Resist pattern formation method

Abstract: A method of forming a resist pattern from a chemically amplified positive radiation sensitive resin composition. The film thickness of an unexposed portion of a resist film formed from the chemically amplified positive radiation sensitive resin composition after wet development is 100 to 400 Å smaller than that before wet development. Alternatively, a resist film formed from the chemically amplified positive radiation sensitive resin composition is wet developed at both a temperature and a time enough to ensure that the film thickness of an unexposed portion of the resist film after wet development is 100 to 400 Å smaller than that before wet development. A resist film which is formed from a chemically amplified positive radiation sensitive resin composition and experiences a 100 to 400 Å reduction in the film thickness of an unexposed portion by wet development is useful as a resist film for forming a resist pattern.

Description: Detailed Description of the Invention The present invention relates to a resist pattern formation method. More specifically, it relates to a method of forming a resist pattern free from a development defect by maintaining the amount of reduction in film thickness after wet development at a relatively large value. There is proposed a chemically amplified resist whose sensitivity is improved by the catalytic function of a radiation sensitive acid generating agent which generates an acid when exposed to radiation (to be referred to as "exposure" hereinafter) as a resist suitable for use with far ultraviolet radiation from a KrF excimer laser or the like, charged beams such as electron beams and X-ray radiation such as synchrotron radiation. As a problem special to this chemically amplified resist, it has been pointed out that its resist pattern is changed in line width or T-shaped according to a post-exposure delay (to be referred to as "PED" hereinafter) which is a time from exposure to a heat treatment. In recent years, there have been proposed various chemically amplified resists which can be applied in the production of devices, including a chemically amplified radiation sensitive resin composition which comprises a polymer consisting of a hydroxystyrene-based recurring unit, a t-butyl (meth)acrylate recurring unit and a recurring unit for reducing the solubility in an aqueous-alkaline developer of the polymer after exposure (JP-A 7-209868) (the term "JP-A" as used herein means an "unexamined published Japanese patent application"). Along with a reduction in the design rule of a device to a level of sub-half micron or less, attention has been paid to a new problem for the chemically amplified resist that development defects such as an undeveloped portion of a fine pattern, a fallen pattern and changes in line width (to be referred to as "development defects" hereinafter) are produced by "differences" in solubility in a developer among exposed portions. Since development defects greatly reduce device yield, needs for a chemically amplified positive radiation sensitive resin composition free from such development defects have been arising. DE 4410441 relates to a chemically sensitized, positive-working, photosensitive composition which exhibits less layer shrinkage on heating subsequent to exposure and has less layer shrinkage after development and gives an excellent profile and a high resolution capacity without standing waves. According to DE 4410441, said positive-working photosensitive composition comprises the following components: (a) a resin containing an acid-decomposable group whose solubility in an alkaline developer increases on reaction with an acid; (b) a compound which forms an acid on irradiation with actinic rays or actinic radiation; and (c) a non-polymeric, acid-decomposable dissolution inhibitor having a molecular weight of not more than 3,000 which contains an acid-decomposable group and whose solubility in an alkaline developer increases on reaction with an acid, where this dissolution inhibitor comprises at least three structural units per molecule, each of which comprises an acid-decomposable group in the form of a substituent on a benzene ring, and where at least nine connecting atoms (without the acid-decomposable groups) are between two acid-decomposable groups at the furthest separation. It is an object of the present invention to provide a resist pattern formation method. It is another object of the present invention to provide a method of forming a resist pattern which is not changed in line width or T-shaped by PED, is free from development defects and does not impair basic performance (resolution, DOF) from a chemically amplified positive radiation sensitive resin composition. It is still another object of the present invention to provide a method of forming a resist pattern from a chemically amplified positive radiation sensitive resin composition which has high sensitivity to various types of radiation including far ultraviolet radiation from a KrF excimer laser or the like, charged beams such as electron beams and X-ray radiation such as synchrotron radiation (small amount of exposure energy). Other objects and advantages of the present invention will become apparent from the following description. According to the present invention, firstly, the above objects and advantages of the present invention are attained by the method of forming a resist pattern from a chemically amplified positive radiation sensitive resin composition, as defined in claim 1. Preferred embodiments are defined in the dependent claims. The present invention will be described in detail hereinunder. The chemically amplified positive radiation sensitive resin composition used in the present invention is a composition comprising (A) a resin consisting essentially of repeating units represented by formula (1) and at least one monomer unit selected from the group consisting of styrene, α-methylstyrene and p-methoxystyrene: wherein R 1 is a hydrogen atom or methyl group, R 2 is a halogen atom or monovalent organic group having 1 to 6 carbon atoms, n is an integer of 0 to 3, and at least one of the hydrogen atoms of the hydroxyl group of the repeat unit of formula (1) are substituted by an acid dissociable group selected from the group consisting of t-butyl, 1-methoxymethyl, 1-methoxyethyl, 1-ethoxyethyl, 1-cyclohexyloxyethyl, 1-ethoxypropyl, 1-propoxyethyl, trimethylsilyl, t-butoxycarbonyl, t-butoxycarbonylmethyl, tetrahydropyranyl, tetrahydrofuranyl, and combinations thereof, and (B) a radiation sensitive acid generating agent which reacts to various types of radiation including far ultraviolet radiation from a KrF excimer laser or the like, charged beams such as electron beams, and X-ray radiation such as synchrotron radiation and generates an acid upon exposure the radiation sensitive acid generating agent being defined in claim 1. (A) Resin The resin (A) in the present invention which is insoluble or hardly soluble in an aqueous-alkaline developer is a resin which consists essentially of repeating units represented by formula (1) and at least one monomer unit selected from the group consisting of styrene, α-methylstyrene and p-methoxystyrene, and whose solubility in an aqueous-alkaline developer increases along with the dissociation of the acid dissociable group with an acid (to be referred to as "acid dissociable group-containing resin (A)" hereinafter). The acid dissociable group-containing resin (A) is a resin which is insoluble or hardly soluble in an aqueous-alkaline developer itself and has such a structure that the hydrogen atom of an acidic functional group in an aqueous-alkaline developer soluble resin having at least one acidic functional group (a phenolic hydroxyl group), an aqueous-alkaline developer soluble resin having at least one recurring unit selected from the group consisting of recurring units represented by the following formula (1) is substituted by at least one acid dissociable group which can be dissociated in the presence of an acid. In the formula (1), R 1 is a hydrogen atom or methyl group, R 2 is a halogen atom or monovalent organic group having 1 to 6 carbon atoms, and n is an integer of 0 to 3. These acid dissociable groups are t-butyl group, 1-methoxymethyl group, 1-methoxyethyl group, 1-ethoxyethyl group, 1-cyclohexyloxyethyl group, 1-ethoxypropyl group, 1-propoxyethyl group, trimethylsilyl group, t-butoxycarbonyl group, t-butoxycarbonylmethyl group, tetrahydropyranyl group and tetrahydrofuranyl group. The acid dissociable group-containing resin (A) may contain at least one monomer selected from the group consisting of styrenes such as styrene, α-methyl styrene and p-methoxystyrene. The content of the recurring unit of the monofunctional monomer is preferably 20 mol% or less, more preferably 15 mol% or less based on the total of all the recurring units in the acid dissociable group-containing resin (A). The protecting ratio of the acid dissociable group (ratio of the number of moles of the acid dissociable group to the total number of moles of the acidic functional group and the acid dissociable group in the acid dissociable group-containing resin (A)) is 15 to 90 mol%. When the protecting ratio of the acid dissociable group into the acid dissociable group-containing resin (A) is lower than 15 mol%, the sensitivity of a resist tends to lower and when the protecting ratio is higher than 90 mol%, the resolution of a resist tends to lower. The acid dissociable group-containing resin (A) can be produced by the following methods (a) to (e). (a) A monomer having an acidic functional group and a monomer having an acid dissociable group are polymerized together with a monomer corresponding to the other recurring unit as the case may be in the presence of a suitably selected radical polymerization initiator by an appropriate method such as bulk polymerization, solution polymerization, precipitation polymerization, emulsion polymerization, suspension polymerization or bulk-suspension polymerization, or cation polymerization. (b) A 4-t-butoxystyrene is polymerized together with a monomer corresponding to the other recurring unit as the case may be in the presence of a suitably selected radical polymerization initiator by an appropriate method such as bulk polymerization, solution polymerization, precipitation polymerization, emulsion polymerization, suspension polymerization or bulk-suspension polymerization, or living anion polymerized, a t-butyl group contained in the obtained copolymer is selectively hydrolyzed and/or solvolyzed in the presence of an acidic catalyst to form an acidic functional group, and the hydrogen atom of the acidic functional group is substituted by an acid dissociable group such as a 1-substituted ethyl group or alkoxycarbonyl group. (c) An 4-acetoxystyrene and a monomer having an acid dissociable group are polymerized together with a monomer corresponding to the other recurring unit as the case may be in the presence of a suitably selected radical polymerization initiator by an appropriate method such as bulk polymerization, solution polymerization, precipitation polymerization, emulsion polymerization, suspension polymerization or bulk-suspension polymerization, an acetyl group contained in the obtained copolymer is selectively hydrolyzed and/or solvolyzed in the presence of a basic catalyst to form an acidic functional group, and the hydrogen atom of the acidic functional group is substituted by an acid dissociable group such as an 1-substituted ethyl group or alkoxycarbonyl group. (d) A monomer having an acid dissociable group such as 4-t-butoxystyrenes is polymerized together with a monomer corresponding to the other recurring unit as the case may be in the presence of a suitably selected radical polymerization initiator by an appropriate method such as bulk polymerization, solution polymerization, precipitation polymerization, emulsion polymerization, suspension polymerization or bulk-suspension polymerization, or living anion polymerized, and a t-butyl group contained in the obtained copolymer is selectively hydrolyzed and/or solvolyzed in the presence of an acidic catalyst. (e) An 4-acetoxystyrene is polymerized together with a monomer corresponding to the other recurring unit as the case may be in the presence of a suitably selected radical polymerization initiator by an appropriate method such as bulk polymerization, solution polymerization, precipitation polymerization, emulsion polymerization, suspension polymerization or bulk-suspension polymerization, and an acetyl group contained in the obtained copolymer is selectively hydrolyzed and/or solvolyzed in the presence of a basic catalyst. The weight average molecular weight in terms of polystyrene (to be referred to as "Mw" hereinafter) measured by gel permeation chromatography (GPC) of the acid dissociable group-containing resin (A) is as follows. Mw of the acid dissociable group-containing resin (A) having no crosslinking structure introduced by a polyfunctional monomer is preferably 1,000 to 100,000, more preferably 3,000 to 40,000, more preferably 3,000 to 30,000. When Mw of the acid dissociable group-containing resin (A) is less than 1,000, the sensitivity and heat resistance of a resist tend to lower and when Mw is more than 100,000, solubility in a developer tends to lower. The ratio (Mw/Mn) of Mw to the number average molecular weight in terms of polystyrene (to be referred to as "Mn" hereinafter) measured by gel permeation chromatography (GPC) of the acid dissociable group-containing resin having no crosslinking structure introduced by a polyfunctional monomer is generally 1.0 to 5.0, preferably 1.0 to 4.0, more preferably 1.0 to 3.0. Mw of the acid dissociable group-containing resin (A) having a crosslinking structure introduced by a polyfunctional monomer is preferably 3,000 to 500,000, more preferably 5,000 to 400,000, much more preferably 8,000 to 300,000. When Mw of the acid dissociable group-containing resin (A) is less than 3,000, the sensitivity and heat resistance of a resist are apt to lower and when Mw is more than 500,000, the developability of a resist is apt to lower, thereby promoting the production of a development defect. Mw/Mn of the acid dissociable group-containing resin (A) having a crosslinking structure introduced by a polyfunctional monomer is generally 1.5 to 20.0, preferably 1.5 to 15.0. (B) Radiation Sensitive Acid Generating Agent The radiation sensitive acid generating agent (B) (to be referred to as "acid generating agent" hereinafter) used in the present invention is a compound which generates an acid when exposed to radiation. The acid generating agent is an (1) onium salt, (2) sulfone compound, (3) sulfonate compound, (4) sulfoneimide compound, (5) diazomethane compound or (6) disulfonylmethane compound. Illustrative examples of the acid generating agent are given below. (1) onium salt such as an iodonium salt, sulfonium salt, phosphonium salt, diazonium salt, ammonium salt or pyridinium salt. Illustrative examples of the onium salt compound include bis(4-t-butylphenyl)iodonium nonafluorobutanesulfonate, bis(4-t-butylphenyl)iodonium trifluoromethanesulfonate, bis(4-t-butylphenyl)iodonium pyrenesulfonate, bis(4-t-butylphenyl)iodonium dodecylbenzenesulfonate, bis(4-t-butylphenyl)iodonium p-toluenesulfonate, bis(4-t-butylphenyl)iodonium benzenesulfonate, bis(4-t-butylphenyl)iodonium 10-camphorsulfonate, bis(4-t-butylphenyl)iodonium octanesulfonate, bis(4-t-butylphenyl)iodonium 2-trifluoromethylbenzenesulfonate, diphenyl iodonium nonafluorobutanesulfonate, diphenyl iodonium trifluoromethanesulfonate, diphenyl iodonium pyrenesulfonate, diphenyl iodonium dodecylbezenesulfonate, diphenyl iodonium p-toluenesulfonate, diphenyl iodonium benzenesulfonate, diphenyl iodonium 10-camphorsulfonate, diphenyl iodonium octanesulfonate, diphenyl iodonium 2-trifluoromethylbenzenesulfonate, triphenylsulfonium nonafluorobutanesulfonate, triphenylsulfonium trifluoromethanesulfonate, triphenylsulfonium pyrenesulfonate, triphenylsulfonium dodecylbenzenesulfonate, triphenylsulfonium p-toluenesulfonate, triphenylsulfonium benzenesulfonate, triphenylsulfonium 10-camphorsulfonate, triphenylsulfonium octanesulfonate, triphenylsulfonium 2-trifluoromethylbenzenesulfonate, triphenylsulfonium hexafluoroantimonate, triphenylsulfonium naphthalenesulfonate, 4-t-butylphenyl·diphenylsulfonium nonafluorobutanesulfonate, 4-t-butylphenyl·diphenylsulfonium trifluoromethanesulfonate, 4-t-butylphenyl·diphenylsulfonium pyrenesulfonate, 4-t-butylphenyl·diphenylsulfonium dodecylbenzenesulfonate, 4-t-butylphenyl·diphenylsulfonium p-toluenesulfonate, 4-t-butylphenyl·diphenylsulfonium benzenesulfonate, 4-t-butylphenyl·diphenylsulfonium 10-camphorsulfonate, 4-t-butylphenyl·diphenylsulfonium octanesulfonate, 4-t-butylphenyl·diphenylsulfonium 2-trifluoromethylbenzenesulfonate, 4-t-butoxyphenyl·diphenylsulfonium trifluoromethanesulfonate, 4-t-butoxyphenyl·diphenylsulfonium nonafluorobutanesulfonate, 4-t-butoxyphenyl·diphenylsulfonium p-toluenesulfonate, 4-t-butoxyphenyl·diphenylsulfonium benzenesulfonate, 4-t-butoxyphenyl·diphenylsulfonium 10-camphorsulfonate, 4-t-butoxyphenyl·diphenylsulfonium octanesulfonate, 4-t-butoxyphenyl·diphenylsulfonium 2-trifluoromethylbenzenesulfonate, 4-hydroxyphenyl·diphenylsulfonium trifluoromethanesulfonate, 4-hydroxyphenyl·diphenylsulfonium nonafluorobutanesulfonate, 4-hydroxyphenyl·diphenylsulfonium p-toluenesulfonate, 4-hydroxyphenyl·diphenylsulfonium benzenesulfonate, 4-hydroxyphenyl·diphenylsulfonium 10-camphorsulfonate, 4-hydroxyphenyl·diphenylsulfonium octanesulfonate, 4-hydroxyphenyl·diphenylsulfonium 2-trifluoromethylbenzenesulfonate and the like. (2) sulfone compound such as a β-ketosulfone, β-sulfonylsulfone or α-diazo compound thereof. Illustrative examples of the sulfone compound include phenacylphenylsulfone, mesitylphenacylsulfone, bis(phenylsulfonyl)methane and 4-trisphenacylsulfone. (3) sulfonate compound such as an alkyl sulfonate, haloalkyl sulfonate, aryl sulfonate or iminosulfonate. Illustrative examples of the sulfonate compound include benzoin tosylate, pyrogallol tristrifluoromethane sulfonate, pyrogallol trisnonafluorobutane sulfonate, pyrogallol methane trisulfonate, nitrobenzyl-9,10-diethoxyanthracene-2-sulfonate, α-methylolbenzoin tosylate, α-methylolbenzoin octanesulfonate, α-methylolbenzoin trifluoromethane sulfonate, α-methylolbenzoin dodecylsulfonate and the like. (4) sulfonimide compound represented by the following formula (2) : wherein R 9 is a divalent group such as an alkylene group, arylene group or alkoxylene group, and R 10 is a monovalent group such as an alkyl group, aryl group, halogen-substituted alkyl group or halogen-substituted aryl group. Illustrative examples of the sulfonimide compound include N-(trifluoromethylsulfonyloxy)succinimide, N-(trifluoromethylsulfonyloxy)phthalimide, N-(trifluoromethylsulfonyloxy)diphenyl maleimide, N-(trifluoromethylsulfonyloxy)bicyclo[2.2.1]hept-5-ene-2,3-dicarboxyimide, N-(trifluoromethylsulfonyloxy)-7-oxabicyclo[2.2.1]hept-5-ene-2,3-dicarboxyimide, N-(trifluoromethylsulfonyloxy)bicyclo[2.2.1]heptan-5,6-oxy-2,3-dicarboxyimide, N-(trifluoromethylsulfonyloxy)naphthylimide, N-(10-camphorsulfonyloxy)succinimide, N-(10-camphorsulfonyloxy)phthalimide, N-(10-camphorsulfonyloxy)diphenyl maleimide, N-(10-camphorsulfonyloxy)bicyclo[2.2.1]hept-5-ene-2,3-dicarboxyimide, N-(10-camphorsulfonyloxy)-7-oxabicyclo[2.2.1]hept-5-ene-2,3-dicarboxyimide, N-(10-camphorsulfonyloxy)bicyclo[2.2.1]heptan-5,6-oxy-2,3-dicarboxyimide, N-(10-camphorsulfonyloxy)naphthylimide, N-(p-toluenesulfonyloxy)succinimide, N-(p-toluenesulfonyloxy)phthalimide, N-(p-toluenesulfonyloxy)diphenyl maleimide, N-(p-toluenesulfonyloxy)bicyclo[2.2.1]hept-5-ene-2,3-dicarboxyimide, N-(p-toluenesulfonyloxy)-7-oxabicyclo[2.2.1]hept-5-ene-2,3-dicarboxyimide, N-(p-toluenesulfonyloxy)bicyclo[2.2.1]heptan-5,6-oxy-2,3-dicarboxyimide, N-(p-toluenesulfonyloxy)naphthylimide, N-(2-trifluoromethylbenzenesulfonyloxy)succinimide, N-(2-trifluoromethylbenzenesulfonyloxy)phthalimide, N-(2-trifluoromethylbenzenesulfonyloxy)diphenyl maleimide, N-(2-trifluoromethylbenzenesulfonyloxy)bicyclo[2.2.1]hept-5-ene-2,3-dicarboxyimide, N-(2-trifluoromethylbenzenesulfonyloxy)-7-oxabicyclo[2.2.1]hept-5-ene-2,3-dicarboxyimide, N-(2-trifluoromethylbenzenesulfonyloxy)bicyclo[2.2.1]heptan-5,6-oxy-2,3-dicarboxyimide, N-(2-trifluoromethylbenzenesulfonyloxy)naphthylimide, N-(nonafluorobutylsulfonyloxy)succinimide, N-(nonafluorobutylsulfonyloxy)phthalimide, N-(nonafluorobutylsulfonyloxy)diphenyl maleimide, N-(nonafluorobutylsulfonyloxy)bicyclo[2.2.1]hept-5-ene-2,3-dicarboxyimide, N-(nonafluorobutylsulfonyloxy)-7-oxabicyclo[2.2.1]hept-5-ene-2,3-dicarboxyimide, N-(nonafluorobutylsulfonyloxy)bicyclo[2.2.1]heptan-5,6-oxy-2,3-dicarboxyimide and N-(nonafluorobutylsulfonyloxy)naphthylimide. (5) diazomethane compound represented by the following formula (3): wherein R 11 and R 12 may be the same or different and each a monovalent group such as an alkyl group, aryl group, halogen-substituted alkyl group or halogen-substituted aryl group. Illustrative examples of the diazomethane compound include bis(trifluoromethylsulfonyl)diazomethane, bis(cyclohexylsulfonyl)diazomethane, bis(phenylsulfonyl)diazomethane, bis(p-toluenesulfonyl)diazomethane, methylsulfonyl-p-toluenesulfonyl diazomethane, 1-cyclohexylsulfonyl-1-(1,1-dimethylethylsulfonyl)diazomethane, bis(1,1-dimethylethylsulfonyl)diazomethane, bis(3,3-dimethyl-1,5-dioxaspiro[5,5]dodecane-8-sulfonyl)diazomethane, bis(1,4-dioxaspiro[4,5]decane-7-sulfonyl)diazomethane and the like. (6) disulfonylmethane compound represented by the following formula (4): wherein R 13 and R 14 may be the same or different and each a monovalent linear or branched aliphatic hydrocarbon group, cycloalkyl group, aryl group, aralkyl group or monovalent other organic group having a hetero atom, and X and Y may be the same or different and each an aryl group, hydrogen atom, monovalent linear or branched aliphatic hydrocarbon group or monovalent other organic group having a hetero atom, with the proviso that at least one of X and Y is an aryl group and that X and Y are connected to each other to form a monocyclic or polycyclic structure having at least one unsaturated bond or to form a group represented by the following formula (5): wherein X' and Y' may be the same or different, X''s may be the same or different, Y''s may be the same or different, and X''s and Y''s are each a hydrogen atom, halogen atom, alkyl group, cycloalkyl group, aryl group or aralkyl group, or X' and Y' bonded to the same carbon atom or different carbon atoms are connected to each other to form a carbon monocyclic structure with the carbon atom(s) that they are bonded to, and n is an integer of 2 to 10. The above acid generating agents may be used alone or in admixture of two or more. In the present invention, the amount of the acid generation agent is preferably 0.1 to 20 parts by weight, more preferably 0.5 to 15 parts by weight based on 100 parts by weight of the acid dissociable group-containing resin (A). Acid Diffusion control Agent Preferably, the radiation sensitive resin composition in the present invention further contains an acid diffusion control agent having the function of controlling such a phenomenon that an acid generated from an acid generating agent by exposure is dispersed in a resist film and the function of suppressing an unfavorable chemical reaction in an unexposed area. By using this acid diffusion control agent, the storage stability of a composition and the resolution of a resist can be improved and changes in the line width of a resist pattern caused by fluctuations in PED can be suppressed, thereby making it possible to obtain very excellent process stability. The acid diffusion control agent is preferably a nitrogen-containing organic compound whose basicity is not changed by exposure or a heat treatment in the formation process of a resist pattern. The nitrogen-containing organic compound is a compound represented by the following formula (6): wherein R 15 , R 16 and R 17 may be the same or different and each a hydrogen atom, alkyl group, aryl group or aralkyl group (whose hydrogen atom may be substituted by a functional group such as a hydroxy group) (to be referred to as "nitrogen-containing compound (I)" hereinafter), diamino compound having two nitrogen atoms in the molecule (to be referred to as "nitrogen-containing compound (II)" hereinafter), diamino polymer having three or more nitrogen atoms (to be referred to as "nitrogen-containing compound (III)" hereinafter), amide group-containing compound, urea compound or nitrogen-containing heterocyclic compound. Illustrative examples of the nitrogen-containing compound (I) include monoalkylamines such as n-hexylamine, n-heptylamine, n-octylamine, n-nonylamine and n-decylamine; dialkylamines such as di-n-butylamine, di-n-pentylamine, di-n-hexylamine, di-n-heptylamine, di-n-octylamine, din-nonylamine and di-n-decylamine; trialkylamines such as triethylamine, tri-n-propylamine, tri-n-butylamine, tri-n-pentylamine, tri-n-hexylamine, tri-n-heptylamine, tri-n-octylamine, tri-n-nonylamine and tri-n-decylamine; aromatic amines such as aniline, N-methylaniline, N,N-dimethylaniline, 2-methylaniline, 3-methylaniline, 4-methylaniline, 4-nitroaniline, diphenylamine, triphenylamine and 1-naphthylamine; and the like. Illustrative examples of the nitrogen-containing compound (II) include ethylenediamine, N,N,N',N'-tetramethylethylenediamine, N,N,N',N'-tetrakis(2-hydroxyropyl)ethylenediamine, tetramethylenediamine, hexamethylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, 4,4'-diaminobenzophenone, 4,4'-diaminodiphenylamine, 2,2'-bis(4-aminophenyl)propane, 2-(3-aminophenyl)-2-(4-aminophenyl)propane, 2-(4-aminophenyl)-2-(3-hydroxyphenyl)propane, 2-(4-aminophenyl)-2-(4-hydroxyphenyl)propane, 1,4-bis[1-(4-aminophenyl)-1-methylethyl]benzene, 1,3-bis[1-(4-aminophenyl)-1-methylethyl]benzene and the like. Illustrative examples of the nitrogen-containing compound (III) include polymers such as polyethylene-imine, polyallylamine and dimethylaminoethyl acrylamide. Illustrative examples of the amide group-containing compound include formamide, N-methylformamide, N,N-dimethylformamide, acetamide, N-methylacetamide, N,N-dimethylacetamide, propionamide, benzamide, pyrrolidone, N-methylpyrrolidone and the like. Illustrative examples of the urea compound include urea, methylurea, 1,1-dimethylurea, 1,3-dimethylurea, 1,1,3,3-tetramethylurea, 1,3-diphenylurea, tributylthiourea and the like. Illustrative examples of the nitrogen-containing heterocyclic compound include imidazoles such as imidazole, benzimidazole, 4-methylimidazole, 2-phenylbenzimidazole and 4-methyl-2-phenylimidazole; pyridines such as pyridine, 2-methylpyridine, 4-methylpyridine, 2-ethylpyridine, 4-ethylpyridine, 2-phenylpyridine, 4-phenylpyridine, N-methyl-4-phenylpyridine, nicotine, nicotinic acid, nicotinic acid amide, quinoline, 8-oxyquinoline and acridine; pyrazine, pyrazole, pyridazine, quinoxaline, purine, pyrrolidine, piperidine, morpholine, 4-methylmorpholine, piperazine, 1,4-dimethylpiperazine, 1,4-diazabicyclo[2.2.2]octane and the like. Out of the above nitrogen-containing organic compounds, nitrogen-containing compounds (I) and nitrogen-containing heterocyclic compounds are preferred. Out of the nitrogen-containing compounds (I), trialkylamines are particularly preferred and, out of the nitrogen-containing heterocyclic compounds, pyridines are particularly preferred. The above acid diffusion control agents may be used alone or in admixture of two or more. The amount of the acid diffusion control agent is preferably 15 parts or less by weight, more preferably 0.001 to 10 parts by weight, the most preferably 0.005 to 5 parts by weight based on 100 parts by weight of the acid dissociable group-containing resin (A). When the amount of the acid diffusion control agent is larger than 15 parts by weight, the photospeed of a resist can shift to recy slow or the developability of an exposed portion can terribly be spoilt. When the amount is smaller than 0.001 part by weight, the pattern shape and accuracy of a resist can be deteriorated under some practical process conditions. Other Additives The radiation sensitive resin composition of the present invention may comprise a surfactant which has the function of improving the coatability and striation of a composition and the developability of a resist. Illustrative examples of the surfactant include polyoxyethylene lauryl ether, polyoxyethylene stearyl ether, polyoxyethylene oleyl ether, polyoxyethylene octylphenol ether, polyoxyethylene nonylphenol ether, polyethylene glycol dilaurate, polyethylene glycol distearate and the like. Commercial products of the surfactant include F Top EF301, EF303 and EF352 (Tokem Products Co., Ltd.), Megafax F171 and F173 (Dainippon Ink and Chemicals, Inc.), Florade FC430 and FC431 (Sumitomo 3M Limited), Asahi Guard AG710 and Surflon S-382, SC101, SC102, SC103, SC104, SC105 and SC106 (Asahi Glass Co., Ltd.), KP341 (Shin-Etsu Chemical Co., Ltd.), Polyflow No. 75 and No. 95 (Kyoeisha Kagaku Co., Ltd.) and the like. The amount of the surfactant is generally 2 parts or less by weight based on 100 parts by weight of the acid dissociable group-containing resin (A). The radiation sensitive resin composition of the present invention may further comprise a sensitizer that absorbs radiation energy and transmits the energy to the acid generating agent, which would finally result in an increase in the amount of inducing acid from acid generating agent and lead a shift of the photospeed to the faster side. Preferred examples of the sensitizer include benzophenones, Rose Bengales, anthracenes and the like. The amount of the sensitizer is generally 50 parts or less by weight based on 100 parts by weight of the acid dissociable group-containing resn (A). The latent image of an exposed portion can be visualized and the influence of halation at the time of exposure can be alleviated by blending a dye and/or pigment and adhesion to a substrate can be further improved by blending an adhesive aid. A halation preventing agent such as 4-hydroxy-4'-methyl chalcone, shape improving agent, storage stabilizer, anti-foaming agent as other additives may also be blended. Solvent The radiation sensitive resin composition of the present invention is prepared in the form of a solution by uniformly dissolving the composition in a solvent to ensure that the total solids content should become 1 to 50 wt%, preferably 5 to 40 wt% when it is used and filtering the resulting solution with a filter having a pore diameter of about 0.2 µm. Illustrative examples of the solvent used to prepare the above composition solution include ethylene glycol monoalkyl ether acetates such as ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol mono-n-propyl ether acetate and ethylene glycol mono-n-butyl ether acetate; propylene glycol monoalkyl ethers such as propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-n-propylene ether and propylene glycol mono-n-butyl ether; propyl glycol dialkyl ethers such as propylene glycol dimethyl ether, propylene glycol diethyl ether, propylene glycol di-n-propyl ether and propylene glycol di-n-butyl ether; propylene glycol monoalkyl ether acetates such as propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, propylene glycol mono-n-propyl ether acetate and propylene glycol mono-n-butyl ether acetate; lactates such as methyl lactate, ethyl lactate, n-propyl lactate and i-propyl lactate; aliphatic carboxylates such as n-amyl formate, i-amyl formate, ethyl acetate, n-propyl acetate, i-propyl acetate, n-butyl acetate, i-butyl acetate, n-amyl acetate, i-amyl acetate, i-propyl propionate, n-butyl propionate and 1-butyl propionate; other esters such as ethyl hydroxyacetate, ethyl 2-hydroxy-2-methylpropionate, methyl 2-hydroxy-3-methylbutyrate, ethyl methoxyacetate, ethyl ethoxyacetate, methyl 3-methoxypropionate, ethyl 3-methoxypropionate, methyl 3-ethoxypropionate, ethyl 3-ethoxypropionate, 3-methoxybutyl acetate, 3-methyl-3-methoxybutyl acetate, 3-methyl-3-methoxybutyl propionate, 3-methyl-3-methoxybutyl butyrate, methyl acetoacetate, ethyl acetoacetate, methyl pyruvate and ethyl pyruvate; aromatic hydrocarbons such as toluene and xylene; ketones such as methyl ethyl ketone, methyl propyl ketone, methyl butyl ketone, 2-heptanone, 3-heptanone, 4-heptanone and cyclohexanone; amides such as N-methylformamide, N,N-dimethylformamide, N-methylacetamide, N,N-dimethylacetamide and N-methylpyrrolidone; lactones such as γ-butyrolactone; and the like. These solvents may be used alone or in admixture of two or more. Formation of Resist Pattern To form a resist pattern from the radiation sensitive resin composition of the present invention, the composition solution prepared as described above is coated on a substrate such as a silicon wafer or a wafer coated with aluminum by suitable coating means such as rotation coating, cast coating, roll coating or the like to form a resist film which is then prebaked at a temperature of 70 to 160° C as the case may be and exposed through a predetermined mask pattern. The radiation used herein is suitably selected from far ultraviolet radiation from an ArF excimer laser (wavelength of 193 nm) or KrF excimer laser (wavelength of 248 nm), X-ray radiation such as synchrotron radiation and charged beams such as electron beams according to the type of acid generating agent. Exposure conditions such as the amount of exposure are suitably selected according to the composition of the radiation sensitive resin composition and the types of additives. To form a highly accurate fine pattern stably in the present invention, postbaking is preferably carried out at a temperature of 70 to 160° C for 30 seconds or more after exposure. When the temperature of postbaking after exposure is lower than 70° C, differences in sensitivity according to the type of substrate may spread. Thereafter, the exposed resist film is developed with an aqueous-alkaline developer at a sufficient temperature for a sufficient time, for example, 10 to 50° C for 30 to 200 seconds, preferably at 15 to 30° C for 30 to 100 seconds, particularly preferably at 20 to 25° C for 30 to 90 seconds to form a predetermined resist pattern with a predetermined amount of reduction in film thickness (to be defined hereinafter). The above aqueous-alkaline developer is, for example, an alkaline aqueous solution prepared by dissolving an alkaline compound such as an alkali metal hydroxide, ammonia water, mono-, di- or tri-alkylamine, mono-, di- or trialkanolamine, heterocyclic amine, tetraalkyl ammonium hydroxide, choline, 1,8-diazabicyclo[5.4.0]-7-undecene or 1,5-diazabicyclo[4.3.0]-5-nonene to a concentration of 1 to 10 wt%, preferably 1 to 5 wt%, particularly preferably 1 to 3 wt%. The developer which is an alkaline aqueous solution may contain a water-soluble organic solvent such as methanol or ethanol, and a surfactant in a suitable amount. When an alkaline aqueous solution is used as the developer, the film is generally rinsed with water after development. A technique for making large a difference in solubility in a developer between an unexposed portion and an exposed portion of a resist has been generally employed to improve the resolution of a resist. Therefore, the film thickness of an unexposed portion is generally reduced by less than 100 Å (corresponding to a difference between the film thickness of an unexposed portion before development and the film thickness of the unexposed portion after development, to be referred to as "amount of reduction in film thickness") with the developer. Unlike the method of the prior art, in the method of the present invention, a resist pattern is formed such that the film thickness of an unexposed portion after development is reduced by 100 to 400 Å, preferably 200 to 400 Å (thinner and smaller) from the film thickness of the unexposed portion before development. Surprisingly, it has been made clear that a resist pattern having very few development defects (for example, 100 or less development defects, preferably 10 or less development defects per wafer (area of about 150 cm 2 )) is thereby formed. With a view to controlling the amount of reduction in film thickness to the above range by the method of the present invention, it is important to control the composition of the chemically amplified positive radiation sensitive resin composition used. The amount of reduction in film thickness changes according to the development temperature, development time, baking temperature after coating and the like. It has been found that as the development temperature becomes higher, the development time becomes longer and the baking temperature after coating becomes lower, the amount of reduction in film thickness increases. Therefore, the method of the present invention should be understood as a method of controlling the composition of the radiation sensitive resin composition in consideration of these factors which influence the amount of reduction in film thickness. For example, when the development temperature and the development time are conditions for reducing the amount of reduction in film thickness, composition which ensures that the amount of reduction in film thickness becomes relatively large should be used to attain a fixed amount of reduction in film thickness. When the baking temperature after coating is low to increase the amount of reduction in film thickness, composition that ensures that the amount of reduction in film thickness becomes relatively small should be used to attain a fixed amount of reduction in film thickness. The factors which greatly influence the amount of reduction in film thickness in the radiation sensitive resin composition include, for example, the protecting ratio of an acid dissociable group into the resin (A), the type and amount of the radiation sensitive acid generating agent, and the like. It has been revealed that the amount of reduction in film thickness tends to becomes smaller as the protecting ratio of the acid dissociable group rises and that the relationship between changes in the protecting ratio and changes in the amount of reduction in film thickness is almost linear. It has also been found that an onium salt exerts a greater influence upon the amount of reduction in film thickness than other radiation sensitive acid generating agents and that the amount of reduction in film thickness can be reduced by increasing the amount of an acid generating agent. According to the present invention, the amount of reduction in film thickness is controlled to a range of 100 to 400 Å, preferably 200 to 400 Å by changing the composition of the radiation sensitive resin composition in consideration of these factors which influence the above amount of reduction in film thickness. According to the present invention, there can be provided a resist having very few development defects without impairing resolution even when the amount of reduction in film thickness is 100 Å or more. When the amount of reduction in film thickness is smaller than 100 Å, there is a tendency that the effect of suppressing development defects cannot be seen and when the amount of reduction in film thickness is more than 400 Å, the effect of suppressing development defects is seen but the resolution of a resist deteriorates. To prevent the influence of basic impurities and the like contained in an environmental atmosphere upon the formation of a resist pattern, a protective film may be formed on the resist film. The following examples are provided for the purpose of further illustrating the present invention but are in no way to be taken as limiting. Examples Reference examples 1-4, 6-11, Example 5 and Comparative Examples 1 and 2 Components shown in Table 1 (parts are based on weight) were mixed together to prepare a uniform solution which was then filtered with a Teflon membrane filter having a pore diameter of 0.2 pm to prepare a composition solution. The composition solution was rotation coated on a silicon water and prebaked at a temperature for a time shown in Table 2 to form a resist film having a thickness of 0.7 pm. This resist film was exposed to KrF excimer laser beams (wavelength of 248 nm) through a mask pattern using the KrF excimer laser of Nikon K.K. (trade name: NSR-2205 EX8A) by changing the amount of exposure. In some of the above Examples, the resist film was exposed to electron beams through a mask pattern using a simple electron beam direct illuminator (50 KeV) in place of KrF excimer laser by changing the amount of exposure. After exposure, the resist film was postbaked at a temperature for a time shown in Table 2. Thereafter, the resist film was developed using a tetramethyl ammonium hydroxide aqueous solution having a concentration shown in Table 2 at a temperature for a time shown in Table 2, rinsed with water for 30 seconds and dried to form a resist pattern. The evaluation results of Examples and Comparative Examples are shown in Table 3. The measurements of Mw and Mw/Mn and the evaluation of each resist were carried out as follows. Mw and Mw/Mn GPC columns (2 x G2000H XL + 1 x G3000H XL + 1 x G4000H XL ) manufactured by Toso Co., Ltd. are used to measure Mw and Mn by GPC using monodisperse polystyrene as the standard under the following analytical conditions. flow rate: 1.0 ml/minute eluting solvent: tetrahydrofuran column temperature: 40°C Sensitivity The amount of exposure for forming a line-and-space pattern (1L1S) having a design line width of 0.26 µm to a line/space width ratio of 1:1 is taken as the optimum amount of exposure and sensitivity is evaluated based on this optimum amount of exposure. Resolution The minimum size (µm) of a resist pattern (1L1S) which is exposed to the optimum amount of light and resolved when a line-and-space pattern (1L1S) having a design line width of 0.26 pm is formed is taken as resolution. Amount of Reduction in Film Thickness The difference between the film thickness of an unexposed portion after coating and prebaking and the film thickness of the unexposed portion after development in a tetraalkylammonium hydroxide aqueous solution as a developer having a concentration shown in Table 2 is taken as the amount of reduction in film thickness. Development Defects Development defects are evaluated by a method for observing the existence of development defects through an optical microscope and the following method using the KLA defect inspection device of KLA Tencole Co., Ltd. Method using KLA defect inspection device: The total number of clustered and unclustered defects extracted from differences produced by superimposing a comparison image on pixel units by observing in an array mode. The detection of the total number of defects is carried out by setting the sensitivity of this device to such a level that 0.15 pm or larger defects can be detected. For evaluation, the total number of defects per wafer (area of about 150 cm 2 ) is counted in the method using the above KLA defect inspection device. PED Stability A sample which is exposed to the optimum amount of light when it is postbaked right after exposure and developed is placed in a chamber in which the concentration of ammonia in the atmosphere is controlled to 5 ppb for 2 hours, postbaked and developed to form a line-and-space pattern (1L1S) having a design line width of 0.26 µm. The line width (Ltop) on the top of the pattern is measured by a scanning electron microscope and evaluated based on the following criteria. 0.26 x 0.85 < Ltop < 0.26 x 1.1: satisfactory 0.26 x 0.85 ≧ Ltop: thin 0.26 x 1.1 ≦ Ltop: thick Components used in Examples and Comparative Examples are as follows. acid dissociable group-containing resin ref. A-1-1: resin prepared by substituting 30 mol% of hydrogen atoms in phenolic hydroxyl groups contained in poly(4-hydroxystyrene) obtained by hydrolyzing the t-butyl groups of poly(4-t-butoxy)styrene synthesized by radical polymerization by a 1-ethoxyethyl group (Mw = 18,000, Mw/Mn = 1.5) A-1-2: resin prepared by substituting 40 mol% of hydrogen atoms in phenolic hydroxyl groups contained in poly(4-hydroxystyrene) obtained by hydrolyzing the t-butyl groups of poly(4-t-butoxy)styrene synthesized by radical polymerization by a 1-ethoxyethyl group (Mw = 18,000, Mw/Mn = 1.5) A-1-3: resin prepared by substituting 30 mol% of hydrogen atoms in phenolic hydroxyl groups contained in poly(4-hydroxystyrene) obtained by party hydrolyzing the t-butyl groups of poly(4-t-butoxy)styrene synthesized by anion polymerization by a 1-ethoxyethyl group (Mw = 15,000, Mw/Mn = 1.1) A-1-4: resin prepared by substituting 20 mol% of hydrogen atoms in phenolic hydroxyl groups contained in poly(4-hydroxystyrene) obtained by partly hydrolyzing the t-butyl groups of poly(4-t-butoxy)styrene synthesized by anion polymerization by a 1-ethoxyethyl group and 10 mol% of the hydrogen atoms by a t-butyl group (Mw = 15,000,) A-2-1: resin prepared by substituting 25 mol% of hydrogen atoms in phenolic hydroxyl groups contained in poly(4-hydroxystyrene) obtained by hydrolyzing the t-butyl groups of poly(4-t-butoxy)styrene synthesized by radical polymerization by a t-butoxycarbonyl group (Mw = 8,000, Mw/Mn = 1.5) A-3-1: resin prepared by substituting 30 mol% of hydrogen atoms in phenolic hydroxyl groups contained in poly(4-hydroxystyrene) obtained by partly hydrolyzing the t-butyl groups of poly(4-t-butoxy)styrene synthesized by anion polymerization by a t-butyl group (Mw = 15,000, Mw/Mn = 1.05) A-3-2: resin prepared by substituting 30 mol% of hydrogen atoms in phenolic hydroxyl groups contained in poly(4-hydroxystyrene) obtained by partly hydrolyzing the t-butyl groups of poly(4-t-butoxy)styrene synthesized by radical polymerization by a t-butyl group (Mw = 12,000, Mw/Mn = 1.5) A-3-3: radical copolymer of 4-hydroxystyrene/ styrene /p-t-butoxystyrene (molar ratio = 70/10/20, Mw = 12,500) [acid dissociable group-containing resin (A)] A-4-1: copolymer of 4-hydroxystyrene/ styrene / t-butyl acrylate (molar ratio = 70/20/10, Mw = 12,000) A-4-2: copolymer of 4-hydroxystyrene/ styrene / t-butyl acrylate (molar ratio = 60/20/20, Mw = 12,000) A-4-3: copolymer of 4-hydroxystyrene/ 4-t-butoxystyrene /t-butyl acrylate (molar ratio = 75/20/5, Mw = 12,000) A-4-4: resin prepared by partly hydrolyzing t-butyl groups in a copolymer of 4-t-butoxystyrene / t-butyl acrylate (molar ratio = 90:10) to convert 80 % of the t-butyl groups into phenolic hydroxyl groups (Mw = 12,000) A-5-1: copolymer of 4-hydroxystyrene/ t-butyl acrylate /2,5-dimethyl-2,5-hexanediol diacrylate (molar ratio = 75/20/5, Mw = 40,000) A-5-2: copolymer of 4-hydroxystyrene/ styrene/ t-butyl acrylate / 2,5-dimethyl-2,5-hexanediol diacrylate (molar ratio = 75/10/10/5, Mw = 30,000) A-5-3: copolymer of 4-hydroxystyrene/ styrene/ t-butyl acrylate / 2,5-dimethyl-2,5-hexanediol diacrylate (molar ratio = 65/10/20/5, Mw = 30,000) acid generating agent (B) B-1: 1,1-bis(cyclohexylsulfonyl)diazomethane B-2: bis(3,3-dimethyl-1,5-dioxaspiro[5,5]dodecane-8-sulfonyl)diazomethane B-3: bis(1,4-dioxaspiro[4,5]decane-7-sulfonyl)diazomethane B-4: triphenylsulfonium trifluoromethane sulfonate B-5: tri(4-methoxyphenyl)sulfonium trifluoromethane sulfonate B-6: bis(4-t-butylphenyl)iodonium 10-camphor sulfonate B-7: bis(4-t-butylphenyl)iodonium trifluoromethane sulfonate B-8: bis(4-t-butylphenyl)iodonium nonafluoro-n-butane sulfonate acid diffusion control agent (C) C-1: N,N,N',N'-tetrakis(2-hydroxypropyl)ethylene diamine C-2: trioctylamine C-3: triethanolamine C-4: 2-phenylbenzimidazole solvent D-1: ethyl lactate D-2: propylene glycol monomethyl ether acetate D-3: 2-heptanone D-4: ethyl-3-ethoxypropionate According to the present invention, there can be obtained a resist pattern which is not changed in line width or T-shaped by PED, is free from development defects, provides a high yield in the production of devices, and has high sensitivity for various types of radiation such as far ultraviolet radiation, charged beams and X-ray radiation (small amount of exposure energy) and excellent resolution.

Claims: A method of forming a resist pattern from a chemically amplified positive radiation sensitive resin composition, comprising: coating said composition on a substrate; exposing the composition through a predetermined mask pattern to form a resist pattern, and developing the resist pattern with an aqueous alkaline developer, wherein the composition comprises (A) a resin consisting essentially of repeating units represented by formula (1) and at least one monomer unit selected from the group consisting of styrene, α-methylstyrene and p-methoxystyrene: wherein R 1 is a hydrogen atom or methyl group, R 2 is a halogen atom or monovalent organic group having 1 to 6 carbon atoms, n is an integer of 0 to 3, and at least one of the hydrogen atoms of the hydroxyl group of the repeat unit of formula (1) are substituted by an acid dissociable group selected from the group consisting of t-butyl, 1-methoxymethyl, 1-methoxyethyl, 1-ethoxyethyl, 1-cyclohexyloxyethyl, 1-ethoxypropyl, 1-propoxyethyl, trimethylsilyl, t-butoxycarbonyl, t-butoxycarbonylmethyl, tetrahydropyranyl, tetrahydrofuranyl, and combinations thereof, (B) a radiation sensitive acid generating agent, wherein the acid generating agent is selected from a group consisting of an onium salt, a sulfone compound, a sulfonate compound, a sulfoneimide compound, a diazomethane compound or a disulfonylmethane compound; and the protecting ratio of the acid dissociable group into the resin (ratio of the number of moles of the acid dissociable group to the total number of moles of an acidic functional group and the acidic dissociable group in the resin (A)) is 15 to 90 mol%. The method of claim 1, wherein the film thickness of an unexposed portion of a resist film formed from the chemically amplified positive radiation sensitive resin composition after wet development is 100 to 400 Å smaller than that before wet development. The method of claim 1, wherein the number of development defects is 100 or less per wafer (area of about 150 cm 2 ). The method of claim 1, wherein the resist film before wet development is baked after exposure. The method of claim 1, wherein the resist film is wet developed after exposure at a temperature of 10 to 50°C and with a wet development time of 30 to 200 seconds. The method of claim 1, wherein the film thickness of an unexposed portion of a resist film after wet development is 200 to 400 Å smaller than before wet development. Use of the resist film which is formed according to the method of one of claims 1 to 6 for forming a resist pattern.

Inventors: KAI TOSHIYUKI, KOBAYASHI EIICHI, NISHIMURA YUKIO, SHIOYA TAKEO, KAI, TOSHIYUKI, KOBAYASHI, EIICHI, NISHIMURA, YUKIO, SHIOYA, TAKEO
Applicants: JSR CORP, JSR CORPORATION
Application year: 2000
Main classification: G03F7
IPC codes: G03F7, H01L21