Quinone diazide photoresist composition containing alkali-soluble resin and an ultraviolet ray absorbing dye

A photoresist composition which comprises a compound of the general formula: ##STR1## wherein R.sub.1, R.sub.2 and R.sub.3 are the same or different and represent a hydrogen atom, a hydroxyl group, --OCOR.sub.4, --O--R.sub.5, --OSi(R.sub.6).sub.3, a halogen atom, an optionally substituted alkyl group, an optionally substituted alkenyl group, an optionally substituted phenyl group or an optionally substituted aralkyl group; R.sub.4, R.sub.5 and R.sub.6 represent an optionally substituted lower alkyl group or an optionally substituted phenyl group; X and Y are the same or different and represent --CN, --COOR.sub.7, --CONR.sub.8 R.sub.9, ##STR2## R.sub.7 represents an alkyl group; R.sub.8 and R.sub.9 are the same or different and represent a hydrogen atom, an optionally substituted alkyl or phenyl group; R.sub.10 represents a hydrogen atom, an optionally substituted alkyl group or a hydroxyl group; and a is a number of 1 to 2, which is suitable for forming fine patterns having high resolution on a substrate having high reflectance.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a photoresist composition which can 
preferably be used to form fine patterns on a substrate having high 
reflectance in the production of semiconductors. 
2. Description of the Related Art 
A photoresist which comprises a sensitizing compound having a quinone 
diazide group and a novolak resin, or which comprises a bisazide 
sensitizer and a cyclized rubber, is used in the production of integrated 
circuits such as LSI. 
In a process for producing the integrated circuits, fine patterns are 
formed on various substrates through photoresists. However, when 
conventional photoresists are used on substrates having high reflectance 
such as those made of aluminum, aluminum-silicon, polysilicon and the 
like, various problems arise. For example, a region which should not be 
exposed may be exposed because of reflection on a surface of the substrate 
and/or side walls of steps. This phenomenon is generally referred to as 
notching or halation. 
To solve these problems and prevent deterioration of resolution, Japanese 
Patent Publication No. 37562/1976 proposes a photoresist composition 
which comprises, as a light absorber, a dye represented by the formula: 
##STR3## 
having characteristic absorptions in the ultraviolet range (Oil Yellow 
[C.I. 11020]). This photoresist composition can decrease light 
transmission through the photoresist layer and reduce the undesirable 
exposure of the substrate. 
In the context of the present specification, a "photoresist" is intended to 
mean a composition which comprises a sensitizer and a resin, e.g., 
novolak, and a "photoresist composition" is intended to mean a composition 
which comprises a "photoresist" and a light absorber. 
In general, if the light absorber is added to the photoresist, undesirable 
problems may arise. For example, the photoresist drastically loses its 
sensitivity, and the productivity of the semiconductors is decreased. 
The photoresist layer is usually formed by applying the photoresist 
composition containing a solvent on a wafer and prebaking the wafer with 
the applied photoresist composition to evaporate off the solvent. However, 
some light absorbers may precipitate during storage of the photoresist 
composition, or sublimate during prebaking, so that the concentration of 
the light absorber in the photoresist layer formed on the wafer may be 
lowered, which leads to unsatisfactory results or variation in the quality 
of the produced semiconductors. 
To solve these problems, phenylazobenzene derivatives are proposed in 
Japanese Patent Kokai (Laid-open) Publication Nos. 36838/1980 and 
174941/1983. However, the use of such derivatives creates some problems. 
For example, the phenylazobenzene derivatives should be used in a large 
amount in order to obtain sufficient absorption at the desired wavelength, 
especially when the prebaking temperature is raised, or such derivatives 
possess inferior antisublimation properties, a broad absorption range, low 
absorbing performance, and undesirable absorption at certain wavelengths. 
Japanese Patent Kokai Publication No. 93445/1986 discloses a photoresist 
composition comprising, as a light absorber, a certain styryl compound. 
Although the disclosed styryl compound can solve the problems associated 
with the prebaking, it greatly decreases the sensitivity of the 
photoresist. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a photoresist composition 
suitable for forming fine patterns having high resolution on a substrate 
having high reflectance without causing any halation or notching. 
Another object of the present invention is to provide a photoresist 
composition which is stable against the prebaking of the substrate and 
suffers from less sensitivity deterioration caused by the addition of a 
light absorber.

DETAILED DESCRIPTION OF THE INVENTION 
As a result of extensive study, it has been found that a photoresist 
composition which comprises a specific compound as a light absorber 
accomplishes the above objects and solves the problems associated with the 
prior art. The present invention has been completed based on this finding. 
According to the present invention, there is provided a photoresist 
composition which comprises a compound of the general formula: 
##STR4## 
wherein R.sub.1, R.sub.2 and R.sub.3 are the same or different and 
represent a hydrogen atom, a hydroxyl group, --OCOR.sub.4, --O--R.sub.5, 
--OSi(R.sub.6).sub.3, a halogen atom, an optionally substituted alkyl 
group, an optionally substituted alkenyl group, an optionally substituted 
phenyl group or an optionally substituted aralkyl group; R.sub.4, R.sub.5 
and R.sub.6 represent an optionally substituted lower alkyl group or an 
optionally substituted phenyl group; X and Y are the same or different and 
represent --CN, --COOR.sub.7, --CONR.sub.8 R.sub.9, 
##STR5## 
R.sub.7 represents an alkyl group; R.sub.8 and R.sub.9 are the same or 
different and represent a hydrogen atom, an optionally substituted alkyl 
or phenyl group; R.sub.10 represents a hydrogen atom, an optionally 
substituted alkyl group or a hydroxyl group; and a is a number of 1 to 2. 
In the general formula (I), an alkyl group as R.sub.1, R.sub.2, R.sub.3, 
R.sub.7, R.sub.8, R.sub.9 or R.sub.10 preferably has up to 4 carbon atoms. 
A lower alkyl group as R.sub.4, R.sub.5 or R.sub.6 preferably has up to 6 
carbon atoms, more preferably up to 4 carbon atoms. Examples of the 
substituent include a hydroxyl group and the like. 
A photoresist which comprises a novolak resin and a naphthoquinone diazide 
compound is preferably used. The novolak resin is obtained through the 
addition condensation reaction of a phenol compound with formaldehyde. 
Also, a photoresist which comprises a cresol novolak resin and an ester of 
polyhydroxybenzophenone with naphthoquinone-1,2-diazide sulfonic acid is 
preferably used. The cresol novolak resin can be prepared by reaction of 
meta-cresol and/or para-cresol with formalin, or reaction of meta-cresol, 
para-cresol and 3,5-xylenol with formalin. Examples of the 
polyhydroxybenzophenone are 2,3,4-trihydroxybenzophenone, 
2,3,4,4'-tetrahydroxybenzophenone, 2,2',4,4'-tetrahydroxybenzophenone, 
2,3,3',4-tetrahydroxybenzophenone, 2,2',3,4,5-pentahydroxybenzophenone, 
2,3,3',4,5-pentahydroxybenzophenone, 2,3,3',4,4'-pentahydroxybenzophenone, 
2,2',3,4,4'-pentahydroxybenzophenone, 
2,2',3,3',4-pentahydroxybenzophenone, and the like. 
Preferred examples of the compounds (I) which are suitable as the light 
absorber in the photoresist composition according to the present invention 
are as follows. These examples should not limit the scope of the present 
invention. 
##STR6## 
Among the compounds of formula (I), those having absorption in the 
wavelength range not longer than 550 nm, particularly between 300 to 450 
nm, are preferably used in the photoresist composition. 
The amount of compound (I) to be added to the photoresist composition is 
from 0.1 to 20% by weight, preferably from 0.2 to 10% by weight, based on 
the weight of the solid component in the photoresist. 
When the amount of compound (I) is in the above range, the photoresist 
composition sufficiently prevents halation and has excellent profile and 
sensitivity. 
The photoresist composition may optionally contain at least one other light 
absorber. 
With the photoresist compositions according to the present invention, the 
problems associated with the prior art can be solved, and patterns with 
high resolution can be formed on the substrate having high reflectance. 
PREFERRED EMBODIMENTS OF THE INVENTION 
The present invention will be illustrated in more detail via the following 
examples, but should not be construed to be limited to these examples. 
REFERENCE EXAMPLE 1 
In a 300 ml four-necked flask with a stirring bar, a condenser, and a 
thermometer, 13.8 g of 2,4-dihydroxybenzaidehyde, 25.2 g of diethyl 
malonate, and 100 g of ethanol were charged and stirred to obtain a 
homogeneous solution. 0.5 Gram of piperidine was added to the solution and 
stirred for 20 hours at 20.degree.-25.degree. C. Ethanol was distilled off 
from a resulting solution by an evaporator to obtain 42.1 g of a tar-like 
yellow compound. To the resulting compound, 84 g of toluene were added, 
stirred for one hour at 70.degree.-75.degree. C. and cooled down to room 
temperature to precipitate the compound. The precipitated compound was 
filterated and dried to obtain 15.1 g of a crude cake. Then, in a 200 ml 
four-necked flask, 15.1 g of the crude cake and 90 g of toluene were 
charged and sintered for 2 hours at 70.degree.-75.degree. C. to obtain a 
dispersion. After cooling down to room temperature, the cake was 
filterated and washed with 30 g of toluene. This was repeated twice to 
obtain 11.7 g of the compound of the following formula (I-a). The purity 
measured by HPLC was 98.8%, and the structure of the compound was 
confirmed by NMR and mass spectroscopy. 
##STR7## 
Absorbance of the compound (I-a) in methanol: 
.lambda..sub.max : 352 nm 
.epsilon.: 2.58.times.10.sup.4 M.sup.-1.cm.sup.-1 
REFERENCE EXAMPLE 2 
In a 200 ml four-necked flask with a stirring bar, a condenser, and a 
thermometer, 12.2 g of parahydroxybenzaldehyde, 9.9 g of malonitrile, and 
50 g of ethanol were charged and stirred to obtain a homogeneous solution. 
0.5 Gram of piperidine was added to the solution, stirred for 16 hours at 
20.degree.-25.degree. C. and filterated to obtain a crystal. 60 Grams of 
toluene were added to the crystal and stirred for 2 hours, filterated, and 
dried under vacuum to obtain a crude cake. 12.8 Grams of the crude cake 
were recrystallized from 32 g of ethyl acetate and dried under vacuum to 
obtain 4.8 g of the pale yellow compound of the following formula (I-b). 
The purity measured by HPLC was 98.2% and the structure of the compound 
was confirmed by NMR and mass spectroscopy. 
##STR8## 
Absorbance of the compound (I-b) in methanol: 
.lambda..sub.max : 535 nm 
.epsilon.: 2.91.times.10.sup.4 M.sup.-1.cm.sup.-1 
REFERENCE EXAMPLE 3 
In a 200 ml four-necked flask with a stirring bar, a condenser, and a 
thermometer, 13.8 g of 2,4-dihydroxybenzaidehyde, 80 g of ethanol and 13.6 
g of ethyl cyanoacetate were charged and stirred to obtain a homogeneous 
solution. 0.3 Gram of piperidine was added to the solution, stirred for 20 
hours at 20.degree.-25.degree. C. and filterated to obtain a crystal. 100 
Grams of ethanol was added to the crystal, and stirred for 2 hours, and 
filterated to obtain a cake. The cake was rinsed with 50 g of ethanol and 
dried under vacuum to obtain 18.4 g of the pale yellow compound of the 
formula (I-c). The purity measured by HPLC was 97.8%, and the structure of 
the compound was confirmed by NMR and mass spectroscopy. 
##STR9## 
Absorbance of the compound (I-c) in methanol: 
.lambda..sub.max : 438 nm 
.epsilon.: 3.46.times.10.sup.4 M.sup.-1.cm.sup.-1 
REFERENCE EXAMPLE 4 
In a 200 ml four-necked flask with a stirring bar, a condenser, and a 
thermometer, 4.20 g of the compound obtained in Reference Example 1, 84 g 
of tetrahydrofuran, and 1.59 g of triethylamine were charged and stirred 
to obtain a homogeneous solution. 1.18 Grams of acetic chloride were 
diluted with 6.0 g of tetrahydrofuran (the molar ratio of the hydroxyl 
group to acetic chloride being 1:1) and added dropwise to the above 
homogeneous solution over 30 minutes at 20.degree.-25.degree. C. After 
stirring for a further 2 hours, the solution was poured into 500 ml of 
water and stirred for one hour. The mixture was filterated, rinsed with 
300 ml of water, and dried under vacuum at 50.degree.-60.degree. C. to 
obtain 4.65 g of a partially acetylated compound of the compound (I-a). 
Absorption of the partially acetylated compound in methanol: 
.lambda..sub.max : 343 nm 
.epsilon.: 1.44.times.10.sup.4 M.sup.-1.cm.sup.-1 
REFERENCE EXAMPLE 5 
The same procedures of Reference Example 4 were repeated except that the 
compound (I-c) obtained in Reference Example 3 was used instead of the 
compound (I-a) to obtain a partially acetylated compound of the formula 
(I-c). 
Absorbance of the partially acetylated compound in methanol: 
.lambda..sub.max : 350 nm 
.epsilon.: 1.01.times.10.sup.4 M.sup.-1.cm.sup.-1 
.lambda..sub.2 max : 438 nm 
.epsilon..sub.2 : 7.70.times.10.sup.4 M.sup.-1.cm.sup.-1 
EXAMPLES 1-4 AND COMATIVE EXAMPLE 2 
Photoresist compositions were prepared by adding each dye compound shown in 
Table I to a positive photoresist PF-6200 (manufactured by Sumitomo 
Chemical Company, Limited; a solid content of 31.0% by weight), which 
comprises a novolak resin and at least one compound having o-quinone 
diazide groups. The amount of each dye compound added was determined to 
have the same absorbance as that in Comparative Example 2 (the amount of 
dye compound was 10% by weight). 
Each of the photoresist compositions was coated on a 4 inch square silicon 
wafer with an aluminum film on its surface by means of a spinner so as to 
form a resist film of 1.80 .mu.m in thickness. Subsequently, the silicon 
wafer was baked for one minute on a hot plate kept at 100.degree. C. and 
exposed to light (i-line of 365 nm) through a test reticule while varying 
the exposure value stepwise by means of a reduced projection exposing 
apparatus. Thereafter, the silicon wafer was developed by a static paddle 
method for 60 seconds at 23.degree. C. in a developing solution SOPD 
(manufactured by Sumitomo Chemical Company, Limited) by means of an 
automatic developing machine. The results are shown in Table I. 
The anti-halation effect was estimated as follows: 
The method of estimation of a preventive effect of halation 
1. Making a substrate having steps for estimation 
On a silicon substrate having a SiO.sub.2 film of 1 .mu.m in thickness, a 
pattern having steps a shape of which is shown in FIGS. 1A and 1B was 
formed by photolithography, etching, and aluminum spattering. Typical 
pattern sizes are a=4 .mu.m, b=2 .mu.m, c=1 .mu.m and d=1 .mu.m. 
2. Estimation of anti-halation effect 
On the above substrate having high reflectance and the steps, a resist film 
of 2 .mu.m in thickness was coated by the spin coat method. 
The resist film was exposed to light and developed to make a resist line 
with a line width of 1.2 .mu.m across the center concave part of the above 
pattern (see FIG. 2). 
A decreasing ratio (R)) of the resist line width in the concave center of 
the step (y) to a line width in the part having no step (x) was calculated 
according to the following equation: 
##EQU1## 
In estimating the preventive effect, the exposure dose was settled 1.3 
times of the exposure dose at which the remaining film thickness becomes 
zero. 
The anti-halation effect was evaluated according to the following criteria: 
Very good: The decreasing ratio of the line width is within 10%. 
Good: The decreasing rate of the line width is from 11 to 20%. 
No good: The decreasing rate of the line width is more than 20%. 
COMATIVE EXAMPLE 1 
The same procedures as in Comparative Example 2 were repeated except that 
no absorber was used. 
The anti-halation effect was estimated by the same method as in Comparative 
Example 2, and the results are summarized in Table I. 
TABLE I 
______________________________________ 
Relative Absor- 
Example Absorber sensi- bance Anti-halation 
No. compound tivity ratio effect 
______________________________________ 
1 (I-a) 1.2 1 Very good 
2 (I-b) 1.2 1 Very good 
3 Partially 1.3 1 Very good 
acetylated 
compound 
of (I-a) 
4 Partially 1.3 1 Very good 
acetylated 
compound 
of (I-c) 
Comp. 1 None 1 0.3 Not good 
Comp. 2 Note *1) 2.3 1 Good 
______________________________________ 
Note: 
##STR10## 
As understood from the results in Table I, patterns with high sensitivity 
were formed in Examples of the present invention. 
The pattern could be resolved sharply. No notching caused by reflected 
light on the side surfaces of patterns was found. The above results 
indicate that the photoresist composition of the present invention imparts 
excellent antihalation properties. 
In comparison with the photoresists in the Examples, the photoresists in 
the Comparative Examples exhibited insufficient sensitivity and 
anti-halation effect.