U.S. patent application number 12/320979 was filed with the patent office on 2009-06-11 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.
Application Number | 20090148611 12/320979 |
Document ID | / |
Family ID | 30002322 |
Filed Date | 2009-06-11 |
United States Patent
Application |
20090148611 |
Kind Code |
A1 |
Sugeta; Yoshiki ; et
al. |
June 11, 2009 |
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 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, with the applied
film of the over-coating agent being removed substantially
completely to form or define fine trace patterns, further
characterized by containing either a water-soluble polymer and an
amide group-containing monomer or a water-soluble polymer which
contains at least (meth)acrylamide as a monomeric component. Also
disclosed is a method of forming fine-line patterns using any one
of said over-coating agents. According to the invention, the
thermal shrinkage of the over-coating agent for forming fine
patterns in the heat treatment can be extensively increased, and
one can obtain fine-line patterns which exhibit good profiles while
satisfying the characteristics required of semiconductor
devices.
Inventors: |
Sugeta; Yoshiki; (Kanagawa,
JP) ; Kaneko; Fumitake; (Kanagawa, JP) ;
Tachikawa; Toshikazu; (Kanagawa, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
1030 15th Street, N.W.,, Suite 400 East
Washington
DC
20005-1503
US
|
Family ID: |
30002322 |
Appl. No.: |
12/320979 |
Filed: |
February 10, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10519542 |
Apr 27, 2005 |
|
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PCT/JP03/08156 |
Jun 26, 2003 |
|
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12320979 |
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Current U.S.
Class: |
427/386 ;
106/200.3; 427/385.5; 523/455; 524/210 |
Current CPC
Class: |
H01L 51/007 20130101;
G03F 7/40 20130101 |
Class at
Publication: |
427/386 ;
524/210; 427/385.5; 106/200.3; 523/455 |
International
Class: |
B05D 3/00 20060101
B05D003/00; C08K 5/20 20060101 C08K005/20; C09D 101/00 20060101
C09D101/00; C09D 163/00 20060101 C09D163/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 28, 2002 |
JP |
2002-191055 |
Jun 28, 2002 |
JP |
2002-191056 |
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, with the applied film of the
over-coating agent being removed substantially completely to form
fine patterns, further characterized by containing a water-soluble
polymer and an amide group-containing monomer.
2. The over-coating agent for forming fine patterns according to
claim 1, wherein the amide group-containing monomer is an amide
compound which is represented by the general formula (I):
##STR00005## where R.sub.1 is a hydrogen atom, an alkyl or
hydroxyalkyl group having 1-5 carbon atoms; R.sub.2 is an alkyl
group having 1-5 carbon atoms; R.sub.3 is a hydrogen atom or a
methyl group; and m is a number of 0-5.
3. The over-coating agent for forming fine patterns according to
claim 2, wherein in the general formula (I), R.sub.1 is a hydrogen
atom, a methyl group or an ethyl group; and m is 0.
4. The over-coating agent for forming fine patterns according to
claim 1, wherein the amide group-containing monomer is acrylamide
and/or methacrylamide.
5. The over-coating agent for forming fine patterns according to
claim 1, which contains 0.1-30 mass % of the amide group-containing
monomer in the over-coating agent (as solids).
6. The over-coating agent for forming fine patterns according to
claim 1, wherein the water-soluble polymer is at least one member
selected from the group consisting of alkylene glycolic polymers,
cellulosic derivatives, vinyl polymers, acrylic polymers, urea
polymers, epoxy polymers, melamine polymers and amide polymers.
7. The over-coating agent for forming fine patterns according to
claim 1, wherein the water-soluble polymer is at least one member
selected from the group consisting of alkylene glycolic polymers,
cellulosic derivatives, vinyl polymers and acrylic polymers.
8. 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, with the applied film of the
over-coating agent being removed substantially completely to form
fine patterns, further characterized by containing a water-soluble
polymer which contains at least (meth)acrylamide as its monomeric
component.
9. The over-coating agent for forming fine patterns according to
claim 8, wherein the water-soluble polymer is a copolymer of
(meth)acrylamide and at least one member selected from among
monomeric components of alkylene glycolic polymers, cellulosic
derivatives, vinyl polymers, acrylic polymers, urea polymers, epoxy
polymers and melamine polymers, with the proviso that monomeric
components of acrylic polymers are those other than
(meth)acrylamide.
10. The over-coating agent for forming fine patterns according to
claim 8, wherein the water-soluble polymer is a copolymer or a
mixture of (meth)acrylamide and at least one member of polymers
selected from the group consisting of alkylene glycolic polymers,
cellulosic derivatives, vinyl polymers, acrylic polymers (with the
exception of poly(meth)acrylamide), urea polymers, epoxy polymers
and melamine polymers.
11. The over-coating agent for forming fine patterns according to
claim 8, wherein the water-soluble polymer is a copolymer of
(meth)acrylamide and at least one member selected from among
monomeric components of acrylic polymers.
12. The over-coating agent for forming fine patterns according to
claim 8, wherein the water-soluble polymer is a copolymer or a
mixture of poly(meth)acrylamide and acrylic polymers.
13. The over-coating agent for forming fine patterns according to
claim 9, wherein the monomeric component of acrylic polymers is
(meth)acrylic acid.
14. The over-coating agent for forming fine patterns according to
claim 11, wherein the monomeric component of acrylic polymers is
(meth)acrylic acid.
15. The over-coating agent for forming fine patterns according to
claim 10, wherein acrylic polymers are poly(meth)acrylate.
16. The over-coating agent for forming fine patterns according to
claim 12, wherein acrylic polymers are poly(meth)acrylate.
17. The over-coating agent for forming fine patterns according to
claim 8 or 9, which is an aqueous solution having a concentration
of 3-50 mass.
18. 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 of any one of claims
1, 8 or 9, then applying heat treatment to shrink the applied
over-coating agent under the action of heat so that the spacing
between the adjacent photoresist patterns is lessened, and
subsequently completely removing the applied film of the
over-coating agent.
19. The method of forming fine patterns according to claim 18,
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.
20. The over-coating agent according to claim 5 which contains 0.1
to 15 mass % of the amide group containing monomer in the
over-coating agent (as solids).
Description
TECHNICAL FIELD
[0001] 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.
BACKGROUND ART
[0002] 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 hole patterns and
trench patterns using the photoresist pattern as a protective layer
(mask pattern).
[0003] 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.
[0004] 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.
[0005] For example, JP-5-166717A discloses a method of forming fine
patterns which comprises the steps of defining patterns
(=photoresist-uncovered patterns) into 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-5-241348A 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.
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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.
However, polyvinyl alcohol 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-7-45510A has yet to be adopted
commercially.
[0010] 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.
DISCLOSURE OF INVENTION
[0011] An object of the present invention is to provide an
over-coating agent for forming fine patterns. It can remarkably
increase the thermal shrinkage of the over-coating agent in the
heat treatment, thereby to form finer patterns effectively, and has
high ability to control pattern dimensions and provides fine-line
patterns that have a satisfactory profile and satisfy the
characteristics required of semiconductor devices. Another object
of the invention is to provide a method of forming fine trace
patterns using the over-coating agent.
[0012] 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, with the applied film of
the over-coating agent being removed substantially completely to
form fine patterns, further characterized by containing either (i)
a water-soluble polymer and an amide group-containing monomer, or
(ii) a water-soluble polymer which contains at least
(meth)acrylamide as its monomeric components.
[0013] 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
either of 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 the adjacent photoresist patterns is lessened, and
subsequently completely removing the applied film of the
over-coating agent.
[0014] 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.
BEST MODE FOR CARRYING OUT THE INVENTION
[0015] The over-coating agent of the invention for forming fine
features of patterns is used to be 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.
[0016] 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.
[0017] The over-coating agent for forming fine patterns of the
invention for forming fine patterns is what either comprising a
water-soluble polymer and an amide-group containing monomer (first
type of the over-coating agent for forming fine patterns), or
comprising a water-soluble polymer which contains at least
(meth)acrylamide as its monomeric components (second type of the
over-coating agent for forming fine patterns).
[First Type of the Over-Coating Agent for Forming Fine
Patterns]
Water-Soluble Polymer
[0018] The water-soluble polymer may be any polymer that can
dissolve in water at room temperature and various types may be
employed without particular limitation; preferred examples include
acrylic polymers, vinyl polymers, cellulosic derivatives, alkylene
glycol polymers, urea polymers, melamine polymers, epoxy polymers
and amide polymers.
[0019] Exemplary acrylic polymers include polymers and copolymers
having monomeric components, such as acrylic acid, methyl acrylate,
methacrylic acid, methyl methacrylate, N,N-dimethylaminoethyl
methacrylate, N,N-diethylaminoethyl methacrylate,
N,N-dimethylaminoethyl acrylate, acryloylmorpholine, etc.
[0020] Exemplary vinyl polymers include polymers and copolymers
having monomeric components, such as N-vinylpyrrolidone, vinyl
imidazolidinone, vinyl acetate, etc.
[0021] Exemplary cellulosic derivatives include 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, methylcellulose, etc.
[0022] Exemplary alkylene glycol polymers include addition polymers
and copolymers of ethylene glycol, propylene glycol, etc.
[0023] Exemplary urea polymers include those having methyllolurea,
dimethylolurea, ethyleneurea, etc. as components.
[0024] Exemplary melamine polymers include those having
methoxymethylated melamine, methoxymethylated isobutoxymethylated
melamine, methoxyethylated melamine, etc. as components.
[0025] Among epoxy polymers and amide polymers, those which are
water-soluble may also be employed.
[0026] It is particularly preferred to employ at least one member
selected from the group consisting of alkylene glycol polymers,
cellulosic derivatives, vinyl polymers and acrylic polymers.
Acrylic polymers are most preferred since they provide ease in pH
adjustment. Copolymers comprising acrylic polymers and
water-soluble polymers other than acrylic polymers are also
preferred since during heat treatment, the efficiency of shrinking
the spacing between the adjacent photo-resist patterns (mask
patterns) can be increased while maintaining the shape of the
photoresist pattern. The water-soluble polymers can be employed
either singly or in combination.
[0027] When water-soluble polymers are used as copolymers, the
proportions of the components are not limited to any particular
values. However, if stability over time is important, the
proportion of the acrylic polymer is preferably adjusted to be
larger than those of other building polymers. Other than by using
excessive amounts of the acrylic polymer, better stability over
time can also be obtained by adding acidic compounds such as
p-toluenesulfonic acid and dodecylbenzene-sulfonic acid.
Amide Group-Containing Monomer
[0028] The amide group-containing monomer should have
characteristics such that when added to the water-soluble polymer,
it is highly soluble, is not suspended, and is compatible with the
polymer component.
[0029] As the amide group-containing monomer, preferred one is an
amide compound represented by the following general formula
(I):
##STR00001##
where R.sub.1 is a hydrogen atom, an alkyl or hydroxyalkyl group
having 1-5 carbon atoms; R.sub.2 is an alkyl group having 1-5
carbon atoms; R.sub.3 is a hydrogen atom or a methyl group; and m
is a number of 0-5. The alkyl group and the hydroxyalkyl group may
be either linear of branched.
[0030] The amide group-containing monomer of the general formula
(I) is more preferred in which R.sub.1 is a hydrogen atom, a methyl
group or an ethyl group, and m is 0. Specific examples of the amide
group-containing monomer include acrylamide, methacrylamide,
N,N-dimethylacrylamide, N,N-dimethylmethacrylamide,
N,N-diethylacrylamide, N,N-diethylmethacrylamide,
N-methylacrylamide, N-methylmethacrylamide, N-ethylacrylamide and
N-ethylmethacrylamide. Among these, acrylamide and methacrylamide
are particularly preferred.
[0031] In the invention, the thermal shrinkage of the over-coating
agent for forming fine patterns can be remarkably increased by the
incorporation of the amide group-containing monomer, and thereby
finer patterns can be formed.
[0032] The content of the amide group-containing monomer added is
preferably about 0.1-30 mass %, and particularly about 1-15 mass %,
based on the over-coating agent for forming fine patterns (solid
content). In the case where the content is less than 0.1 mass %, a
large thermal shrinkage cannot be obtained of the over-coating
agent for forming fine patterns. However, in the case where the
content exceeds 30 mass %, there is no appreciable improvement in
the thermal shrinkage that justifies the increased content.
[Second Type of the Over-Coating Agent for Forming Fine
Patterns]
[0033] In one preferred embodiment in the second type of the
over-coating agent of the invention, a water-soluble polymer is a
copolymer of (meth)acrylamide and at least one member selected from
among monomeric components of alkylene glycol polymers, cellulosic
derivatives, vinyl polymers, acrylic polymers, urea polymers, epoxy
polymers and melamine polymers, provided that monomeric components
of acrylic polymers are those other than (meth)acrylamide).
[0034] Exemplary monomeric components of acrylic polymers include
acrylic acid, methyl acrylate, methacrylic acid, methyl
methacrylate, N,N-dimethylaminoethyl methacrylate,
N,N-diethylaminoethyl methacrylate, N,N-dimethylaminoethyl
acrylate, acryloylmorpholine, etc.
[0035] Exemplary monomeric components of vinyl polymers include
N-vinylpyrrolidone, vinyl imidazolidinone, vinyl acetate, etc.
[0036] Exemplary monomeric components of cellulosic derivatives
include hydroxypropylmethyl cellulose phthalate,
hydroxypropylmethyl cellulose acetate phthalate,
hydroxypropyl-methyl cellulose hexahydrophthalate,
hydroxypropylmethyl cellulose acetate succinate,
hydroxypropylmethyl cellulose, hydroxypropyl cellulose,
hydroxyethyl cellulose, cellulose acetate hexahydrophthalate,
carboxymethyl cellulose, ethyl cellulose, methylcellulose, etc.
[0037] Exemplary monomeric components of alkylene glycol polymers
include ethylene glycol, propylene glycol, etc.
[0038] Exemplary monomeric components of urea polymers include
methylolurea, dimethylolurea, ethyleneurea, etc.
[0039] Exemplary monomeric components of melamine polymers include
methoxymethylated melamine, methoxymethylated isobutoxymethylated
melamine, methoxyethylated melamine, etc.
[0040] Among monomeric components of epoxy polymers, those which
are water-soluble may also be employed.
[0041] It is particularly preferred to employ monomeric components
of acrylic polymers, specifically (meth)acrylic acid, are most
preferred since during heat treatment, the efficiency of shrinking
the spacing between the adjacent photoresist patterns can be
extensively increased while maintaining the shape of the
photoresist pattern. They are also preferred in terms of stability
over time.
[0042] Copolymers of (meth)acrylamide and the monomeric components
of the above-described polymers are preferably used in which the
monomers are used in an amount of 0.1-30 mass %, more preferably
about 1-15 mass %, relative to (meth)acrylamide.
[0043] In another preferred embodiment in the second type of the
over-coating agent of the invention, a water-soluble polymer is a
copolymer or a mixture of (meth)acrylamide and at least one member
selected from among polymers of alkylene glycol polymers,
cellulosic derivatives, vinyl polymers, acrylic polymers (with the
exception of poly(meth)acrylamide), urea polymers, epoxy polymers
and melamine polymers.
[0044] Alkylene glycol polymers, cellulosic derivatives, vinyl
polymers, acrylic polymers, urea polymers, epoxy polymers and
melamine polymers are preferably used the same ones having
monomeric components as descried above.
[0045] Among them, acrylic polymers, particularly
poly(meth)acrylate, such as poly(meth)acrylic acid, are most
preferred since during heat treatment, the efficiency of shrinking
the spacing between the adjacent photoresist patterns (mask
patterns) can be extensively increased while maintaining the shape
of the photoresist pattern. It is also preferred in terms of
stability over time.
[0046] Copolymers or mixed resins of (meth)acrylamide and each of
the above polymers are preferably used in which the copolymers are
used in an amount of 0.1-30 mass %, more preferably about 1-15 mass
%, relative to (meth)acrylamide.
[0047] In either of the two embodiments above, it is also possible
to improve the stability over time by adding an acidic compound
such as p-toluenesulfonic acid or dodecylbenzenesulfonic acid.
Optional Additives
[0048] In the first and second types of 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.
[0049] Exemplary water-soluble amines include amines having pKa
(acid dissociation constant) values of 7.5-13 in aqueous solution
at 25.degree. C. 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-ethyl-ethylenediamine, 1,2-propanediamine, 1,3-propanediamine and
1,6-hexanediamine; aliphatic amines, such as 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 water-soluble amines are those having boiling points of
140.degree. C. (760 mmHg), as exemplified by monoethanolamine and
triethanolamine.
[0050] 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 for forming fine
patterns (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.
[0051] For such purposes as reducing the dimensions of patterns and
controlling the occurrence of defects, the first and second types
of over-coating agent for forming fine patterns may further
optionally contain non-amine based, water-soluble organic
solvents.
[0052] 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
monobuthyl ether, ethylene glycol monomethyl ether acetate,
ethylene glycol monoethyl ether acetate, diethylene glycol,
diethylene glycol monomethyl ether, diethylene glycol monoethyl
ether, diethylene glycol monobuthyl 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.
[0053] 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.
[0054] In addition, the first and second type of over-coating agent
may optionally contain a surfactant for attaining special effects
such as coating uniformity and wafer's in-plane uniformity.
[0055] Suitable surfactants include N-alkylpyrrolidones, quaternary
ammonium salts and phosphate esters of polyoxyethylene.
[0056] N-alkylpyrrolidones as surfactant are preferably represented
by the following general formula (II):
##STR00002##
where R.sub.4 is an alkyl group having at least 6 carbon atoms.
[0057] 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.
[0058] Quaternary ammonium salts as surfactant are preferably
represented by the following general formula (III):
##STR00003##
where R.sub.5, R.sub.6, R.sub.7 and R.sub.8 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.
[0059] Specific examples of quaternary ammonium salts as surfactant
include dodecyltrimethylammonium hydroxide,
tridecyltrimethylammonium hydroxide, tetradecyltrimethylammonium
hydroxide, pentadecyltrimethylammonium hydroxide,
hexadecyl-trimethylammonium hydroxide, heptadecyltrimethylammonium
hydroxide and octadecyltrimethylammonium hydroxide. Among these,
hexadecyltrimethylammonium hydroxide is preferably used.
[0060] Phosphate esters of polyoxyethylene are preferably
represented by the following general formula (IV):
##STR00004##
where R.sub.9 is an alkyl or alkylaryl group having 1-10 carbon
atoms; R.sub.10 is a hydrogen atom or (CH.sub.2CH.sub.2O)R.sub.9
(where R.sub.9 is as defined above); n is an integer of 1-20.
[0061] To mention specific examples, phosphate esters of
poly-oxyethylene that can be used as surfactants are commercially
available under trade names "PLYSURF A212E" and "PLYSURF A210G"
from Dai-ichi Kogyo Seiyaku Co., Ltd.
[0062] The first and second types of over-coating agent of the
invention for forming fine patterns are 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.
[0063] As already mentioned, the first and second types of
over-coating agent of the invention for forming fine patterns are
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 %.
[0064] The first and second types of over-coating agent of the
invention for forming fine patterns have the advantage of improving
resolution beyond the values inherent in photoresist materials and
it can attain wafer's in-plane uniformity by eliminating the
pattern variations in the plane of the substrate. Further, the
over-coating agent of the invention can form patterns of good
profile by eliminating the irregularities (roughness) in the shape
of patterns due, for example, to the reflection of fluorescent
light from the substrate. Also it has remarkable improvement in
forming finer patterns.
[0065] 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 either of the
first and second types of 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 the adjacent photoresist patterns is reduced, and
subsequently removing the applied film of the over-coating agent
substantially completely.
[0066] 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 photo-resist 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.
[0067] 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).
[a.] Over-Coating Agent Application Step
[0068] 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.
[0069] 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 whirl coating with a spinner,
etc.
[b.] Heat Treatment (Thermal Shrinkage) Step
[0070] 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 the adjacent photoresist patterns lessens. The
spacing between the adjacent photoresist patterns determines the
diameter or width of the patterns to be finally obtained, so the
decrease in the spacing between the adjacent photoresist patterns
contributes to reducing the diameter of each element of hole
patterns or the width of each element of trench patterns,
eventually leading to the definition of a pattern with smaller
feature sizes.
[0071] 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 photo-resist 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 (for example,
dimensional changes due to spontaneously fluidized deforming).
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.
[0072] Considering the softening points of a variety of
photo-resist 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.
[0073] The thickness of the film of the over-coating agent for the
formation of fine-line patterns is preferably just comparable to
the height of the photoresist pattern or high enough to cover
it.
[c.] Over-Coating Agent Removal Step
[0074] 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. tetramethyl-ammonium 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.
[0075] 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.
[0076] 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.
[0077] 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. The over-coating agent of
the invention contains a water-soluble polymer and an amide
group-containing monomer, so even if it is subjected to a plurality
of washing steps, it can be completely removed each time it is
washed with water. Consequently, even in the case of using a
substrate having a thick film of photoresist pattern, a fine-line
pattern of good profile can be formed on the substrate without
causing pattern distortion or deformation.
[0078] 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
[0079] 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 %.
[First Type of the Over-Coating Agent for Forming Fine
Patterns]
Example 1
[0080] A copolymer of acrylic acid and vinylpyrrolidone [5.83 g;
acrylic acid/vinylpyrrolidone=2:1 (polymerization ratio)],
triethanolamine (0.53 g), acrylamide (0.58 g) and "PLY-SURF A210G",
product of Dai-ichi Kogyo Seiyaku Co., as phosphate esters of
polyoxyethylene surfactant (0.06 g) were dissolved in water (93 g)
to prepare an over-coating agent.
[0081] A substrate was whirl coated with a positive-acting
photoresist TArF-7a-52 EM (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 0.40 .mu.m.
[0082] The photoresist layer was exposed with a laser exposure unit
(Nikon S-302 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 161.0 nm.
[0083] Then above-described over-coating agent was applied onto the
substrate including the hole patterns and subjected to heat
treatment at 150.degree. C. for 60 seconds. Subsequently, the
over-coating agent was removed using pure water at 23.degree. C.
The each diameter of the hole patterns was reduced to 122.0 nm.
Example 2
[0084] A copolymer of acrylic acid and vinylpyrrolidone [6.14 g;
acrylic acid/vinylpyrrolidone=2:1 (polymerization ratio)], glycerol
(0.18 g), acrylamide (0.62 g) and "PLYSURF A210G", product of
Dai-ichi Kogyo Seiyaku Co., as phosphate esters of polyoxyethylene
surfactant (0.06 g) were dissolved in water (93 g) to prepare an
over-coating agent.
[0085] Then above-described over-coating agent was applied onto the
substrate including the hole patterns (each diameter of patterns:
161.0 nm) which was prepared in the same manner as described in
EXAMPLE 1, and subjected to heat treatment at 150.degree. C. for 60
seconds. Subsequently; the over-coating agent was removed using
pure water at 23.degree. C. The each diameter of the hole patterns
was reduced to 121.7 nm.
Example 3
[0086] A copolymer of acrylic acid and vinylpyrrolidone [6.14 g;
acrylic acid/vinylpyrrolidone=2:1 (polymerization ratio)], glycerol
(0.18 g), methacrylamide (0.62 g) and "PLYSURF A210G", product of
Dai-ichi Kogyo Seiyaku Co., as phosphate esters of polyoxyethylene
surfactant (0.06 g) were dissolved in water (93 g) to prepare an
over-coating agent.
[0087] Then above-described over-coating agent was applied onto the
substrate including the hole patterns (each diameter of patterns:
161.0 nm) which was prepared in the same manner as described in
EXAMPLE 1, and subjected to heat treatment at 150.degree. C. for 60
seconds. Subsequently, the over-coating agent was removed using
pure water at 23.degree. C. The each diameter of the hole patterns
was reduced to 122.6 nm.
[Second Type of the Over-Coating Agent for Forming Fine
Patterns]
Example 4
[0088] A copolymer of acrylamide and acrylic acid [6.37 g;
acrylamide/acrylic acid=1:2 (polymerization ratio)],
triethanolamine (0.57 g) and "PLYSURF A210G", product of Daiichi
Kogyo Seiyaku Co., as phosphate esters of polyoxyethylene
surfactant (0.06 g) were dissolved in water (93 g) to prepare an
over-coating agent.
[0089] Then above-described over-coating agent was applied onto the
substrate including the hole patterns (each diameter of patterns:
161.0 nm) which was prepared in the same manner as described in
EXAMPLE 1, and subjected to heat treatment at 150.degree. C. for 60
seconds. Subsequently, the over-coating agent was removed using
pure water at 23.degree. C. The each diameter of the hole patterns
was reduced to 121.8 nm.
Example 5
[0090] A mixed resin of polyacrylamide and polyacrylate [6.40 g;
polyacrylamide/polyacrylate=1:2 (mass ratio)], triethanolamine
(0.54 g) and "PLYSURF A21G", product of Dai-ichi Kogyo Seiyaku Co.,
as phosphate esters of polyoxyethylene surfactant (0.06 g) were
dissolved in water (93 g) to prepare an over-coating agent.
[0091] Then above-described over-coating agent was applied onto the
substrate including the hole patterns (each diameter of patterns:
161.0 nm) which was prepared in the same manner as described in
EXAMPLE 1, and subjected to heat treatment at 150.degree. C. for 60
seconds. Subsequently, the over-coating agent was removed using
pure water at 23.degree. C. The each diameter of the hole patterns
was reduced to 123.0 nm.
Comparative Example 1
[0092] A copolymer of acrylic acid and vinylpyrrolidone [5.83 g;
acrylic acid/vinylpyrrolidone=2:1 (polymerization ratio)],
triethanolamine (0.53 g) and "PLYSURF A210G", product of Dai-ichi
Kogyo Seiyaku Co., as phosphate esters of polyoxyethylene
surfactant (0.06 g) were dissolved in water (93.58 g) to prepare an
over-coating agent.
[0093] Then above-described over-coating agent was applied onto the
substrate including the hole patterns (each diameter of patterns:
161.0 nm) which was prepared in the same manner as described in
EXAMPLE 1, and subjected to heat treatment at 150.degree. C. for 60
seconds. Subsequently, the over-coating agent was removed using
pure water at 23.degree. C. The each diameter of the hole patterns
was 139.0 nm.
Comparative Example 2
[0094] A copolymer of acrylic acid and vinylpyrrolidone [6.73 g;
acrylic acid/vinylpyrrolidone=2:1 (polymerization ratio)], glycerol
(0.20 g) and "PLYSURF A210G", product of Daiichi Kogyo Seiyaku Co.,
as phosphate esters of polyoxyethylene surfactant (0.07 g) were
dissolved in water (93 g) to prepare an over-coating agent.
[0095] Then above-described over-coating agent was applied onto the
substrate including the hole patterns (each diameter of patterns:
161.0 nm) which was prepared in the same manner as described in
EXAMPLE 1, and subjected to heat treatment at 150.degree. C. for 60
seconds. Subsequently, the over-coating agent was removed using
pure water at 23.degree. C. The each diameter of the hole patterns
was 140.6 nm.
INDUSTRIAL APPLICABILITY
[0096] As described above in detail, according to the present
inventions of the over-coating agent for forming fine-line patterns
and the method of forming fine-line patterns using the agent, the
thermal shrinkage of the over-coating agent in the heat treatment
can be extensively increased, and one can obtain fine-line patterns
which exhibit good profiles while satisfying the characteristics
required of semiconductor devices.
* * * * *