JPH0887110A - Positive resist composition - Google Patents

Abstract

PURPOSE: To provide a positive photosensitive compsn. capable of preventing halation without impairing sensitivity, resolving power and the depth of a focus. CONSTITUTION: This resist compsn. contains alkali-soluble phenolic resin, a quinonediazidosulfonic ester type photosensitive agent and a compd. represented by the formula, wherein each of R<1> -R<6> is H, halogen, hydroxyl, substitutable alkyl, substitutable alkoxy or -OCOR<7> and R<7> is substitutable alkyl.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a resist composition, and more particularly to a positive resist composition having an excellent antihalation effect.

[0002]

2. Description of the Related Art When manufacturing a semiconductor, a resist is coated on the surface of a silicon wafer to form a photosensitive film, which is irradiated with light to form a latent image, which is then developed to form a negative or positive image. A semiconductor element is formed by a lithographic technique. Conventionally, as a resist composition for forming a semiconductor element, a positive resist composed of an alkali-soluble resin and a quinonediazide compound has been widely used because of its excellent resolution. Further, the improvement of the performance of the positive resist and the improvement of the performance of the exposure device have improved the resolution, and it has become possible to form a fine pattern of 1 μm or less.

However, this positive type resist has a drawback that the resolution is lowered on a thin film (hereinafter referred to as a substrate) such as aluminum and chrome for a photomask having a high light reflectance used for manufacturing a silicon semiconductor device. are doing. That is, at the time of exposure, after the light passing through the transparent portion of the mask exposes the positive resist, the light is reflected by the substrate and wraps around to the area of the positive resist under the light shield, which is not desired to be exposed. The so-called halation phenomenon of exposing to light occurs, and as a result, there are problems that the resolution is lowered and the pattern shape becomes thinner than a desired size.

For the purpose of improving this drawback, a resist composition obtained by adding a compound in which an electron-withdrawing group such as a cyano group, an ester group or a carboxyl group is bonded to the β-position carbon of a styrene compound (Japanese Patent Publication No. 3-69095). Gazette, Japanese Patent Laid-Open No. 2-
269346). But,
Although such a resist composition has been improved in terms of sensitivity, sublimation property, storage stability and the like by adding a styrene compound, there has been a problem that characteristics such as resolution and depth of focus are deteriorated.

[0005]

DISCLOSURE OF THE INVENTION Under the above-mentioned conventional techniques, the inventors of the present invention have earnestly studied to obtain an antihalation agent that does not impair the resist properties, and as a result, the number of phenyl groups was higher than that of conventional styrene compounds. It has been found that the addition of a large amount of diphenylmethane-based compound is excellent in sublimation resistance after prebaking and can prevent halation without impairing resist characteristics such as sensitivity, resolution and depth of focus, and completed the present invention.

[0006]

According to the present invention, the alkali-soluble phenolic resin (a), the quinonediazide sulfonic acid ester-based photosensitizer (b) and the compound (c) represented by the following general formula (I) are thus obtained.

Embedded image (R ^{1 to} R ⁶ may be different from each other and are a hydrogen atom, a halogen atom, a hydroxyl group, a substitutable alkyl group, a substitutable alkoxy group, —OCOR ⁷ and R ⁷ is a substitutable alkyl group). A positive resist composition is provided. Hereinafter, the present invention will be described in detail.

Examples of the alkali-soluble phenol resin (a) used in the present invention include condensation reaction products of phenols and aldehydes, condensation reaction products of phenols and ketones, vinylphenol polymers,
Examples thereof include isopropenylphenol-based polymers and hydrogenation reaction products of these phenolic resins. Specific examples of phenols used here include phenol, o
-Cresol, m-cresol, p-cresol, 2,
3-dimethylphenol, 2,5-dimethylphenol, 3,4-dimethylphenol, 3,5-dimethylphenol, 2,4-dimethylphenol, 2,6-dimethylphenol, 2,3,5-trimethylphenol,
3,4,5-Trimethylphenol, 2-t-butylphenol, 3-t-butylphenol, 4-t-butylphenol, 2-methylresorcinol, 4-methylresorcinol, 5-methylresorcinol, 4-t-butylcatechol, 2 -Methoxyphenol, 3-methoxyphenol, 2-propylphenol, 3-propylphenol, 4-propylphenol, 2-isopropylphenol, 3-isopropylphenol, 4-isopropylphenol, 2-methoxy-5-methylphenol, 2- t-Butyl-5-methylphenol, thymol, isothymol and the like are exemplified. Of these, o
-Cresol, m-cresol, p-cresol, 2,
3-dimethylphenol, 2,5-dimethylphenol, 3,4-dimethylphenol, 3,5-dimethylphenol, 2,3,5-trimethylphenol, 3,
A preferred example is 4,5-trimethylphenol. These compounds may be used alone or in combination of two or more.

Specific examples of aldehydes include formalin, paraformaldehyde, acetaldehyde, propylaldehyde, benzaldehyde, phenylacetaldehyde, α-phenylpropylaldehyde, β-phenylpropylaldehyde, o-hydroxybenzaldehyde, m-hydroxybenzaldehyde and p-. Hydroxybenzaldehyde, o-chlorobenzaldehyde, m-
Chlorobenzaldehyde, p-chlorobenzaldehyde, o-nitrobenzaldehyde, m-nitrobenzaldehyde, p-nitrobenzaldehyde, o-methylbenzaldehyde, m-methylbenzaldehyde, p-methylbenzaldehyde, p-ethylbenzaldehyde,
Examples thereof include pn-butylbenzaldehyde and terephthalaldehyde. Of these, formaldehyde, paraformaldehyde, acetaldehyde and benzaldehyde are preferred. These compounds may be used alone or in combination of two or more. Specific examples of the ketones include acetone, methyl ethyl ketone, diethyl ketone, diphenyl ketone and the like. These compounds may be used alone or in combination of two or more. These condensation reaction products can be obtained by a conventional method, for example, by reacting phenols with aldehydes or ketones in the presence of an acidic catalyst.

The vinylphenol polymer is selected from a homopolymer of vinylphenol and a copolymer of vinylphenol and a component copolymerizable with vinylphenol. The isopropenylphenol polymer is a polymer of isopropenylphenol. It is a homopolymer or a copolymer of a component capable of copolymerizing with isopropenylphenol. Specific examples of components copolymerizable with vinylphenol and isopropenylphenol include acrylic acid, methacrylic acid, styrene,
Examples thereof include maleic anhydride, maleic imide, vinyl acetate, acrylonitrile, and their derivatives. The copolymer can be obtained by a known method. The hydrogenation reaction product of a phenol resin is obtained by a conventional method, for example, by dissolving the above-mentioned phenol resin in an organic solvent and hydrogenating it in the presence of a homogeneous or heterogeneous catalyst.

These alkali-soluble phenol resins (a) can also be used as those whose molecular weight and molecular weight distribution are controlled by known means. As a method for controlling the molecular weight and the molecular weight distribution, the resin is crushed, and solid-liquid extraction is performed with an organic solvent having an appropriate solubility, or the resin is dissolved in a good solvent and then dropped into a poor solvent, or a poor solvent is used. Is added dropwise to perform solid-liquid or liquid-liquid extraction. The polystyrene-converted weight average molecular weight (hereinafter, simply referred to as average molecular weight) of the alkali-soluble phenol resin used in the present invention is usually 2,000 to 25,000.
It is 0, preferably 3,500 to 20,000. If the average molecular weight is less than 3,500, the pattern shape, resolution and developability tend to deteriorate, and if it is less than 2,000, it is not practical. Further, if it exceeds 20,000, the pattern shape, developability and sensitivity are deteriorated, and if it exceeds 25,000, it is not practical.

These alkali-soluble phenolic resins can be used alone or in a mixture of two or more kinds. In the positive resist composition of the present invention, if necessary, in order to improve developability, storage stability, heat resistance, etc., a copolymer of styrene and acrylic acid, methacrylic acid or maleic anhydride, an alkene and A copolymer with maleic anhydride, a vinyl alcohol polymer, a vinylpyrrolidone polymer, rosin, shellac and the like can be added. The amount of such a polymer added is 0 to 50 of the above polymer based on 100 parts by weight of the alkali-soluble phenol resin.
Parts by weight, preferably 5 to 20 parts by weight.

The quinone diazide sulfonic acid ester type photosensitizer (b) used in the present invention is an esterified product of a hydroxy compound and a quinone diazide sulfonic acid compound which are usually used as photosensitizers. The esterification may be carried out on some or all of the hydroxyl groups of the hydroxy compound. As the hydroxy compound used here, a known one having a phenol group is used, and specific examples thereof include 2,3,4-trihydroxybenzophenone, 2,4,4′-trihydroxybenzophenone and 2,3,4. Polyhydroxybenzophenones such as 4,4′-tetrahydroxybenzophenone, 2,4,2 ′, 4′-tetrahydroxybenzophenone and 2,3,4,2 ′, 4′-pentahydroxybenzophenone;
Gallic acid esters such as methyl gallate, ethyl gallate and propyl gallate; polyhydroxybis such as 2,2-bis (4-hydroxyphenyl) propane and 2,2-bis (2,4-dihydroxyphenyl) propane Phenylalkanes; tris (4-hydroxyphenyl) methane, 1,1,1-tris (4-hydroxy-3-methylphenyl) ethane, 1,1,1-tris (4-hydroxy-3-methylphenyl) ethane , 1,1,1-tris (4-hydroxyphenyl) ethane, 1,1-bis (4
-Hydroxy-3-methylphenyl) -1- (4-hydroxyphenyl) ethane, bis (4-hydroxy-3-)
Polyhydroxytrisphenylalkanes such as methylphenyl) -2-hydroxy-4-methoxyphenylmethane; 1,1,2,2-tetrakis (4-hydroxyphenyl) ethane, 1,1,2,2-tetrakis (3 -Methyl-4-hydroxyphenyl) ethane, 1,1,3,3
-Polyhydroxytetrakisphenylalkanes such as tetrakis (4-hydroxyphenyl) propane; α,
α, α ′, α′-tetrakis (4-hydroxyphenyl) -3-xylene, α, α, α ′, α′-tetrakis (4-hydroxyphenyl) -4-xylene, α, α,
Polyhydroxytetrakisphenyl xylenes such as α ′, α′-tetrakis (3-methyl-4-hydroxyphenyl) -3-xylene; 2,6-bis (2,4-dihydroxybenzyl) -p-cresol, 2, 6-bis (2,4-dihydroxy-3-methylbenzyl) -p-
Cresol, 4,6-bis (4-hydroxybenzyl)
Resorcin, 4,6-bis (4-hydroxy-3-methylbenzyl) resorcin, 4,6-bis (4-hydroxybenzyl) -2-methylresorcin, 4,6-bis (4-hydroxy-3-methylbenzyl) ) -2-Methylresorcin and the like trimers of phenols and formalin, tetramers of phenols and formalin represented by the following general formula (II), and the like.

[Chemical 3] (In the formula, R ⁸ and R ⁹ are each independently a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and R ^{10 to} R ¹³ are each independently an alkyl group having 1 to 4 carbon atoms.)

Specific examples of quinonediazide sulfonic acid include
1,2-benzoquinonediazide-4-sulfonic acid, 1,
2-naphthoquinonediazide-4-sulfonic acid, 1,2-
Examples thereof include naphthoquinonediazide-5-sulfonic acid, 2,1-naphthoquinonediazide-4-sulfonic acid, and 2,1-naphthoquinonediazide-5-sulfonic acid. By converting this quinonediazidesulfonic acid into a quinonediazidesulfonic acid halide and then reacting it with the hydroxy compound, the quinonediazidesulfonic acid ester-based photosensitizer used in the present invention can be obtained.

The photosensitizers used in the present invention may be used alone or in admixture of two or more. The compounding amount of the photosensitizer is the alkali-soluble phenol resin (a)
It is usually 1 to 100 parts by weight, preferably 3 to 40 parts by weight, relative to 100 parts by weight. If the amount is less than 1 part by weight, it becomes difficult to form a pattern, and if it exceeds 100 parts by weight, the sensitivity is lowered and the undeveloped portion is liable to occur.

In the present invention, the compound (c) represented by the above formula (I) is further added. The compound represented by the above formula (I) can be obtained by a conventional method, for example, by dehydration condensation of an aromatic amine and an aldehyde compound. The aldehyde compound used here is obtained by condensing hydroxybenzaldehydes and formaldehyde in the presence of an acid catalyst.

Specific examples of the present invention thus obtained include the following formulas (1) to (10).

[Chemical 4]

[Chemical 5]

[Chemical 6]

[Chemical 7]

Embedded image

[Chemical 9]

[Chemical 10]

[Chemical 11]

[Chemical 12]

[Chemical 13] Examples of such compounds include compounds represented by general formula (III)

Embedded image (In the formula, R ^{14 to} R ¹⁷ are a hydrogen atom, a hydroxyl group, and 1 to 4 carbon atoms.
Is an alkoxy group. ) Is a preferred example.

In the present invention, the compound (c) may be used alone or in combination of two or more kinds. With respect to 100 parts by weight of the alkali-soluble phenolic resin (a), the lower limit of the compound (c) is usually 1 part by weight, and the upper limit is usually 30 parts by weight, preferably 10 parts by weight. If the compounding amount of the compound (c) is too small, the effect of the present invention cannot be exhibited, and conversely, if it is too large, the resolution and the sensitivity may decrease.

Furthermore, in the resist composition of the present invention, the alkali solubility of the alkali-soluble phenol resin is increased,
For the purpose of improving sensitivity, residual film rate, resolution and heat resistance,
A low molecular weight phenolic compound can be added.

The low molecular weight phenol compound used in the present invention is not particularly limited as long as it has a molecular weight of 1,000 or less, but preferably has a molecular weight of 700 or less.
Specific examples of the low molecular weight phenol compound include monophenols such as p-phenylphenol and p-isopropylphenol; biphenol, 4,4′-dihydroxydiphenyl ether, 4,4′-dihydroxybenzophenone and bisphenol A (Honshu Chemical Industry Co., Ltd. Made), bisphenol C (made by Honshu Chemical Industry Co., Ltd.), bisphenol E
(Manufactured by Honshu Chemical Industry Co., Ltd.), bisphenol F (manufactured by Honshu Chemical Industry Co., Ltd.), bisphenol AP (manufactured by Honshu Chemical Industry Co., Ltd.),
Bisphenol M (Mitsui Petrochemical Industry Co., Ltd.), Bisphenol P (Mitsui Petrochemical Industry Co., Ltd.), Bisphenol Z
(Manufactured by Honshu Chemical Industry Co., Ltd.), 1,1-bis (4-hydroxyphenyl) cyclopentane, 9,9-bis (4-hydroxyphenyl) fluorene, 1,1-bis (5-methyl-2-hydroxyphenyl). Bisphenols such as methane and 3,5-dimethyl-4-hydroxybenzylphenol; 1,1,1-tris (4-hydroxyphenyl)
Methane, 1,1,1-tris (4-hydroxyphenyl) ethane, 1,1-bis (3-methyl-4-hydroxyphenyl) -1- (4-hydroxyphenyl) methane, 1,1-bis (2 , 5-dimethyl-4-hydroxyphenyl) -1- (2-hydroxyphenyl) methane,
1,1-bis (3,5-dimethyl-4-hydroxyphenyl) -1- (2-hydroxyphenyl) methane, 2,
6-bis (5-methyl-2-hydroxybenzyl) -4
-Methylphenol, 2,6-bis (4-hydroxybenzyl) -4-methylphenol, 2,6-bis (3-
Methyl-4-hydroxybenzyl) -4-methylphenol, 2,6-bis (3,5-dimethyl-4-hydroxybenzyl) -4-methylphenol, trisphenol-PA (manufactured by Honshu Chemical Industry Co., Ltd.), trisphenol -T
C (manufactured by Honshu Chemical Industry Co., Ltd.), 2,6-bis (2,4-difodoxybenzyl) -p-cresol, 2,6-bis (2,4-dihydroxy-3-methylbenzyl) -p-
Trisphenols such as cresol; 1,1,2,2-
Tetrakis (4-hydroxyphenyl) ethane, 1,
1,2,2-Tetrakis (3-methyl-4-hydroxyphenyl) ethane, 1,1,3,3- (4-hydroxyphenyl) propane, 1,1,5,5-tetrakis (4
-Hydroxyphenyl) pentane α, α, α ', α'-
Tetrakis (4-hydroxyphenyl) -3-xylene, α, α, α ′, α′-tetrakis (4-hydroxyphenyl) -4-xylene, α, α, α ′, α′-tetrakis (3-methyl- 4-hydroxyphenyl) -3-
Xylene, α, α, α ′, α′-tetrakis (3-methyl-4-hydroxyphenyl) -4-xylene, tetrakisphenols such as tetramers of the phenols represented by the above formula (II) and formalin, etc. Is exemplified.
Among these, bisphenol Z, 1,1-bis (4
-Hydroxyphenyl) cyclopentane, α, α,
α ′, α′-tetrakis (4-hydroxyphenyl)-
4-xylene and trisphenol PA are preferred examples.

The amount of the low-molecular phenol compound added is determined by the composition of the alkali-soluble phenol resin, the molecular weight,
Depending on the molecular weight distribution and the type and amount of other additives,
With respect to 100 parts by weight of the alkali-soluble phenol resin,
The upper limit is usually 100 parts by weight, preferably 60 parts by weight, and the lower limit is usually 0 parts by weight, preferably 3 parts by weight.

The positive resist composition of the present invention is usually dissolved in a solvent and used in order to form a resist film by coating it on a substrate. Specific examples of the solvent that can be used in the present invention include ketones such as acetone, methyl ethyl ketone, and cyclopentanone; alcohols such as n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, and cyclohexanol; ethylene glycol dimethyl ether. , Ethers such as ethylene glycol diethyl ether, dioxane; alcohol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether; propyl formate, butyl formate, propyl acetate, butyl acetate, methyl propionate,
Esters such as ethyl propionate, methyl butyrate, ethyl butyrate, methyl lactate, ethyl lactate; cellosolve acetates such as cellosolve acetate, methyl cellosolve acetate, ethyl cellosolve acetate, propyl cellosolve acetate, butyl cellosolve acetate; propylene glycol, propylene glycol monomethyl ether Propylene glycols such as acetate, propylene glycol monoethyl ether acetate, propylene glycol monobutyl ether; diethylene glycols such as diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether; halogenated hydrocarbons such as trichloroethylene Toluene, aromatic hydrocarbons such as xylene; dimethylacetamide, dimethylformamide, such as a polar solvent such as N- methyl acetamide and the like, which may be used by either singly or in combination.

The positive resist composition of the present invention may optionally contain compatible additives such as a surfactant, a storage stabilizer, a sensitizer, an anti-striation agent, and a plasticizer. it can. Examples of the surfactant include polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether, polyoxyethylene stearyl ether, and polyoxyethylene oleyl ether; polyoxyethylene octylphenyl ether, polyoxyethylene nonylphenol ether, and the like. Oxyethylene aryl ethers; polyethylene glycol dialkyl esters such as polyethylene glycol dilaurate and ethylene glycol stearate; F-top E
F301, EF303, EF352 (manufactured by Shin-Akita Kasei Co., Ltd.), Megafax F171, F172 (manufactured by Dainippon Ink and Chemicals), Florard FC430, FC431 (manufactured by Sumitomo 3M), Asahi Guard AG710, Surflon S-382, SC-101, SC-102, SC
-103, SC-104, SC-105, SC-106
(Asahi Glass Co., Ltd.) and other fluorosurfactants; organosiloxane polymer KP341 (Shin-Etsu Chemical Co., Ltd.); acrylic acid-based or methacrylic acid-based (co) polymer Polyflow N
o. 75, no. 95 (manufactured by Kyoeisha Oil and Fat Chemical Co., Ltd.). The amount of these surfactants to be compounded is usually 2 parts by weight or less, preferably 1 part by weight or less, per 100 parts by weight of the solid content of the composition.

The developer suitable for the positive resist composition of the present invention is an alkaline aqueous solution, and specific examples thereof include inorganic alkalis such as sodium hydroxide, potassium hydroxide, sodium silicate and ammonia; ethylamine. , Primary amines such as propylamine; secondary amines such as diethylamine and dipropylamine; tertiary amines such as trimethylamine and triethylamine; N, N
Alcohol alcohols such as dimethylmethanolamine and triethanolamine; tetramethylammonium hydroxide, tetraethylammonium hydroxide,
Examples thereof include aqueous solutions of quaternary ammonium salts such as triethylhydroxymethylammonium hydroxide and trimethylhydroxyethylammonium hydroxide. Further, if necessary, the alkaline aqueous solution,
A water-soluble organic solvent such as methanol, ethanol, propanol, or ethylene glycol, a surfactant, a storage stabilizer, a resin dissolution inhibitor, and the like can be appropriately added.

[0024]

【Example】

(Synthesis Example 1) In the presence of 0.17 g of paratoluenesulfonic acid, 2.56 g of bis (3-formyl-4-hydroxyphenyl) methane and 2.18 g of 4-hydroxyaniline were suspended in toluene, and water was added. It heated and refluxed for 2 hours, removing. Toluene was distilled off, and the obtained crude product was washed with 10 ml of ethyl acetate and then dried under reduced pressure to obtain 2.10 g of the compound represented by the formula (1).

Synthesis Example 2 Synthesis Example 1 except that 3.16 g of bis (3-formyl-4-hydroxy-5-methoxyphenyl) methane was used instead of bis (3-formyl-4-hydroxyphenyl) methane. By the same method, 1.94 g of the compound represented by the above formula (2) was obtained.

(Synthesis Example 3) 2.88 g of bis (3-formyl-4,6-dihydroxyphenyl) methane instead of bis (3-formyl-4-hydroxyphenyl) methane
2.35 g of the compound represented by the above formula (3) was obtained by the same method as in Synthesis Example 1 except that was used.

(Examples 1 to 3 and Comparative Examples 1 and 2) The compounds shown in Table 1 were added to a positive photoresist (trade name "ZIR9300"; manufactured by Zeon Corporation) containing a novolak resin and o-quinonediazide. A photoresist composition was prepared. The absorbance ratio of each composition is as shown in Table 1.
This resist composition was spin-coated on a stepped silicon wafer having an aluminum film so as to have a film thickness of 2.04 μm, and further prebaked at 90 ° C. for 90 seconds on a hot plate. This was exposed through a test reticle using a reduction projection exposure device (exposure wavelength 365 nm) while changing the exposure amount and focus position in stages. After exposure, 6 at 110 ° C
After post-baking on a hot plate for 0 seconds, a positive type developer (trade name "ZTMA-100"; manufactured by Zeon Corporation)
Was developed by a static paddle method at 23 ° C. for 70 seconds using an automatic processor to form a positive pattern.

Observing this wafer with an electron microscope, the sensitivity,
The resolution, depth of focus, and antihalation effect were evaluated.
The results are shown in Table 1. The sensitivity, resolving power, and depth of focus are relative evaluations based on a 5-step evaluation based on Comparative Example 1 in which a compound corresponding to the compound (c) is not added.
The sensitivity and resolution show that the smaller the number, the better the resolution, and the larger the number, the larger the depth of focus. This evaluation is a relative evaluation. Regarding the halation prevention effect, the degree of jaggedness on the side surface of the pattern caused by the reflected light from the substrate and the degree of pattern thinning in the step portion of the substrate were comprehensively evaluated, and three grades of excellent, good and bad were evaluated.

[0029]

[Table 1]

From the results of the above Examples and Comparative Examples, it was found that a resist pattern excellent in sensitivity, resolution and pattern shape can be obtained by using the resist composition of the present invention.

[0031]

INDUSTRIAL APPLICABILITY According to the present invention, there can be obtained a resist composition capable of preventing halation without impairing sensitivity, resolution and depth of focus. From the results of the above Examples and Comparative Examples,
It was found that a resist pattern excellent in sensitivity, resolution and pattern shape can be obtained by using the resist composition of the present invention.

Front Page Continuation (72) Inventor Atsushi Sone 1-2-1 Nikko, Kawasaki-ku, Kawasaki-shi, Kanagawa Zeon Corporation (72) Masami Togo 1-2-1 Nikko, Kawasaki-ku, Kawasaki-shi, Kanagawa Within Zeon Corporation

Claims (1)

[Claims] 1. An alkali-soluble phenolic resin (a),
A positive resist composition comprising a quinonediazide sulfonic acid ester-based photosensitizer (b) and a compound (c) represented by the following general formula (I). Embedded image (R ^{1 to} R ⁶ may be different from each other and are a hydrogen atom, a halogen atom, a hydroxyl group, a substitutable alkyl group, a substitutable alkoxy group or —OCOR ⁷ , and R ⁷ is a substitutable alkyl group.)