Resist composition with polymeric dissolution inhibitor and alkali soluble resin

A resist composition comprising an alkali-soluble resin, typically a partially t-butoxycarbonylated polyhydroxystyrene, a p-butoxystyrene/t-butylacrylate copolymer or p-butoxystyrene/maleic anhydride copolymer as a dissolution inhibitor, and a iodonium or sulfonium salt as a photoacid generator is effective for forming a resist film which can be precisely and finely patterned using high energy radiation such as a KrF excimer laser.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a resist composition of the chemically amplified 
type for use in forming fine patterns upon manufacture of super LSIs 
(large scale integration). 
2. Prior Art 
As the LSI technology tends toward higher integration and higher speed, 
further refinement of pattern rules is required. The patterning technology 
mostly relies on light exposure which is now approaching to the essential 
limit of resolution which is dictated by the wavelength of a light source. 
It is generally recognized that in light exposure using g-ray (wavelength 
436 nm) or i-ray (wavelength 365 nm) as a light source, a pattern rule of 
about 0.5 .mu.m is the limit. For LSIs fabricated by such light exposure 
technique, a degree of integration equivalent to 16 mega-bit DRAM is the 
limit. At present, LSIs fabricated in the laboratory have reached this 
stage. It is urgently required to develop a finer patterning technique. 
Under such circumstances, deep-ultra-violet lithography is regarded 
promising as the next generation of fine patterning technology. The 
deep-UV lithography is capable of working on the order of 0.3 to 0.4 
.mu.m. If a less light absorbing resist is used, it is possible to form a 
pattern having a side wall nearly perpendicular to the substrate. The 
deep-UV lithography is also capable of pattern transfer all at once and 
thus affords an advantageous throughput than the electron beam 
lithography. Great attention is now paid to the technique of utilizing a 
high illuminance KrF excimer laser as a deep-UV light source. In order to 
employ this technique on a mass production scale, a resist material having 
low light absorption and high sensitivity is desired. 
Well-known positive resists adapted for g- and i-ray exposure use 
diazonaphthoquinone-novolak resins. However, since these resins are very 
low in sensitivity and undergo light absorption in the deep-UV region, 
they cannot be used as deep-UV positive resists. For this reason, the 
mainstream of recently developed deep-UV positive resists is a chemically 
amplified resist composition comprising a photoacid generator capable of 
generating an acid upon exposure and a resin having an acid unstable group 
in its backbone. 
One exemplary resin having an acid-sensitive substituent is 
polyhydroxystyrene having OH groups protected. Upon removal of the 
protective group with acid, the resin becomes soluble in a developer. A 
resist composition of two component system consisting essentially of such 
a resin and a photoacid generator is disclosed in Japanese Patent 
Application Kokai (JP-A) No. 251259/1992 or EP 476865. In this 
two-component system resist composition, however, many OH groups must be 
protected so that unexposed areas may not be dissolved in the developer 
while many protective groups must be decomposed so that exposed areas may 
be dissolved in the developer. This undesirably leaves the increased 
possibility of changing film thickness and introducing stresses and 
bubbles in the film. 
Then proposed was a chemically amplified resist composition having 
functions further diversified, that is, a three-component system 
comprising an alkali-soluble resin, a dissolution inhibitor, and a 
photoacid generator. This three-component system resist is more effective 
for precise fine patterning because the amount of dissolution inhibitor 
which is to be decomposed with the acid is reduced and the above-mentioned 
possibility of changing film thickness and generating bubbles is 
minimized. 
One exemplary three-component system resist is disclosed in JP-A 
212159/1992. However, the resin used in this resist is a novolak resin 
which has light absorption in the deep-UV region and is thus inadequate 
for fine patterning. 
Resins having less light absorption in the deep-UV region include 
polyhydroxystyrene having OH groups protected. One exemplary 
three-component resist composition comprising polyhydroxystyrene having OH 
groups protected, a dissolution inhibitor, and a photoacid generator is 
disclosed in JP-A 289659/1991. Since the photoacid generator used therein 
is an alkyl-sulfonic acid, this resist is very low in sensitivity and 
requires a longer exposure time. 
A number of chemically amplified positive resist compositions have been 
proposed as mentioned above although they have some problems and are 
difficult to use in practice. 
SUMMARY OF THE INVENTION 
Making investigations on a positive resist composition of high energy ray 
exposure type having high sensitivity, high resolution and process 
adaptability, the inventors have found that a three-component system 
resist composition comprising an alkali-soluble resin, a dissolution 
inhibitor, and a photoacid generator is improved by using an onium salt of 
the general formula (1) as the photoacid generator and a polymer of the 
general formula (2) and/or (3) as the dissolution inhibitor, the formulae 
being shown below. Use of such specific agents minimizes the possibility 
of changing film thickness and generating bubbles. The resulting positive 
resist composition is highly sensitive to high energy radiation such as 
deep ultraviolet rays, electron rays, and X rays and useful in precise 
fine patterning. 
Photoacid generator: 
EQU (R.sup.1).sub.n MX (1) 
In formula (1), R.sup.1 is independently selected from substituted or 
unsubstituted aromatic groups, M is sulfonium or iodonium, X is 
p-toluenesulfonate or trifluoromethane-sulfonate, and letter n is 2 or 3. 
Dissolution inhibitor: 
##STR1## 
In formula (2), R.sup.2 is a hydrogen atom, an alkyl group having 1 to 6 
carbon atoms or an alkoxy group having 1 to 6 carbon atoms, R.sup.3 is a 
hydrogen atom or a methyl group, R.sup.4 is a hydrogen atom, a COOH group 
or a COOt-Bu group, t-Bu is a t-butyl group, and m, x, y and z are 
0.ltoreq.m.ltoreq.0.9, 0&lt;x.ltoreq.0.9, 0&lt;y.ltoreq.0.9, 0.ltoreq.z 
.ltoreq.0.5 and m+x+y+z=1. The weight average molecular weight of the 
polymer of formula (2) is in the range of 500 to 10,000. 
##STR2## 
In formula (3), R.sup.5 is a hydrogen atom or a methyl group, and letters p 
and q are such that q/(p+q) is from 0.1 to 0.9. The weight average 
molecular weight of the polymer of formula (3) is in the range of 500 to 
10,000. 
In chemically amplified positive resist compositions of the three-component 
system, known means for enhancing sensitivity is to use an onium salt as a 
photoacid generator capable of generating an acid upon light exposure. 
Resist compositions using onium salts tend to form an overhang (T top) in 
patterning, failing to achieve fine resolution. This is partially because 
of shortage of solubility required when a three-component system resist 
film upon exposure follows the mechanism that protective groups unstable 
to acid in the base resin and dissolution inhibitor are decomposed by the 
acid resulting from the photoacid generator so that the resist film 
becomes soluble in an aqueous alkali solution or developer. The 
dissolution inhibitor and base resin of the resist composition in 
unexposed areas remains insoluble in the aqueous alkali solution or 
developer while they lose the dissolution inhibition effect in exposed 
areas so that the dissolution rate is accelerated over that available 
prior to exposure. At the (exposed) surface of the resist film, however, 
less of the photoacid generator is distributed and the acid resulting 
therefrom can volatilize off or be inactivated by contamination from the 
ambient atmosphere so that protective groups survive in the base resin and 
dissolution inhibitor to retain the dissolution inhibition effect or form 
a substantially insoluble surface layer, resulting in a T-top pattern. 
Seeking for the dissolution inhibitor which is more effective than 
conventional ones in solubility in an aqueous alkali solution not only at 
the resist interior, but also at the resist surface, the inventors have 
found that the solubility of the substituent group in the aqueous alkali 
solution decreases in the order of COOH group&gt;phenolic OH group&gt;alcoholic 
OH group and that a dissolution inhibitor having a COOH group protected by 
a substituent group in a molecule is effective. The acid-sensitive 
protective groups include t-butoxycarbonyl, tetrahydropyranyl, t-butyl 
groups and carboxylic anhydrides. Among these, the t-butyl group and 
carboxylic anhydrides are effective protective groups because the 
t-butoxycarbonyl group is thermally unstable and the tetrahydropyranyl 
group is decomposable with acid in an aqueous system, but not in a 
water-free system as in resist film. We have also found that among such 
dissolution inhibitors from monomeric to polymeric forms, the polymer of 
general formula (2) or (3) provides a greater dissolution inhibition 
effect and after exposure, yields COOH groups as a result of splitting off 
of the protective groups and is thus substantially increased in 
solubility. Rather than the monomer, the polymer is easy to control its 
molecular weight, degree of copolymerization and solubility. The polymer 
is also advantageous in increasing the thermal and mechanical strength of 
a resist film. The present invention is predicated on these findings. 
Briefly stated, the present invention provides a resist composition 
comprising 
(A) an onium salt of the general formula (1), 
(B) an alkali-soluble resin, and 
(C) a dissolution inhibitor of the general formula (2) and/or (3). 
Preferably, alkali-soluble resin (B) is a polyhydroxystyrene in which some 
hydroxyl groups are replaced by acid unstable groups, having a molecular 
weight of 5,000 to 100,000. 
DETAILED DESCRIPTION OF THE INVENTION 
Component (A) is an onium salt of the general formula (1) which is capable 
of generating a strong acid upon exposure to high energy radiation such as 
deep-ultraviolet rays, electron rays and X-rays. 
EQU (R.sup.1).sub.n MX (1) 
In formula (1), R.sup.1 groups, which may be identical or different, are 
selected from substituted or unsubstituted aromatic groups, M is sulfonium 
or iodonium, X is p-toluene-sulfonate or trifluoromethanesulfonate, and 
letter n is 2 or 3. A phenyl group is a typical unsubstituted aromatic 
group. Examples of substituted aromatic group include phenyl and other 
aromatic groups having a substituent such as linear or branched alkyl, 
alkoxy, cycloalkyl and haloalkyl groups having 1 to 10 carbon atoms, and 
halogen atoms. Iodonium and sulfonium salts are preferred among these 
onium salts and their examples are shown below. 
##STR3## 
The onium salt used herein is not limited to these examples as long as it 
is capable of generating an acid upon exposure to high energy radiation. 
Onium salt (A) as the photoacid generator is preferably used in an amount 
of 0.5 to 15% by weight of the total weight of components (A) to (C). With 
less than 0.5% by weight of the photoacid generator, the composition would 
sometimes have low sensitivity though it still retains positive resist 
performance. As the amount of photoacid generator increases, the resist is 
increased in sensitivity and improved in contrast. Above 15% by weight of 
the photoacid generator, no further increase of sensitivity is expected 
though the composition still retains positive resist performance. Since 
the photoacid generator is an expensive reagent and an increase of a low 
molecular weight component in the resist can lower the mechanical strength 
of a resist film, it is recommended to add the photoacid generator in an 
amount of up to 15% by weight. 
The alkali-soluble resin as component (B) may be selected from 
polyhydroxystyrenes and novolak resins, for example. Since the novolak 
resins have light absorption in the far-UV region, use of 
polyhydroxystyrene is preferred. Preferred polyhydroxystyrenes are those 
in which some hydroxyl (OH) groups are replaced by acid unstable groups 
such as t-butyl (t-Bu) and t-butoxycarbonyl (t-Boc) groups. 
The degree of substitution of the acid unstable group is preferably 5 to 50 
mol %, preferably 10 to 30 mol % of OH groups. Less than 5 mol % would 
cause a large film loss of resist films. More than 50 mol % would result 
in a low dissolution. They preferably have a molecular weight of 5,000 to 
100,000. 
Component (B) is preferably blended in an amount of at least 55% by weight, 
especially 60 to 80% by weight of the total weight of components (A) to 
(C). A composition containing less than 55% by weight of resin would be 
inconvenient to coat and would form a weak resist film. 
The dissolution inhibitor as component (C) is represented by the following 
formula (2) or (3). 
##STR4## 
In formula (2), R.sup.2 is a hydrogen atom, an alkyl group having 1 to 6 
carbon atoms or an alkoxy group having 1 to 6 carbon atoms. Preferably, 
R.sup.2 is hydrogen atom or t-butoxy group. More preferably, R.sup.2 is 
t-butoxy group which can be removed with an acid to become alkali soluble. 
R.sup.3 is a hydrogen atom or a methyl group, R.sup.4 is a hydrogen atom, 
a COOH group or a COOt-Bu group, t-Bu is a t-butyl group, and m, x, y and 
z are 0.ltoreq.m.ltoreq.0.9, 0&lt;x.ltoreq.0.9, 0&lt;y.ltoreq.0.9, 
0.ltoreq.z.ltoreq.0.5 and m+x+y+z=1. Preferably, 0.3.ltoreq.m.ltoreq.0.7, 
0&lt;x.ltoreq.0.9, 0&lt;y.ltoreq.0.9 and 0.ltoreq.z.ltoreq.0.5, and more 
preferably, 0.3.ltoreq.m.ltoreq.0.5, 0&lt;x.ltoreq.0.9, 0&lt;y.ltoreq.0.9 and 
0.ltoreq.z.ltoreq.0.1. If m is over 0.9 or z is over 0.5, the dissolution 
inhibitor effect would not be exerted well and the film loss of the resist 
film would become much. If x is over 0.9 or y is over 0.9, the 
compatibility to a base polymer and the wettability to a developing 
solution would not be improved well. 
As the polymer of formula (2), the following polymer having a formula of 
(2a) is preferred. 
##STR5## 
In formula (2a), 0.1.ltoreq.p.ltoreq.0.9 and 0.1.ltoreq.q.ltoreq.0.9, 
preferably, 0.3.ltoreq.p.ltoreq.0.7 and 0.3.ltoreq.q.ltoreq.0.7, 
q/(p+q)=0.1 to 0.9, preferably 0.3 to 0.7. R.sup.3, R.sup.4, m and z are 
the same meanings as above. 
In this connection, the introduction of a hydroxystyrene structural unit 
and/or an acrylic or methacrylic acid structural unit to the polymer of 
formula (2) can improve the solubility of the polymer to a solvent for a 
resist composition and the compatibility to the base resin, resulting in 
an excellent film forming ability upon application of a resist composition 
solution on a silicon wafer. Further, the introduction of the 
hydroxystyrene structural unit and/or an acrylic or methacrylic acid 
structural unit can improve the wettability of the resist film to an 
alkali developer aqueous solution. 
##STR6## 
In the formula (3), R.sup.5 is a hydrogen atom or a methyl group, and 
letters p and q are such that q/(p+q) is from 0.1 to 0.9, preferably from 
0.3 to 0.7. 
These polymers (2) and (3) preferably have a weight average molecular 
weight of 500 to 10,000, preferably 500 to 4,000. The compounds of 
formulae (2) and (3) may be used alone or in admixture of two or more. 
The dissolution inhibitor of formula (2) can be readily prepared by 
copolymerizing hydroxystyrene, substituted or unsubstituted styrene, 
t-butyl acrylate or methacrylate and acrylic or methacrylic acid at a 
molar ratio of m:x:y:z. Similarly the dissolution inhibitor of formula (3) 
can be readily prepared by copolymerizing t-butoxystyrene with maleic 
anhydride. 
Component (C) is preferably blended in an amount of 7 to 40% by weight, 
especially 10 to 30% by weight of the total weight of components (A) to 
(C). Less than 7% by weight of the dissolution inhibitor would provide 
less dissolution inhibition effect whereas more than 40% by weight of the 
dissolution inhibitor would make it difficult to control solubility after 
exposure. 
The resist composition of the present invention is generally prepared by 
dissolving components (A), (B) and (C) in an organic solvent. The organic 
solvent used herein is desirably one in which the respective components 
are fully soluble and which allows for uniform spread of a resist film. 
Examples include butyl acetate, xylene, acetone, cellosolve acetate, 
ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, 
ethylene glycol monoethyl ether, diethylene glycol dibutyl ether, 
diethylene glycol dimethyl ether (diglyme), ethyl lactate, methyl lactate, 
propyl lactate, and butyl lactate alone or in admixture of two or more. 
The amount of organic solvent blended is preferably a multiple of the 
total amount of components (A) to (C). 
The resist composition may be subject to a patterning process as described 
below. 
The resist composition solution is spin coated on a substrate to form a 
resist film which is pre-baked and exposed to high energy radiation. Upon 
exposure, the photoacid generator is decomposed to generate an acid. 
Baking after exposure causes the acid to catalyze decomposition of the 
anti-dissolution or protective group, with the dissolution inhibition 
effect being lost. The resist film is then developed with an aqueous 
alkali solution and rinsed with water, yielding a resist having a positive 
pattern. 
The resulting pattern is characterized by increased contrast and high 
resolution since the dissolution inhibition effect of the present 
inhibitor is greater than conventional dissolution inhibitors before 
exposure and is lost after exposure to more greatly enhance solubility. 
Increased solubility after exposure is also effective in improving a T top 
pattern. 
There has been described a positive resist composition which is sensitive 
to high energy radiation, improved in sensitivity, resolution and plasma 
etching resistance, and yields a resist pattern having higher heat 
resistance. The resist pattern has little tendency of overhanging, 
implying improved dimensional control. The composition is free of metal 
elements, requires post-exposure baking (PEB) during chemical 
amplification process so that the time dependency of resist properties 
after exposure is minimized. Eliminated need for water in the chemical 
amplification process renders the system simpler. Therefore, the 
composition is useful in fine patterning using electron and deep-UV rays. 
By virtue of reduced absorption at the exposure wavelength of a KrF 
excimer laser, a fine pattern having perpendicular walls to the substrate 
can be readily formed.

EXAMPLE 
Examples of the present invention are given below by way of illustration 
and not by way of limitation. 
Synthesis 1 
Synthesis of p-butoxystyrene/t-butyl acrylate copolymer 
In an autoclave equipped with a 1.5-liter glass polymerization vessel and 
purged with nitrogen, polymerization reaction was carried out by 
dissolving 225.0 grams (1.28 mol) of p-butoxystyrene and 25.0 grams (0.20 
mol) of t-butyl acrylate in 500 grams of acetone, adding 7.5 grams of 
t-butylperoxy(2-ethylhexanoate) as a polymerization catalyst, and heating 
the mixture at 90.degree. C. Thereafter, the catalyst was added in 
incremental amounts, that is, 5.0 grams after 21/2 hours and 2.5 grams 
after 41/2 hours from the start of polymerization reaction. After 6 hours 
of polymerization, the reaction solution was cooled down and the acetone 
was distilled off. A 9/1 methanol/water mixture was added to the reaction 
solution, causing the copolymer to crystallize. The copolymer had a weight 
average molecular weight (Mw) of 9,200, a dispersity (Mw/Mn) of 1.64, and 
a copolymerization ratio of 6:1. The yield was 70.0%. 
Synthesis 2 
Synthesis of p-butoxystyrene/p-hydroxystyrene/t-butyl acrylate copolymer 
In an autoclave equipped with a 1.0-liter glass polymerization vessel and 
purged with nitrogen, polymerization reaction was carried out by 
dissolving 19.4 grams (0.11 mol) of p-butoxystyrene, 13.2 grams (0.11 mol) 
of p-hydroxystyrene and 25.0 grams (0.20 mol) of t-butyl acrylate in 300 
grams of acetone, adding 3.5 grams of t-butylperoxy(2-ethylhexanoate) as a 
polymerization catalyst, and heating the mixture at 90.degree. C. 
Thereafter, the catalyst was added in incremental amounts, that is, 1.0 
grams after 21/2 hours and 1.0 grams after 41/2 hours from the start of 
polymerization reaction. After 6 hours of polymerization, the reaction 
solution was cooled down and the acetone was distilled off. A 9/1 
methanol/water mixture was added to the reaction solution, causing the 
copolymer to crystallize. The copolymer had a weight average molecular 
weight (Mw) of 6,900, a dispersity (Mw/Mn) of 1.72, and a copolymerization 
ratio (p-butoxystyrene/p-hydroxystyrene/t-butyl acrylate) of 1:1:2. The 
yield was 70.0%. 
Synthesis 3 
Synthesis of p-butoxystyrene/p-hydroxystyrene/t-butyl acrylate/acrylic acid 
copolymer 
In an autoclave equipped with a 1.0-liter glass polymerization vessel and 
purged with nitrogen, polymerization reaction was carried out by 
dissolving 19.4 grams (0.11 mol) of p-butoxystyrene, 13.2 grams (0.11 mol) 
of p-hydroxystyrene, 25.0 grams (0.20 mol) of t-butyl acrylate, and 0.7 
grams (0.01 mol) of acrylic acid in 300 grams of acetone, adding 3.5 grams 
of t-butylperoxy(2-ethylhexanoate) as a polymerization catalyst, and 
heating the mixture at 90.degree. C. Thereafter, the catalyst was added in 
incremental amounts, that is, 1.0 grams after 21/2 hours and 1.0 grams 
after 41/2 hours from the start of polymerization reaction. After 6 hours 
of polymerization, the reaction solution was cooled down and the acetone 
was distilled off. A 9/1 methanol/water mixture was added to the reaction 
solution, causing the copolymer to crystallize. The copolymer had a weight 
average molecular weight (Mw) of 6,200, a dispersity (Mw/Mn) of 1.70, and 
a copolymerization ratio (p-butoxystyrene/p-hydroxystyrene/t-buyl 
acrylate/acrylic acid) of 1:1:2:0.1. the yeild was 58.0%. 
Synthesis 4 
Synthesis of p-butoxystyrene/t-butyl acrylate/acrylic acid copolymer 
In an autoclave equipped with a 1.0-liter glass polymerization vessel and 
purged with nitrogen, polymerization reaction was carried out by 
dissolving 19.4 grams (0.11 mol) of p-butoxystyrene, 25.0 grams (0.20 mol) 
of t-butyl acrylate and 0.7 grams (0.01 mol) of acrylic acid in 300 grams 
of acetone, adding 3.5 grams of t-butylperoxy(2-ethylhexanoate) as a 
polymerization catalyst, and heating the mixture at 90.degree. C. 
Thereafter, the catalyst was added in incremental amounts, that is, 1.0 
grams after 21/2 hours and 1.0 grams after 41/2 hours from the start of 
polymerization reaction. After 6 hours of polymerization, the reaction 
solution was cooled down and the acetone was distilled off. A 9/1 
methanol/water mixture was added to the reaction solution, causing the 
copolymer to crystallize. The copolymer had a weight average molecular 
weight (Mw) of 6,000, a dispersity (Mw/Mn) of 1.70, and a copolymerization 
ratio (p-butoxystyrene/t-butyl acrylate/acrylic acid) of 1:2:0.1. the 
yield was 64.0%. 
Synthesis 5 
Synthesis of p-butoxystyrene/maleic anhydride copolymer 
In an autoclave equipped with a 1.5-liter glass polymerization vessel and 
purged with nitrogen, polymerization reaction was carried out by 
dissolving 125.0 grams (0.71 mol) of p-butoxystyrene and 125.0 grams (1.28 
mol) of maleic anhydride in 500 grams of acetone, adding 7.5 grams of 
t-butylperoxy(2-ethylhexanoate) as a polymerization catalyst, and heating 
the mixture at 90.degree. C. Thereafter, the catalyst was added in 
incremental amounts, that is, 5.0 grams after 21/2 hours and 2.5 grams 
after 41/2 hours from the start of polymerization reaction. After 6 hours 
of polymerization, the reaction solution was cooled down and the acetone 
was distilled off. A 9/1 methanol/water mixture was added to the reaction 
solution, causing the copolymer to crystallize. The copolymer had a weight 
average molecular weight (Mw) of 9,600, a dispersity (Mw/Mn) of 1.58, and 
a copolymerization ratio of 6:7. The yield was 70.0%. 
EXAMPLE 1 
______________________________________ 
Components Parts by weight 
______________________________________ 
Base resin: 
partially t-butoxycarbonylated 
80.0 
polyhydroxystyrene 
(t-Boc content: 20.0% 
Mw = 14,000, Mw/Mn = 1.07) 
Dissolution inhibitor: 
Copolymer of Synthesis 1 
16.0 
Photoacid generator: 
triphenylsulfonium triflate 
4.0 
Solvent: 
diethylene glycol dimethyl 
500 
ether 
______________________________________ 
A resist solution of these components was spin coated on a silicon 
substrate at 2,000 rpm and pre-baked at 100.degree. C. for 2 minutes on a 
hot plate. The resist film was 0.95 .mu.m thick. Using a KrF excimer 
laser, a pattern was drawn on the resist film. The resist film was baked 
at 80.degree. C. for one minute, then developed for one minute with an 
aqueous solution of 2.38% tetramethylammonium hydroxide (TMAH), and rinsed 
with water for 30 seconds. 
The resist film had a sensitivity of 10.0 mJ/cm.sup.2 (Eth value) and bore 
a positive pattern. The resolution was 0.25 .mu.m for line and space 
patterns and 0.30 .mu.m for a hole pattern and the pattern had 
perpendicular side walls. 
EXAMPLE 2 
A resist film was prepared by the same procedure as in Example 1 except 
that the dissolution inhibitor was changed to the copolymer of Synthesis 
2. The sensitivity of the resist film was 8 mJ/cm.sup.2 (Eth value 
(exposure of threshold)). The resolution was 0.25 .mu.m for line and space 
patterns and 0.30 .mu.m for a hole pattern and the pattern had 
perpendicular side walls. 
EXAMPLE 3 
A resist film was prepared by the same procedure as in Example 1 except 
that the dissolution inhibitor was changed to the copolymer of Synthesis 
3. The sensitivity of the resist film was 8 mJ/cm.sup.2 (Eth value). The 
resolution was 0.25 .mu.m for line and space patterns. 
EXAMPLE 4 
A resist film was prepared by the same procedure as in Example 1 except 
that the dissolution inhibitor was changed to the copolymer of Synthesis 
4. The sensitivity of the resist film was 8 mJ/cm (Eth value). The 
resolution was 0.25 .mu.m for line and space patterns. 
EXAMPLE 5 
______________________________________ 
Components Parts by weight 
______________________________________ 
Base resin: 
partially t-butoxycarbonylated 
80.0 
polyhydroxystyrene 
(t-Boc content: 
15.0% Mw = 14,000, Mw/Mn = 1.07) 
Dissolution inhibitor: 
Copolymer of Synthesis 5 
16.0 
Photoacid generator: 
p-butoxyphenyldiphenyl- 
4.0 
sulfonium triflate 
Solvent: 
diethylene glycol dimethyl 
500 
ether 
______________________________________ 
A resist solution of these components was spin coated on a silicon 
substrate at 2,000 rpm and pre-baked at 100.degree. C. for 2 minutes on a 
hot plate. The resist film was 0.95 .mu.m thick. Using a KrF excimer 
laser, a pattern was drawn on the resist film. The resist film was baked 
at 80.degree. C. for one minute, then developed for one minute with an 
aqueous solution of 2.38% tetramethylammonium hydroxide (TMAH), and rinsed 
with water for 30 seconds. 
The resist film had a sensitivity of 10.0 mJ/cm.sup.2 (Eth value) and bore 
a positive pattern. The resolution was 0.25 .mu.m for line and space 
patterns and 0.3 .mu.m for a hole pattern and the pattern had 
perpendicular side walls. 
EXAMPLE 6 
A resist film was prepared by the same procedure as in Example 1 except 
that the acid release agent was changed to bis(t-butylphenyl)iodonium 
triflate. The sensitivity of the resist film lowered to 15 mJ/cm.sup.2 
(Eth value), but the resolution was 0.25 .mu.m for line and space 
patterns. 
EXAMPLE 7 
A resist film was prepared by the same procedure as in Example 2 except 
that the acid release agent was changed to bis(t-butylphenyl)iodonium 
triflate. The sensitivity of the resist film lowered to 15 mJ/cm.sup.2 
(Eth value), but the resolution was 0.30 .mu.m for line and space 
patterns. 
EXAMPLE 8 
A resist film was prepared by the same procedure as in Example 3 except 
that the acid release agent was changed to bis(t-butylphenyl)iodonium 
triflate. The sensitivity of the resist film lowered to 12 mJ/cm.sup.2 
(Eth value), but the resolution was 0.25 .mu.m for line and space 
patterns. 
EXAMPLE 9 
A resist film was prepared by the same procedure as in Example 4 except 
that the acid release agent was changed to bis(t-butylphenyl)iodonium 
triflate. The sensitivity of the resist film lowered to 12 mJ/cm.sup.2 
(Eth value), but the resolution was 0.30 .mu.m for line and space 
patterns. 
EXAMPLE 10 
A resist film was prepared by the same procedure as in Example 5 except 
that the photoacid generator was changed to bis(t-butylphenyl)iodonium 
triflate. The sensitivity of the resist film lowered to 15 mJ/cm.sup.2 
(Eth value), but the resolution was 0.25 .mu.m for line and space 
patterns. 
Although some preferred embodiments have been described, many modifications 
and variations may be made thereto in the light of the above teachings. It 
is therefore to be understood that within the scope of the appended 
claims, the invention may be practiced otherwise than as specifically 
described.