottom of
the patterned resist layer resulting in an undesirable
non-orthogonal cross sectional profile thereof eventually with
trailing skirts. The dimension of the upper resist layer depends on
the mixing baking which is a heat treatment to cause crosslinking.
Further, the temperature dependency obtained by these methods is
relatively large to be 10 nm/.degree. C. or larger so that it is
very difficult to ensure high uniformity of the pattern dimension
within the substrate surface when the substrate has a large size or
the patterned resist layer is extremely fine resulting in poor
controllability in reduction of the pattern dimension.
[0011] Besides, a proposal is made in Japanese Patent Kokai
1-307228 and 4-364021 for the so-called thermal flow process in
which a patterned photoresist layer formed on a substrate is
subjected to a heat treatment or radiation-irradiation treatment to
effect mobilization of the resist layer so as to accomplish
reduction of the pattern dimension to become finer than the
resolution limit of the photoresist composition.
[0012] This method, however, is defective because products of
reproducible quality can hardly be obtained due to the difficulty
encountered in controlling the mobility of the resist by means of
heat or radiation. As a further development of this thermal flow
process, Japanese Patent Kokai 7-45510 proposes a method in which
the mobility of the resist is controlled by providing a coating
layer of a water-soluble resin on the patterned photoresist layer
formed on a substrate. Since the water-soluble resin used in this
method, such as polyvinyl alcohols, is insufficient in the
solubility in water required in the removal with water and
long-term stability, troubles are sometimes caused by the residual
resin film remaining unremoved with water.
SUMMARY OF THE INVENTION
[0013] In view of the above described problems and disadvantages in
the prior art, the present invention has an object to provide an
improvement in the method for reducing the dimension of a patterned
photoresist layer by a post-patterning treatment in which the
patterned resist layer is provided thereon with a coating layer of
a water-soluble resin composition followed by a heat treatment to
cause reduction of the pattern dimension or the distance between
the resist patterns and then removal of the water-soluble coating
layer away from the patterned resist layer by washing with
water.
[0014] Thus, in a first aspect of the invention, the present
invention provides, in a method for reducing a pattern dimension in
a patterned photoresist layer formed on a substrate by a
post-patterning heat treatment, referred to as the coated thermal
flow process hereinafter, comprising the steps of: (a) forming a
coating layer of a water-soluble resin composition on the patterned
resist layer, (b) drying the coating layer of the aqueous coating
solution, (c) subjecting the dried coating layer and the patterned
resist layer to a heat treatment to effect thermal shrinkage of the
patterned resist layer with reduction of the pattern dimension and
(d) removing the coating layer of the water-soluble resin
composition, the improvement which comprises: using, in step (a), a
coating solution containing a water-soluble resin and a
water-soluble amine compound having, preferably, a pKa value of 7.5
to 13.0 at 25.degree. C. for the formation of the coating
layer.
[0015] In a second aspect of the invention, the improvement
provided by the present invention comprises, in step (a) of the
coated thermal flow process, using an aqueous coating solution
containing a water-soluble resin which is a copolymer of (A)
acrylic acid, methacrylic acid or a combination thereof and (B) a
water-soluble ethylenically unsaturated compound which is
exemplified by N-vinylpyrrolidone, N-vinylimidazolidinone, methyl
acrylate, methyl methacrylate, N,N-dimethylacrylamide,
N,N-dimethylaminopropyl methacrylamide, N,N-dimethylaminopropyl
acrylamide, N-methhylacrylamide, diacetoneacrylamide,
N,N-dimethylaminoethyl methacrylate, N,N-diethylaminoethyl
methacrylate, N,N-dimethylaminoethyl acrylate, N-acryloylmorpholine
and the like, of which those nitrogen-containing water-soluble
compounds are preferable, or a combination thereof.
[0016] In a third aspect of the invention, the present invention is
directed to an improvement of the aqueous coating solution for use
in step (a) of the coated thermal flow process in which the
water-soluble resin is a copolymer of N-vinylpyrrolidone and a
water-soluble monomeric vinyl compound other than
N-vinylpyrrolidone which is preferably N-vinylimidazolidinone.
[0017] In a fourth aspect of the invention, the present invention
provides, in the above-mentioned coated thermal flow process of a
patterned resist layer, the improvement which comprises, as a
guideline for the selection of the water-soluble resin in step (a)
of the method using an aqueous coating solution containing a
water-soluble resin exhibiting such a water-solubility behavior
that, in a testing procedure comprising the steps of forming a
coating layer of the resin on an unpatterned photocured layer of
the photoresist composition, subjecting the coating layer to a heat
treatment at 140.degree. C. for 60 seconds and removing away the
coating film by washing with water at 23.degree. C., the coating
layer can be completely removed within 60 seconds.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] The present invention provides, according to the first
aspect of the invention, an improvement in the formulation of the
aqueous coating solution used for the formation of a water-soluble
coating layer on a patterned photoresist layer in step (a) of the
so-called coated thermal flow process, in which the coating layer
and the patterned resist layer are subjected to a heat treatment,
for example, at 80 to 160.degree. C. for 30 to 90 seconds followed
by complete removal of the coating layer by washing with water. The
temperature of this heat treatment should preferably be lower than
the softening point of the patterned resist layer. When the heat
treatment is conducted at such a temperature, the patterned resist
layer receives a tension from the coating layer to give more
remarkable reduction in the dimension of holes and trenches with a
decrease in the dependency on the duty ratio, i.e. the line
distance within the plane of substrate surface. The above-mentioned
softening point of the resist layer is a temperature at which, when
the patterned resist layer formed on a substrate is gradually
heated, an incipient spontaneous flow of the mobilized resist layer
is detected.
[0019] The water-soluble resin contained in the aqueous coating
solution used in the coated thermal flow process is not
particularly limitative and can be selected from a variety of
water-soluble polymers including alkyleneglycol-based polymers,
cellulosic polymers, vinyl polymers, acrylic polymers, urea-based
polymers, epoxy polymers, melamine-based polymers and polyamide
polymers. Although any of these water-soluble polymers can be used
either singly or as a combination of two kinds or more, it is
preferable in respect of the efficiency for reduction of the
pattern distance without affecting the cross sectional profile of
the patterned resist layer that the water-soluble resin is a
homopolymer of an acrylic monomer or a copolymer of an acrylic
monomer with other copolymerizable monomers.
[0020] Examples of the above-mentioned acrylic monomer include
acrylic acid, methyl acrylate, methacrylic acid, methyl
methacrylate, N,N-dimethyl acrylamide, N,N-dimethylaminopropyl
methacrylamide, N,N-dimethylaminopropyl acrylamide, N-methyl
acrylamide, diacetone acrylamide, N,N-dimethylaminoethyl
methacrylate, N,N-diethylaminoethyl methacrylate,
N,N-dimethylaminoethyl acrylate and N-acryloylmorpholine.
[0021] Examples of the comonomer compound copolymerized with the
above named acrylic monomers include vinyl monomers such as
N-vinylpyrrolidone, N-vinylimidazolidinone, vinyl acetate and the
like.
[0022] The aqueous coating solution used in step (a) of the coated
thermal flow process is prepared by dissolving one or a combination
of the above named water-soluble resins in water in a concentration
of 3 to 50% by weight or, preferably, 5 to 20% by weight. When the
concentration is too low, the coating layer formed from the coating
solution is sometimes incomplete while, when the concentration is
too high, the desired effect of the coated thermal flow process can
little be accomplished.
[0023] According to the first aspect of the invention, the aqueous
coating solution as described above is further admixed with a
water-soluble amine compound which, preferably, has a pKa value of
7.5 to 13.0 at 25.degree. C. Examples of suitable amine compounds
include alkanolamines such as monoethanolamine, diethanolamine,
triethanolamine, 2-(2-aminoethoxy)ethanol,
N,N-dimethylethanolamine, N,N-diethylethanolamine,
N,N-dibutylethanolamine, N-methylehtanolamine, N-ethylethanolamine,
N-butylethanolamine, N-methyldiethanolamine, monoisopropanolamine,
diisopropanolamine, triisopropanolamine and the like, polyalkylene
polyamines such as diethylenetriamine, triethylenetetramine,
propylenediamine, N,N'-diethylethylenediamine, 1,4-butanediamine,
N-ethylethylenediamine, 1,2-propanediamine, 1,3-propanediamine,
1,6-hexanediamine and the like, aliphatic amines such as
2-ethylhexylamine, dioctylamine, tributylamine, tripropylamine,
triallylamine, heptylamine, cyclohexylamine and the like, aromatic
amines such as benzylamine, diphenylamine and the like and cyclic
amines such as piperazine, N-methylpiperazine, methylpiperazine,
hydroxyethylpiperazine and the like. These amine compounds can be
used either singly or as a combination of two kinds or more. It is
preferable, however, that the water-soluble amine compound has a
boiling point of 140.degree. C. or higher under normal pressure in
order not to be lost by the heat treatment of the coating layer. In
this regard, monoethanolamine and triethanolamine are suitable.
[0024] The amount of the water-soluble amine compound added to the
aqueous coating solution is in the range from 0.1 to 30% by weight
or, preferably, from 2 to 15% by weight based on the amount of the
water-soluble resin. When the amount of the amine compound is too
small, the aqueous coating solution eventually suffers a decrease
in storage stability due to degradation. When the amount exceeds
30% by weight, in particular, an adverse effect is caused on the
cross sectional profile of the patterned resist layer. The problem
of denaturation of the aqueous coating solution can be at least
partly solved by admixing the coating solution with an acidic
compound such as p-toluene sulfonic acid and dodecylbenzene
sulfonic acid. The coating layer can be imparted with increased
stability by admixing the aqueous coating solution with a surface
active agent.
[0025] In the method according to the first aspect of the present
invention, the patterned resist layer formed on a substrate is
coated at least partly with the above described aqueous coating
solution followed by drying to give a dried coating layer and then
subjected to a heat treatment which can be conducted in
substantially the same manner as in the conventional thermal flow
process. Namely, the patterned resist layer is coated with the
coating solution of the water-soluble resin by using a coating
machine such as a spinner and the coating layer is dried by heating
at about 80 to 160.degree. C. for 30 to 90 seconds. It is optional
that the patterned resist layer coated with the water-soluble resin
is subjected beforehand to a pre-baking treatment at 80 to
100.degree. C. for 30 to 90 seconds. The concentration of the
water-soluble resin in the aqueous coating solution is in the range
from 3 to 50% by weight or, preferably, from 5 to 20% by weight
depending on the desired thickness of the coating layer which is in
the range from 0.1 to 0.5 .mu.m.
[0026] The aqueous solvent used in the above-described aqueous
coating solution is usually water but it is optional that the
solvent is a mixture of water with a water-miscible alcoholic
solvent such as methyl alcohol, ethyl alcohol, propyl alcohol,
isopropyl alcohol, glycerin, ethyleneglycol, propyleneglycol,
1,2-butyleneglycol, 1,3-butyleneglycol and 2,3-butyleneglycol.
These water-miscible alcoholic solvents can be added to water in a
mixing proportion not exceeding 30% by weight based on water.
[0027] According to the first aspect of the invention, reduction of
the resist pattern dimension accomplished by the coated thermal
flow process can be to such an extent that the width of a trench
pattern is decreased from 220 nm to 160 nm and the diameter of a
hole pattern is decreased from 180 nm to 160 nm. After the thus
accomplished thermal shrinkage of the patterned resist layer, the
coating layer of the water-soluble resin formed thereon is
completely removed by washing for 10 to 60 seconds with an aqueous
solvent which is preferably water.
[0028] A finely patterned resist layer formed by the
photolithographic technology can be imparted in this way with an
increased fineness of the pattern dimension to exceed the
resolution limit accomplished in a conventional process without
affecting other characteristics required for the finely patterned
resist layer.
[0029] According to the second aspect of the invention, the present
invention provides an aqueous coating solution for use in the
coated thermal flow process, of which the water-soluble resin is a
copolymer consisting of the monomeric units comprising (A) the
monomeric units derived from acrylic acid, methacrylic acid or a
combination of acrylic and methacrylic acids and (B) the monomeric
units derived from various kinds of ethylenically unsaturated
monomeric compounds named before including, as preferable ones,
N-vinylpyrrolidone, N-vinylimidazolidinone, N-acryloylmorpholine or
a combination thereof in a molar ratio of (A):(B) in the range from
4:1 to 1:1. It is preferable that the molar fraction of the
monomeric units (A) is larger than that of the units (B). Though
not particularly limitative, it is preferable in respect of good
film-forming behavior that the above-mentioned binary copolymeric
resin has a weight-average molecular weight in the range from 10000
to 50000 as measured by the gel permeation chromatographic method
making reference to polymethyl methacrylate resins having known
molecular weights.
[0030] While the coating solution used in step (a) of the inventive
method is basically an aqueous solution of the aforementioned
water-soluble copolymeric resin, it is optional that the aqueous
solution further contains water-soluble resins of other types in a
limited amount including cellulose derivatives,
alkyleneglycol-based polymers, urea-based polymers and
melamine-based polymers.
[0031] The cellulose derivative mentioned above is exemplified by
hydroxypropyl methyl cellulose phthalate, hydroxypropyl methyl
cellulose acetate phthalate, hydroxypropyl methyl cellulose
hexahydrophthalate, hydroxypropyl methyl cellulose acetate
succinate, hydroxypropyl methyl cellulose, hydroxypropyl cellulose,
hydroxyethyl cellulose, cellulose acetate hexahydrophthalate,
carboxylmethyl cellulose, ethyl cellulose and methyl cellulose. The
alkyleneglycol-based copolymer is exemplified by
addition-polymerized polymers and copolymers of ethyleneglycol,
propyleneglycol, butyleneglycol and the like. The urea-based
polymer is exemplified by the polymers of methylolated urea,
dimethylolated urea, ethyleneurea and the like. The melamine-based
polymer is exemplified by the polymers of methoxymethylated
melamine, methoxymethylated isobutoxymethylated melamine,
methoxyethylated melamine and the like. Besides, epoxy-based
polymers and amide-based polymers can also be used, if
water-soluble. These water-soluble resins can be used either singly
or as a combination of two kinds or more.
[0032] The aqueous solvent used in the above-described aqueous
coating solution is usually water but it is optional that the
solvent is a mixture of water with a water-miscible alcoholic
solvent such as methyl alcohol, ethyl alcohol, propyl alcohol,
isopropyl alcohol, glycerin, ethyleneglycol, propyleneglycol,
1,2-butyleneglycol, 1,3-butyleneglycol and 2,3-butyleneglycol.
These water-miscible alcoholic solvents can be added to water in a
mixing proportion not exceeding 30% by weight based on water.
[0033] In the fine resist pattern-forming method according to the
invention, a desired fine resist pattern can be obtained with good
efficiency by successively undertaking the steps including: step
(a2) for the formation of a resist pattern on a substrate; step
(b2) for the formation of a coating layer of a water-soluble resin
on the resist pattern; step (c2) for a heat treatment of the
coating layer and step (d2) for the removal of the coating layer by
washing with water each as described below.
[0034] The step (a2) is a step for the formation of a resist
pattern on a substrate by using a resist composition. In this step,
which can be conducted according to a conventional
photolithographic fine patterning procedure in the manufacture of
semiconductor devices, a substrate such as a semiconductor silicon
wafer is coated by spin coating with a solution of a
chemical-amplification resist, electron beam resist or F.sub.2
laser beam resist to form a resist layer which is pattern-wise
exposed to light through a photomask bearing a desired pattern or
subjected to scanning with electron beams followed by a
post-exposure baking treatment and then subjected to a development
treatment with an aqueous alkaline solution as a developer such as
a 1-10% by weight aqueous solution of tetramethylammonium hydroxide
to form the desired resist pattern.
[0035] The step (b2) is for the formation of a water-soluble
resinous coating layer on the resist pattern wholly or partially by
using the above-described aqueous coating solution of a
water-soluble resin. The coating method can be the same as that
under conventional use in the thermal flow process by using, for
example, a spinner, if necessary, followed by heating for drying.
The coating layer has a thickness, preferably, in the range from
0.1 to 0.5 .mu.m.
[0036] The step (c2) is for a heat treatment of the resist pattern
coated with a water-soluble resinous layer in step (b2) so as to
decrease the distance between adjacent resist patterns. The heat
treatment is conducted usually at a temperature of 80 to
160.degree. C. for 30 to 120 seconds. It is preferable that the
heat treatment is conducted at a temperature lower than the
softening point of the patterned resist layer because the shrinkage
rate of the resist pattern is free from dependency on the duty
ratio and fineness of holes and trenches can be further increased
by the attractive force exerted by the water-soluble resinous
coating layer on the resist pattern. By this heat treatment, a
decrease in the dimensions of the resist pattern can be obtained
from 220 nm to 160 nm for trenches and from 180 nm to 160 nm for
holes.
[0037] In step (d2), the water-soluble coating layer covering the
resist pattern after the heat treatment in step (c2) is removed by
washing with an aqueous solvent or, preferably, deionized water.
Removal of the coating layer can be complete by washing usually for
10 to 60 seconds.
[0038] In essence, the present invention according to the second
aspect of the invention also provides an improved coated thermal
flow process in which the aqueous coating solution for the
formation of a coating layer on a patterned resist layer contains
the above defined copolymeric resin as the resinous ingredient and
the heat treatment of the water-soluble coating layer is conducted
at a temperature lower than the softening temperature of the
patterned resist layer. While the above mentioned heat treatment of
the coating layer is conducted usually at 80 to 160.degree. C. for
30 to 120 seconds, it is preferable that the heat treatment
temperature is lower than the softening point of the patterned
resist layer so that the patterned resist layer is subjected to
traction by the thermally shrinking coating layer to cause
efficient reduction of the resist pattern dimension with a rate of
shrinkage not depending on the duty ratio.
[0039] According to the third aspect of the invention, the present
invention provides an improved aqueous coating solution used in the
coated thermal flow process, in which the water-soluble resinous
ingredient contained in the aqueous coating solution is a
copolymeric resin consisting of the monomeric units comprising (A1)
the monomeric units derived from N-vinylpyrrolidone and (B1) the
monomeric units derived from a water-soluble monomeric vinyl
compound other than N-vinylpyrrolidone which is preferably
N-vinylimidazolidinone in a molar ratio of (A1):(B1) in the range
from 1:9 to 9:1. Though not particularly limitative, it is
preferable in respect of good film-forming behavior and heat
resistance to withstand the heat treatment that the above-mentioned
binary copolymeric resin has a weight-average molecular weight in
the range from 10000 to 50000 as measured by the gel permeation
chromatographic method making reference to polymethyl methacrylate
resins having known molecular weights. The coated thermal flow
process using the aqueous coating solution containing the
above-defined copolymeric resin is conducted in the same way as in
the second aspect of the invention.
[0040] According to the fourth aspect of the invention, the
improvement provided by the present invention is related to a
testing procedure for selection of the water-soluble resin as the
solute in the aqueous coating solution for the formation of a
water-soluble coating layer on a patterned resist layer in the
coated thermal flow process.
[0041] In practicing the solubility test of the water-soluble
resin, a coating layer of the water-soluble resin is formed on an
unpatterned but photocured resist layer on a substrate and
subjected to a heat treatment at 140.degree. C. for 60 seconds.
Thereafter, the thus heat-treated coating layer of the
water-soluble resin is washed with water at 23.degree. C. to
determine the time taken for complete removal of the coating layer
by dissolving away with water, which must be 60 seconds or shorter
in order for the resin to be used in the coated thermal flow
process according to the present invention.
[0042] According to the above-described testing procedure for the
solubility behavior of the water-soluble resin, a polymeric resin
selected from water-soluble acrylic polymers, vinyl polymers,
cellulose derivatives, alkyleneglycol-based polymers, urea-based
polymers, melamine-based polymers, epoxy-based polymers and
amide-based polymers which passes the test can be used as the
resinous ingredient in the aqueous coating solution. The solubility
behavior of the water-soluble resin can be adjusted by
copolymerizing the above-mentioned acrylic monomer with a minor
amount of comonomers of other types.
[0043] In the following, the present invention in various aspects
is described in more detail by way of Examples and Comparative
Examples, which, however, never limit the scope of the invention in
any way.
[0044] In the Examples and Comparative Examples described below,
the water-soluble resins as a solute in the aqueous coating
solution were subjected to a solubility test in the following
manner. Thus, a semiconductor silicon wafer was uniformly coated on
a spinner with a chemical-amplification positive-working
photoresist solution (TDUR-P036PM, a product by Tokyo Ohka Kogyo
Co.) followed by a drying heat treatment at 80.degree. C. for 90
seconds to give a dried resist layer having a thickness of 0.7
.mu.m. The resist layer was then coated uniformly with an aqueous
solution of the resin on test and the coating layer was subjected
to a heat treatment at 140.degree. C. for 60 seconds to give a
coating layer of 0.3 .mu.m thickness. The substrate bearing the
thus heat-treated coating layer was kept in water at 23.degree. C.
under vibration to determine the length of time taken before
complete dissolution and removal of the coating layer. As a
criterion, the water-soluble resins were taken as acceptable when
this dissolving took a time not exceeding 60 seconds.
EXAMPLE 1
[0045] A semiconductor silicon wafer was uniformly coated on a
spinner with a positive-working photoresist composition
(TDUR-P036PM, a product by Tokyo Ohka Kogyo Co.) followed by a
baking treatment at 80.degree. C. for 90 seconds to form a
photoresist layer having a thickness of 560 nm.
[0046] The photoresist layer was subjected to a patterning
light-exposure treatment with KrF excimer laser beams on a
light-exposure machine (Model Canon FPA-3000EX3, manufactured by
Canon Co.) followed by a post-exposure baking treatment at
120.degree. C. for 90 seconds and then subjected to a development
treatment with a 2.38% by weight aqueous solution of
tetramethylammonium hydroxide to give a hole pattern having a
diameter of 182.3 nm.
[0047] In the next place, the resist layer having the thus formed
hole pattern was coated with a coating solution prepared by
dissolving 9.1 g of a copolymeric resin of acrylic acid and
N-vinylpyrrolidone in a copolymerization ratio of 2:1 by weight and
0.9 g of triethanolamine in 90 g of water to form a coating layer
which was subjected to a heat treatment at 120.degree. C. for 60
seconds to cause thermal shrinkage followed by washing with water
at 23.degree. C. to dissolve away the coating layer. The result was
that the coating layer could be completely removed by washing for
about 1 minute with a reduction of the hole pattern diameter to
161.5 nm.
COMPARATIVE EXAMPLE 1
[0048] The experimental procedure was substantially the same as in
Example 1 except that the coating solution was a 5% by weight
aqueous solution of a polyvinyl alcohol. The result obtained by
washing away of the coating film with water was that visually
recognizable residue of the coating layer was found.
EXAMPLE 2
[0049] A semiconductor silicon wafer was uniformly coated on a
spinner with a positive-working photoresist composition
(TDMR-AR2000, a product by Tokyo Ohka Kogyo Co.) followed by a
pre-baking treatment at 90.degree. C. for 90 seconds to form a
photoresist layer having a thickness of 1.3 .mu.m.
[0050] In the next place, the photoresist layer was subjected to
patterning light exposure on an i-line light-exposure machine
(Model Nikon NSR-2205 il4E, manufactured by Nikon Co.) followed by
a post-exposure baking treatment at 110.degree. C. for 90 seconds
and then subjected to a development treatment to give a trench
pattern of 411.1 nm width.
[0051] The thus formed trench-patterned resist layer was provided
in the same manner as in Example 1 with a coating layer of the
water-soluble resin followed by a heat treatment to effect thermal
shrinkage and then washing away of the coating layer with water.
The result was that the width of the trench pattern had been
reduced from 411.1 nm to 219.5 nm.
EXAMPLE 3
[0052] The experimental procedure was substantially the same as in
Example 1 except that the coating solution of a water-soluble resin
was prepared by dissolving, in 90 g of water, 9.5 g of a
copolymeric resin of acrylic acid and N-vinylpyrrolidone in a
copolymerization ratio of 2:1 by weight and 0.5 g of
monoethanolamine. The result was that the hole pattern diameter
could be reduced from 182.3 nm to 160.3 nm.
EXAMPLE 4
[0053] A semiconductor silicon wafer was uniformly coated with a
positive-working photoresist composition (EP-TF004EL, a product by
Tokyo Ohka Kogyo Co.) on a spinner followed by a pre-baking
treatment at 150.degree. C. for 300 seconds to form a resist layer
having a thickness of 2.0 .mu.m.
[0054] The thus formed resist layer was pattern-wise irradiated by
scanning electron beams on an electron-beam image tracing machine
(Model HITACHI HL800D50 Kv, manufactured by Hitachi Ltd.) followed
by a post-exposure baking treatment at 140.degree. C. for 300
seconds and then subjected to a development treatment with a 2.38%
by weight aqueous solution of tetramethylammonium hydroxide to give
a trench-patterned resist layer having a trench width of 228.0
nm.
[0055] The thus trench-patterned resist layer was coated with the
same aqueous coating solution as used in Example 1 and the coating
layer was subjected to a heat treatment at 150.degree. C. for 90
seconds to effect thermal shrinkage followed by washing away of the
coating layer with water to find that removal of the coating layer
was complete after washing for about 60 seconds. The width of the
trench pattern was reduced from 228.0 nm to 155.0 nm.
EXAMPLE 5
[0056] A semiconductor silicon wafer was uniformly coated on a
spinner with a positive-working photoresist solution (TDUR-P036PM,
supra) followed by a pre-baking treatment at 80.degree. C. for 90
seconds to give a photoresist layer of 560 nm thickness, which was
pattern-wise light-exposed on a light-exposure machine (Model Canon
FPA-3000EX3, supra) and, after a post-exposure baking treatment at
120.degree. C. for 90 seconds, subjected to a development treatment
with a 2.38% by weight aqueous solution of tetramethylammonium
hydroxide to give a patterned resist layer having a hole pattern of
178.1 nm diameter.
[0057] Separately, an aqueous coating solution was prepared by
dissolving, in 45 g of water, 20 g of a resin mixture consisting of
a polyacrylic acid resin and a poly(N-vinylpyrrolidone) resin in a
weight proportion of 55:45. The resin mixture had been subjected to
the test of solubility behavior as described before to find that
the dissolving time of the resin mixture was one second.
[0058] The above prepared patterned resist layer was coated with
the aqueous coating solution followed by a heat treatment at
120.degree. C. for 60 seconds to effect thermal shrinkage.
Thereafter, the coating layer was washed with water at 23.degree.
C. to find that removal of the coating layer was complete by
washing for 60 seconds. The hole pattern diameter could be reduced
to 157.4 nm and the cross sectional profile of the patterned resist
layer was excellently orthogonal.
COMPARATIVE EXAMPLE 2
[0059] A coating solution for comparative test was prepared by
dissolving 5 g of a polyvinyl alcohol resin in 95 g of water.
Separately, the polyvinyl alcohol resin was subjected to the
solubility test to find that removal of the coating layer was still
incomplete even after 120 seconds of the washing time.
[0060] A test of coated thermal flow process was undertaken in the
same manner as in Example 5 excepting the use of the above prepared
polyvinyl alcohol solution as the coating solution to find that no
acceptable patterned resist layer could be obtained due to
remaining residue of the coating layer on the substrate.
COMPARATIVE EXAMPLE 3
[0061] The testing procedure was substantially the same as in
Example 5 except that no coating layer was formed on the patterned
resist layer. The result of the test was that substantially no
reduction of the pattern dimension could be obtained.
EXAMPLE 6
[0062] A semiconductor silicon wafer was spin-coated with a
positive-working photoresist composition (TDUR-P036PM, supra) and
subjected to a pre-baking treatment at 80.degree. C. for 90 seconds
to form a photoresist layer of 560 nm thickness.
[0063] The photoresist layer was pattern-wise exposed to light on a
light-exposure machine (Model Canon FPA-3000EX3, supra) followed by
a post-exposure baking treatment at 120.degree. C. for 90 seconds
and then subjected to a development treatment with a 2.38% by
weight aqueous solution of tetramethylammonium hydroxide to give a
patterned resist layer having a hole pattern of 178.1 nm
diameter.
[0064] Separately, a polyacrylic acid resin was subjected to the
water-solubility test by using an aqueous solution of 5.0 g of the
resin in 45 g of water to find that the dissolving time was 1
second.
[0065] The hole-patterned resist layer was coated with the aqueous
solution of the polyacrylic acid resin followed by drying to form a
dried coating layer thereon and then subjected to a heat treatment
at 120.degree. C. for 60 seconds to effect thermal shrinkage of the
patterned resist layer followed by washing with water at 23.degree.
C. to find that removal of the coating layer was complete by
washing for 1 second and the diameter of the hole pattern was
reduced to 161.4 nm.
EXAMPLE 7
[0066] A semiconductor wafer was spin-coated with the same
positive-working photoresist composition as used in Example 6
followed by a pre-baking treatment at 80.degree. C. for 90 seconds
to form a photoresist layer of 560 nm thickness which was subjected
to a pattern-wise light-exposure in the same manner as in Example 6
followed by a post-exposure baking treatment at 120.degree. C. for
90 seconds and then a development treatment in the same manner as
in Example 6 to give a hole-patterned resist layer having a hole
diameter of 178.1 nm.
[0067] Separately, a water-soluble poly(N-acryloylmorpholine) resin
was subjected to the water-solubility test by using a 10% by weight
aqueous solution of the resin to find that the dissolving time of
the resinous layer was 1 second.
[0068] The above prepared hole-patterned resist layer was coated
with an aqueous solution of the water-soluble resin tested above
and dried to form a coating layer of the resin which was subjected
to a heat treatment at 120.degree. C. for 60 seconds to effect
thermal shrinkage of the patterned resist layer followed by removal
of the coating layer by washing with water to find that removal of
the coating layer was complete by washing for 1 second and the
diameter of the hole pattern was reduced to 166.9 nm.
EXAMPLE 8
[0069] A semiconductor silicon wafer was spin-coated with the same
positive-working photoresist composition as used in Example 6
followed by a pre-baking treatment at 80.degree. C. for 90 seconds
to form a photoresist layer of 560 nm thickness which was
pattern-wise exposed to light followed by a post-exposure baking
treatment and a development treatment in the same manner as in
Example 6 to form a patterned resist layer having a hole pattern of
180.3 nm diameter.
[0070] The thus formed patterned resist layer was coated with a 10%
by weight aqueous coating solution of a water-soluble resin which
was a copolymer of acrylic acid and N-vinylpyrrolidone in a
copolymerization ratio of 55:45 by weight followed by a heat
treatment at 120.degree. C. for 60 seconds to effect thermal
shrinkage of the patterned resist layer and then removal of the
coating layer by washing with water to find that removal of the
coating layer was complete by washing for 60 seconds and the
diameter of the hole pattern, of which the cross sectional profile
was excellently orthogonal, was reduced to 157.4 nm.
EXAMPLE 9
[0071] A semiconductor silicon wafer was spin-coated with a
photoresist composition (TDMR-AF2000, a product by Tokyo Ohka Kogyo
Co.) followed by a pre-baking treatment at 90.degree. C. for 90
seconds to form a photoresist layer of 1.3 .mu.m thickness, which
was pattern-wise exposed to light on the same exposure machine as
used in Example 2 followed by a post-exposure baking treatment at
110.degree. C. for 90 seconds and development in the same manner as
in Example 2 to give a trench-patterned resist layer of 411.1 nm
dimension.
[0072] The thus obtained trench-patterned resist layer was
subjected to the coated thermal flow process in just the same
manner as in Example 8 so that the dimension of the trench pattern
of the resist layer, which had an excellently orthogonal cross
sectional profile, was reduced to 219.5 nm.
COMPARATIVE EXAMPLE 4
[0073] The experimental procedure was substantially the same as in
Example 9 excepting for the omission of coating on the patterned
resist layer with a coating solution of a water-soluble resin. The
result was that no reduction could be obtained in the width of the
trench-patterned resist layer.
COMPARATIVE EXAMPLE 5
[0074] The experimental procedure was just the same as in Example 9
except that the aqueous coating solution of the water-soluble resin
was replaced with a 5% by weight aqueous solution of a polyvinyl
alcohol. The result was that, after removal of the coating layer by
washing with water, trace of the coating layer could be clearly
detected by visual inspection.
EXAMPLE 10
[0075] The experimental procedure was just the same as in Example 8
except that the coating layer of a water-soluble resin on the
patterned resist layer was formed by using a 10% by weight aqueous
solution of a copolymeric resin of acrylic acid and
N-acryloylmorpholine in a copolymerization ratio of 1:1 by weight.
The result was that removal of the coating layer by washing with
water was complete by washing for 1 second and the hole diameter of
the hole-patterned resist layer, which had an excellent cross
sectional profile, was reduced to 159.7 nm.
EXAMPLE 11
[0076] The procedure for the formation of a hole-patterned resist
layer on a semiconductor silicon wafer was just the same as in
Example 1 except that the hole pattern obtained had a diameter of
180.3 nm. The procedure of the coated thermal flow process was also
just the same as in Example 1 except that the aqueous coating
solution of a water-soluble resin was a 10% by weight aqueous
solution of a copolymeric resin of N-vinylpyrrolidone and
N-vinylimidazolidinone in a copolymerization ratio of 1:3 by
weight. The result was that removal of the coating layer was
complete by washing with water for 60 seconds and the diameter of
the hole pattern of the resist layer, which had an excellently
orthogonal cross sectional profile, was reduced to 170.1 nm.
EXAMPLE 12
[0077] The experimental procedure was just the same as in Example 2
except that the aqueous coating solution of a water-soluble resin
in Example 2 was replaced with the coating solution used in Example
10. The result was that the trench width of the trench-patterned
resist layer, which had an excellently orthogonal cross sectional
profile, was reduced to 345.3 nm.
* * * * *