U.S. patent application number 11/790212 was filed with the patent office on 2007-09-13 for over-coating agent for forming fine patterns and a method of forming fine patterns using such agent.
Invention is credited to Fumitake Kaneko, Yoshiki Sugeta, Toshikazu Tachikawa, Naohisa Ueno.
Application Number | 20070213447 11/790212 |
Document ID | / |
Family ID | 35187961 |
Filed Date | 2007-09-13 |
United States Patent
Application |
20070213447 |
Kind Code |
A1 |
Sugeta; Yoshiki ; et
al. |
September 13, 2007 |
Over-coating agent for forming fine patterns and a method of
forming fine patterns using such agent
Abstract
It is disclosed an over-coating agent for forming fine-line
patterns which is applied to cover a substrate having thereon
photoresist patterns and allowed to shrink under heat so that the
spacing between adjacent photoresist patterns is lessened, further
characterized by comprising a water-soluble polymer which contains
at least methacrylic acid and/or methyl methacrylate as the
constitutive monomer thereof. Also disclosed is a method of forming
fine-line patterns using the over-coating agent. The advantages of
the invention are that the exposure margin is large, that the
dimension control of photoresist patterns can be reflected on the
dimension controllability in forming fine-line patterns, that the
dimension control and planning of forming fine trace patterns after
treatment for thermal shrinkage can be attained with ease in the
stage of photoresist patterning, that the original photoresist
pattern profile can be kept as such and the top of the photoresist
pattern is not rounded after thermal shrinkage, that the degree of
thermal shrinkage of the over-coating agent is large and thus the
agent is effective in forming fine-line patterns.
Inventors: |
Sugeta; Yoshiki; (Kanagawa,
JP) ; Kaneko; Fumitake; (Kanagawa, JP) ;
Tachikawa; Toshikazu; (Kanagawa, JP) ; Ueno;
Naohisa; (Kanagawa, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
35187961 |
Appl. No.: |
11/790212 |
Filed: |
April 24, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11116251 |
Apr 28, 2005 |
|
|
|
11790212 |
Apr 24, 2007 |
|
|
|
Current U.S.
Class: |
524/459 ;
257/E21.026; 257/E21.039; 257/E21.257; 430/331 |
Current CPC
Class: |
H01L 21/31144 20130101;
H01L 21/0273 20130101; H01L 21/0338 20130101; G03F 7/40
20130101 |
Class at
Publication: |
524/459 |
International
Class: |
G03C 1/494 20060101
G03C001/494 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 30, 2004 |
JP |
2004-135458 |
Claims
1. An over-coating agent for forming fine patterns which is applied
to cover a substrate having photoresist patterns thereon and
allowed to shrink under heat so that the spacing between adjacent
photoresist patterns is lessened, further characterized by
comprising a water-soluble polymer which contains at least
methacrylic acid and/or methyl methacrylate as the constitutive
monomer thereof.
2. The over-coating agent for forming fine patterns according to
claim 1, further comprising an aliphatic amine.
3. The over-coating agent for forming fine patterns according to
claim 2, wherein the aliphatic amine is triethylamine.
4. The over-coating agent for forming fine patterns according to
claim 1, wherein the water-soluble polymer is a copolymer of
methacrylic acid and/or methyl methacrylate with at least one
monomer selected from those constituting alkylene glycol-based
polymers, cellulosic derivatives, vinylic polymers, acrylic
polymers, urea-based polymers, epoxy polymers, amide-based polymers
and melamine-based polymers (in which the monomers to constitute
acrylic polymers do not include methacrylic acid and methyl
methacrylate).
5. The over-coating agent for forming fine patterns according to
claim 4, wherein the water-soluble polymer contains methacrylic
acid and/or methyl methacrylate in a ratio of 60-99 mass % of the
polymer.
6. The over-coating agent for forming fine patterns according to
claim 1, wherein the water-soluble polymer is a copolymer or a
mixed resin of polymethacrylic acid and/or polymethyl methacrylate
with at least one polymer selected from alkylene glycol-based
polymers, cellulosic derivatives, vinylic polymers, acrylic
polymers (excluding polymethacrylic acid and polymethyl
methacrylate), urea-based polymers, epoxy polymers, amide-based
polymers and melamine-based polymers.
7. The over-coating agent for forming fine patterns according to
claim 6, wherein the water-soluble polymer contains polymethacrylic
acid and/or polymethyl methacrylate in a ratio of 60-99 mass % of
the polymer.
8. The over-coating agent for forming fine patterns according to
claim 1, wherein the water-soluble polymer is a copolymer of
methacrylic acid and/or methyl methacrylate, acrylic acid and/or
methyl acrylate, and at least one monomer selected from polymers
constituting alkylene glycol-based polymers, cellulosic
derivatives, vinylic polymers, acrylic polymers, urea-based
polymers, epoxy polymers, amide-based polymers and melamine-based
polymers (in which the monomers to constitute acrylic polymers do
not include methacrylic acid, methyl methacrylate, acrylic acid and
methyl acrylate).
9. The over-coating agent for forming fine patterns according to
claim 8, wherein the water-soluble polymer contains methacrylic
acid and/or methyl methacrylate in a ratio of 5-35 mass % of the
polymer, and acrylic acid and/or methyl acrylate in a ratio of
35-75 mass % of the polymer.
10. The over-coating agent for forming fine patterns according to
claim 1, wherein the water-soluble polymer is a copolymer or a
mixed resin of polymethacrylic acid and/or polymethyl methacrylate,
polyacrylic acid and/or polymethyl acrylate, and at least one
polymer selected from alkylene glycol-based polymers, cellulosic
derivatives, vinylic polymers, acrylic polymers (not including
polymethacrylic acid, polymethyl methacrylate, polyacrylic acid and
polymethyl acrylate), urea-based polymers, epoxy polymers,
amide-based polymers and melamine-based polymers.
11. The over-coating agent for forming fine patterns according to
claim 10, wherein the water-soluble polymer contains
polymethacrylic acid and/or polymethyl methacrylate in a ratio of
5-35 mass % of the polymer, and polyacrylic acid and/or polymethyl
acrylate in a ratio of 35-75 mass % of the polymer.
12. The over-coating agent for forming fine patterns according to
claim 1, which is an aqueous solution having a concentration of
3-50 mass %.
13. A method of forming fine patterns comprising the steps of
covering a substrate having thereon photoresist patterns with the
over-coating agent for forming fine patterns according to claim 1,
then applying heat treatment to shrink the applied over-coating
agent under the action of heat so that the spacing between adjacent
photoresist patterns is lessened, and subsequently removing the
applied film of the over-coating agent substantially
completely.
14. The method of forming fine patterns according to claim 13,
wherein the heat treatment is performed by heating the substrate at
a temperature that does not cause thermal fluidizing of the
photoresist patterns on the substrate.
Description
[0001] This is a continuation of Ser. No. 11/116,251, filed Apr.
28, 2005, now abandoned.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to an over-coating agent for forming
fine patterns in the field of photolithographic technology and a
method of forming fine-line patterns using such agent. More
particularly, the invention relates to an over-coating agent for
forming or defining fine-line patterns, such as hole patterns and
trench patterns, that can meet today's requirements for higher
packing densities and smaller sizes of semiconductor devices.
[0004] 2. Description of the Related Art
[0005] In the manufacture of electronic components such as
semiconductor devices and liquid-crystal devices, there is employed
the photolithographic technology which, in order to perform a
treatment such as etching on the substrate, first forms a film
(photoresist layer) over the substrate using a so-called
radiation-sensitive photoresist which is sensitive to activating
radiations, then performs exposure of the film by selective
illumination with an activating radiation, performs development to
dissolve away the photoresist layer selectively to form an image
pattern (photoresist pattern), and forms a variety of patterns
including contact providing patterns such as a hole pattern and a
trench pattern using the photoresist pattern as a protective layer
(mask pattern).
[0006] With the recent increase in the need for higher packing
densities and smaller sizes of semiconductor devices, increasing
efforts are being made to form sufficiently fine-line patterns and
submicron-electronic fabrication capable of forming patterns with
linewidths of no more than 0.20 .mu.m is currently required. As for
the activating light rays necessary in the formation of mask
patterns, short-wavelength radiations such as KrF, ArF and F.sub.2
excimer laser beams and electron beams are employed. Further,
active R&D efforts are being made to find photoresist materials
as mask pattern formers that have physical properties adapted to
those short-wavelength radiations.
[0007] In addition to those approaches for realizing
submicron-electronic fabrication which are based on photoresist
materials, active R&D efforts are also being made on the basis
of pattern forming method with a view to finding a technology that
can provide higher resolutions than those possessed by photoresist
materials.
[0008] For example, JP-5-166717A discloses a method of forming fine
patterns which comprises the steps of defining patterns
(=photoresist-uncovered patterns) in a pattern-forming resist on a
substrate, then coating over entirely the substrate with a mixing
generating resist that is to be mixed with said pattern-forming
resist, baking the assembly to form a mixing layer on both
sidewalls and the top of the pattern-forming resist, and removing
the non-mixing portions of said mixing generating resist such that
the feature size of the photoresist-uncovered pattern is reduced by
an amount comparable to the dimension of said mixing layer.
JP-5-241348 discloses a pattern forming method comprising the steps
of depositing a resin, which becomes insoluble in the presence of
an acid, on a substrate having formed thereon a resist pattern
containing an acid generator, heat treating the assembly so that
the acid is diffused from the resist pattern into said resin
insoluble in the presence of an acid to form a given thickness of
insolubilized portion of the resist near the interface between the
resin and the resist pattern, and developing the resist to remove
the resin portion through which no acid has been diffused, thereby
ensuring that the feature size of the pattern is reduced by an
amount comparable to the dimension of said given thickness.
[0009] However, in these methods, it is difficult to control the
thickness of layers to be formed on the sidewalls of resist
patterns. In addition, the in-plane heat dependency of wafers is as
great as ten-odd nanometers per degree Celsius, so it is extremely
difficult to keep the in-plane uniformity of wafers by means of the
heater employed in current fabrication of semiconductor devices and
this leads to the problem of occurrence of significant variations
in pattern dimensions.
[0010] Another approach known to be capable of reducing pattern
dimensions is by fluidizing resist patterns through heat treatment
and the like. For example, JP-1-307228A discloses a method
comprising the steps of forming a resist pattern on a substrate and
applying heat treatment to deform the cross-sectional shape of the
resist pattern, thereby defining a fine pattern. In addition,
JP-4-364021A discloses a method comprising the steps of forming a
resist pattern and heating it to fluidize the resist pattern,
thereby changing the dimensions of its resist pattern to form or
define a fine-line pattern.
[0011] In these methods, the wafer's in-plane heat dependency is
only a few nanometers per degree Celsius and is not very
problematic. On the other hand, it is difficult to control the
resist deformation and fluidizing on account of heat treatment, so
it is not easy to provide a uniform resist pattern in a wafer's
plane.
[0012] An evolved version of those methods is disclosed in
JP-7-45510A and it comprises the steps of forming a resist pattern
on a substrate, forming a stopper resin on the substrate to prevent
excessive thermal fluidizing of the resist pattern, then applying
heat treatment to fluidize the resist so as to change the
dimensions of its pattern, and thereafter removing the stopper
resin to form or define a fine-line pattern. As the stopper resin,
a water-soluble resin, specifically, polyvinyl alcohol is employed
singly. However, polyvinyl alcohol alone is not highly soluble in
water and cannot be readily removed completely by washing with
water, introducing difficulty in forming a pattern of good profile.
The pattern formed is not completely satisfactory in terms of
stability over time. In addition, polyvinyl alcohol cannot be
applied efficiently by coating. Because of these and other
problems, the method disclosed in JP-7-45510 has yet to be adopted
commercially.
[0013] For solving these prior-art problems, the present applicant
has proposed a technique directed to an over-coating agent for
forming fine patterns and to a method of forming fine patterns in
JP 2003-084459A, JP 2003-084460A, JP 2003-107752A, JP 2003-142381A,
JP 2003-195527A, and JP 2003-202679A, etc. The technique shown in
these patent publications has made it possible to form fine-line
patterns that satisfy pattern dimension controllability, good
profile and other necessary properties for semiconductor
devices.
[0014] In the technique of forming fine-line patterns using the
above over-coating agent for forming fine patterns, a photoresist
layer is first formed on a substrate and this is exposed to light
and developed to form a photoresist pattern (mask pattern). Next,
the over-coating agent for forming fine patterns is applied to
cover the entire surface of the substrate, and then this is heated,
whereby the width of the photoresist pattern lines is enlarged by
utilizing the thermal shrinking effect of the over-coating agent
for forming fine patterns, and, as a result, the distance between
the adjacent photoresist pattern lines is thereby narrowed and the
width of the pattern line (of various patterns such as hole
pattern, and trench pattern) to be determined by the distance
between the photoresist pattern lines is also narrowed to give
finer trace patterns.
[0015] The above-mentioned forming fine-line pattern process
undergoes the influence of pattern dimension control in two stages:
that is, a photoresist patterning stage (first stage) and a thermal
shrinking stage of the over-coating agent for forming fine patterns
(second stage). In the process comprising said two stages, when
photoresist patterning is performed by increasing the luminous
exposure of light to which a photoresist is exposed in the first
stage, the degree of thermal shrinkage of the over-coating agent in
the second stage is apt to be larger than the expected degree
thereof and, as a result, it is often difficult to anticipate the
dimension controllability in forming fine-line patterns in the
process.
[0016] In that situation, it is desirable that the degree of
thermal shrinkage of the over-coating agent could be kept constant
even when the luminous exposure is varied relative to CD (critical
dimension) of the photoresist pattern just after development.
[0017] In addition, it is also desirable that, even when various
patterns differing in the pattern dimension and the line-to-line
distance exist on one substrate, all the patterns could enjoy the
same degree of thermal shrinkage.
[0018] In view of the shape of photoresist patterns, even when
photoresist patterns having a good rectangular cross-sectional
profile could be formed in the photoresist patterning stage (first
stage), there may occur in the second stage a problematic
phenomenon that the top of the photoresist pattern may be rounded
owing to the thermal shrinkage of the over-coating agent applied
thereto for forming fine patterns. In particular, when an ArF
photoresist is used for forming finer line patterns, the top of the
photoresist pattern could not keep the original rectangular profile
thereof but is often rounded in the thermal shrinkage step for the
over-coating agent applied onto the photoresist pattern.
[0019] Accordingly, an over-coating agent for forming fine patterns
has been studied and developed, which ensures a high degree of
thermal shrinkage and a large exposure margin and enables pattern
dimension control while keeping a good photoresist pattern profile
as such.
[0020] JP 2001-281886A discloses a method comprising the steps of
covering a surface of a resist pattern with an acidic film made of
a resist pattern size reducing material containing a water-soluble
resin, rendering the surface layer of the resist pattern
alkali-soluble, then removing said surface layer and the acidic
film with an alkaline solution to reduce the feature size of the
resist pattern. JP-2002-184673A discloses a method comprising the
steps of forming a resist pattern on a substrate, then forming a
film containing a water-soluble film forming component on said
resist pattern, heat treating said resist pattern and film, and
immersing the assembly in an aqueous solution of
tetramethylammonium hydroxide, thereby forming a fine-line resist
pattern without involving a dry etching step. However, both methods
are simply directed to reducing the size of resist trace patterns
themselves and therefore are totally different from the present
invention in object.
SUMMARY OF THE INVENTION
[0021] The present invention has been accomplished in order to
solve the aforementioned problems of the prior art and has as an
object providing an over-coating agent for forming fine line
patterns whose advantages are that, in forming fine line patterns
utilizing the over-coating agent, the exposure margin is large, the
photoresist pattern dimension control can be reflected on the
fine-line pattern dimension control, the photoresist pattern
profile is kept rectangular after a step of thermal shrinkage while
its top is prevented from being rounded, and the degree of thermal
shrinkage of the over-coating agent is large relative to the
heating temperature at which the agent is heated.
[0022] Another object of the invention is to provide a method of
forming fine trace patterns using the over-coating agent.
[0023] In order to attain the first object, the present invention
provides an over-coating agent for forming fine patterns which is
applied to cover a substrate having photoresist patterns thereon
and allowed to shrink under heat so that the spacing between
adjacent photoresist patterns is lessened, further characterized by
comprising a water-soluble polymer which contains at least
methacrylic acid and/or methyl methacrylate as the constitutive
monomer thereof.
[0024] In order to attain the second object, the present invention
provides a method of forming fine patterns comprising the steps of
covering a substrate having thereon photoresist patterns with the
above-described over-coating agent for forming fine patterns, then
applying heat treatment to shrink the applied over-coating agent
under the action of heat so that the spacing between adjacent
photoresist patterns is lessened, and subsequently removing the
applied film of the over-coating agent substantially
completely.
[0025] In a preferred embodiment, the heat treatment is performed
by heating the assembly at a temperature that does not cause
thermal fluidizing of the photoresist patterns on the
substrate.
DETAILED DESCRIPTION OF THE INVENTION
[0026] The over-coating agent of the invention for forming fine
features of patterns is applied to cover a substrate, having
photoresist patterns (mask patterns) thereon, including patterns
typified by hole patterns or trench patterns, each of these
patterns are defined by spacing between adjacent photoresist
patterns (mask patterns). Upon heating, the applied film of
over-coating agent shrinks to increase the width of each of the
photoresist patterns, thereby narrowing or lessening adjacent hole
patterns or trench patterns as defined by spacing between the
photoresist patterns and, thereafter, the applied film is removed
substantially completely to form or define fine patterns.
[0027] The phrase "removing the applied film substantially
completely" as used herein means that after lessening the spacing
between adjacent photoresist patterns by the heat shrinking action
of the applied over-coating agent, said film is removed in such a
way that no significant thickness of the over-coating agent will
remain at the interface with the photoresist patterns. Therefore,
the present invention does not include methods in which a certain
thickness of the over-coating agent is left intact near the
interface with the photoresist pattern so that the feature size of
the pattern is reduced by an amount corresponding to the residual
thickness of the over-coating agent.
[0028] The over-coating agent for forming fine patterns of the
invention comprises a water-soluble polymer that contains at least
methacrylic acid and/or methyl methacrylate as the constitutive
monomer thereof.
[0029] Since the water-soluble polymer in the agent contains
methacrylic acid and/or methyl methacrylate as the constitutive
monomer thereof, it is possible to significantly improve the degree
of thermal shrinkage of the over-coating agent to thereby reduce
the line-to-line distance of the photoresist pattern during the
thermal shrinkage of the agent under heat treatment while keeping
the photoresist pattern profile as such.
[0030] For preferred embodiments of the over-coating agent of the
invention, the water-soluble polymer is preferably any of the
following embodiments (i) to (iv), to which, however, the invention
should not be limited.
[0031] (i) The water-soluble polymer is a copolymer of methacrylic
acid and/or methyl methacrylate with at least one monomer selected
from those constituting alkylene glycol-based polymers, cellulosic
derivatives, vinylic polymers, acrylic polymers, urea-based
polymers, epoxy polymers, amide-based polymers and melamine-based
polymers (in which the monomers to constitute acrylic polymers do
not include methacrylic acid and methyl methacrylate).
[0032] The monomers to constitute alkylene glycol-based polymers
include, for example, ethylene glycol and propylene glycol.
[0033] The monomers to constitute cellulosic derivatives include,
for example, hydroxypropylmethyl cellulose phthalate,
hydroxypropylmethyl cellulose acetate phthalate,
hydroxypropylmethyl cellulose hexahydrophthalate,
hydroxypropylmethyl cellulose acetate succinate,
hydroxypropylmethyl cellulose, hydroxypropyl cellulose,
hydroxyethyl cellulose, cellulose acetate hexahydrophthalate,
carboxymethyl cellulose, ethyl cellulose and methyl cellulose.
[0034] The monomers to constitute vinylic polymers include, for
example, N-vinylpyrrolidone, vinylimidazolidinone and vinyl
acetate.
[0035] The monomers to constitute acrylic polymers (excluding
methacrylic acid and methyl methacrylate) include, for example,
acrylic acid, methyl acrylate, N,N-dimethylacrylamide,
N,N-dimethylaminopropylmethacrylamide,
N,N-dimethylaminopropylacrylamide, N-methylacrylamide,
diacetoneacrylamide, N,N-dimethylaminoethyl methacrylate,
N,N-diethylaminoethyl methacrylate, N,N-dimethylaminoethyl acrylate
and acryloylmorpholine.
[0036] The monomers to constitute urea-based polymers include, for
example, methylolated urea, dimethylolated urea and
ethylene-urea.
[0037] The monomers to constitute melamine-based polymers include,
for example, methoxymethylated melamine, methoxymethylated
isobutoxymethylated melamine and methoxyethylated melamine.
[0038] Of monomers constituting epoxy polymers and amide-based
polymers, water-soluble monomers are usable herein.
[0039] In the copolymer of methacrylic acid and/or methyl
methacrylate with the monomer to constitute the above-mentioned
polymers, the monomer preferably accounts for 60-99 mass %, more
preferably 80-99 mass % of methacrylic acid and/or methyl
methacrylate.
[0040] (ii) The water-soluble polymer is a copolymer or a mixed
resin of polymethacrylic acid and/or polymethyl methacrylate with
at least one polymer selected from alkylene glycol-based polymers,
cellulosic derivatives, vinylic polymers, acrylic polymers
(excluding polymethacrylic acid and polymethyl methacrylate),
urea-based polymers, epoxy polymers, amide-based polymers and
melamine-based polymers.
[0041] Preferably, the alkylene glycol-based polymers, the
cellulosic derivatives, the vinylic polymers, the acrylic polymers
(excluding polymethacrylic acid and polymethyl methacrylate), the
urea-based polymers, the epoxy polymers, the amide-based polymers
and the melamine-based polymers are those comprising any of the
above-mentioned constitutive monomers.
[0042] Preferably, the content of polymethacrylic acid and/or
polymethyl methacrylate in the water-soluble polymer is 60-99 mass
%, more preferably 80-99 masse.
[0043] (iii) The water-soluble polymer is a copolymer of
methacrylic acid and/or methyl methacrylate, acrylic acid and/or
methyl acrylate, and at least one monomer selected from those
constituting alkylene glycol-based polymers, cellulosic
derivatives, vinylic polymers, acrylic polymers, urea-based
polymers, epoxy polymers, amide-based polymers and melamine-based
polymers (in which the monomers to constitute acrylic polymers do
not include methacrylic acid, methyl methacrylate, acrylic acid and
methyl acrylate).
[0044] Preferably, the alkylene glycol-based polymers, the
cellulosic derivatives, the vinylic polymers, the acrylic polymers,
the urea-based polymers, the epoxy polymers, the amide-based
polymers and the melamine-based polymers (in which the monomers
constituting acrylic polymers do not include methacrylic acid,
methyl methacrylate, acrylic acid and methyl acrylate) are those
comprising any of the above-mentioned constitutive monomers.
[0045] In the copolymer of methacrylic acid and/or methyl
methacrylate with the monomer constituting the above-mentioned
polymers, the monomer preferably accounts for 5-35 mass %, more
preferably 10-25 mass % of methacrylic acid and/or methyl
methacrylate. Also preferably, the content of acrylic acid and/or
methyl acrylate in the water-soluble copolymer is 35-75 mass %,
more preferably 50-70 mass %.
[0046] (iv) The water-soluble polymer is a copolymer or a mixed
resin of polymethacrylic acid and/or polymethyl methacrylate,
polyacrylic acid and/or polymethyl acrylate, and at least one
polymer selected from alkylene glycol-based polymers, cellulosic
derivatives, vinylic polymers, acrylic polymers (excluding
polymethacrylic acid, polymethyl methacrylate, polyacrylic acid and
polymethyl acrylate), urea-based polymers, epoxy polymers,
amide-based polymers and melamine-based polymers.
[0047] Preferably, the alkylene glycol-based polymers, the
cellulosic derivatives, the vinylic polymers, the acrylic polymers
(excluding polymethacrylic acid, polymethyl methacrylate,
polyacrylic acid and polymethyl acrylate), the urea-based polymers,
the epoxy polymers, the amide-based polymers and the melamine-based
polymers are those comprising any of the above-mentioned
constitutive monomers.
[0048] Preferably, the content of polymethacrylic acid and/or
polymethyl methacrylate in the water-soluble polymer is 5-35 mass
%, more preferably 10-25 mass %. Also preferably, the content of
polyacrylic acid and/or polymethyl acrylate in the water-soluble
polymer is 35-75 mass %, more preferably 50-70 mass %.
[0049] Comprising the water-soluble polymer of the above-mentioned
embodiments (i) to (iv), the over-coating agent for forming
fine-line patterns of the invention carries the advantages that the
exposure margin is large and the dimension control of photoresist
patterns can be reflected on the dimension controllability of
fine-line patterns, and therefore it enjoys the best effects of
invention in that the dimension control and planning of fine-line
patterns which is obtained after treatment for thermal shrinkage
can be attained with ease in the stage of photoresist patterning;
that the original photoresist pattern profile can be kept as such
and the top of the photoresist pattern is not rounded after thermal
shrinkage; that the degree of thermal shrinkage of the over-coating
agent relative to the temperature at which the over-coating agent
is heated can be increased more than that in conventional
technology; and that the intended fine-line patterns can be formed
more efficiently.
[0050] In particular, the embodiments (iii) and (iv) comprising
(poly)methacrylic acid (ester) and additionally (poly)acrylic acid
(ester) are especially preferred as compared with the embodiments
(i) and (ii), since the exposure margin can be broadened more while
the degree of thermal shrinkage can be kept on the same level, and
since they are more effective for smoothing the profile of the side
wall of pattern lines (smoothing effect).
[0051] In the embodiments (i) to (iv), the polymer to be selected
preferably comprises at lease one polymer selected from alkylene
glycol-based polymers, cellulosic derivatives, vinylic polymers and
acrylic polymers. One or more additional polymers may be in the
copolymer. Preferred examples of the additional polymers in the
invention are polyvinylpyrrolidone, polyvinylimidazole and
acryloylmorpholine.
[0052] The over-coating agent for forming fine patters may
additionally contain water-soluble amines. For special purposes
such as preventing the generation of impurities and pH adjustment,
water-soluble amines that have pKa (acid dissociation constant)
values of 7.5-13 in aqueous solution at 25.degree. C. are
preferably used. Specific examples include the following:
alkanolamines, such as monoethanolamine, diethanolamine,
triethanolamine, 2-(2-aminoethoxy)ethanol,
N,N-dimethylethanolamine, N,N-diethylethanolamine,
N,N-dibutylethanolamine, N-methylethanolamine, N-ethylethanolamine,
N-butylethanolamine, N-methyldiethanolamine, monoisopropanolamine,
diisopropanolamine and triisopropanolamine; polyalkylenepolyamines,
such as diethylenetriamine, triethylenetetramine, propylenediamine,
N,N-diethylethylenediamine, 1,4-butanediamine,
N-ethylethylenediamine, 1,2-propanediamine, 1,3-propanediamine and
1,6-hexanediamine; aliphatic amines, such as triethylamine,
2-ethyl-hexylamine, dioctylamine, tributylamine, tripropylamine,
triallylamine, heptylamine and cyclohexylamine; aromatic amines,
such as benzylamine and diphenylamine; and cyclic amines, such as
piperazine, N-methyl-piperazine and hydroxyethylpiperazine.
Preferred ones are aliphatic amines in view of easiness of keeping
shapes of patterns, as exemplified by triethylamine.
[0053] If the water-soluble amine is to be added, it is preferably
incorporated in an amount of about 0.1-30 mass %, more preferably
about 2-15 mass %, of the over-coating agent (in terms of solids
content). If the water-soluble amine is incorporated in an amount
of less than 0.1 mass %, the coating fluid may deteriorate over
time. If the water-soluble amine is incorporated in an amount
exceeding 30 mass %, the photoresist pattern being formed may
deteriorate in shape.
[0054] For such purposes as reducing the dimensions of patterns and
controlling the occurrence of defects, the over-coating agent for
forming fine patterns may further optionally contain non-amine
based, water-soluble organic solvents.
[0055] As such non-amine based, water-soluble organic solvents, any
non-amine based organic solvents that can mix with water may be
employed and they may be exemplified by the following: sulfoxides,
such as dimethyl sulfoxide; sulfones, such as dimethylsulfone,
diethylsulfone, bis(2-hydroxyethyl)sulfone and
tetramethylenesulfone; amides, such as N,N-dimethylformamide,
N-methylformamide, N,N-dimethylacetamide, N-methylacetamine and
N,N-diethylacetamide; lactams, such as N-methyl-2-pyrrolidone,
N-ethyl-2-pyrrolidone, N-propyl-2-pyrrolidone,
N-hydroxymethyl-2-pyrrolidone and N-hydroxyethyl-2-pyrrolidone;
imidazolidinones, such as 1,3-dimethyl-2-imidazolidinone,
1,3-diethyl-2-imidazolidinone and
1,3-diisopropyl-2-imidazolidinone; and polyhydric alcohols and
derivatives thereof, such as ethylene glycol, ethylene glycol
monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol
monobutyl ether, ethylene glycol monomethyl ether acetate, ethylene
glycol monoethyl ether acetate, diethylene glycol, diethylene
glycol monomethyl ether, diethylene glycol monoethyl ether,
diethylene glycol monobutyl ether, propylene glycol, propylene
glycol monomethyl ether, glycerol, 1,2-butylene glycol,
1,3-butylene glycol and 2,3-butylene glycol. Among those mentioned
above, polyhydric alcohols and their derivatives are preferred for
the purposes of reducing the dimensions of patterns and controlling
the occurrence of defects and glycerol is particularly preferred.
The non-amine based, water-soluble organic solvents may be used
either singly or in combination.
[0056] If the non-amine based, water-soluble organic solvent is to
be added, it is preferably incorporated in an amount of about
0.1-30 mass %, more preferably about 0.5-15 mass %, of the
water-soluble polymer. If the non-amine based, water-soluble
organic solvent is incorporated in an amount of less than 0.1 mass
%, its defect reducing effect tends to decrease. Beyond 30 mass %,
a mixing layer is liable to form at the interface with the
photoresist pattern.
[0057] In addition, the over-coating agent may optionally contain a
surfactant for attaining special effects such as coating uniformity
and wafer's in-plane uniformity.
[0058] The surfactant is preferably employed that, when added to
the water-soluble polymer, exhibits certain characteristics such as
high solubility, non-formation of a suspension and miscibility with
the polymer component. By using surfactants that satisfy these
characteristics, the occurrence of defects can be effectively
controlled that is considered to be pertinent to forming fine-line
patters upon coating the over-coating agent.
[0059] From the points above, surfactants in the invention are
preferably employed at least the one selected among
N-alkylpyrrolidones, quaternary ammonium salts and phosphate esters
of polyoxyethylene.
[0060] N-alkylpyrrolidones as surfactant are preferably represented
by the following general formula (I): ##STR1## where R.sub.1 is an
alkyl group having at least 6 carbon atoms.
[0061] Specific examples of N-alkylpyrrolidones as surfactant
include N-hexyl-2-pyrrolidone, N-heptyl-2-pyrrolidone,
N-octyl-2-pyrrolidone, N-nonyl-2-pyrrolidone,
N-decyl-2-pyrrolidone, N-undecyl-2-pyrrolidone,
N-dodecyl-2-pyrrolidone, N-tridecyl-2-pyrrolidone,
N-tetradecyl-2-pyrrolidone, N-pentadecyl-2-pyrrolidone,
N-hexadecyl-2-pyrrolidone, N-heptadecyl-2-pyrrolidone and
N-octadecyl-2-pyrrolidone. Among these, N-octyl-2-pyrrolidone
("SURFADONE LP 100" of ISP Inc.) is preferably used.
[0062] Quaternary ammonium salts as surfactant are preferably
represented by the following general formula (II): ##STR2## where
R.sub.2, R.sub.3, R.sub.4 and R.sub.5 are each independently an
alkyl group or a hydroxyalkyl group (provided that at least one of
them is an alkyl or hydroxyalkyl group having not less than 6
carbon atoms); X.sup.- is a hydroxide ion or a halogenide ion.
[0063] Specific examples of quaternary ammonium salts as surfactant
include dodecyltrimethylammonium hydroxide,
tridecyltrimethylammonium hydroxide, tetradecyltrimethylammonium
hydroxide, pentadecyltrimethylammonium hydroxide,
hexadecyltrimethylammonium hydroxide, heptadecyltrimethylammonium
hydroxide and octadecyltrimethylammonium hydroxide. Among these,
hexadecyltrimethylammonium hydroxide is preferably used.
[0064] Phosphate esters of polyoxyethylene are preferably
represented by the following general formula (III): ##STR3## where
R.sub.6 is an alkyl or alkylaryl group having 1-10 carbon atoms;
R.sub.7 is a hydrogen atom or (CH.sub.2CH.sub.2O)R.sub.6 (where
R.sub.6 is as defined above); n is an integer of 1-20.
[0065] To mention specific examples, phosphate esters of
polyoxyethylene that can be used as surfactants are commercially
available under trade names "PLYSURF A212E" and "PLYSURF A210G"
from Dai-ichi Kogyo Seiyaku Co., Ltd.
[0066] If the surfactant is to be added, it is preferably
incorporated in an amount of about 0.1-10 masse, more preferably
about 0.2-2 mass %, of the over-coating agent (in terms of solids
content). By adopting the amount as described above ranges, it may
effectively prevent the variations in the percent shrinkage of
patterns, potentially depending on the wafer's in-plane uniformity
which is caused by the deterioration of coating property, and also
prevent the occurrence of defects that are considered to have
cause-and-effect relations with microfoaming on the applied film
that generates as the coating conditions are worsened.
[0067] The over-coating agent of the invention for forming fine
patterns is preferably used as an aqueous solution at a
concentration of 3-50 mass %, more preferably at 5-30 mass %. If
the concentration of the aqueous solution is less than 3 mass %,
poor coverage of the substrate may result. If the concentration of
the aqueous solution exceeds 50 mass %, there is no appreciable
improvement in the intended effect that justifies the increased
concentration and the solution cannot be handled efficiently.
[0068] As already mentioned, the over-coating agent of the
invention for forming fine patterns is usually employed as an
aqueous solution using water as the solvent. A mixed solvent system
comprising water and an alcoholic solvent may also be employed.
Exemplary alcoholic solvents are monohydric alcohols including
methyl alcohol, ethyl alcohol, propyl alcohol and isopropyl
alcohol. These alcoholic solvents are mixed with water in amounts
not exceeding about 30 mass %.
[0069] The over-coating agent for forming fine patterns of the
invention carries the advantages that the exposure margin is large
and the dimension control of photoresist patterns can be reflected
on the dimension control of forming fine-line patterns, that the
photoresist pattern profile after thermal shrinkage stage can be
kept rectangular and the top thereof is prevented from being
rounded, and that the degree of thermal shrinkage of the
over-coating agent is large relative to the temperature at which
the agent is heated.
[0070] The method of forming fine-line patterns according to the
second aspect of the invention comprises the steps of covering a
substrate having photoresist patterns thereon with the
above-described over-coating agent for forming fine patterns, then
applying heat treatment to shrink the applied over-coating agent
under the action of heat so that the spacing between adjacent
photoresist patterns is reduced, and subsequently removing the
applied film of the over-coating agent substantially
completely.
[0071] The method of preparing the substrate having photoresist
patterns thereon is not limited to any particular type and it can
be prepared by conventional methods employed in the fabrication of
semiconductor devices, liquid-crystal display devices, magnetic
heads and microlens arrays. In an exemplary method, a photoresist
composition of chemically amplifiable or other type is spin- or
otherwise coated on a substrate such as a silicon wafer and dried
to form a photoresist layer, which is illuminated with an
activating radiation such as ultraviolet, deep-ultraviolet or
excimer laser light through a desired mask pattern using a
reduction-projection exposure system or subjected to electron beam
photolithography, then heated and developed with a developer such
as an alkaline aqueous solution, typically a 1-10 mass %
tetramethylammonium hydroxide (TMAH) aqueous solution, thereby
forming a photoresist pattern on the substrate.
[0072] The photoresist composition serving as a material from which
photoresist patterns are formed is not limited in any particular
way and any common photoresist compositions may be employed
including those for exposure to i- or g-lines, those for exposure
with an excimer laser (e.g. KrF, ArF or F.sub.2) and those for
exposure to EB (electron beams). According to the invention, even
in a photoresist having a low thermal flow temperature of around
150.degree. C. or lower, the top of the photoresist pattern can be
prevented from being rounded, and while the degree of thermal
shrinkage of the over-coating agent is kept as such, the exposure
margin may be broadened. Still another advantage of the invention
is that the controllability in patterning is good.
[a.] Over-Coating Agent Application Step
[0073] After thusly forming the photoresist pattern as a mask
pattern, the over-coating agent for forming fine patterns is
applied to cover entirely the substrate. After applying the
over-coating agent, the substrate may optionally be pre-baked at a
temperature of 80-100.degree. C. for 30-90 seconds.
[0074] The over-coating agent may be applied by any methods
commonly employed in the conventional heat flow process.
Specifically, an aqueous solution of the over-coating agent for
forming fine patterns is applied to the substrate by any known
application methods including bar coating, roll coating and whirl
coating with a spinner.
[b.] Heat Treatment (Thermal Shrinkage) Step
[0075] In the next step, heat treatment is performed to cause
thermal shrinkage of the film of the over-coating agent. Under the
resulting force of thermal shrinkage of the film, the dimensions of
the photoresist pattern in contact with the film will increase by
an amount equivalent to the thermal shrinkage of the film and, as
the result, the photoresist pattern widens and accordingly the
spacing between adjacent photoresist patterns lessens. The spacing
between adjacent photoresist patterns determines the diameter or
width of the pattern elements to be finally obtained, so the
decrease in the spacing between adjacent photoresist patterns
contributes to reducing the diameter of each element of a hole
pattern or the width of each element of a trench pattern,
eventually leading to the definition of a pattern with smaller
feature sizes.
[0076] The heating temperature is not limited to any particular
value as long as it is high enough to cause thermal shrinkage of
the film of the over-coating agent and form or define a fine
pattern. Heating is preferably done at a temperature that will not
cause thermal fluidizing of the photoresist pattern. The
temperature that will not cause thermal fluidizing of the
photoresist pattern is such a temperature that when a substrate on
which the photoresist pattern has been formed but no film of the
over-coating agent has been formed is heated, the photoresist
pattern will not experience any dimensional changes. Performing a
heat treatment under such temperature conditions is very effective
for various reasons, e.g. a fine-line pattern of good profile can
be formed more efficiently and the duty ratio in the plane of a
wafer, or the dependency on the spacing between photoresist
patterns in the plane of a wafer, can be reduced. Considering the
softening points of a variety of photoresist compositions employed
in current photolithographic techniques, the preferred heat
treatment is usually performed within a temperature range of about
80-160.degree. C. for 30-90 seconds, provided that the temperature
is not high enough to cause thermal fluidizing of the
photoresist.
[c.] Over-Coating Agent Removal Step
[0077] In the subsequent step, the remaining film of the
over-coating agent on the patterns is removed by washing with an
aqueous solvent, preferably pure water, for 10-60 seconds. Prior to
washing with water, rinsing may optionally be performed with an
aqueous solution of alkali (e.g. tetramethylammonium hydroxide
(TMAH) or choline). The over-coating agent of the present invention
is easy to remove by washing with water and it can be completely
removed from the substrate and the photoresist pattern.
[0078] As a result, each pattern on the substrate has a smaller
feature size because each pattern is defined by the narrowed
spacing between the adjacent widened photoresist patterns.
[0079] The fine-line pattern thus formed using the over-coating
agent of the present invention has a pattern size smaller than the
resolution limit attainable by the conventional methods. In
addition, it has a good enough profile and physical properties that
can fully satisfy the characteristics required of semiconductor
devices.
[0080] Steps [a.]-[c.] may be repeated several times. By repeating
steps [a.]-[c.] several times, the photoresist trace patterns (mask
patterns) can be progressively widened.
[0081] The technical field of the present invention is not limited
to the semiconductor industry and it can be employed in a wide
range of applications including the fabrication of liquid-crystal
display devices, the production of magnetic heads and even the
manufacture of microlens arrays.
EXAMPLES
[0082] The following examples are provided for further illustrating
the present invention but are in no way to be taken as limiting.
Unless otherwise noted, all amounts of ingredients are expressed in
mass %.
Example 1
[0083] A copolymer of methacrylic acid and vinylpyrrolidone (2 g;
polymerization ratio=9:1), triethylamine (0.12 g) and a
polyoxyethylene phosphate ester surfactant (0.02 g; "PLYSURF
A210G", product of Dai-ichi Kogyo Seiyaku Co, Ltd.) were dissolved
in water (27 g) to prepare an over-coating agent.
[0084] A substrate was whirl coated with a positive-acting
photoresist TARF-P7052 (product of Tokyo Ohka Kogyo Co., Ltd.) and
baked at 150.degree. C. for 90 seconds to form a photoresist layer
in a thickness of 0.34 .mu.m.
[0085] The photoresist layer was exposed with an exposure unit
(NSR-S302, product of Nikon Corp.), subjected to heat treatment at
100.degree. C. for 90 seconds and developed with an aqueous
solution of 2.38 mass % TMAH (tetramethylammonium hydroxide) to
form photoresist patterns which defined hole patterns with an each
diameter of 140.2 nm (i.e., the spacing between the photoresist
patterns, or the initial hole dimension, was 140.2 nm).
[0086] The previously prepared over-coating agent was applied onto
the substrate including hole patterns and subjected to heat
treatment at 155.degree. C. for 60 seconds, thereby reducing the
each size of the hole patterns. Subsequently, the substrate was
brought into contact with pure water at 23.degree. C. to remove the
over-coating agent. The each diameter of the hole patterns was
reduced to 120.5 nm. The photoresist pattern profile was kept
rectangular and its top was prevented from being rounded.
Example 2
[0087] A copolymer of methacrylic acid and vinylpyrrolidone (1 g;
polymerization ratio=9:1), a copolymer of acrylic acid and
vinylpyrrolidone (1 g; polymerization ratio=2:1), triethylamine
(0.12 g) and a polyoxyethylene phosphate ester surfactant (0.02 g;
"PLYSURF A210G", product of Dai-ichi Kogyo Seiyaku Co, Ltd.) were
dissolved in water (27 g) to prepare an over-coating agent.
[0088] A substrate was whirl coated with a positive-acting
photoresist TARF-P7052 (product of Tokyo Ohka Kogyo Co., Ltd.) and
baked at 115.degree. C. for 90 seconds to form a photoresist layer
in a thickness of 0.34 .mu.m.
[0089] The photoresist layer was exposed with an exposure unit
(NSR-S302, product of Nikon Corp.), subjected to heat treatment at
100.degree. C. for 90 seconds and developed with an aqueous
solution of 2.38 mass % TMAH (tetramethylammonium hydroxide) to
form photoresist patterns which defined hole patterns with an each
diameter of 140.2 nm (i.e., the spacing between the photoresist
patterns, or the initial hole dimension, was 140.2 nm).
[0090] The previously prepared over-coating agent was applied onto
the substrate including hole patterns and subjected to heat
treatment at 155.degree. C. for 60 seconds, thereby reducing the
each size of the hole patterns. Subsequently, the substrate was
brought into contact with pure water at 23.degree. C. to remove the
over-coating agent. The each diameter of the hole patterns was
reduced to 119.7 nm. The photoresist pattern profile was kept
rectangular and its top was prevented from being rounded.
Example 3
[0091] A copolymer of methacrylic acid, acrylic acid and
vinylpyrrolidone (2 g; polymerization ratio=17:60:23),
triethylamine (0.12 g) and a polyoxyethylene phosphate ester
surfactant (0.02 g; "PLYSURF A210G", product of Dai-ichi Kogyo
Seiyaku Co, Ltd.) were dissolved in water (27 g) to prepare an
over-coating agent.
[0092] A substrate was whirl coated with a positive-acting
photoresist TARF-P7052 (product of Tokyo Ohka Kogyo Co., Ltd.) and
baked at 115.degree. C. for 90 seconds to form a photoresist layer
in a thickness of 0.34 .mu.m.
[0093] The photoresist layer was exposed with an exposure unit
(NSR-S302, product of Nikon Corp.), subjected to heat treatment at
100.degree. C. for 90 seconds and developed with an aqueous
solution of 2.38 mass % TMAH (tetramethylammonium hydroxide) to
form photoresist patterns which defined hole patterns with an each
diameter of 140.2 nm (i.e., the spacing between the photoresist
patterns, or the initial hole dimension, was 140.2 nm).
[0094] The previously prepared over-coating agent was applied onto
the substrate including hole patterns and subjected to heat
treatment at 155.degree. C. for 60 seconds, thereby reducing the
each size of the hole patterns. Subsequently, the substrate was
brought into contact with pure water at 23.degree. C. to remove the
over-coating agent. The each diameter of the hole patterns was
reduced to 119.5 nm. The photoresist pattern profile was kept
rectangular and its top was prevented from being rounded.
Comparative Example 1
[0095] A copolymer of acrylic acid and vinylpyrrolidone (2 g;
polymerization ratio=2:1), triethylamine (0.12 g) and a
polyoxyethylene phosphate ester surfactant (0.02 g; "PLYSURF
A210G", product of Dai-ichi Kogyo Seiyaku Co, Ltd.) were dissolved
in water (27 g) to prepare an over-coating agent.
[0096] The thusly prepared over-coating agent was then applied onto
the substrate including hole patterns that were formed in the same
manner as described in Example 1 (the initial hole dimension, was
140.2 nm), and subjected to heat treatment at 155.degree. C. for 60
seconds, thereby reducing the each size of the hole patterns.
Subsequently, the substrate was brought into contact with pure
water at 23.degree. C. to remove the over-coating agent. The each
diameter of the hole patterns was reduced to 119.9 nm, however the
top of the photoresist pattern was rounded.
[0097] As described in detail hereinabove, the over-coating agent
for forming fine patterns of the invention carries the advantages
that the exposure margin is large and the dimension control of
photoresist patterns can be reflected on the dimension control of
forming fine-line patterns, that the photoresist pattern profile
after thermal shrinkage stage can be kept rectangular and the top
thereof is prevented from being rounded, and that the degree of
thermal shrinkage of the over-coating agent is large relative to
the temperature at which the agent is heated.
* * * * *