U.S. patent application number 09/901657 was filed with the patent office on 2002-03-14 for novel copolymer, photoresist composition , and process for forming resist pattern with high aspect ratio.
This patent application is currently assigned to TOKYO OHKA KOGYO CO., LTD.. Invention is credited to Doi, Kousuke, Ikegawa, Taeko, Kohara, Hidekatsu, Nakamura, Tsuyoshi, Sawano, Atsushi.
Application Number | 20020031720 09/901657 |
Document ID | / |
Family ID | 18710022 |
Filed Date | 2002-03-14 |
United States Patent
Application |
20020031720 |
Kind Code |
A1 |
Nakamura, Tsuyoshi ; et
al. |
March 14, 2002 |
Novel copolymer, photoresist composition , and process for forming
resist pattern with high aspect ratio
Abstract
A novel copolymer includes a repeating unit (B) derived from an
unsaturated carboxylic anhydride, a repeating unit (C) represented
by Formula (II), and a repeating unit (D) represented by Formula
(III). 1
Inventors: |
Nakamura, Tsuyoshi;
(Kanagawa, JP) ; Ikegawa, Taeko; (Kanagawa,
JP) ; Sawano, Atsushi; (Kanagawa, JP) ; Doi,
Kousuke; (Kanagawa, JP) ; Kohara, Hidekatsu;
(Kanagawa, JP) |
Correspondence
Address: |
SUGHRUE, MION, ZINN, MACPEAK & SEAS, PLLC
2100 Pennsylvania Avenue, N.W.
Washington
DC
20037
US
|
Assignee: |
TOKYO OHKA KOGYO CO., LTD.
|
Family ID: |
18710022 |
Appl. No.: |
09/901657 |
Filed: |
July 11, 2001 |
Current U.S.
Class: |
430/270.1 ;
430/312; 430/314; 528/25 |
Current CPC
Class: |
G03F 7/0758 20130101;
Y10S 430/111 20130101; G03F 7/0397 20130101; C08F 222/06 20130101;
G03F 7/405 20130101; Y10S 430/106 20130101 |
Class at
Publication: |
430/270.1 ;
430/312; 430/314; 528/25 |
International
Class: |
G03F 007/004; G03F
007/26 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 14, 2000 |
JP |
2000-214451. |
Claims
What is claimed is:
1. A novel copolymer comprising: a repeating unit (B) derived from
an unsaturated carboxylic anhydride; a repeating unit (C)
represented by Formula (II); and a repeating unit (D) represented
by Formula (III): 17wherein R.sup.1 is a hydrogen atom or a methyl
group; and R.sup.2 is an alkyl group having from 1 to 4 carbon
atoms.
2. A novel copolymer according to claim 1, wherein said repeating
unit (B) is a repeating unit (B-1) derived from a unsaturated
cyclic carboxylic anhydride.
3. A novel copolymer according to claim 2, wherein said repeating
unit (B-1) is a unit (B-2) represented by Formula (V): 18
4. A novel copolymer according to claim 2, wherein said repeating
unit (B-1) is a unit (B-3) represented by Formula (XVI): 19
5. A novel copolymer according to claim 1, wherein said repeating
unit (D) is a unit (D-1) represented by Formula (VI): 20
6. A novel copolymer according to claim 1, wherein the content of
repeating unit (B) is equal to or more than 15% and equal to or
less than 60% of all repeating units constituting said novel
copolymer.
7. A novel copolymer according to claim 1, wherein the content of
repeating unit (C) is equal to or more than 10% and equal to or
less than 40% of all repeating units constituting said novel
copolymer.
8. A novel copolymer according to claim 1, wherein the content of
repeating unit (D) is more than 0% and equal to or less than 40% of
all repeating units constituting said novel copolymer.
9. A novel copolymer according to any one of claims 1 to 8, wherein
said novel copolymer has a weight average molecular weight (Mw) in
terms of polystyrene of from 7000 to 30000 and a molecular-weight
distribution (Mw/Mn, where Mn is a number average molecular weight)
of equal to or less than 3.5.
10. A photoresist composition comprising: a novel copolymer
according to claim 1; a photosensitive acid generator; and an
organic solvent.
11. A photoresist composition according to claim 10, wherein said
photosensitive acid generator is a triphenylsulfonium-based onium
salt.
12. A photoresist composition according to claim 10, wherein said
organic solvent is propylene glycol monomethyl ether acetate
(PGMEA).
13. A process for forming a resist pattern with a high aspect
ratio, said process comprising the steps of: (a) applying a first
resist on a substrate and drying the applied first resist to
thereby form a first resist layer, applying a photoresist
composition of claim 10 onto the first resist layer and drying the
applied photoresist composition to thereby form a second resist
layer; (b) exposing the second resist layer to imaging radiation,
subjecting the exposed second resist layer to a heat treatment, and
dissolving and removing exposed portions or unexposed portions of
the second resist layer by developing in an alkaline aqueous
solution to thereby form a resist pattern; (c) applying a
silylation agent onto the formed resist pattern, rinsing the
applied resist pattern to thereby enlarge the resist pattern and to
form a silylation coating on the resist pattern, said silylation
coating being resistant to corrosion induced by oxygen-containing
plasma etching; and (d) etching the first resist layer under the
second resist layer with oxygen-containing plasma by using, as a
mask, the enlarged resist pattern carrying the silylation coating.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a chemically amplified
photoresist composition that is excellent in transparency to light
with wavelengths in the deep ultraviolet region (deep UV light)
such as KrF or ArF laser light, and exhibits high sensitivity and
definition, to a novel copolymer that is suitable for the
preparation of the photoresist composition, and to a process for
the formation of a resist pattern with a high aspect ratio.
Specifically, the present invention relates to a chemically
amplified photoresist composition that is suitable for a process
for the formation of a resist pattern with a high aspect ratio
using a silylation agent, and to a process for the formation of a
resist pattern with a high aspect ratio.
[0003] 2. Description of the Related Art
[0004] To form an ultrafine resist pattern of not more than 0.35
.mu.m, specifically of not more than 0.25 .mu.m, a variety of
highly sensitive photoresist compositions having satisfactory
transparency to deep UV light such as KrF or ArF laser light have
been reported.
[0005] Among them, "chemically amplified" photoresist compositions
containing a substance carrying an acid-decomposable group, and a
photosensitive acid generator are predominant. However, demands
have been made to further improve the sensitivity and definition of
these chemically amplified photoresist compositions.
[0006] Additionally, the use of this type of photoresist
compositions alone cannot significantly form a resist pattern with
a good shape, especially a hole-type resist pattern with a high
aspect ratio and a good shape. As a possible solution to this
problem, a technique has been reported in which a second film or
coating composed of a silylation agent is formed on the surface of
a resist pattern, and using this second film, a resist pattern with
a high aspect ratio is formed.
[0007] This technique using a silylation agent is reported, for
example, in Microelectronic Engineering 11 (1990) 531-534
(Reference 1), and is performed substantially in the following
manner.
[0008] Initially, a resist film (bottom resist) is formed on a
substrate, and this bottom resist is resistant to etching treatment
for the substrate. Another resist film is then formed on the bottom
resist, using a photoresist composition containing, for example, a
polymer having a repeating unit represented by Formula (V) below,
and the formed resist film is selectively patterned by exposure and
developing to thereby form a resist pattern.
[0009] Next, a solution of, for example, a compound represented by
Formula (VIII) below (silylation agent) is applied onto the resist
pattern and is then rinsed to thereby form a silylation coating on
the resist pattern, and the resulting silylation coating is
resistant to corrosion induced by oxygen plasma etching.
[0010] The underlayer bottom resist is removed by etching using, as
a mask, the resist pattern carrying the silylation coating to
thereby form a resist pattern with a high aspect ratio. 2
[0011] Such photoresist compositions that can be applied to this
process comprising the above operations must essentially react with
a silylation agent to form a silylation coating and must have high
sensitivity and definition.
[0012] Japanese Patent Laid-Open No. 5-11450 (Reference 2)
discloses, as the aforementioned photoresist compositions, a
photoresist composition containing a polymer and a photosensitive
acid generator, which polymer comprises a (meth)acrylic tert-butyl
ester group and a maleic anhydride functional group, and a
photoresist composition containing a polymer and a photosensitive
acid generator, which polymer comprises a (meth)acrylic tert-butyl
ester group, a maleic anhydride functional group, and an
allyltrimethylsilane group.
[0013] These compositions have satisfactory transparency to deep UV
light and have high sensitivity, but their definition must be
further improved.
[0014] Japanese Patent Laid-Open No. 11-212265 (Reference 3)
discloses a photoresist composition comprising a polymer and a
photosensitive acid generator, which polymer has a repeating unit
represented by Formula (III) and a repeating unit represented by
Formula (VII): 3
[0015] wherein R.sup.1 is a hydrogen atom or a methyl group; and
R.sup.2 is an alkyl group having from 1 to 4 carbon atoms.
[0016] Even this composition must be further improved in
sensitivity and definition.
[0017] Additionally, when this composition is applied to the
process using a silylation agent, it cannot significantly react
with the silylation agent to thereby fail to form a silylation
coating, and a hole pattern with a high aspect ratio cannot be
significantly obtained.
SUMMARY OF THE INVENTION
[0018] Accordingly, an object of the present invention is to
provide a chemically amplified photoresist composition that has
satisfactory transparency, high sensitivity and definition in the
field of photolithography using a deep UV light source such as KrF
or ArF laser, and to provide a novel copolymer that is suitable for
the preparation of the photoresist composition.
[0019] Another object of the present invention is to provide a
chemically amplified photoresist composition that is suitable for a
process for the formation of a resist pattern with a high aspect
ratio using a silylation agent, and to provide a process for the
formation of a resist pattern with a high aspect ratio.
[0020] After intensive investigations, the present inventors have
found that the above objects can be achieved by the use of novel
copolymers having specific repeating units.
[0021] Specifically, the present invention provides, in an aspect,
a novel copolymer including a repeating unit (B) derived from an
unsaturated carboxylic anhydride, a repeating unit (C) represented
by Formula (II), and a repeating unit (D) represented by Formula
(III): 4
[0022] wherein R.sup.1 is a hydrogen atom or a methyl group; and
R.sup.2 is an alkyl group having from 1 to 4 carbon atoms.
[0023] In the novel copolymer, repeating unit (B) is preferably a
repeating unit (B-1) derived from an unsaturated cyclic carboxylic
anhydride.
[0024] Repeating unit (B-1) is preferably a unit (B-2) represented
by Formula (V): 5
[0025] Alternatively, repeating unit (B-1) is preferably a unit
(B-3) represented by Formula (XVI): 6
[0026] In the novel copolymer, repeating unit (D) may be a unit
(D-1) represented by Formula (VI): 7
[0027] The content of repeating unit (B) is preferably equal to or
more than 15% and equal to or less than 60% of all repeating units
constituting the novel copolymer.
[0028] The content of repeating unit (C) is preferably equal to or
more than 10% and equal to or less than 40% of all repeating units
constituting the novel copolymer.
[0029] The content of repeating unit (D) is preferably more than 0%
and equal to or less than 40% of all repeating unit constituting
the novel copolymer.
[0030] The novel copolymer may have a weight average molecular
weight (Mw) in terms of polystyrene of from 7000 to 30000 and a
molecular-weight distribution (Mw/Mn, where Mn is a number average
molecular weight) of equal to or less than 3.5.
[0031] In another aspect, the present invention provides a
photoresist composition including the novel copolymer, a
photosensitive acid generator, and an organic solvent.
[0032] In the photoresist composition, the photosensitive acid
generator is preferably a triphenylsulfonium-based onium salt.
[0033] The organic solvent is preferably propylene glycol
monomethyl ether acetate (PGMEA).
[0034] In addition and advantageously, the present invention
provides a process for forming a resist pattern with a high aspect
ratio, which process includes the steps of (a) applying a first
resist on a substrate and drying the applied first resist to
thereby form a first resist layer, applying the photoresist
composition the first resist layer and drying the applied
photoresist composition to thereby form a second resist layer; (b)
exposing the second resist layer to imaging radiation, subjecting
the exposed second resist layer to a heat treatment, and dissolving
and removing exposed portions or unexposed portions of the second
resist layer by developing in an alkaline aqueous solution to
thereby form a resist pattern; (c) applying a silylation agent onto
the formed resist pattern, rinsing the applied resist pattern to
thereby enlarge the resist pattern and to form a silylation coating
on the resist pattern, which silylation coating is resistant to
corrosion induced by oxygen-containing plasma etching; and (d)
etching the first resist layer under the second resist layer with
oxygen-containing plasma by using, as a mask, the enlarged resist
pattern carrying the silylation coating.
DETAILED DESCRIPTION OF THE INVENTION
[0035] [Novel Copolymers]
[0036] Novel copolymers of the present invention can be
synthetically obtained by a known polymerization reaction using
specific comonomers. Repeating units (B), (C) and (D) (hereinafter
briefly referred to as "Ingredients (B), (C) and (D)") will be
illustrated in further detail below, as constitutional comonomers
for the preparation of the novel copolymers.
[0037] [Ingredient (B)]
[0038] Ingredient (B) constituting the invented copolymers is a
repeating unit derived from an unsaturated carboxylic anhydride and
is an essential unit, since the repeating unit serves to react with
a silylation agent (e.g., a siloxane polymer having an amino group)
to thereby form a silylation coating in the process using the
silylation agent.
[0039] Comonomers corresponding to Ingredient (B) are not
specifically limited and include, for example, unsaturated
carboxylic anhydrides described in Japanese Patent Laid-Open Nos.
2-282746, 2-308255, 2-308256, 5-9231,2-11450, 5-11456, and
11-212265. Such unsaturated carboxylic anhydrides include, for
example, compounds represented by Formulae (IX) and (X), and other
unsaturated acyclic carboxylic anhydrides; and compounds
represented by Formulae (XI), (XII), (XIII), (XIV), and (XV), and
other unsaturated cyclic carboxylic anhydrides: 8
[0040] wherein R.sup.4 is an alkyl group having from 1 to 5 carbon
atoms or an aryl group; and R.sup.5 is a hydrogen atom or an alkyl
group having from 1 to 4 carbon atoms, 9
[0041] wherein each of R.sup.5 and R.sup.6 is independently a
hydrogen atom or an alkyl group having from 1 to 4 carbon atoms,
10
[0042] wherein R.sup.7 is a hydrogen atom or an alkyl group having
from 1 to 4 carbon atoms, 11
[0043] wherein each of R.sup.8 and R.sup.9 is independently a
hydrogen atom or an alkyl group having from 1 to 4 carbon atoms,
12
[0044] wherein R.sup.10 is a hydrogen atom or an alkyl group having
from 1 to 4 carbon atoms. 13
[0045] Among these comonomers, maleic anhydride is typically
preferable for its high reactivity with a silylation agent and
satisfactory transparency to deep UV light such as KrF or ArF laser
light. Preferred Ingredients (B) for use in the invented copolymers
are repeating units (B-2) and (B-3) represented by Formulae (XI)
and (XV) which are derived from unsaturated cyclic carboxylic
anhydrides.
[0046] [Ingredient (C)]
[0047] Ingredient (C) constituting the invented copolymers is a
repeating unit represented by Formula (II) and serves to enhance
reactivity with a silylation agent (e.g., a siloxane polymer having
an amino group) in the process using the silylation agent.
Additionally, the resulting photoresist composition obtained by
using a copolymer containing Ingredient (C) has improved
sensitivity and definition.
[0048] A comonomer corresponding to Ingredient (C) is
allyltrimethylsilane.
[0049] [Ingredient (D)]
[0050] Ingredient (D) constituting the invented copolymers is a
repeating unit represented by Formula (III), which has an
2-alkyl-2-adamantyl group as an acid-decomposable group and is
satisfactory in transparency to deep UV light such as KrF or ArF
laser light. The substituent R.sup.1 in the formula is a hydrogen
atom or a methyl group, and R.sup.2 is an alkyl group having from 1
to 4 carbon atoms. The resulting photoresist composition prepared
by using a copolymer containing Ingredient (D) has further improved
sensitivity and definition.
[0051] Comonomers corresponding to Ingredient (D) include, for
example, 2-methyl-2-adamantyl acrylate, 2-ethyl-2-adamantyl
acrylate, 2-propyl-2-adamantyl acrylate, 2-butyl-2-adamantyl
acrylate, 2-methyl-2-adamantyl methacrylate, 2-ethyl-2-adamantyl
methacrylate, 2-propyl-2-adamantyl methacrylate, and
2-butyl-2-adamantyl methacrylate. Among them, 2-methyl-2-adamantyl
methacrylate is typically preferred to yield higher sensitivity and
definition of the resulting photoresist composition. These
comonomers corresponding to Ingredient (D) can be synthetically
obtained by known processes as described in, for example, Japanese
Patent Laid-Open No. 11-212265. For example, these comonomers can
be obtained by an esterification reaction of an
2-alkyl-2-adamantanol with acryloyl chloride or methacryloyl
chloride.
[0052] [Contents of Ingredients (B), (C) and (D)]
[0053] The content of Ingredient (B) preferably falls within a
range from 15% to 60% inclusive, and more preferably from 35% to
50% inclusive, of all the repeating units constituting the novel
copolymer.
[0054] If the content of Ingredient (B) is less than 15%, the
reactivity with the silylation agent may be insufficient, and if it
exceeds 60%, Ingredient (B) may be readily converted into a
dicarboxylic acid moiety by a reaction with moisture in the air or
in the photoresist film to thereby vary the composition of the
copolymer.
[0055] The content of Ingredient (C) preferably falls within a
range from 10% to 40% inclusive, and more preferably from 20% to
30% inclusive, of all the repeating units constituting the novel
copolymer.
[0056] If the content of Ingredient (C) is less than 10%, the
reactivity with the silylation agent may not be sufficiently
enhanced and the sensitivity and definition may not be
satisfactorily improved. If it exceeds 40%, the definition and
focal depth range properties may be decreased.
[0057] The content of Ingredient (D) preferably falls within a
range of more than 0% and equal to or less than 40%, and more
preferably from 5% to 30% inclusive, of all the repeating units
constituting the novel copolymer.
[0058] If the content of Ingredient (D) is 0%, the resulting
photoresist composition may not have satisfactory sensitivity and
definition, and if it exceeds 40%, the shape of resist pattern and
focal depth range properties may be deteriorated.
[0059] The most preferred embodiment is a copolymer comprising all
Ingredients (B), (C) and (D).
[0060] [Polymerization Reaction]
[0061] The invented novel copolymers can be synthetically obtained
by subjecting the individual comonomers to a polymerization
reaction with a polymerization initiator.
[0062] Such polymerization initiators include, but are not limited
to, those described in, for example, Japanese Patent Laid-Opens No.
5-11450 and No. 11-212265, such as azobisisobutyronitrile and
dimethyl-2,2-azoisobisbutyrate. Among them, azobisisobutyronitrile
is typically preferred, since this compound can enhance the
polymerization reaction to thereby yield a copolymer having narrow
molecular-weight distribution.
[0063] An example of the production process of the invented novel
copolymers will be schematically illustrated below, but the
invention is not limited thereto.
[0064] (Step 1)
[0065] Initially, the material comonomers, polymerization
initiator, and additives are added to an organic solvent (e.g.,
ethyl acetate) in a reactor and are dissolved in the organic
solvent by stirring at room temperature for several ten
minutes.
[0066] (Step 2)
[0067] The resulting mixture is heated to a temperature from about
60.degree. C. to about 75.degree. C., and is stirred at this
temperature for several ten hours.
[0068] (Step 3)
[0069] After the completion of stirring, heating procedure is
ceased, and the reaction mixture is cooled to about 30.degree. C.
and is then added dropwise to a poor solvent such as petroleum
benzine or 2-propanol with stirring to thereby precipitate a
copolymer.
[0070] (Step 4)
[0071] The precipitated copolymer is rinsed with several portions
of, for example, petroleum benzine and is then dried in a vacuum
dessicator set at several ten degrees Celsius to thereby yield a
target copolymer.
[0072] The invented copolymer has a weight average molecular weight
(Mw) in terms of polystyrene of preferably from about 7000 to about
30000 and more preferably from about 10000 to about 20000. If the
average molecular weight (Mw) in terms of polystyrene is less than
7000, the copolymer may have low solubility in alcohols, and if it
exceeds 30000, the resulting photoresist composition may have low
definition.
[0073] The copolymer has a molecular-weight distribution (Mw/Mn) of
preferably equal to or less than 3.5 and more preferably equal to
or less than 2.5. If the molecular-weight distribution (Mw/Mn)
exceeds 3.5, the resulting photoresist composition may have
insufficient definition.
[0074] [Photoresist Composition]
[0075] Photoresist compositions according to the present invention
can be prepared by mixing the invented novel copolymer, a
photosensitive acid generator, and an organic solvent. The content
of the novel copolymer is preferably from 1 to 30% by weight and
more preferably from 3 to 10% by weight relative to the total
weight of the composition.
[0076] [Photosensitive Acid Generator]
[0077] When the invented photoresist composition is used for the
formation of a resist pattern, the photosensitive acid generator
liberates an acid in exposed portions in the step of exposing a
photoresist film to imaging radiation. Additionally, a subsequent
heat treatment permits an "acid-decomposable group" (e.g., an
2-alkyl-2-adamantyl group) in the copolymer skeleton of the
composition to eliminate, which acid-decomposable group is
decomposed by the catalytic reaction of the acid and becomes
soluble in alkali. Consequently, exposed portions of the resist
film are dissolved in a developer solution, an alkaline aqueous
solution, to thereby yield a resist pattern.
[0078] Photosensitive acid generators for use in the present
invention include, but are not specifically limited to, those
described in, for example, Japanese Patent Laid-Open Nos. 5-11450
and 11-212265, such as onium salt compounds, organohalogen
compounds, sulfone compounds, and sulfonate compounds. Among them,
onium salt-based photosensitive acid generators are preferred,
since the resulting photoresist compositions have high sensitivity
and can form a resist pattern with a good shape, of which
triphenylsulfonium-based onium salts are typically preferred for
high sensitivity.
[0079] Such triphenylsulfonium-based onium salts include, for
example, the following compounds represented by Formulae (E-1) to
(E-3): 14
[0080] The amount of the photosensitive acid generator is
preferably from 0.01 to 3.0% by weight and more preferably from
0.03 to 0.8% by weight relative to the total weight of the
composition.
[0081] [organic Solvent]
[0082] Organic solvents for use in the invention include, but are
not specifically limited to, acetone, methyl ethyl ketone,
cyclohexanone, methyl isoamyl ketone, 2-heptanone, and other
ketones; ethylene glycol, propylene glycol, diethylene glycol,
ethylene glycol monoacetate, propylene glycol monoacetate,
diethylene glycol monoacetate, or monomethyl ethers, monoethyl
ethers, monopropyl ethers, monobutyl ethers, or monophenyl ethers
of these compounds, and other polyhydric alcohols and derivatives
thereof; dioxane and other cyclic ethers; and ethyl lactate, methyl
acetate, ethyl acetate, butyl acetate, methyl pyruvate, ethyl
pyruvate, methyl methoxypropionate, ethyl ethoxypropionate, and
other esters. Each of these organic solvents can be used alone or
in combination.
[0083] Among them, propylene glycol monomethyl ether acetate
(PGMEA) is preferred, since this solvent has good coating
performance, low hygroscopicity, and a high boiling point. Solvents
having high hygroscopicity are not desirable, since the resulting
photoresist composition takes in moisture in the air to thereby
deteriorate the copolymer. Additionally, solvents having a low
boiling point are also undesirable, since the amount of solvent
remained in the formed photoresist film is low and the
photosensitive acid generator does not efficiently diffuse in the
procedure of, for example, post-exposure baking (PEB).
[0084] [Other Additives]
[0085] The invented photoresist compositions may further comprise
known or conventional additives according to necessity, within
ranges not adversely affecting the objects of the present
invention. Such additives include, for example, dissolution
inhibitors, other resins, stabilizers, organic polymeric compounds,
thermopolymerization inhibitors, sensitizers, improvers for
adhesion to substrates, surfactants, and dyes.
[0086] The invented photoresist compositions are suitable as
positive photoresist compositions, but can be used as negative
photoresist compositions for the formation of negative resist
patterns, by incorporating acid-crosslinkable materials (substances
which are crosslinked by action of an acid generated from a
photosensitive acid generator) into the photoresist
compositions.
[0087] The invented composition is preferably used, for example, in
the following manner. Initially, a solution of the (positive)
photoresist composition is applied on a substrate such as a silicon
wafer, and is then dried to thereby form a photosensitive layer;
and the photosensitive layer is exposed to light through a
patterned photomask.
[0088] Next, the exposed portions of the photosensitive layer are
subjected to post-exposure baking (PEB) and are then dissolved and
removed by dipping the substrate in a developer solution, for
example, an alkaline aqueous solution such as a 1% to 10% by weight
tetramethylammonium hydroxide (TMAH) aqueous solution, thus forming
an image (resist pattern) being in exact accordance with the mask
pattern. To further improve the definition of the resist pattern,
an anti-reflection coating is preferably formed between the
substrate and the photosensitive layer composed of the invented
composition.
[0089] [Process for Forming Resist Pattern with High Aspect
Ratio]
[0090] The invented photoresist compositions are specifically
suitable for the process for the formation of a resist pattern
using a silylation agent. In the process, adjacent resist patterns
(line width) are enlarged and grooves (space width) are narrowed by
using a silylation agent to thereby form a resist pattern with a
high aspect ratio, and the invented photoresist compositions can be
advantageously used in this process. The process will be
schematically illustrated below, but the invention is not limited
thereto.
[0091] (Step a)
[0092] A first resist that can be smoothed is applied on a
substrate and is dried to thereby form a first resist layer (herein
after referred to as "bottom resist", which will be described
later), and the invented photoresist composition that can form a
resist pattern by photolithography is applied onto the first resist
layer and is dried to thereby form a second resist layer
(hereinafter referred to as "top resist").
[0093] (Step b)
[0094] Subsequently, the top resist is exposed to imaging radiation
and is then subjected to a heat treatment, and the exposed portions
(in case of a positive photoresist composition) or unexposed
portions (in case of a negative photoresist composition) are
dissolved and removed by developing in an alkaline aqueous solution
to thereby form a resist pattern in exact accordance with the mask
pattern.
[0095] (Step c)
[0096] Next, a silylation agent, which will be described later, is
applied onto the formed resist pattern and the resist pattern is
rinsed to enlarge the resist pattern (line width) and to form a
silylation coating. The silylation coating is resistant to
corrosion induced by oxygen-containing plasma etching.
[0097] (Step d)
[0098] The groove (space pattern) or hole (hole pattern) is
narrowed by enlargement of the resist pattern carrying the
silylation coating, and the bottom resist is etched with
oxygen-containing plasma using the narrowed groove or hole as a
mask to thereby form a resist pattern with a desired height in the
bottom resist.
[0099] This process can therefore form a resist pattern with a
higher aspect ratio.
[0100] [Bottom Resist]
[0101] In the above process, the bottom resist is preferably
composed of a material resistant to etching of the underlayer
substrate, and is more preferably composed of a novolak resin. As
such materials, photoresist compositions mainly containing a
novolak resin and a quinonediazide are suitable. By heating the
applied bottom resist on the substrate, cross-linking of the
novolak resin occurs to thereby improve resistance to etching and
to inhibit dissolution of the bottom resist and the top resist (the
invented photoresist composition) in each other.
[0102] [Silylation Agent]
[0103] Silylation agents for use in the above process are enlarging
reagents that can be bonded with the resist pattern of the top
resist (the invented photoresist composition) and can increase the
volume of the resist pattern. Additionally, the resist pattern
carrying a silylation coating composed of the silylation agent can
become a layer that is very resistant to corrosion induced by dry
developing in oxygen-containing plasma etching for etching the
bottom resist.
[0104] Silylation agents having a Si-O (siloxane) structure are
preferred as the silylation agents, since a nonvolatile oxide is
formed from a silicon-containing group in the silylation coating
during oxygen-containing plasma etching to thereby enhance
corrosion resistance, and the siloxane compounds are highly
thermally stable to thereby avoid pattern deformation during the
etching step at high temperatures. These siloxane compounds can be
easily directly converted into silicon dioxide and produce little
volatile organosilicon compound in oxygen-containing plasma. Among
them, siloxane compounds having an amino group are preferred, such
as aminosiloxane, diaminosiloxane, and
bisaminopropylpolydimethylsiloxane. The amino group in the
silylation agent rapidly reacts with Ingredient (B) of the
copolymer in the invented photoresist composition on the surface of
the resist pattern of the top resist to increase the volume of the
resist pattern to thereby narrow the space pattern.
[0105] Commercially available agents can be used as the silylation
agents. For example, a preferred silylation agent solution for use
in the invention is a 1% by weight
bisaminopropylpolydimethylsiloxane solution prepared by dissolving
bisaminopropylpolydimethylsiloxane (available from Shin-Etsu
Chemical Co., Ltd., under the trade name of "X-22-161 AS") in an
aqueous 1-hexanol solution.
BRIEF DESCRIPTION OF THE DRAWINGS
[0106] FIG. 1 is a diagram showing the spectrum of Copolymer 1
obtained in Synthesis Example 1, measured by Fourier transform
infrared spectrophotometry (FT-IR); and
[0107] FIG. 2 is a diagram showing the chart of Copolymer 1
obtained in Synthesis Example 1, measured by gel permeation
chromatography (GPC).
EXAMPLES
[0108] The present invention will be illustrated in further detail
with reference to several examples and comparative examples below,
which are not intended to limit the scope of the invention.
[0109] The physical properties of the photoresist compositions were
determined according to the following methods.
[0110] (1) Sensitivity Evaluation
[0111] Initially, a novolak resin-quinonediazide positive
photoresist composition (available from Tokyo Ohka Kogyo Co., Ltd.,
under the trade name of "THMR-iP5700) was applied on a silicon
wafer, and was cured by heat to thereby form a resist film (bottom
resist) 0.6 .mu.m thick. This was used as a substrate in the
subsequent procedure. A sample was applied onto the substrate using
a spinner, and was dried on a hot plate at 110.degree. C. for 90
sec. to form a resist film 0.2 .mu.m thick. The resist film was
then irradiated through a mask corresponding to a hole diameter of
0.23 .mu.m and a duty ratio of 1:0.57 (interval between holes: 0.13
.mu.m) using a reducing-type projection aligner NSR-S203B
(available from Nikon Corporation, Japan; NA=0.60, .delta.=0.68)
with increasing bias from 10 mJ/cm.sup.2 at intervals of 1
mJ/cm.sup.2. The film was then post-exposure baked (PEB) at
130.degree. C. for 90 sec.; was subjected to developing in a 2.38%
by weight tetramethylammonium hydroxide aqueous solution at
23.degree. C. for 40 sec., was washed with water for 15 sec., and
was dried. In this procedure, the sensitivity was defined as the
exposure time period (Eop) (mJ/cm.sup.2) to reproduce a 0.18-tm
hole pattern.
[0112] (2) Definition
[0113] The definition was defined as the minimum mask size (.mu.m)
in the critical definition to separate the bottom of the pattern at
an exposure of Eop in the procedure of Evaluation (1).
[0114] (3) Focal Depth Range Properties
[0115] A sample was subjected to exposure and developing in the
same manner as in Evaluation (1), except that the focus was shifted
up and down at an exposure of Eop as the standard exposure. The
resulting hole pattern was subjected to a scanning electron
micrographic (SEM) observation. Based upon the SEM photograph, the
focal depth range property was defined as the maximum value (am) of
the focal shift (defocus) to reproduce a 0.18-.mu.m hole pattern
when the hole pattern was formed under bias using a 0.23-.mu.m
mask.
Synthesis Example 1
[0116] Synthesis of Copolymer 1
[0117] To 69.4 parts by weight of ethyl acetate in a reactor, 15.9
parts by weight (0.36 mole) of 2-methyl-2-adamantyl methacrylate,
9.9 parts by weight (0.54 mole) of maleic anhydride, 6.4 parts by
weight (0.30 mole) of allyltrimethylsilane, and 0.6 part by weight
of azobisisobutyronitrile were added, and were stirred at room
temperature (25.degree. C.) for 60 minutes.
[0118] Next, the resulting mixture was heated to about 70.degree.
C. and was stirred at this temperature for about 22 hours.
[0119] To the resulting reaction mixture, 11.5 g (0.36 mole) of a
2.0% by weight methanol aqueous solution was added dropwise, and
the mixture was further stirred for about 22 hours.
[0120] After the completion of stirring, the heating operation was
stopped, and the reaction mixture was cooled to about 30.degree. C.
and was then added dropwise to petroleum benzine with stirring to
thereby precipitate a copolymer.
[0121] The precipitated copolymer was rinsed several portions of
petroleum benzine and was dried in a vacuum dessicator set at about
60.degree. C. for 3 hours to thereby yield Copolymer 1.
[0122] Copolymer 1 was subjected to FT-IR assay by the KBr method
using an FT-IR system (available from The Perkin-Elmer Corporation,
under the trade name of "SPECTRUM 2000").
[0123] The results are shown in FIG. 1.
[0124] FIG. 1 shows that the characteristic band of adamantyl
moiety of 2-methyl-2-adamantyl methacrylate in the vicinity of 1100
cm.sup.-1, the absorption of C.dbd.O stretching vibration of maleic
anhydride in the vicinity of 1780 cm.sup.-1, and the absorption of
the deformation vibration of Si--CH.sub.3 of allyltrimethylsilane
in the vicinity of 1250 cm.sup.-1 were respectively observed.
[0125] Separately, Copolymer 1 was subjected to gel permeation
chromatographic (GPC) analysis by the R.I. method using a GPC
system (available from Shodex, under the trade name of
"GPC-SYSTEM-11").
[0126] The results are shown in FIG. 2.
[0127] FIG. 2 shows that Copolymer 1 was a polymer having a weight
average molecular weight (Mw) in terms of polystyrene of about
18700 and a molecular-weight distribution (Mw/Mn) of about
1.67.
Synthesis Examples 2 to 4
[0128] Synthesis of Copolymers 2 to 4
[0129] Copolymers 2 to 4 containing the repeating units indicated
in Table 1 were synthetically obtained in the same manner as in
Synthesis Example 1, except that the types and compositional ratios
of individual comonomers were varied.
Comparative Synthesis Examples 1 and 2
[0130] Synthesis of Copolymers 5 and 6
[0131] Copolymers 5 and 6 containing the repeating units indicated
in Table 1 were synthetically obtained in the same manner as in
Synthesis Example 1, except that the types and compositional ratios
of individual comonomers were varied. Copolymer 5 as a comparative
example was obtained by using tert-butyl methacrylate as a
comonomer. The repeating unit derived from tert-butyl methacrylate
is a unit represented by Formula (X-1) below.
1TABLE 1 (X-1) 15 Example No. (Copolymer) (B) (C) (D) (X) (MW)
(Mw/Mn) (mole %) (mole %) (mole %) (mole %) Synthesis Example 1 B-2
C D-1 none (Copolymer 1) (45) (25) (30) (18700) (1.67) Synthesis
Example 2 B-3 C D-1 none (Copolymer 2) (45) (25) (30) (10000) (1.6)
Synthesis Example 3 B-2 C D-1 none (Copolymer 3) (45) (20) (35)
(15000) (1.9) Synthesis Example 4 B-2 C D-1 none (Copolymer 4) (45)
(30) (25) (16800) (1.9) Comp. Syn. Ex. 1 B-2 C none X-1 (Copolymer
5) (50) (27.5) (22.5) (20000) (2.0) Comp. Syn. Ex. 2 B-2 none D-1
none (Copolymer 6) (70) (30) (20000) (2.0)
Examples 1 to 4 and Comparative Examples 1 and 2
[0132] Each of Copolymers 1 to 6 synthetically obtained in
Synthesis Examples 1 to 4 and Comparative Synthesis Examples 1 and
2 was dissolved in PGMEA to thereby yield a 7% by weight polymer
solution.
[0133] In 30 g of the above-prepared polymer solution, 0.158 g of a
triphenylsulfonium-based onium salt represented by Formula (E-3)
below was dissolved, and the resulting solution was filtrated
though a membrane filter of 0.1 to 0.2 .mu.m pore size to thereby
yield a series of photoresist compositions. 16
[0134] Evaluations (1) to (3) were conducted on the photoresist
compositions prepared according to Examples 1 to 4 and Comparative
Examples 1 and 2, and the results are shown in Table 2.
2 TABLE 2 Sensitivity Definition Focal depth range (mJ/cm.sup.2)
(.mu.m) property (.mu.m) Example 1 45 0.16 0.6 Example 2 45 0.17
0.6 Example 3 30 0.16 0.5 Example 4 55 0.17 0.5 Comp. Ex. 1 40 0.18
0.6 Comp. Ex. 2 80 0.18 0.4
Synthesis Example 5
[0135] Preparation of Silylation Agent Solution
[0136] Bisaminopropylpolydimethylsiloxane (available from Shin-Etsu
Chemical Co., Ltd., under the trade name of "X-22-161 AS") was
dissolved in a 98.5% by weight 1-hexanol aqueous solution to
thereby yield a 1% by weight silylation agent solution.
Example 5
[0137] Formation of a Resist Pattern with a High Aspect Ratio using
the Silylation Agent
[0138] A hole pattern [a hole pattern 0.18 .mu.m wide] was formed
on a substrate at depth of focus of 0 in the same manner as in
Evaluation (3) in Example 1, and the above-prepared silylation
agent solution was carefully placed as a heap on the substrate
carrying the hole pattern, and was allowed to stand for 30 seconds,
and the substrate was rinsed with isopropanol for 15 seconds.
[0139] The cross section (profile) of the resist pattern after the
silylation was subjected to SEM photographic observation and was
found that the initial hole diameter, 0.18 .mu.m, was narrowed to
0.14 .mu.m by the formation of a silylation coating and that the
hole profile was not deteriorated.
Comparative Example 3
[0140] Formation of a Resist Pattern with a High Aspect Ratio using
the Silylation Agent
[0141] A hole pattern [a hole pattern 0.18 .mu.m wide] was formed
on a substrate at depth of focus of 0 in the same manner as in
Evaluation (3) in Comparative Example 1, and the above-prepared
silylation agent solution was carefully placed as a heap on the
substrate carrying the hole pattern, and was allowed to stand for
30 seconds, and the substrate was rinsed with isopropanol for 15
seconds.
[0142] The cross section (profile) of the resist pattern after the
silylation was subjected to SEM photographic observation and was
found that the initial hole diameter, 0.18 .mu.m, was narrowed to
0.15 .mu.m by the formation of the silylation coating but that the
hole profile was deteriorated.
Comparative Example 4
[0143] Formation of a Resist Pattern with a High Aspect Ratio using
the Silylation Agent
[0144] A hole pattern [a hole pattern 0.18 .mu.m wide] was formed
on a substrate at depth of focus of 0 in the same manner as in
Evaluation (3) in Comparative Example 2, and the above-prepared
silylation agent solution was carefully placed as a heap on the
substrate carrying the hole pattern, and was allowed to stand for
30 seconds, and the substrate was rinsed with isopropanol for 15
seconds.
[0145] The cross section (profile) of the resist pattern after the
silylation was subjected to SEM photographic observation and was
found that no silylation coating was formed and that the hole
diameter was not narrowed.
[0146] Advantages
[0147] The present invention can provide a chemically amplified
photoresist composition that has satisfactory transparency, high
sensitivity and definition in the field of photolithography using a
deep UV light source such as KrF or ArF laser, and provide a novel
copolymer that is suitable for the preparation of the photoresist
composition.
[0148] Additionally, the present invention can provide a chemically
amplified photoresist composition that is suitable for a process
for the formation of a resist pattern with a high aspect ratio
using a silylation agent, and provide a process for the formation
of a resist pattern with a high aspect ratio.
[0149] Other embodiments and variations will be obvious to those
skilled in the art, and this invention is not to be limited to the
specific matters stated above.
* * * * *