U.S. patent application number 10/681145 was filed with the patent office on 2004-06-24 for method of forming fine patterns.
Invention is credited to Kaneko, Fumitake, Sugeta, Yoshiki, Tachikawa, Toshikazu.
Application Number | 20040121615 10/681145 |
Document ID | / |
Family ID | 32287206 |
Filed Date | 2004-06-24 |
United States Patent
Application |
20040121615 |
Kind Code |
A1 |
Kaneko, Fumitake ; et
al. |
June 24, 2004 |
Method of forming fine patterns
Abstract
It is disclosed a method of forming fine patterns comprising:
covering a 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 by way of bringing
thusly treated substrate into contact with a remover solution for
over 60 seconds.
Inventors: |
Kaneko, Fumitake;
(Kanagawa-ken, JP) ; Sugeta, Yoshiki;
(Kanagawa-ken, JP) ; Tachikawa, Toshikazu;
(Kanagawa-ken, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
32287206 |
Appl. No.: |
10/681145 |
Filed: |
October 9, 2003 |
Current U.S.
Class: |
438/758 ;
257/E21.027; 430/331 |
Current CPC
Class: |
H01L 21/0274 20130101;
G03F 7/40 20130101 |
Class at
Publication: |
438/758 |
International
Class: |
H01L 021/31 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 10, 2002 |
JP |
2002-297525 |
Claims
What is claimed is:
1. A method of forming fine patterns comprising: covering a
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 by way of bringing thusly treated
substrate into contact with a remover solution for over 60
seconds.
2. The method of forming fine patterns according to claim 1,
wherein the over-coating agent contains a water-soluble
polymer.
3. The method of forming fine patterns according to claim 2,
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.
4. 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 %.
5. 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 INVETNION
[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 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.
[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-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-5-241348 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 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.
[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] In addition, in forming patterns by utilizing
photolithography techniques, it is required the prevention of the
occurrence of defects on the substrate- and the improvement of
throughput.
[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. Further, those publications do not describe or
suggest the effects of reducing the occurrence of defects by way of
adjusting the times of removing step by washing with water.
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. The method
has high ability to reduce the occurrence of defects and to improve
throughput.
[0015] In order to attain this object, the present invention
provides a method of forming fine patterns comprising: covering a
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 by way of bringing thusly treated substrate into contact
with a remover solution for over 60 seconds.
[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 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.
[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.] Over-Coating Agent Application Step
[0020] An over-coating agent is applied to cover entirely the said
substrate having photoresist patterns (mask patterns) thereon.
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.
[0021] 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.
[0022] The over-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.
[0023] 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.
[0024] In the present invention, the over-coating agent is
preferably employed that contains a water-soluble polymer.
[0025] 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.
[0026] 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-dimethylamlnoethyl methacrylate,
N,N-diethylaminoethyl methacrylate, N,N-dimethylamlnoethyl
acrylate, acryloylmorpholine, etc.
[0027] Exemplary vinyl polymers include polymers and copolymers
having monomeric components, such as N-vinylpyrrolidone, vinyl
imidazolidinone, vinyl acetate, etc.
[0028] 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.
[0029] Exemplary alkylene glycol polymers include addition polymers
and copolymers of ethylene glycol, propylene glycol, etc.
[0030] Exemplary urea polymers include those having methylolurea,
dimethylolurea, ethyleneurea, etc. as components.
[0031] Exemplary melamine polymers include those having
methoxymethylated melamine, methoxymethylated isobutoxymethylated
melamine, methoxyethylated melamine, etc. as components.
[0032] Among epoxy polymers and amide polymers, those which are
water-soluble may also be employed.
[0033] 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 water-soluble polymers can be employed
either singly or in combination.
[0034] 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 dodecylbenzenesulfonic acid.
[0035] 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,
diisopropanolamine and triisopropanolamine; polyalkylenepolyamines,
such as diethylenetriamine, triethylenetetramine, propylenediamine,
N,N-diethylethylenedlamlne, 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 water-soluble amines are those having boiling points of
140.degree. C. (760 mmHg) and above, as exemplified by
monoethanolamine and triethanolamine.
[0036] 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.
[0037] 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.
[0038] 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.
[0039] 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.
[0040] 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.
[0041] 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.
[0042] 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 microforming upon
coating the over-coating agent.
[0043] 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.
[0044] N-alkylpyrrolidones as surfactant are preferably represented
by the following general formula (I): 1
[0045] where R.sub.1 is an alkyl group having at least 6 carbon
atoms.
[0046] 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.
[0047] Quaternary ammonium salts as surfactant are preferably
represented by the following general formula (II): 2
[0048] 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.
[0049] Specific examples of quaternary ammonium salts as surfactant
include dodecyltrimethylammonium hydroxide,
tridecyltrimethylammonium hydroxide, tetradecyltrimethylammonium
hydroxide, pentadecyltrimethylammo- nium hydroxide,
hexadecyltrimethylammonium hydroxide, heptadecyltrimethylammonlum
hydroxide and octadecyltrimethylammonium hydroxide. Among these,
hexadecyltrimethylammonium hydroxide is preferably used.
[0050] Phosphate esters of polyoxyethylene are preferably
represented by the following general formula (III): 3
[0051] 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.
[0052] 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.
[0053] 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.
[0054] 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.
[0055] As already mentioned, the over-coating agent in 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 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 %.
[0056] [b.] Heat Treatment (Thermal Shrinkage) Step
[0057] 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.
[0058] 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.
[0059] 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.
[0060] [c.] Over-Coating Agent Removal Step
[0061] In the subsequent step, the remaining film of the
over-coating agent on the patterns is removed substantially
completely by bringing thusly treated substrate into contact with a
remover solution for over 60 seconds, and preferably 70 seconds or
over. By adjusting the contact time of the substrate with the
remover solution to be over 60 seconds, it is extremely effective
in reducing the occurrence of defects on the substrate without
lowering throughput. If the contact time is 60 second or less,
defects occur on the substrate and the yields be lowered. The upper
time of the contact is not specifically limited, however, it is
preferred 300 seconds or less in view of the reduction of the
occurrence of defects and the improvement of throughput, etc. The
method of the contact may be employed such as a puddle method, a
dipping method, a shower method, a spray method, etc., but not
limited thereto.
[0062] The remover solution is suitably used a water-based solvent,
and more preferably pure water. Prior to the removal step, rinsing
may optionally be performed with an aqueous solution of alkali
(e.g. tetramethylammonium hydroxide (TMAH) or choline). The
over-coating agent in the present invention is easy to remove by
washing with water and it can be completely removed from the
substrate and the photoresist pattern. The present invention can
effectively reduce the occurrence of defects entirely.
Specifically, among varieties of defects, the present invention is
extremely effective in reducing the occurrence of the defects that
are filled in the portions of holes and spacing areas.
[0063] 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.
[0064] 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.
[0065] 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. 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 the
substrate without causing pattern distortion or deformation.
[0066] The technical field of the present invention is the
semiconductor industry, etc., but it is not limited thereto.
EXAMPLES
[0067] 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
[0068] A copolymer including polyacrylate (PAA) and
polyvinylpyrrolidone (PVP) [2 g: PAA/PVP=2:1 (polymerization
ratio)], triethanolamine (0.18 g) and a polyoxyethyelene phosphate
ester surfactant (0.02 g; "PLYSURF A210G", product of Dai-ichi
Kogyo Seiyaku Co, Ltd.) were dissolved in water (52 g) to prepare
an over-coating agent.
[0069] 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.
[0070] The photoresist layer was exposed with an exposure unit
(Canon EPA-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 178.9 nm (i.e., the spacing between the
photoresist patterns, or the initial hole dimension, was 178.9
nm).
[0071] The previously prepared over-coating agent was applied onto
the substrate including hole patterns and 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 150.8 nm. The state of defects on the substrate was
observed with KLA (product of KLA Tencor), however, few defects
were occurred on the entire substrate.
Example 2
[0072] The same procedure as described in Example 1 was repeated,
except that the substrate was brought into contact with pure water
by dropping it on the substrate for 90 seconds. Each diameter of
the hole patterns was narrowed to 158.3 nm, and few defects were
occurred on the entire substrate
Comparative Example 1
[0073] The same procedure as described in Example 1 was repeated,
except that the substrate was brought into contact with pure water
by dropping it on the substrate for 60 seconds. Each diameter of
the hole patterns was narrowed to 158.8 nm. However, the
observation with KLA revealed the occurrence of defects on the
order of 10-20 in numbers on the substrate.
[0074] As described above in detail, the present invention provide
a method for forming fine patterns, by which advantages obtained of
reducing the occurrence of defects and improving throughput.
* * * * *