U.S. patent application number 10/691537 was filed with the patent office on 2005-01-13 for method of forming fine patterns.
Invention is credited to Kaneko, Fumitake, Sugeta, Yoshiki, Tachikawa, Toshikazu.
Application Number | 20050009365 10/691537 |
Document ID | / |
Family ID | 32456100 |
Filed Date | 2005-01-13 |
United States Patent
Application |
20050009365 |
Kind Code |
A1 |
Sugeta, Yoshiki ; et
al. |
January 13, 2005 |
Method of forming fine patterns
Abstract
It is disclosed a method of forming fine patterns comprising:
subjecting a substrate having photoresist patterns to a hydrophilic
treatment, covering the substrate having photoresist patterns with
an over-coating agent for forming fine patterns, applying heat
treatment to cause thermal shrinkage of the over-coating agent so
that the spacing between adjacent photoresist patterns is lessened
by the resulting thermal shrinking action, and removing the
over-coating agent substantially completely.
Inventors: |
Sugeta, Yoshiki;
(Kawasaki-shi, JP) ; Kaneko, Fumitake;
(Kawasaki-shi, JP) ; Tachikawa, Toshikazu;
(Kawasaki-shi, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
32456100 |
Appl. No.: |
10/691537 |
Filed: |
October 24, 2003 |
Current U.S.
Class: |
438/781 ;
257/E21.026; 430/331; 438/640; 438/677; 438/760; 438/780;
438/800 |
Current CPC
Class: |
H01L 21/0273 20130101;
G03F 7/40 20130101 |
Class at
Publication: |
438/781 ;
438/780; 438/760; 438/800; 438/677; 438/640 |
International
Class: |
H01L 021/31; H01L
021/469; H01L 021/00; H01L 021/4763 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 25, 2002 |
JP |
2002-310671 |
Claims
What is claimed is:
1. A method of forming fine patterns comprising: subjecting a
substrate having photoresist patterns to a hydrophilic treatment,
covering the substrate having photoresist patterns with an
over-coating agent for forming fine patterns, applying heat
treatment to cause thermal shrinkage of the over-coating agent so
that the spacing between adjacent photoresist patterns is lessened
by the resulting thermal shrinking action, and removing the
over-coating agent substantially completely.
2. The method of forming fine patterns according to claim 1,
wherein the hydrophilic treatment is performed by applying a
hydrophilic solvent on the substrate having photoresist
patterns.
3. The method of forming fine patterns according to claim 2,
wherein the hydrophilic solvent is at least one member selected
from the group consisting of pure water, a water-soluble surfactant
aqueous solution, and an alcohol aqueous solution.
4. The method of forming fine patterns according to claim 3,
wherein the hydrophilic solvent is pure water.
5. The method of forming fine patterns according to claim 1,
wherein the over-coating agent contains a water-soluble
polymer.
6. The method of forming fine patterns according to claim 5,
wherein the water-soluble polymer is at least one member selected
from the group consisting of alkylene glycolic polymers c ilulosic
derivatives, vinyl polymers, acrylic polymers, urea polymers, epoxy
polymers, melamine polymers and amide polymers.
7. The method of forming fine patterns according to claim 1,
wherein the over-coating agent is an aqueous solution having a
solids content of 3-50 mass %.
8. The method of forming fine patterns according to claim 1,
wherein the heat treatment is performed at a temperature that does
not cause thermal fluidizing of the photoresist patterns on the
substrate.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a method of forming fine patterns
in the field of photolithographic technology. More particularly,
the invention relates to a method of forming or defining fine
patterns, such as hole patterns and trench patterns, that can meet
today's requirements for higher packing densities and smaller sizes
of semiconductor devices.
[0003] 2. Description of the Related Art
[0004] 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).
[0005] 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 fineline 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.
[0006] 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.
[0007] For example, JP-5-166717A discloses a method of forming fine
patterns which comprises the steps of defining
patterns(=photoresist-unco- vered 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-5-241348 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.
[0008] 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.
[0009] 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.
[0010] In th se methods, the waf r's in-plane h at 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.
[0011] 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, the use of polyvinyl alcohol singly 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.
[0012] Furthermore, in those traditional methods, as hydrophilic
resins are coated to form resin layers on the top or on the side
walls of the photoresist patterns that are being hydrophobic, it
sometimes causes difficulties in coating of the hydrophilic resins
uniformly. In addition, with the recent tendency of wafers become
larger in diameters, the requirements for the formation of fine
patterns becomes highly difficulties, and the reduction of the
usage amounts of hydrophillc resins in forming the patterns is also
required. Specifically, with the increase in the need of forming
ultra fine patterns, it becomes difficult to apply the resins
completely into on the portions of the substrate between the
photoresist patterns: there are some portions whereto the resins
cannot be applied into, and microfoaming occur, thereby to cause
defectives in the formation of the patterns.
[0013] 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
[0014] The present invention has been accomplished under these
circumstances and has as an object providing a method of forming
fine patterns on a substrate having photoresist patterns (mask
patterns) as it is covered with an over-coating agent, In which
having improvements in coating properties of the over-coating agent
and coating uniformity, as well as the reduction of the usage
amounts of the over-coating agent.
[0015] In order to attain this object, the present invention
provides a method of forming fine patterns comprising: subjecting a
substrate having photoresist patterns to a hydrophilic treatment,
covering the substrate having photoresist patterns with an
over-coating agent for forming fine patterns, applying heat
treatment to cause thermal shrinkage of the over-coating agent so
that the spacing between adjacent photoresist patterns is lessened
by the resulting thermal shrinking action, and removing the
over-coating agent substantially completely.
[0016] In a preferred embodiment, the heat treatment is performed
at a temperature that does not cause thermal fluidizing of the
photoresist patterns on the substrate.
DETAILED DESCRIPTION OF THE INVENTION
[0017] The method of preparing the substrate used in the present
invention 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 spinor 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.
[0018] 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).
[0019] [a.] Substrate Hydrophilic Treatment Step
[0020] A substrate having photoresist patterns (mask patterns)
thereon is subjected to a hydrophilic treatment. Any method can be
used for the hydrophilic treatment so far as it can provide
hydrophilicity to the surfaces of the substrate and the photoresist
patterns without producing no ill effects to them. More
specifically, methods such as applying a small amount of a
hydrophilic solvent (an application improving agent) on the
substrate, exposing the substrate in an atmosphere of steam,
irradiating UV rays to the entire substrate, O.sub.2 plasma ashing
treating to the substrate, and the like. are exemplified.
[0021] In the present invention, a method of applying a small
amount of a hydrophilic solvent (an application improving agent) on
the substrate is preferred. As the hydrophilic solvent, pure water,
a water-soluble surfactant aqueous solution, and an alcohol aqueous
solution are preferably used.
[0022] As water-soluble surfactants in the invention, at least the
one selected among N-alkylpyrrolidones, quaternary ammonium salts
and phosphate esters of polyoxyethylene are preferably employed, in
view of the provision of no ill effects to the substrate and the
photoresist patterns, and the most effectively exhibition of the
advantages of the present invention. However, they are not limited
thereto.
[0023] N-alkylpyrrolidones as surfactant are preferably represented
by the following general formula (I): 1
[0024] where R.sub.1 is an alkyl group having at least 6 carbon
atoms.
[0025] 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-pyrrolldone,
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 pr ferably used.
[0026] Quaternary ammonium salts as surfactant are preferably
represented by the following general formula (II): 2
[0027] 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.
[0028] Specific examples of quaternary ammonium salts as surfactant
include dodecyltrimethylammonium hydroxide,
tridecyl-trimethylammonium hydroxide, tetradecyltrimethylammonium
hydroxide, pentadecyltrimethylammo- nium hydroxide,
hexadecyl-trimethylammonium hydroxide, heptadecyltrimethylammonium
hydroxide and octadecyltrimethylammonium hydroxide. Among these,
hexadecyltrimethylammonium hydroxide is preferably used.
[0029] Phosphate esters of polyoxyethylene are preferably
represented by the following general formula (III): 3
[0030] 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.
[0031] 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.
[0032] The water-soluble surfactants are preferably used by solving
in pure water to obtain a water-soluble surfactant aqueous solution
having a preferable concentration of 0.001-10 mass %, and more
preferably 0.01-3 mass %.
[0033] As the alcohol, a monohydric alcohol, such as methyl
alcohol, ethyl alcohol, propylene alcohol, and butyl alcohol; and a
polyhydric alcohol, such as ethylene glycol, propylene glycol, and
glycerol are exemplified, but are not limited thereto. The alcohols
are preferably used by solving in pure water to obtain an alcohol
aqueous solution having a preferable concentration of 0.01-30 mass
%, and more preferably 0.1-20 mass %.
[0034] The coating amount of the hydrophilic solvent (an
application improving agent) can be the minimum amount so far as
the solvent can be applied entirely over the substrate having
photoresist patterns thereon, and not limited to any particular
amounts. The preferable amount is about 0.05-10 mL, and more
preferably 0.1-3 mL for the coating on an 8-inch silicon wafer. The
solvent is generally applied on the substrate by whirl coating with
a spinner, but not limited thereto. In the case where the amount of
the solvent for the application is too little, the effects
obtainable by the utilization of the hydrophilic solvent cannot be
exhibited. On the other hand, in the case where the amount of the
solvent is too much, a takt time is liabl to be longer.
[0035] [b.] Over-Coating Agent Application Step
[0036] In the next step, an over-coating ag nt is appli d to cover
entirely the said substrate having photoresist patterns (mask
patterns) thereon. In the present Invention, the over-coating agent
application step is performed after step [a.], the usage amount of
the over-coating agent could be reduced sharply. For example, in
applying the over-coating agent to an 8-inch silicon wafer, it was
able to reduce the amount of the over-coating agent to 1-3 mL in
the present invention, whereas in a common applying method without
including step [a.] where 4-6 mL of the over-coating coating was
applied. Even the amount of the over-coating agent could be reduced
one half like this, the same coating uniformity was obtained as
that of in the common application method. Further, even for the
substrate that have photoresist patterns having ultra-fine lines
and being formed thickly thereon, the over-coating agent is easily
and completely applied into on the portions of the substrate
between such photoresist patterns without the occurrence of
microfoaming. The over-coating agent was applied in uniformity with
efficiency.
[0037] 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.
[0038] 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.
[0039] The ov r-coating agent employed in the invention is to cover
entirely the 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 featured
patterns.
[0040] 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.
[0041] In the present invention, the over-coating agent is
preferably employed that contains a water-soluble polymer.
[0042] 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, c llulosic derivatives, alkylene
glycol polymers, urea polymers, melamine polymers, epoxy polymers
and amide polymers.
[0043] Exemplary acrylic polymers include polymers and copolymers
having monomeric components, such as acrylic acid, methyl acrylate,
methacrylic acid, methyl methacrylate, N,N-dimethylacrylamide,
N,N-dimethylaminopropylmethacrylamide,
N,N-dimethylaminopropylacrylamide, N-methylacrylamide, diacetone
acrylamide, N,N-dimethylaminoethyl methacrylate,
N,N-diethylaminoethyl methacrylate, N,N-dimethylaminoethyl
acrylate, acryloylmorpholine, etc.
[0044] Exemplary vinyl polymers include polymers and copolymers
having monomeric components, such as N-vinylpyrrolidone, vinyl
imidazolidinone, vinyl acetate, etc.
[0045] 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.
[0046] Exemplary alkylene glycol polymers include addition polymers
and copolymers of ethylene glycol, propylene glycol, etc.
[0047] Exemplary urea polymers include those having methylolur a,
dimethylolurea, ethyleneurea, to, as components.
[0048] Exemplary melamine polymers include those having
methoxymethylated melamine, methoxymethylat d isobutoxymethylated
melamine, methoxyethylated melamine, etc. as components.
[0049] Among epoxy polymers and amide polymers, those which are
water-soluble may also be employed.
[0050] 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 photoresist patterns (mask
patterns) can be increased while maintaining the shape of the
photoresist pattern. The watersoluble polymers can be employed
either singly or in combination.
[0051] 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-toluenesulfonlc acid and dodecylbenzene-sulfonic acid.
[0052] The over-coating agent for forming fine patterns may
additionally contain water-soluble amines. Preferred ones include
amines having pKa (acid dissociation constant) values of 7.5-13 in
aqueous solution at 25.degree. C. in view of the prevention of the
generation of Impurities and pH adjustment. 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,
dilsopropanolamine and triisopropanolamine; polyalkylenepolyamines,
such as diethylenetriamine, triethylenetetramine, propylenedlamine,
N,N-diethylethylenediamine, 1,4-butanediamine,
N-ethyl-ethylenediamine, 1,2-propanediamine, 1,3-propanediamline
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 water-soluble amines are those having boiling points of
140.degree. C. (760 mmHg) and above, as exemplified by
monoethanolamine and triethanolamine.
[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] The over-coating agent for forming fine patterns is adjusted
to have pH values of 2-3 by the addition of the water-soluble
amine. There may be cases where the over-coating agent for forming
fine patterns Is applied to the substrate having metallic layers
easily corroded by an acid, the pH values may be adjusted to
3-5.
[0055] 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.
[0056] 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 di-methylsulfone,
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 mono thyl ether acetate, diethylene glycol,
diethylene glycol monom thyl 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.
[0057] 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.
[0058] 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.
[0059] Beyond 30 mass %, a mixing layer is liable to form at the
interface with the photoresist pattern.
[0060] 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.
[0061] 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 microfoaming upon
coating th over-coating agent.
[0062] 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, that are used for a hydrophilic solvent used in
step [a.] above.
[0063] If the surfactant is to be added, It is preferably
incorporated in an amount of about 0.1-10 mass %, 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.
[0064] 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.
[0065] As already mentioned, the over-coating agent in th 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 Include methyl alcohol, ethyl alcohol,
propyl alcohol, isopropyl alcohol, glycerol. ethylene glycol,
propylene glycol, 1,2-butylene glycol, 1,3-buthylene glycol and
2,3-butylene glycol, etc. These alcoholic solvents are mixed with
water in amounts not exceeding about 30 mass %.
[0066] [c.] Heat treatment (thermal shrinkage) step
[0067] 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.
[0068] 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
temperatur 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 fluldizing of the
photoresist.
[0069] 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.
[0070] [d.] Over-coating Agent Removal Step
[0071] 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. Prior to washing with
water, rinsing may optionally be performed with an aqueous solution
of alkali (e.g. tetramethylammonium hydroxid (TMAH) or choline).
The over-coating agent of the present inv ntion is easy to remove
by washing with water and it can be completely removed from the
substrate and the photoresist pattern. The contact method of the
substrate with the aqueous solution can be performed by, for
example, a puddle method, a dip method, a shower method, a spray
method, etc., but is not limited thereto. The contact time of the
substrate with the aqueous solution is in usual for 10-300 seconds,
but is not limited thereto.
[0072] 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.
[0073] 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.
[0074] Steps [a.]-[d.] may be repeated several times. By re-peating
steps [a.]-[d.] several times, the photoresist trace patterns (mask
patterns) can be progressively widened.
[0075] Furthermore, the use of the over-coating agent for forming
fine patterns containing a water-soluble polymer allows the
over-coating agent be completely removed with water every time in
repeating the removal step plural times. Therefore, the present
invention offers the advantage that even in the case of using a
substrate having thick-film photoresist patterns, fine-line
patterns of good profile can be formed on th substrate without
causing pattern distortion or deformation.
[0076] Furthermore, the adopting a substrate hydrophilic treatment
step prior to the coating step of the over-coating allows the
application of the over-coating agent into on the portions of the
substrate between photoreslst patterns easily and completely. Owing
to this, the In-plane uniformity of the 10 heat shrinkage of the
over-coating agent was improved, and good profile patterns can be
formed entirely across even on a large-diameter substrate.
[0077] The technical field of the present invention is the
semiconductor industry, etc., but it Is not limited thereto.
EXAMPLES
[0078] 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
[0079] A copolymer including polyvinylpyrrolidone (PVP)
polyacrylate (PAA) [6.37 g; NVP copolymer, NOF Corporation],
triethanolamine (0.57 g) and a polyoxyethyelene phosphate ester
surfactant (0.06 g; "PLYSURF A21OG", product of Dai-ichi Kogyo
Seiyaku Co, Ltd.) were dissolved in water (93 g) to prepare an
over-coating agent.
[0080] A substrate (8-inch diameter) was whirl coated with a
positive-acting photoresist TDUR-PO36PM (product of Tokyo Ohka
Kogyo Co., Ltd.) and baked at 80.degree. C. for 90 seconds to form
a photoresist layer In a thickness of 0.48 .mu.m.
[0081] The photoresist layer was exposed with an exposure unit
(Canon FPA-3000EX3, product of Canon Inc.), subjected to heat
treatment at 120.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 180.2 nm (i.e., the spacing between the
photoresist patterns, or the initial hole dimension, was 180.2
nm).
[0082] Next, pure water (2 mL) was applied onto the substrate for
the hydrophilic treatment. After that, the previously prepared
over-coating agent (3 mL) was applied onto the substrate including
hole patterns. There were no coating variations and a good coating
uniformity was obtained.
[0083] Then, the thusly treated substrate was subjected to heat
treatment at 116.degree. C. for 60 seconds, thereby reducing the
each size of the hole patterns. Subsequently, the substrate, while
being kept Whirling at 1500 rpm, was brought into contact with pure
water by dropping it on the substrate for 120 seconds to remove the
over-coating agent. The each diameter of the hole patterns was
reduced to 160.5 nm.
Example 2
[0084] A copolymer including polyvinylpyrrolidone (PVP)
polyacrylate (PAA) [6.37 g; NVP copolymer, NOF Corporation],
triethanolamine (0.57 g) and a polyoxyethyelene phosphate ester
surfactant (0.06 g; "PLYSURF A210G", product of Dai-ichi Kogyo
Seiyaku Co, Ltd.) were dissolved in water (93 g) to prepare an
over-coating agent.
[0085] Also, a polyoxyethyelene phosphate ester surfactant (0.1 g;
"PLYSURF A21OG", product of Dai-ichi Kogyo Seiyaku Co. Ltd.) was
dissolved in water (99 g) to prepare a hydrophilic solvent (an
application improving agent).
[0086] A substrate (8-inch diameter) was whirl coated with a
positive-acting photoresist TDUR-PO36PM (product of Tokyo Ohka
Kogyo Co., Ltd.) and baked at 80.degree. C. for 90 seconds to form
a photoresist layer in a thickness of 0.48 .mu.m.
[0087] The photoresist layer was exposed with an exposure unit
(Canon FPA-3000EX3, product of Canon Inc.), subjected to heat
treatment at 120.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 180.2 nm (i.e., the spacing between the
photoresist patterns, or the initial hole dimension, was 180.2
nm).
[0088] Next, the above-described hydrophilic solvent (the
ap-placation improving agent) (2 mL) was applied onto the substrate
for the hydrophilic treatment. After that, the previously prepared
over-coating agent (3 mL) was applied onto the substrate including
hole patterns. There were no coating variations and a good coating
uniformity was obtained.
[0089] Then, the thusly treated substrate was subjected to heat
treatment at 116.degree. C. for 60 seconds, thereby reducing the
each size of the hole patterns. Subsequently, the substrate, while
being Kept whirling at 1500 rpm, was brought into contact with pure
water by dropping it on the substrate for 120 seconds to remove the
over-coating agent. The each diameter of the hole patterns was
reduced to 160.0 nm.
Comparative Example 1
[0090] The same procedure as described in Example 1 was repeated,
except that the application step of pure water (an application
improving agent) was omitted. As a result, coating variations were
occurred and the substrate having the photoresist patterns thereon
was not entirely covered with the over-coating agent, and therefore
the patterns partially could not be lessened.
[0091] In addition, when the procedure of Comparative Example 1 was
repeated, except that the amount of the over-coating agent was
increased to double (6 mL), the coating variations did not
occur.
[0092] As described above in detail, the present invention provide
a method for forming fine patterns, by which advantages obtained of
improving coating properties of the over-coating agent and
uniformity of the film thickness, as well as reducing the usage
amount of the over-coating agent.
* * * * *