Photosensitive polyimide precursor composition

Abstract: The present invention provides photosensitive com positions which comprise polyimide precursors having a chemical structure selected from several specific chemical structures and/or specific amide bond density and are adjusted so that the film obtained by applying and drying the composition may exhibit a specific absorbance to light. The polyimide film obtained by heat-curing the above photosensitive composition exhibits excellent physical properties and water resistance, and has high adhesive strength to epoxy resins, inorganic materials and metals.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel photosensitive composition suitably used to manufacture semiconductor devices or multilayer circuit boards in the field of electric and electronics. Particularly, this invention relates to a photosensitive composition applicable to a lithography process with a short wavelength light source in order to obtain polyimide patterns after annealing. Such a composition is becoming popular in the production process of semiconductors. 2. Prior Art Polyimides have been recognized as a material used in the field of electronics for their high thermal and chemical stabilities, low dielectric constant and excellent ability in planarization. These polyimides have been widely used as materials for surface protective layers, interlayer dielectrics of semiconductors and insulating layers in multichip modules. In order to obtain a desired pattern from ordinary polyimide coatings, an indirect lithographic method wherein, for example, a polyimide layer with a patterned photoresist as an etching mask is employed. In this method, however, the process is complicated. Moreover, the method has drawbacks since e.g. the use of harmful agents like hydrazine is required in the etching process and the resolution of the polyimide pattern is reduced because of the indirect lithographic method. Accordingly, investigations into methods for direct pattern formation of polyimides with photoreactive compounds having polyimides or polyimide precursors have been conducted. In such methods, the polyamic acid derivatives having double bonds linked through ester bonds, amide bonds, acid ammonium salt and the like are used. The polyamic acid derivatives can be used in the direct photolithography process with photoinitiators. The photosensitive components are removed by heating to obtain thermally stable polyimides (T. Yamaoka and T. Omote, "Polyfile", vol.27, no.2, pp.14-18 (1990)). This technology is generally referred to as a photosensitive polyimide technology. A demand for miniaturising of semiconductors such as IC, LSI, VLSI has been gradually increasing. According to this demand, processing technologies for fine materials have been expected. In one of the technologies, the pattern formation of photoresists is conducted by using short wavelength light such as i-line light of a Hg lamp (365 nm wavelength) instead of ordinary g-line light (436 nm wavelength), for which a high resolution can be expected. It has been anticipated that all exposure apparatuses will employ i-line light at semiconductor manufacturing factories in the near future. On the other hand, in the case of conventional polyimide precursor technology, the compositions to be used in this technology have relatively high absorbance to i-line light. Further, the polyimide precursor compositions are applied to be rather thick, that is, 12 µm or more, in view of the shrinkage caused by removing the photosensitive components during curing, because the polyimide coating requires a thickness of 6 µm or more from the standpoint of the physical properties. Therefore, conventional polyimide precursor compositions do not allow i-line light to reach the bottom of its coating. As a result, the bottom of the coating is not sufficiently hardened by exposure and the pattern is washed away during development. Consequently, i-line light is not suitable as the exposure light source for obtaining a polyimide coating having more than a certain thickness. (C. Schuoket, et al., "IEEE/SEMI Advanced Semiconductor Manufacturing Conference", pp.72-74 (1990)). When i-line light is used, the pattern formation using thin coatings must be conducted several times to obtain sufficiently thick polyimide coating, so that the accuracy of the resultant patterns cannot be improved and the production process becomes complicated. Therefore, i-line light exposure is not practical. It has been known that a film of a fluorine-containing polyimide precursor has high i-line light transmittancy (T. Omote, T. Yamaoka and K. Kosei, "Journal of Applied Polymer Sience", vol.38, pp.389-402 (1989)). Polyimides, which are obtained by heat-curing the precursors and contain fluorine in their main frame work, have drawbacks in practical use. That is, they have a low adhesive strength to other materials used with polyimides, such as base inorganic materials, epoxy resins in coating layers and metals for distributing wires when they are used for semiconductor devices and multilayer circuit boards. A photosensitive polyimide precursor composition, which can form patterns by means of i-line light and is applicable to practical uses, has not yet been obtained. European Patent Applications EP-A-0 379 377, EP-A-0 3 41 028 and EP-A-0 119 162 disclose photosensitive compositions which comprise (A) an aromatic polyamide precursor; (B) a photopolymerization inhibitor; and (C) a solvent. They, however, do not satisfy at least one of the following conditions: (i) the amide bond density is 2.42 mole/kg or less and, in the repeating unit of the aromatic polyamide precursor represented by the general formula (1), R and R' independently represent -O - N + R 3 R 4 R 5 R 6 or -OH groups; and (ii) X is a tetravalent group wherein the aromatic groups connected to -CONH groups have a chemical structure in which the aromatic group is substituted with an aprotic electron donating group. European Patent Application EP-A-0 262 446 discloses a photosensitive amphiphilic aromatic polyamide precursor for Langmuir-Blogett film which has a repeating unit represented by the present general formula (I) wherein R and R' independently represent -O - N + R 3 R 4 R 5 R 6 and at least one of R 3 , R 4 , R 5 and R 6 represents an organic group having an olefinically unsaturated bond. However, EP-A-0 262 446 is silent about amide bond density. Moreover, no calculation of amide bond density is possible for the above-mentioned polymer in the absence of concrete examples of R 3 , R 4 , R 5 and R 6 . All these prior patent applications do not solve the problem sufficiently to provide an excellent i-line light transmittance of the polyimide precursors. It is further noted from the publication of A. St. Clair et al., Int. SAMPE Techn. Conf. (1991), 23, 817 to 830 that introducing a polar aprotic electron donating group -O- between phenyl rings in order to reduce conjugation in the polymer claim may improve the transparency of polyimide films; it is, however, silent on the influence of said group on other important mechanical and thermal properties of films made from such polyimide precursors. SUMMARY OF THE INVENTION The present invention provides a photosensitive polyimide composition. From the composition, a polyimide film having more than a certain thickness can be obtained by applying the process of pattern formation by i-line exposure and a heat-cure. The composition is applicable to practical uses. A desirable pattern is formed by exposing the photosensitive polyimide precursor composition to i-line light, which composition comprises polyimide precursors having a chemical structure selected from several specific chemical structures and/or specific amide bond density and is adjusted so that the film obtained by applying and drying the composition may exhibit specific absorbance. The polyimide film obtained by heat-curing the above pattern exhibits excellent physical properties and water resistance, and has high adhesive strength to epoxy resins, inorganic materials and metals. DETAILED DESCRIPTION OF THE INVENTION The present invention provides photosensitive compositions capable of producing a film that exhibits an absorbance of 1.5 or less at a film thickness of 10 µm upon exposure to light of a wavelength of 365 nm, said composition comprising: (A) an aromatic polyimide precursor having an amide bond density of 1.5 mol/kg or more, defined as the number of amide groups (in mol) present in 1 kg of the polyimide precursor, and a repeating unit represented by the general formula (I): wherein X represents a tetravalent aromatic group not including a fluorine atom or a tetravalent organic group having a chemical structure in which 2 to 4 aromatic groups are linked through at least one type of bond selected from the group consisting of a single bond, an ether bond, a thioether bond, a carbonyl bond, a methylene bond, a sulfoxide bond and a sulfone bond, and which does not include a fluorine atom; -COR and -COR' groups take the ortho positions against -CONH group; R and R' independently represent -NHR 2 , -0 - N + R 3 R 4 R 5 R 6 or -OH groups, wherein R 2 and R 3 represent organic groups having olefinically unsaturated bonds; and R 4 to R 6 independently represent a hydrogen atom or a hydrocarbon group having 1 to 6 carbon atoms; and Y represents a divalent aromatic group not including a fluorine atom or a divalent organic group having a chemical structure in which 2 to 6 aromatic groups are linked through at least one type of bond selected from the group consisting of a single bond, an ether bond, a thioether bond, a carbonyl bond, a methylene bond, a 2,2-propylene bond, a sulfoxide bond and a sulfone bond, and which does not include a fluorine atom, (B) a photopolymerization initiator, and (C) a solvent. Moreover, the polyimide precursor of the photosensitive composition satisfies at least one of the following conditions: (i) amide bond density is 2.42 mol/kg or less, and (ii) X is a tetravalent group wherein the aromatic group connected with -CONH groups has a chemical structure in which the aromatic group is substituted with an aprotic electron donating group. A film, which is obtained by applying and drying the photosensitive composition, has absorbance of 1.5 or less at a thickness of 10 µm at 365 nm wavelength light. In the composition of the present invention, the polyimide precursor used as component (A) is represented by the general formula (I). As for each aromatic group contained in X and Y in the general formula (I), groups having a benzene ring, a naphthalene ring or an anthracene ring are preferred because the heat resistance of a polyimide film obtained by heat-curing the photosensitive composition having such radicals is high. As for the type of bond between the aromatic groups, one or more selected from the group consisting of a single bond, an ether bond, a carbonyl bond and a sulfone bond are preferred because of the the same reason as mentioned above. When the -COR or -COR' group in the general formula (I) is an amide group represented by the general formula (V-2): -CONHR 2 wherein R 2 is as defined above, it is necessary that the amide group includes a group having an olefinically unsaturated bond such as a N-(2-acryloyloxyethyl)aminocarbonyl group and a N-(2-methacryloxyethyl)-aminocarbonyl group. Additionally, the amide group may include a group not having an olefinically unsaturated bond such as a methylaminocarbonyl group, an ethylaminocarbonyl group or a N-(2-ethoxyethyl)aminocarbonyl group. When the -COR or -COR' group in the general formula (I) is an ammonium salt of a carboxylic acid as represented by the general formula (V-3): -COO - N + R 3 R 4 R 5 R 6 wherein R 3 , R 4 , R 5 and R 6 are as defined as above, it is necessary that the ammonium salt of the carboxylic acid includes a group having an olefinically unsaturated bond such as a carboxylic acid 2-methacroyloxyethyl-trimethylammonium salt or a carboxylic acid 2-acryloyloxyethyl-dimethylammonium salt. Additionally, the ammonium salt of the carboxylic acid may include a group not having an olefinically unsaturated bond wherein all the R 3 to R 6 are hydrogen atoms or hydrocarbon groups. When the -COR or -COR' group in the general formula (I) is a carboxylic acid group, it is necessary that the groups mentioned in the general fomulas (V-2) or (V-3) also exist in the repeating units of the polyimide precursor. A polyimide precursor, which has a group selected from the groups represented by the general formula (V-2) and a carboxylic acid is preferably used because a coating thickness of the obtained photosensitive composition is almost unchanged during development and the polyimide pattern has good reproducibility from the photomask and has high resolution. In the composition of the present invention, the polyimide precursor used as component (A) should have amide bond density of 1.5 mol/kg or more. The amide bond density means a value obtained by dividing 2000 by a molecular weight of the repeating unit of the polyimide precursor or a value obtained by dividing 2000 by an average molecular weight, which is calculated from a molecular weight of each repeating unit and a molar ratio of each repeating unit if the polyimide precursor has several kinds of the repeating unit. The amide bond density is a parameter representing a mol value of an amide group present in 1 kg of the polyimide precursor. When the amide bond density is lower than 1.5 mol/kg, heat resistance is considerably decreased. The polyimide precursor used represented by the general formula (I) is produced by known methods described by, for example, R. Rubner et al. ("Photographic Science Engineering", vol.23, p.303 (1979)), M. T. Pottiger et al. ("The 38th Electronic Components Conference", p.315 (1988)), L. Minnema et al. ("Polymer Engineering and Science". vol.28, no.12, p.815 (1988)) and Davis et al. ("Chemical & Engineering News; Sept. 26, 1983, p.23). Additionally, the polyimide precursor can be also produced by the methods described in U.S. Patent Nos. 4,645,823 and 4,243,743, European Patent Unexamined Publication No. 421,195 and Japanese Patent Application Laid-Open No. 4226/1991. According to these methods, the polyimide precursor is produced by using an aromatic tetracarboxylic dianhydride (hereinafter referred to as ATC dianhydride) represented by the general formula (VI), an aromatic diamino compound represented by the general formula (VII) as a part of raw materials. wherein X is as defined above. H 2 N-Y-NH 2 wherein Y is as defined above. When a compound having a group containing a fluorine atom such as a fluorine group and a trifluoromethyl group is used as a raw material for the polyimide precursor of the present invention, a fluorine-containing polyimide obtained by heat-curing the photosensitive composition is not applicable to practical uses because of its low adhesive strength to other material. It is necessary to use a polyimide precursor satisfying at least one or more specific conditions in order to obtain the photosensitive composition of the present invention. Specific conditions mean the conditions (i) to (ii) mentioned above. As long as the photosensitive composition of the present invention satisfies the other conditions described above, conditions (i) to (ii) can be used without any restriction. The amide bond density must be at least 1.5 mol/kg as mentioned above. When the amide bond density is 2.42 mol/kg or less and the condition of polyimide precursor described in (A) is satisfied, the composition of the present invention can be obtained regardless of the structure of the polyimide precursor and i-line absorbance of the obtained polymer coating becomes lower and water resistance of the heat-cured film becomes higher with a decrease in the amide bond density. The polyimide precursor having amide bond density of from 2.0 to 2.42 mol/kg is preferred because the obtained polyimide film has higher mechanical strength and heat resistance. For the preparation of the polyimide precursor satisfying condition (ii), an ATC dianhydride is used, wherein the aromatic group carrying a carboxylic anhydride group has a chemical structure in which the aromatic group is substituted with an aprotic electron donating group (hereinafter referred to as ATC dianhydride under condition (ii)). Herein, the aprotic group may not be a group having active hydrogen such as an alcohol, an amine and a carboxylic acid. The electron donating group indicates a substituting group, whose value of σp or σm is minus in Hammett's rule. The rule and value are widely known, for example, Section 365 of "Kagaku Binran Kisohen II" edited by Nippon Kagaku Kai and published by Maruzen Company, Limited in 1984. Representative examples of the aprotic electron donating groups include a dialkylamino group, an alkoxy group, an aryloxy group, a trialkylsilyl group, a benzyl group and an alkyl group. Representative examples of the ATC dianhydrides under condition (ii) include 3,3',4,4'-diphenylether tetracarboxylic dianhydride, 1,4-dimethoxy-2,3,5,6-benzene tetracarboxylic dianhydride, 1,4-ditrimethylsilyl-2,3,5,6-benzene tetracarboxylic dianhydride, 1,4-bis-(3,4-dicarboxylphenoxy)benzene dianhydride, 1,3-bis(3,4-dicarboxylphenoxy)benzene dianhydride, 3,3',4,4'-diphenylmethane tetracarboxylic dianhydride, bis(3,4-dicarboxylphenoxy)dimethylsilane dianhydride, bis(3,4-dicarboxylphenoxy)methylamine dianhydride, 4,4'-bis(3,4-dicarboxylphenoxy)biphenyl dianhydride and 4,41-bis(3,4-dicarboxylphenoxy)diphenylsulfone dianhydride. In the present invention, as long as the absorbance of a coating obtained from the photosensitve composition is 1.5 or less at a film thickness of 10 µm thick at 365 nm wavelength, the ATC dianhydride represented by the general formula (VI) other than the one under condition (ii) can be used: (1) by mixing with the ATC dianhydride under condition (ii); (2) by combining with the specific aromatic diamino compound mentioned below; or (3) if an aromatic polyimide precursor having specific amide bond density is obtained. Representative examples of these compounds include pyromellitic dianhydride, 2,3,5,6-naphthalene tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylicdianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,5,6-pyridine tetracarboxylic dianhydride, 2,3,6,7-quinoline tetracarboxylic dianhydride, 3,3',4,4'diphenylsulfone tetracarboxylic dianhydride, 3,3',4,4'diphenylsulfide tetracarboxylic dianhydride and 3,3',4,4'diphenylsulfoxide tetracarboxylic dianhydride. In addition, they include 1,2,8,9-anthracene tetracarboxylic dianhydride, 1,4-bis(3,4-dicarboxylphenylsulfonyl)benzene dianhydride, 1,4-bis(3,4-dicarboxylphenylthio)benzene dianhydride, 3,3',4,4'-terphenyl tetracarboxylic dianhydride, 4-phenylbenzophenone-3,3',4,4'-tetracarboxylic dianhydride, 1,4-bis(3,4-dicarboxylbenzoyl)-benzene dianhydride, 3,3',4,4'quaterphenyl tetracarboxylic dianhydride, 4,4'-bis(3,4-dicarboxylphenoxy)-benzophenone dianhydride and 4,4'-bis(3,4-dicarboxylphenoxy)-diphenylsufoxidedianhydride. In the present invention, as long as the absorbance of a coating obtained from the photosensitive composition is 1.5 or less at a film thickness of 10 µm at 365 nm wavelength, the aromatic diamino compound represented by the general formula (VII) other than the specific aromatic diamino compound mentioned above can be used: (1) by mixing with the specific aromatic diamino compound mentioned above; (2) by combining with the ATC dianhydride under condition (ii),; or (3) if an aromatic polyimide precursor having specific amide bond density is obtained. Representative examples of the aromatic diamino compounds include 4,4'-diaminodiphenylether, 4,4'-diaminodiphenylsulfide, 3,4'-diaminodiphenylether, 1,4-phenylenediamine, 2,7-naphthalenediamine, 3,3'-dimethyl-4,4'-diaminobiphenyl, 3,3'-dimethoxy-4,4'-diaminobiphenyl, 3,3'-dichloro-4,4'-diaminobiphenyl, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, 5,8-diaminoquinoline, 4,4'-bis(4-aminophenoxy)biphenyl, 4,4'-diaminodiphenylmethane, bis[4-(4-aminophenoxy)phenyl]ether, 1,4-bis(4-aminophenyl)benzene, 9,10-bis(4-aminophenyl)anthracene, 4,4'-bis(4-aminophenoxy)diphenylmethane, 4,4'-bis(4-aminophenoxy)diphenylsulfide, bis[2-(4-aminophenyl)-benzothiazolyl]ether, bis[2-(4-aminophenyl)-benzimidazolyl]sulfoxide, bis[2-(4-aminophenyl)-benzoxazolyl], 4-(4-aminophenylsulfonyl)4'-aminobiphenyl, 4,4'-bis(4-aminophenyl)diphenylether and 1,4-di-(4-aminobenzoyloxy)butane. Representative examples of component (B) used as a photopolymerization initiator include benzophenone derivatives such as benzophenone, o-benzoyl methyl benzoate, 4-benzoyl-4'methyl diphenyl ketone, dibenzyl ketone and fluorenone; acetophenone derivatives such as 2,2'-diethoxyacetophenone, 1-hydroxycyclohexylphenyl ketone and 2-hydroxy-2-methyl propiophenone; thioxanthone derivatives such as thioxanthone, 2-methylthioxanthone, 2-isopropyl thioxanthone and diethyl thioxanthone; benzil derivatives such as benzil, benzil dimethyl ketal and benzil-β-methoxyethyl acetal; benzoin derivatives such as benzoin and benzoin methylether; azido derivatives such as 2,6-di(4-azidobenzylidene)-4-methylcyclohexanone and 2,6-di(4-azidobenzylidene)cyclohexanone; and oxime derivatives such as 1-phenyl-1,2-butadione-2-(O-methoxycarbonyl)oxime, 1-phenyl-1,2-propanedione-2-(O-methoxycarbonyl)oxime, 1-phenyl-1,2-propanedione-2-(O-ethoxycarbonyl)oxime,1-phenyl-1,2-propanedione-2-(O-benzoyl)oxime, 1,3-diphenylpropanetrione-2-(0-ethoxycarbonyl)oxime and 1-phenyl-3-ethoxy-propanetrione-2-(0-benzoyl)oxime. Of these, oxime derivatives are preferred for its high photosensitivity. The amount of the photopolymerization initiator is preferably in the range of from 1 to 15 parts by weight per 100 parts by weight of polyimide precursor. Representative examples of component (C) used as solvents include N,N'-dimethylformamide, N-methylpyrrolidone, N-acetyl-2-pyrrolidone, N,N'-dimethylacetamide, diethylene glycol dimethylether, cyclopentanone, γ-butyrolactone and α-acetyl-γ-butyrolactone. They may be used individually or in combination. These solvents may be employed in the range of from 100 to 400 parts by weight per 100 parts by weight of the polyimide precursor according to the thickness of the films or the viscosity of the composition. The compounds having a reactive carbon-carbon double bond can be used in addition to the above-mentioned components (A) to (C) to improve photosensitivity of the present composition, if desired. Representative examples of such compounds include 1,6-hexandioldiacrylate, neopentyl glycol diacrylate, ethylene glycol diacrylate, polyethylene glycol diacrylate having 2 to 20 of repeating units, pentaerythritol diacrylate, dipentaerythritol hexacrylate, trimethylolpropane triacrylate, tetramethylolmethane tetraacrylate, methylene bisacrylamide, N-methylolacrylamide, and the corresponding methacrylate and methacrylamide to the above-mentioned compounds. These compounds may be employed in the range of from 1 to 30 parts by weight per 100 parts by weight of the polyimide precursor. Sensitizers can be used to improve photosensitivity of the present composition, if desired. Representative examples of the sensitizers include Michler's ketone, 4,4'-bis(diethylamino)benzophenone, 2,5-bis(4-diethylaminobenzylidene)cyclopentanone, 2,6-bis(4-diethylaminobenzylidene)cyclohexanone, 2,6-bis(4-dimethylaminobenzylidene)-4-methylcyclohexanone, 2,6-bis(4-diethylaminobenzylidene)-4-methylcyclohexanone, 4,4'-bis(dimethylamino)chalcone, 4,4'-bis(diethylamino)chalcone, 2-(4'-dimethylamino cinnamylidene)indanone, 2-(4'-dimethylamino benzylidene)indanone, 2-(p-4'-dimethylaminobiphenyl)-benzothiazole, 1,3-bis(4-dimethylaminobenzylidene)acetone, 1,3-bis(4-diethylaminobenzylidene)acetone, 3,3'-carbonyl-bis(7-diethylamino coumarin), 3-acetyl-7-dimethylamino coumarin, 3-ethoxycarbonyl-7-dimethylamino coumarin, 3-benzyloxycarbonyl-7-dimethylamino coumarin, 3-methoxycarbonyl-7-diethylamino coumarin, 3-ethoxycarbonyl7-diethylamino coumarin, N-ethyl-N-phenyl-ethanolamine, N -phenyldiethanolamine, N-p-tolyldiethanolamine, N-phenylethanolamine, 4-morpholino-benzophenone, 4-dimethylamino isoamylbenzoate, 4-diethylamino isoamylbenzoate, 2-mercaptobenzimidazole, 1-phenyl-5-mercapto-1,2,3,4-tetrazole, 2-mercapto-benzothiazole,2-(p-dimethylaminostyryl)benzoxazole, 2-(p-dimethylaminostyryl)-benzothiazole, 2-(p-dimethylaminostyryl)naphtho(1,2-d)-thiazole and 2-(p-dimethylaminobenzoyl)styrene. Of these, a combination of compounds having a mercapto group and compounds having a dialkylaminophenyl group is preferred for its sensitivity. They may be used individually or in combination of two to five compounds. The amount of the sensitizer is preferably in the range of from 0.1 to 10 parts by weight per 100 parts by weight of the polyimide precursor. An adhesion promoter can be added to the composition of the present invention to improve the adhesive strength, if desired. Representative examples of the promoter include γ-aminopropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-mercaptopropylmethyldimethoxysilane, 3-methacryloxypropyldimethoxymethylsilane, 3-methacryloxypropyltrimethoxysilane, dimethoxymethyl-3-piperidinopropylsilane,diethyoxy-3-glycidoxypropylmethylsilane, N-(3-diethoxymethylsilylpropyl)succinimide, N[3-(triethoxysilyl)propyl]phthalamic acid, benzophenone-3,3'-bis(3-triethoxysilylpropylaminocarbonyl)-4,4'-dicarboxylic acid and benzene-1,4-bis(3-triethoxysilylpropylaminocarbonyl)-2,5-dicarboxylic acid. The amount of the promoter is preferably in the range of from 0.5 to 10 parts by weight per 100 parts by weight of the polyimide precursor. A polymerization inhibitor can be added to the composition of the present invention to improve stability of sensitivity and viscosity of the composition solution during storage, if desired. Representative examples of the inhibitor include hydroquinone, N-nitrosodiphenylamine, p-tert-butylcatechol, phenothiazine, N-phenylnaphthylamine, ethylenediamine tetraacetic acid, 1,2-cyclohexanediamine tetraacetic acid, 2',2'-diethyletherdiamine tetraacetic acid, 2,6-di-tert-butyl-p-methylphenol, 5-nitroso-8-hydroxyquinoline, 1-nitroso-2-naphthol, 2-nitroso-1-naphthol, 2-nitroso-5-(N-ethyl-N-sulfopropylamino)phenol, N-nitroso-N-phenylhydroxylamine ammonium salt, N-nitroso-N-(1-naphthyl)hydroxylamine ammonium salt and bis(4-hydroxy-3,5-tertbutylphenyl)methane. The amount of the inhibitor is preferably in the range of from 0.005 to 5 parts by weight per 100 parts by weight of the polyimide precursor. In the present invention, it is necessary that the absorbance at 365 nm wavelength (i-line) light at a thickness of a 10 µm dried coating obtained from a polyimide precursor composition be 1.5 or less to form a pattern on the film with i-line wavelength light. When the absorbance is over 1.5, the light intensity is not sufficient at the bottom of the film so that a satisfactory pattern is not formed. The above-mentioned absorbance can be adjusted by the amounts of essential components (A) to (C) and other additives. The photosensitive compositions of the present invention can be produced by mixing the above-mentioned components (A) to (C) and others. And, from the thus obtained composition, a polyimide film can be obtained by taking steps as described below. The compositions of the present invention are applied to a substrate by using, for instance, a spin-coater, a barcoater, a blade-coater, a curtain-coater, screen printing press and a spray-coater. The resultant coating can be dried by air-drying, heating in an oven or on a hot plate, and vacuum drying. The dried coating should be exposed with a ultraviolet ray, etc. as a light source by using an exposure equipment such as a contact aligner, a mirror projection aligner and a stepper. Of these, a stepper and i-line as a light source are preferred for its high resolution and easy handling. The irradiated film can be developed by conventional methods for developing photoresist such as a spin-spray method, a puddle method and a dipping method with a supersonic wave. Preferably, a developing solution is a combination of good and poor solvents to the above-mentioned polyimide precursor. Representative examples of good solvents include N-methylpyrrolidone, N-acetyl-2-pyrrolidone, N,N'-dimethylacetamide, cyclopentanone, cyclohexanone, γ-butyrolactone, α-acetyl-γ-butyrolactone. Representative examples of poor solvents include toluene, xylene, methyl alcohol, ethyl alcohol, isopropyl alcohol and water. The ratio of both solvents is adjusted according to the solubility of the polyimide precursor. They may be used in combination. If necessary, when the polyimide precursor contains carboxylic acids, the aqueous solution of organic bases such as cholinehydroxide and tetramethylammonium hydroxide can be used as a developing solution, or used by being added to the above-mentioned organic solvents according to the solubility of the polyimide precursor. The resultant patterned film are heat-cured to obtain a polyimide film as a result of evaporation of volatile components. This process can be carried out by using a hot plate, an oven, and an oven capable of storing temperature program. Air, nitrogen and inert gas such as argon may be used as an atmosphere in heat-curing the patterned film. DESCRIPTION OF PREFERRED EMBODIMENT The present invention is now described in more detail by referring to Examples. Each characteristic of the compositions in Examples and Comparative Examples was determined as follows: (1) Amide bond density Amide bond density [C] is calculated according to the equation below. [C] = 2000 (M) C + (M) A + (M) S In the equation, [M] C represents the molecular weight of a tetracarboxylic acid unit, and it is calculated by subtracting 32 (= the atomic weight of oxygen atom x 2) from the molecular weight of an ATC dianhydride used as a starting material. When two or more of ATC dianhydrides are employed, their average molecular weight is used for the calculation. [M] A represents the molecular weight of an aromatic diamine unit, and it is calculated by subtracting 2 (= the atomic weight of hydrogen atom x 2) from the molecular weight of an aromatic diamino compound used as a starting material. When two or more of the aromatic diamino compounds are employed, their average molecular weight is used for the calculation. [M] S represents the total amount of substituting groups R and R' which bind to aromatic rings through carbonyl group in the polyimide precursor, and it is calculated by doubling the average molecular weight of R and R, radicals. The atomic weights used in the above calculation are 12 for carbon, 14 for nitrogen, 16 for oxygen, 32 for sulfur and 1 for hydrogen, respectively. A numerator 2000 is the coefficient to calculate the mole value of amide bonds per 1 kg of the polyimide precursor. (2) Absorbance of polyimide precursor N-methylpyrrolidone solution of polyimide precursor is applied on a 1 mm thick quartz plate using a spin-coater and dried in an oven at 80° C for 40 min. to form a 10 µm thick polyimide precursor coating. Then, its absorbance (referred to hereinafter as precursor absorbance) at 365 nm is measured by ultraviolet spectroscope UV-240 type (manufactured by Shimazu Corporation) and is calculated according to the following equation: Absorbance = log 10 I o /I (wherein I o represents incident light intensity; I represents transmitted light intensity through a film.) (3) Absorbance of photosensitive composition coating A photosensitive composition is applied on a 1 mm thick quartz plate using a spin-coater and dried in an oven at 80° C for 40 min. to form a 10 µm thick photosensitive composition coating. Then, its absorbance (referred to hereinafter as coating absorbance) is measured by the same method as (2). (4) Viscosity number of polyimide precursor Viscosity number (ηsp/c) of polyimide precursor in N-methylpyrrolidone (1 g/dl) is measured by Auto Viscometer AVL-2C (manufactured by San Denshi Ind. Co., Ltd.) at 30° C. (5) Viscosity of photosensitive composition Viscosity of the photosensitive composition solution is measured by an E type viscometer (manufactured by Tokyo Keiki Co., Ltd.: VISCONIC-EMD type) at 23° C. (6) Tensile strength and elongation of polyimide film In each Example, the general procedure is repeated except that the obtained film on the wafer is exposed without a photomask and is not developed. The resultant polyimide film is peeled from the wafer, and its tensile strength and elongation are measured according to ASTM D-882-88. (7) Pull test Adhesive strength between a polyimide film and a silicon wafer is measured as follows. After the photosensitive composition on the wafer is heat-cured, a pin having a diameter of 2 mm is attached to the polyimide film with epoxy resin adhesive (Araldite® standard manufactured by Showa Highpolymer Co., Ltd.). The obtained sample is subjected to a pull test using a pull tester (manufactured by Quad Company Group, SEBASTIAN 5 type).The standard of judgement: Pulling stress (kg/mm 2 ) Adhesive strength 7 or less Good 6 to 5 Usable Less than 5 Poor (8) Water resistance test After the photosensitive composition on the wafer is heat-cured, it is kept in boiling water for 48 hrs. and dried in an oven at 50° C for 2 hrs. Then, it is subjected to the above-mentioned pull test.The standard of judgement: Pulling stress (kg/mm 2 ) Water resistance 7 or more Good 6 to 3 Usable Less than 3 Poor (9) Raw material ATC dianhydrides used in Preparations are represented by the following symbols. The structural formulas shown below represent X in the general formula (VI). X-1: 3,3',4,4'-benzophenone tetracarboxylic dianhydride X-2: 3,3',4,4'-diphenylether tetracarboxylic dianhydride X-3: 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride X-4: 3,3'4,4'-terphenyltetracarboxylic dianhydride X-5: 1,4-bis(3,4-dicarboxylphenoxy)benzene dianhydride X-6: 4,4'-bis(3,4-dicarboxylphenoxy)bipheny dianhydride X-7: 4,4'-bis(3,4-dicarboxylphenoxy)diphenyl sulfone dianhydride X-8: 3,3',4,4'-biphenyl tetracarboxylic dianydride X-9: 1,4-dimethoxy-2,3,5,6-benzene tetracarboxylic dianhydride X-10: 3,3',4,4'-diphenylmethane tetracarboxylic dianhydride X-11: pyromellitic dianhydride Aromatic diamino compounds used in the Preparations are represented by the following symbols. The structural formulas shown below represent Y in the general formula (VII). Y-1: 4,4'-bis(4-aminophenoxy)biphenyl Y-2: 9,10-bis(4-aminophenyl)anthracene Y-3: bis[4-(4-aminophenoxy)phenyl]ether Y-4: bis[4-(3-aminophenoxy)phenyl]sulfone Y-5: 3,3'-diaminodiphenylsulfone Y-6: 1,4-bis(4-aminophenoxy)benzene Y-7: 1,3-bis(3-aminophenoxy)benzene Y-8: bis[4-(4-aminophenoxy)phenyl]sulfone Y-9: 4,4'-bis(3-aminophenoxy)biphenyl Y-10: 4,4'-diaminodiphenylether Y-11: p-phenylene diamine Y-12: 4,4'-diaminodiphenylsufide Y-13: 4,4'-diaminobenzophenone Y-14: 4,4'-bis[4-(4-aminophenoxy)phenoxy]diphenylsulfone Y-15: 3,4'-diaminodiphenylether Y-16: 4,4'-diaminodiphenylsulfoxide Y-17: 3,3'-dimethyl-4,4'-diaminobiphenyl Y-18: 2,4-di-aminomesitylene Y-19: m-phenylene diamine Y-20: 4,4'-diaminodiphenylsulfone Y-21: 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane Y-22: 3,5-diamino ethylbenzoate Y-23: 2,4-diaminobenzamide Y-24: 3'5-diaminobenzophenone Y-25: 3,5-diamino(2-methacryloxyethyl)benzoate Y-26: 3,5-diaminobenzonitrile Y-27: 2,2-bis[4-(3-aminophenoxy)phenyl]hexafluoropropane Y-28: 4,4'-diamino-3,3',5,5'-tetramethyldiphenylmethane Compounds used in the Preparations to form -COR or -COR' groups (R-raw material) are represented by the following symbols. E-3: 2-diethylamino ethyl methacrylate E-8: 2-methacryloxyethyltrimethylammoniumhydroxide [Preparation 1) 76.8 g of Y-3 was dissolved in 450 g of N-methylpyrrolidone. 71.6 g of X-3 was added to the resultant solution and reacted at 50° C for 6 hrs. A solution obtained by dissolving 74.0 g of E-3 in 110 g of N-methylpyrrolidone was slowly added to the above reacted solution at room temperature. As a result, a solution of polyimide precursor (A3-1) was obtained. Amide bond density and precursor absorbance of A3-1 are shown in Table 2. [Preparations 2 to 9] Solutions of polyimide precursors (A3-2 to A3-9) were prepared in the same manner as in Preparation 1 except that ATC dianhydrides, aromatic diamino compounds and R-raw materials shown in Table 1 were used respectively in the amounts shown in Table 1. Their amide bond density and precursor absorbance are shown in Table 2. [Preparation 10] 160.6 g of Y-7 was dissolved in 770 g of N-methylpyrrolidone. 120 g of X-11 was added to the resultant solution and reacted at 50° C for 6 hrs. A solution obtained by dissolving 2.5 g of E-3 in 50 g of N-methylpyrrolidone was added to 50 g of the above reacted solution. As a result, a solution of polyimide precursor (A3-10) was obtained. The amide bond density and precursor absorbance of A3-10 are shown in Table 2. [Preparation 11] 22.8 g of Y-20 was dissolved in 150 g of N-methylpyrrolidone. 35.8 g of X-3 was added to the resultant solution and reacted at 50° C for 6 hrs. A solution obtained by dissolving 37.2 g of E-3 in 66 g of N-methylpyrrolidone was slowly added to the above reacted solution at room temperature. As a result, a solution of polyimide precursor (A3-11) was obtained. Amide bond density and precursor absorbance of A3-11 are shown in Table 2. [Preparations 12 and 13] Solutions of polyimide precursors (A3-12 and A3-13) were prepared in the same manner as in Preparation 11 except that R-raw materials shown in Table 1 were used respectively in the amounts shown in Table 1. Viscosity numbers, amide bond density and precursor absorbance of A3-12 and A3-13 are shown in Table 2. Before describing the Examples, symbols used for each compound in the Examples are shown. Photopolymerization initiator (Component B) I-1: benzophenone I-2: benzil I-3: 2-isopropylthioxanthone I-4: 1,3-diphenyl-propanetrione-2-(0-ethoxycarbonyl)oxime I-5: 1-phenyl-3-ethoxy-propanetrione-2-(0-benzoyl)oxime Reactive carbon-carbon double bond-containing compound M-1: tetraethylene glycol dimethacrylate M-2: pentaerythritol diacrylate M-3: methylenebisacrylamide M-4: N-methylolacrylamide M-5: trimethylolpropane triacrylate Sensitizer S-1: Michler's ketone S-2: 4,4'-bis(diethylamino)benzophenone S-3: 2-(p-dimethylaminostyryl)benzoxazole S-4: 2-(p-dimethylaminobenzoyl)styrene S-5: N-phenyldiethanolamine S-6: N-p-toluyldiethanolamine S-7: N-phenylethanolamine S-8: 2-mercaptobenzimidazole S-9: 1-phenyl-5-mercapto-1,2,3,4-tetrazole S-10: 2-mercaptobenzothiazole Adhesion promoter F-1: γ-glycidoxypropylmethyldimethoxysilane F-2: 3-methacryloxypropyltrimethoxysilane F-3: 3-methacryloxypropylmethyldimethoxysilane F-4: N-[3-(triethoxysilyl)propyl]phthalamic acid F-5: benzophenone-3,3'-bis(3-triethoxysilylpropylaminocarbonyl)-4,4'-dicarboxylic acid Polymerization inhibitor Z-1: N-nitrosodiphenylamine Z-2: bis(4-hydroxy-3,5-tert-butylphenyl)methane Z-3: 2,6-di-tert-butyl-p-methylphenol Z-4: 2-nitroso-1-naphthol [Example 1] 0.2 g of I-3, 0.8 g of M-3, 0.02 g of S-3, 0.3 g of S-6, 0.15 g of S-10, 0.1 g of F-3 and 0.01 g of Z-3 were dissolved in 77 g of the solution of polyimide precursor (A3-1) prepared in Preparation 1 to obtain photosensitive composition (W-3). Its coating absorbance and viscosity were 0.8 and 55.0 P, respectively. The obtained composition was applied on 3 inch silicon wafers by using a spin-coater, and dried to form 17 mm thick films. Using an exposure machine PLA 501F (manufactured by Canon Inc.) and i-line band pass filter UVD 36C (manufactured by Toshiba Glass Co., Ltd.), the films on the wafers were exposed through a photomask at an exposure energy of 1000 mJ/cm 2 . Then, they were developed by spraying a mixed solvent of N,N1-dimethylacetoamide and ethyl alcohol (80/20 vol. %), and rinsed with isopropyl alcohol. As a result, a sharp 10 µm line/space pattern was obtained. The irradiated films on the wafers were heat-cured at 140°C for 1 hr. and at 300° C for 1 hr. under nitrogen atmosphere in a convection oven to form 8 mm thick patterned polyimide films. The resultant films were broken at a pulling stress of 8 kg/mm 2 in both of the pull and water resistance tests. They showed good adhesive strength and water resistance. The tensile strength and elongation of the polyimide films were 12 kg/mm 2 and 70 %, respectively. [Examples 2 to 9) Photosensitive compositions (W-19 to W-26) were prepared by the same method as in Example 3 except that various kinds of polyimide precursor solutions, which are shown in Table 3, prepared in Preparations 2 to 9 were employed instead of the polyimide precursor (A3-1). Their coating absorbance and viscosity are shown in Table 3. Using these compositions, films were produced by the same method as in Example 1 and subjected to the same tests as in Example 1. The resolution of the patterned films, the results of the pull and water resistance tests, and the tensile strength and elongation of the polyimide films are shown in Table 3. [Example 10] The general procedure in Example 1 was repeated except that polyimide precursor (A3-10) was used instead of polyimide precursor (A3-1) to prepare photosensitive composition (W-31). Its coating absorbance and viscosity was 1.4 and 50 P, respectively. Using the composition, 17 mm thick films were produced by the same method as in Example 1. Then, they were developed to obtain a sharp 10 µm line/space pattern. The irradiated films on the wafers were heat-cured under the same condition as in Example 1 to obtain 9 µm thick patterned polyimide films. The resultant films were broken at a pulling stress of 8 kg/mm 2 in both of the pull and water resistance test. They showed good adhesive strength and water resistance. The tensile strength and elongation of the polyimide films were 16 kg/mm 2 and 10 %, respectively. [Examples 11 to 13] 0.2 g of I-3, 0.8 g of M-3, 0.02 g of S-3, 0.3 g of S-6, 0.15g of S-10, 0.1 g of F-3 and 0.01 g of Z-3 were dissolved in 77 g of polyimide precursor shown in Table 4 to obtain photosensitive compositions (W-43 to W-45). Their coating absorbance and viscosity are shown in Table 4. The obtained compositions were applied on 3 inch silicon wafers by using a spin-coater and dried. Thickness of the resultant films is shown in Table 4. Using an i-line stepper, the films on -the wafers were exposed through a patterned reticle at exposure energy shown in Table 4. Then, they were developed by spraying a mixed solvent of N,N'-dimethylacetamide and ethyl alcohol (80/20 vol. %) and rinsed with isopropyl alcohol. The resultant films showed sharp pattern profiles. Their resolution is shown in Table 4. The irradiated films on the wafers were heat-cured at 140° C for 1 hr. and at 350° C for 1 hr. under nitrogen atmosphere in a convection oven to obtain polyimide patterned films having thicknesses shown in Table 4. The results of the pull and water resistance tests, and the tensile strength and elongation of the polyimide films are shown in Table 4.

Claims: A photosensitive composition capable of producing a film that exhibits an absorbance of 1.5 or less at a film thickness of 10 µm upon exposure to light of a wavelength of 365 nm, sald composition comprising (A) an aromatic polyimide precursor having an amide bond density of 1.5 mol/kg or more, defined as the number of amide groups (in mol) present in 1 kg of the polyimide precursor, and a repeating unit represented by the general formula (I): wherein X represents a tetravalent aromatic group not including a fluorine atom or a tetravalent organic group having a chemical structure in which 2 to 4 aromatic groups are linked through at least one type of bond selected from the group consisting of a single bond, an ether bond, a thioether bond, a carbonyl bond, a methylene bond, a sulfoxide bond, and a sulfone bond, and which does not include a fluorine atom; -COR and -COR' groups take the ortho position against the -CONH group; R and R' independently represent -NHR 2 , -0 - N + R 3 R 4 R 5 R 6 or -OH groups, wherein R 2 to R 3 represent organic groups having olefinically unsaturated bonds, and R 4 to R 6 independently represent a hydrogen atom or a hydrocarbon group having 1 to 6 carbon atoms, and Y represents a divalent aromatic group not including a fluorine atom or a divalent organic group having a chemical structure in which 2 to 6 aromatic groups are linked through at least one type of bond selected from the group consisting of a single bond, an ether bond, a thioether bond, a carbonyl bond, a methylene bond, a 2,2-propylene bond, a sulfoxide bond, and a sulfone bond, and which does not contain a fluorine atom; (B) a photopolymerization initiator; and (C) a solvent; wherein the aromatic polyimide precursor of the photosensitive composition satisfies at least one condition selected from the group consisting of the following conditions: (i) the amide bond density is 2.42 mol/kg or less and, in the repeating unit of the aromatic polyimide precursor represented by the general formula (I), R and R' independently represent -0 - N + R 3 R 4 R 5 R 6 or -OH groups; and (ii) X is a tetravalent group wherein the aromatic groups connected to -CONH groups have a chemical structure in which the aromatic group is substituted with an aprotic electron donating group. The photosensitive composition according to claim 1, wherein the aromatic polyimide precursor is contained in an amount of 100 parts by weight, the photopolymerization initiator is contained in an amount of from 1 to 15 parts by weight and the solvent is contained in an amount of from 100 to 400 parts by weight. The photosensitive composition according to claim 1 or claim 2, wherein the aromatic polyimide precursor satisfies condition (ii). The photosensitive composition according to any of the claims 1 to 3, wherein the aromatic polyimide precursor satisfies condition (i). The photosensitive composition according to claims 1 to 4, wherein the amide bond density is in the range of from 2.0 to 2.42 mole/kg. The photosensitive composition according to any of the claims 1 to 5, wherein each aromatic group contained in X and Y in the general formula (I) has a benzene ring, a naphthalene ring or an anthracene ring. The photosensitive composition according to any of the claims 1 to 6, wherein X in the general formula (I) represents a tetravalent organic group having a chemical structure in which 2 to 4 aromatic groups are connected through at least one type of bond selected from the group consisting of a single bond, an ether bond, a carbonyl bond and a sulfone bond. The photosensitive composition according to claims 1 to 7, wherein Y in the general formula (I) represents a divalent organic group having a chemical structure in which 2 to 6 aromatic groups are connected through at least one type of bond selected from the group consisting of a single bond, an ether bond, a carbonyl bond, and a sulfone bond. The use of a photosensitive composition according to any of the claims 1 to 8 in a process for producing a pattern by exposure to i-line light. A process for forming a polyimide pattern which process comprises the steps of (I) applying to a substrate a photosensitive composition capable of producing a film that exhibits an absorbance of 1.5 or less at a film thickness of 10 µm upon exposure to light of a wavelength of 365 nm, said composition comprising (A) an aromatic polyimide precursor having an amide bond density of 1.5 mole/kg or more, defined as the number of amide groups (in mol) present in 1 kg of the polyimide precursor, and a repeating unit represented by the general formula (I): wherein X represents a tetravalent aromatic group not including a fluorine atom or a tetravalent organic group having a chemical structure in which 2 to 4 aromatic groups are linked through at least one type of bond selected from the group consisting of a single bond, an ether bond, a thioether bond, a carbonyl bond, a methylene bond, a sulfoxide bond, and a sulfone bond, and which does not include a fluorine atom; -COR and -COR' groups take the ortho position against the -CONH group; R and R' independently represent -NHR 2 , -0 - N + R 3 R 4 R 5 R 6 or -OH groups-, wherein R 2 to R 3 represent organic groups having olefinically unsaturated bonds, and R 4 to R 6 independently represent a hydrogen atom or a hydrocarbon group having 1 to 6 carbon atoms, and Y represents a divalent aromatic group not including a fluorine atom or a divalent organic group having a chemical structure in which 2 to 6 aromatic groups are linked through at least one type of bond selected from the group consisting of a single bond, an ether bond, a thioether bond, a carbonyl bond, a methylene bond, a 2.2-propylene bond, a sulfoxide bond, and a sulfone bond, and which does not contain a fluorine atom; (B) a photopolymerization initiator and (C) a solvent; wherein the aromatic polyimide precursor of the photosensitive composition satisfies at least one condition selected from the group consisting of the following conditions: (i) the amide bond density is 2.42 mole/kg or less and in the repeating unit of the aromatic polyimide precursor represented by the general formula (I), R and R' independently represent -0 - N + R 3 R 4 R 5 R 6 or -OH groups; and (ii) X is a tetravalent group wherein the aromatic groups connected to -CONH groups have a chemical structure in which the aromatic group is substituted with an aprotic electron donating group; (2) exposing the applied film by using i-line stepper, (3) removing unexposed areas with a developing solution; and (4) heat-curing the resultant pattern.

Inventors: KATAOKA YASUHIRO, MATSUOKA YOSHIO, YOKOTA KANICHI, KATAOKA, YASUHIRO, MATSUOKA, YOSHIO, YOKOTA, KANICHI
Applicants: ASAHI CHEMICAL IND, ASAHI KASEI KABUSHIKI KAISHA
Application year: 1993
Main classification: G03F7
IPC codes: H05K1, G03F7