Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F220/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride ester, amide, imide or nitrile thereof
  • C08F220/02—Monocarboxylic acids having less than ten carbon atoms; Derivatives thereof
  • C08F220/10—Esters
  • C08F220/22—Esters containing halogen
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F212/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an aromatic carbocyclic ring
  • C08F212/02—Monomers containing only one unsaturated aliphatic radical
  • C08F212/04—Monomers containing only one unsaturated aliphatic radical containing one ring
  • C08F212/14—Monomers containing only one unsaturated aliphatic radical containing one ring substituted by heteroatoms or groups containing heteroatoms
  • C08F212/22—Oxygen
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/004—Photosensitive materials
  • G03F7/039—Macromolecular compounds which are photodegradable, e.g. positive electron resists
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/20—Exposure; Apparatus therefor
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/26—Processing photosensitive materials; Apparatus therefor
  • G03F7/30—Imagewise removal using liquid means
  • G03F7/32—Liquid compositions therefor, e.g. developers
  • G03F7/325—Non-aqueous compositions

Definitions

• the present invention relates to a copolymer, a positive resist composition, and a method for forming a resist pattern.
• ionizing radiation such as electron beams and extreme ultraviolet (EUV) radiation, or non-ionizing radiation including short-wavelength light such as ultraviolet radiation (hereinafter, these may be collectively referred to as "ionizing radiation, etc."
• ionizing radiation such as electron beams and extreme ultraviolet (EUV) radiation
• non-ionizing radiation including short-wavelength light such as ultraviolet radiation
• Patent Document 1 discloses a main-chain-scission type positive resist capable of efficiently forming fine resist patterns with high resolution, which contains a copolymer having ⁇ -chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units, 4-methyl- ⁇ -methylstyrene units or ⁇ -methylstyrene units and has a weight-average molecular weight of more than 100,000.
• main chain scission type positive resists are required to have a wide exposure margin (i.e., a wide tolerance range for the amount of exposure in the exposure step.)
• main chain scission type positive resists are also required to have an excellent shape of the resist pattern formed through the exposure step and the development treatment (development step) using a developer.
• the above-mentioned conventional positive resists have room for improvement in terms of widening the exposure margin and imparting a good shape to the resist pattern.
• the present inventors have conducted extensive research to achieve the above object.
• the inventors have discovered that by using a copolymer containing a monomer unit having a specific electron-donating group, it is possible to form a resist pattern having a good shape while widening the exposure margin of the resist, and have completed the present invention.
• the object of the present invention is to advantageously solve the above-mentioned problems, and the present invention provides a compound according to the present invention, comprising: (In formula (I), R 1 is a halogen atom or an alkyl group substituted with a halogen atom, R 2 is an organic group, and R 3 and R 4 are a hydrogen atom, a halogen atom, an unsubstituted alkyl group or an alkyl group substituted with a halogen atom, and may be the same or different from each other.)
• R 6 is an electron-donating group having a heteroatom which may have a substituent; p
• the monomer unit (I) is represented by the following formula (III): (In formula (III), L is a divalent linking group having a fluorine atom, and Ar is an aromatic ring group which may have a substituent.) It is preferable that the monomer unit is represented by the following formula: In this way, when the monomer unit (I) is a monomer unit represented by the above formula (III), the sensitivity of the copolymer to ionizing radiation and the like can be improved.
• R 5 is an unsubstituted alkyl group
• R 7 and R 8 are hydrogen atoms.
• R 6 is preferably an alkoxy group. In this way, when R 6 is an alkoxy group, it is possible to form a resist pattern having a better shape while further expanding the exposure margin.
• the calculated lowest unoccupied molecular orbital (LUMO) of the monomer unit (II) is preferably 0.13 eV or more. In this way, if the calculated lowest unoccupied molecular orbital (LUMO) of the monomer unit (II) is equal to or more than the above lower limit, it is possible to form a resist pattern having a better shape while further expanding the exposure margin.
• the value of the lowest unoccupied molecular orbital (LUMO) of the monomer unit (II) can be determined by the method described in the Examples.
• the calculated value of the distribution coefficient Log P of the monomer unit (II) is preferably 3.4 or more. In this way, when the calculated value of the distribution coefficient Log P of the monomer unit (II) is equal to or more than the above lower limit, it is possible to form a resist pattern having a better shape while further expanding the exposure margin.
• the distribution coefficient Log P of the monomer unit (II) can be determined by the method described in the Examples.
• the present invention also aims to advantageously solve the above problems, and provides a positive resist composition [7] comprising any of the copolymers [1] to [6] above and a solvent.
• the positive resist composition makes it possible to form a resist pattern having a better shape while further expanding the exposure margin.
• the resist pattern forming method includes the steps of exposing the resist film to light and developing the exposed resist film. According to the resist pattern forming method, a resist pattern having a good shape with a wide exposure margin can be formed.
• the development is preferably carried out using an alcohol-based solvent. If development is carried out using an alcohol-based solvent, a resist pattern having a better shape can be formed.
• a copolymer and a positive resist composition which are capable of forming a resist pattern having a wide exposure margin and a good shape. Furthermore, according to the present invention, there can be provided a method for forming a resist pattern which has a wide exposure margin and is capable of forming a resist pattern having a good shape.
• the copolymer of the present invention can be used, for example, in the production of a main chain scission type positive resist composition in which the main chain is scissed by ionizing radiation or the like to reduce the molecular weight, and can be suitably used in the production of the positive resist composition of the present invention.
• the positive resist composition of the present invention contains the copolymer of the present invention, and can be suitably used, for example, in the method of forming a resist pattern of the present invention.
• the method of forming a resist pattern of the present invention can be suitably used, for example, when forming a resist pattern in the production process of printed circuit boards such as build-up boards, semiconductors, photomasks, molds, etc.
• the copolymer of the present invention has the following formula (I): (In formula (I), R 1 is a halogen atom or an alkyl group substituted with a halogen atom, R 2 is an organic group, and R 3 and R 4 are a hydrogen atom, a halogen atom, an unsubstituted alkyl group or an alkyl group substituted with a halogen atom, and may be the same or different from each other.)
• the copolymer of the present invention may contain monomer units other than the monomer units (I) and (II). However, the proportion of the monomer units (I) and (II) in the total monomer units (100 mol%) constituting the copolymer is preferably 70 mol% or more, and more preferably 100 mol% (i.e., the copolymer is composed of the monomer units (I) and (II)).
• the copolymer of the present invention is not particularly limited as long as it contains the monomer unit (I) and the monomer unit (II), and may be any of a random copolymer, a block copolymer, and the like.
• the copolymer of the present invention contains monomer units (I) and (II), and when irradiated with ionizing radiation or the like, the main chain of the copolymer is effectively cut only in the irradiated portion, resulting in a low molecular weight.
• the low molecular weight component dissolves well in the developer.
• the reason why the exposure margin of the resulting resist is widened and a good shape can be imparted to the resist pattern by the monomer unit (II) having an electron donating group with a heteroatom in the copolymer of the present invention is not necessarily clear, but it is presumed to be as follows.
• the monomer unit (II) having an electron donating group with a heteroatom makes the copolymer more energetically stable, and it becomes possible to receive large energy such as ionizing radiation. It is presumed that the main chain of the copolymer is effectively cut by irradiation with ionizing radiation or the like.
• the monomer unit (I) contained in the copolymer of the present invention is represented by the following formula (a): (In formula (a), R 1 to R 4 have the same meaning as in formula (I)).
• the halogen atoms which may constitute R 1 , R 3 , and R 4 in formula (I) and formula (a) are not particularly limited, and include chlorine atoms, fluorine atoms, bromine atoms, and iodine atoms.
• the alkyl groups substituted with halogen atoms which may constitute R 1 , R 3 , and R 4 in formula (I) and formula (a) are not particularly limited, and include groups having a structure in which some or all of the hydrogen atoms in the alkyl group are substituted with the above-mentioned halogen atoms.
• the unsubstituted alkyl group that can constitute R3 and R4 in formula (I) and formula (a) is not particularly limited, and examples thereof include unsubstituted alkyl groups having 1 to 10 carbon atoms. Among them, the unsubstituted alkyl group that can constitute R3 and R4 is preferably a methyl group or an ethyl group.
• R 1 in formula (I) and formula (a) is preferably a chlorine atom, a fluorine atom, or an alkyl group having 1 to 5 carbon atoms substituted with a fluorine atom, more preferably a chlorine atom, a fluorine atom, or a perfluoromethyl group, even more preferably a chlorine atom or a fluorine atom, and particularly preferably a chlorine atom.
• the monomer (a) in which R 1 in formula (a) is a chlorine atom is excellent in polymerizability, and the copolymer having a monomer unit (I) in which R 1 in formula (I) is a chlorine atom is also excellent in terms of easy preparation.
• R3 and R4 in formula (I) and formula (a) are each preferably a hydrogen atom or an unsubstituted alkyl group, more preferably a hydrogen atom or an unsubstituted alkyl group having from 1 to 5 carbon atoms, and even more preferably a hydrogen atom.
• the "organic group” that can constitute R2 in formula (I) and formula (a) is preferably an alkyl group which may have a substituent, an alkoxyalkyl group which may have a substituent, an alkoxyalkenyl group which may have a substituent, or a group represented by L-Ar (wherein L is a single bond or a divalent linking group, and Ar is an aromatic ring group which may have a substituent).
• the above-mentioned substituent is not particularly limited, and examples thereof include halogen atoms such as a chlorine atom, a fluorine atom, a bromine atom, and an iodine atom.
• the number of fluorine atoms in R2 is preferably 0 or more and 11 or less.
• the number of fluorine atoms in R2 is more preferably 3 or more, more preferably 4 or more, and preferably 9 or less.
• the number of carbon atoms in R2 is usually 1 or more and 12 or less.
• R2 in formula (I) and formula (a) is more preferably an alkyl group, an alkoxyalkyl group, an alkoxyalkenyl group, a fluoroalkyl group, a fluoroalkoxyalkyl group, a fluoroalkoxyalkenyl group, or a group represented by L-Ar.
• the alkyl group constituting R2 is preferably a methyl group, an ethyl group, a propyl group, or a butyl group.
• the alkoxyalkyl group constituting R2 is preferably a methoxymethyl group, an ethoxymethyl group, or an ethoxyethyl group.
• the alkoxyalkenyl group constituting R2 is preferably a methoxyvinyl group or an ethoxyvinyl group.
• Examples of the fluoroalkyl group constituting R2 include a monofluoromethyl group (having one fluorine atom and one carbon atom), a monofluoroethyl group (having one fluorine atom and two carbon atoms), a 2,2-difluoroethyl group (having two fluorine atoms and two carbon atoms), a 2,2,2-trifluoromethyl group (having three fluorine atoms and one carbon atom), a 2,2,2-trifluoroethyl group (having three fluorine atoms and two carbon atoms), a 2,2,3,3,3-pentafluoropropyl group (having five fluorine atoms and three carbon atoms), a 3,3,4,4,4-pentafluorobutyl group (having five fluorine atoms and four carbon atoms), a 2-(perfluorobutyl)ethyl group (having nine fluorine atoms and six carbon
• the fluoroalkoxyalkyl group constituting R2 is preferably, for example, a pentafluoromethoxymethyl group (having 5 fluorine atoms and 2 carbon atoms), a pentafluoroethoxymethyl group (having 5 fluorine atoms and 3 carbon atoms) or a pentafluoroethoxyethyl group (having 5 fluorine atoms and 4 carbon atoms).
• the fluoroalkoxyalkenyl group constituting R2 is preferably, for example, a pentafluoroethoxyvinyl group (having 5 fluorine atoms and 4 carbon atoms).
• the divalent linking group that can constitute L in the group represented by formula L-Ar is preferably a divalent linking group having a fluorine atom.
• the divalent linking group having a fluorine atom include a divalent chain alkyl group having 1 to 5 carbon atoms and having a fluorine atom.
• examples of the divalent linking group having a fluorine atom include a trifluoromethylmethylene group, a pentafluoroethylmethylene group, and a bis(trifluoromethyl)methylene group. Among these, the pentafluoroethylmethylene group and the bis(trifluoromethyl)methylene group are preferred, and the bis(trifluoromethyl)methylene group is more preferred.
• the number of fluorine atoms in L is preferably 3 or more, more preferably 4 or more, and even more preferably 5 or more, and is preferably 11 or less, and more preferably 7 or less.
• the number of fluorine atoms in L is equal to or greater than the above lower limit, the sensitivity to exposure light can be further improved.
• the number of fluorine atoms in L is equal to or less than the above upper limit, the production efficiency of the copolymer can be improved.
• examples of Ar in the group represented by the formula L-Ar include aromatic hydrocarbon ring groups which may have a substituent and aromatic heterocyclic groups which may have a substituent.
• the aromatic hydrocarbon ring group is not particularly limited, and examples thereof include a benzene ring group, a biphenyl ring group, a naphthalene ring group, an azulene ring group, an anthracene ring group, a phenanthrene ring group, a pyrene ring group, a chrysene ring group, a naphthacene ring group, a triphenylene ring group, an o-terphenyl ring group, an m-terphenyl ring group, a p-terphenyl ring group, an acenaphthene ring group, a coronene ring group, a fluorene ring group, a fluoranthrene ring group, a pentacene ring group, a perylene ring group, a pentaphene ring group, a picene ring group, and a pyranthrene ring
• aromatic heterocyclic groups include, but are not limited to, a furan ring group, a thiophene ring group, a pyridine ring group, a pyridazine ring group, a pyrimidine ring group, a pyrazine ring group, a triazine ring group, an oxadiazole ring group, a triazole ring group, an imidazole ring group, a pyrazole ring group, a thiazole ring group, an indole ring group, a benzimidazole ring group, a benzothiazole ring group, a benzoxazole ring group, a quinoxaline ring group, a quinazoline ring group, a phthalazine ring group, a benzofuran ring group, a dibenzofuran ring group, a benzothiophene ring group, a dibenzothiophene
• the substituents that Ar may have are not particularly limited, and examples thereof include an alkyl group, a fluorine atom, and a fluoroalkyl group.
• the alkyl group as a substituent that Ar may have include chain alkyl groups having 1 to 6 carbon atoms, such as a methyl group, an ethyl group, a propyl group, an n-butyl group, and an isobutyl group.
• the fluoroalkyl group as a substituent that Ar may have include fluoroalkyl groups having 1 to 5 carbon atoms, such as a trifluoromethyl group, a trifluoroethyl group, and a pentafluoropropyl group.
• Ar is preferably an aromatic hydrocarbon ring group which may have a substituent, more preferably an unsubstituted aromatic hydrocarbon ring group, and even more preferably a benzene ring group (phenyl group).
• R 1 is a chlorine atom
• R 3 and R 4 are hydrogen atoms
• R 2 is a group represented by L-Ar
• L is a divalent linking group having a fluorine atom. That is, the monomer unit (I) is preferably a monomer unit represented by the following formula (III).
• L is a divalent linking group having a fluorine atom
• Ar is an aromatic ring group which may have a substituent.
• the monomer (a) represented by the above formula (a) capable of forming the monomer unit (I) represented by the above formula (I) is not particularly limited, and examples thereof include ⁇ -chloroacrylic acid alkyl esters such as methyl ⁇ -chloroacrylate, ethyl ⁇ -chloroacrylate, propyl ⁇ -chloroacrylate, and butyl ⁇ -chloroacrylate; ⁇ -fluoroacrylic acid alkyl esters such as methyl ⁇ -fluoroacrylate, ethyl ⁇ -fluoroacrylate, propyl ⁇ -fluoroacrylate, and butyl ⁇ -fluoroacrylate; ⁇ -chloroacrylic acid alkoxyalkyl esters such as methoxymethyl ⁇ -chloroacrylate, ethoxymethyl ⁇ -chloroacrylate, and ethoxyethyl ⁇ -chloroacrylate; ⁇ -fluoroacrylic acid alkoxyalkyl est
• the proportion of the monomer unit (I) in the copolymer is preferably 20 mol% or more, more preferably 30 mol% or more, and even more preferably 40 mol% or more, and is preferably 80 mol% or less, more preferably 75 mol% or less, and even more preferably 70 mol% or less, when the total monomer units in the copolymer is 100 mol%.
• the proportion of the monomer unit (I) in the copolymer is within the above range, assuming that the total monomer units in the copolymer is 100 mol %, the sensitivity to ionizing radiation and the like can be increased.
• the monomer unit (II) contained in the copolymer of the present invention is represented by the following formula (b): (In formula (b), R 5 to R 8 have the same meaning as in formula (II)).
• the calculated value of the lowest unoccupied molecular orbital (LUMO) of the monomer unit (II) is preferably 0.13 eV or more, and more preferably 0.15 eV or more. If the calculated value of the lowest unoccupied molecular orbital (LUMO) of the monomer unit (II) is equal to or more than the above lower limit, it is possible to form a resist pattern having a better shape while further expanding the exposure margin.
• the upper limit of the calculated lowest unoccupied molecular orbital (LUMO) of the monomer unit (II) is not limited, but the calculated lowest unoccupied molecular orbital (LUMO) of the monomer unit (II) is usually 1.50 eV or less, and preferably 1.00 eV or less.
• the calculated distribution coefficient Log P of the monomer unit (II) is preferably 3.4 or more, and more preferably 3.45 or more.
• the upper limit of the calculated partition coefficient Log P of the monomer unit (II) is not limited, but the calculated partition coefficient Log P of the monomer unit (II) is usually 10.0 or less, and preferably 8.0 or less.
• the halogen atom or the alkyl group substituted with a halogen atom which may constitute R5 , R7 , and R8 in formula (II) and formula (b) is not particularly limited, and examples thereof include halogen atoms such as chlorine, fluorine, bromine, and iodine atoms; and groups having a structure in which some or all of the hydrogen atoms in an alkyl group are substituted with the above-mentioned halogen atoms.
• the unsubstituted alkyl group that may constitute R5 , R7 , and R8 in formula (II) and formula (IV) is not particularly limited, and may be an unsubstituted alkyl group having from 1 to 5 carbon atoms. Among these, the unsubstituted alkyl group that may constitute R5 , R7 , and R8 is preferably a methyl group or an ethyl group.
• R5 is an unsubstituted alkyl group and R7 and R8 are hydrogen atoms, and it is more preferable that R5 is a methyl group and R7 and R8 are hydrogen atoms.
• the "electron-donating group having a heteroatom which may have a substituent" which may constitute R6 in formula (II) and formula (b) is not particularly limited as long as it is an electron-donating group having a heteroatom (oxygen atom, nitrogen atom, sulfur atom, halogen atom (e.g., chlorine atom, fluorine atom, bromine atom, iodine atom), etc.), and examples thereof include electron-donating groups having an oxygen atom or a nitrogen atom as a heteroatom, electron-donating groups in which a heteroatom is directly bonded to a benzene ring, etc., and specific examples thereof include a hydroxyl group, an alkoxy group, an alkylamino group, a dialkylamino group, etc.
• an alkoxy group is preferable.
• the alkoxy group include alkoxy groups having 1 to 12 carbon atoms, such as a methoxy group, an ethoxy group, and a butoxy group. Of these, a methoxy group is preferable.
• alkylamino group examples include alkylamino groups having 1 to 12 carbon atoms, such as a methylamino group, an ethylamino group, an n-propylamino group, an i-propylamino group, a cyclopropylamino group, an n-butylamino group, an i-butylamino group, an s-butylamino group, a t-butylamino group, and a cyclobutylamino group.
• alkylamino groups having 1 to 12 carbon atoms such as a methylamino group, an ethylamino group, an n-propylamino group, an i-propylamino group, a cyclopropylamino group, an n-butylamino group, an i-butylamino group, an s-butylamino group, a t-butylamino group, and
• the dialkylamino group includes dialkylamino groups having 2 to 12 carbon atoms, such as a dimethylamino group, a diethylamino group, a dipropylamino group, and a dibutylamino group.
• the above-mentioned substituent is not limited as long as it does not inhibit the electron donating property of R6 , and examples thereof include a hydroxyl group.
• p is preferably an integer of 1 or more and 3 or less, more preferably 1 or 2, and even more preferably 1.
• the three R6 are preferably substituted at the 3rd, 4th, and 5th positions of the benzene ring, respectively.
• the two R6 are preferably substituted at the 3rd and 4th positions of the benzene ring, respectively.
• R6 is preferably substituted at the 3rd or 4th position of the benzene ring.
• the ring that can be formed by bonding with the plurality of R6s is not particularly limited as long as it has electron donating properties, and may be either a monocycle or a polycycle.
• the heterocycle include a heterocycle containing an oxygen atom, such as a dioxolane ring or a dioxane ring; a heterocycle containing a nitrogen atom, such as an imidazole ring; and a heterocycle containing a sulfur atom, such as a tetrahydrothiophene ring.
• the multiple R 6 may be the same or different from each other. Furthermore, at least one of the multiple R 6 is preferably an alkoxy group, and more preferably a methoxy group.
• the monomer (b) represented by formula (b) include 2-methoxy- ⁇ -methylstyrene, 3-methoxy- ⁇ -methylstyrene, 4-methoxy- ⁇ -methylstyrene, 2-ethoxy- ⁇ -methylstyrene, 3-ethoxy- ⁇ -methylstyrene, 4-ethoxy- ⁇ -methylstyrene, 2,3-dimethoxy- ⁇ -methylstyrene, 3,4-dimethoxy- ⁇ -methylstyrene, 3,5-dimethoxy- ⁇ -methylstyrene, 2,3-diethoxy- ⁇ -methylstyrene, 3,4-diethoxy- ⁇ -methylstyrene,
• styrene copolymers include styrene, 3,5-diethoxy- ⁇ -methylstyrene, 3,4,5-trimethoxy- ⁇ -methylstyrene, 3,4,5-triethoxy- ⁇ -methylstyrene, 3-(d
• the monomer (b) represented by formula (b) is preferably 3-methoxy- ⁇ -methylstyrene, 4-methoxy- ⁇ -methylstyrene, 3,4-dimethoxy- ⁇ -methylstyrene, 3,4,5-trimethoxy- ⁇ -methylstyrene, 3-(dimethylamino)- ⁇ -methylstyrene, 4-(dimethylamino)- ⁇ -methylstyrene, 3-methoxy-4-hydroxy- ⁇ -methylstyrene, 3,5-dimethoxy-4-hydroxy- ⁇ -methylstyrene, or 5-isopropenyl-1,3-benzodioxole, more preferably 3-methoxy- ⁇ -methylstyrene, 4-methoxy- ⁇ -methylstyrene, 3,4-dimethoxy- ⁇ -methylst
• the copolymer preferably contains, as monomer unit (II), at least one monomer unit selected from the group consisting of 3-methoxy- ⁇ -methylstyrene unit, 4-methoxy- ⁇ -methylstyrene unit, 3,4-dimethoxy- ⁇ -methylstyrene unit, 3,4,5-trimethoxy- ⁇ -methylstyrene unit, 3-(dimethylamino)- ⁇ -methylstyrene unit, 4-(dimethylamino)- ⁇ -methylstyrene unit, 3,5-dimethoxy-4-hydroxy- ⁇ -methylstyrene unit, and 3-isopropenyl-1,2-methylenedioxybenzene unit.
• monomer unit (II) at least one monomer unit selected from the group consisting of 3-methoxy- ⁇ -methylstyrene unit, 4-methoxy- ⁇ -methylstyrene unit, 3,4-dimethoxy- ⁇ -methylstyrene unit, 3,4,5-trimethoxy-
• the monomer contains at least one monomer unit selected from the group consisting of a 3-methoxy- ⁇ -methylstyrene unit, a 4-methoxy- ⁇ -methylstyrene unit, a 3,4-dimethoxy- ⁇ -methylstyrene unit, a 3,4,5-trimethoxy- ⁇ -methylstyrene unit, and a 3-(dimethylamino)- ⁇ -methylstyrene unit, and it is even more preferable that the monomer contains at least one monomer unit selected from the group consisting of a 3-methoxy- ⁇ -methylstyrene unit, a 4-methoxy- ⁇ -methylstyrene unit, and a 3,4-dimethoxy- ⁇ -methylstyrene unit.
• the proportion of monomer units (II) in the copolymer is not particularly limited, and when the total monomer units in the copolymer is taken as 100 mol%, it is preferably 30 mol% or more, more preferably 35 mol% or more, and even more preferably 40 mol% or more, and is preferably 70 mol% or less, more preferably 60 mol% or less, and even more preferably 55 mol% or less.
• the weight average molecular weight (Mw) of the copolymer is preferably 10,000 or more, more preferably 17,000 or more, and even more preferably 25,000 or more, and is preferably 300,000 or less, more preferably 250,000 or less, and even more preferably 200,000 or less.
• the weight average molecular weight (Mw) of the copolymer is at least as large as the above lower limit, the solubility of the resist film in a developer can be prevented from increasing excessively even at a low irradiation dose, making it possible to form a resist pattern with a better shape.
• the weight average molecular weight (Mw) of the copolymer is not more than the above upper limit, a positive resist composition can be easily prepared.
• the "weight average molecular weight” can be measured by the method described in the Examples.
• the number average molecular weight (Mn) of the copolymer is preferably 7,000 or more, more preferably 10,000 or more, and even more preferably 20,000 or more, and is preferably 200,000 or less, and 150,000 or less. It is more preferable that the molecular weight is 140,000 or less, and even more preferable that the molecular weight is 100,000 or less.
• the solubility of the resist film in a developer can be further prevented from increasing excessively even at a low irradiation dose, and a resist pattern with a better shape can be formed. .
• the number average molecular weight of the copolymer is not more than the above upper limit, a positive resist composition can be prepared more easily.
• the "number average molecular weight" can be measured by the method described in the Examples.
• the molecular weight distribution (Mw/Mn) of the copolymer is preferably 1.10 or more, more preferably 1.20 or more, and even more preferably 1.50 or more, and is preferably 2.20 or less. It is preferable that the ratio is equal to or less than 1.90, more preferably equal to or less than 1.70.
• the molecular weight distribution (Mw/Mn) of the copolymer is equal to or higher than the above lower limit, the ease of production of the copolymer can be improved.
• the molecular weight distribution (Mw/Mn) of the copolymer is not more than the above upper limit, the shape of the obtained resist pattern can be made even better.
• the "molecular weight distribution" can be determined by calculating the ratio of the weight average molecular weight to the number average molecular weight (weight average molecular weight/number average molecular weight).
• the method for preparing the copolymer is not particularly limited.
• the copolymer containing the monomer unit (I) and the monomer unit (II) can be prepared by polymerizing the monomer composition containing the monomer (a), the monomer (b), and any monomer that can be copolymerized with these monomers, and then recovering the obtained copolymer and optionally purifying it.
• the composition, molecular weight distribution, number average molecular weight, and weight average molecular weight of the copolymer can be adjusted by changing the polymerization conditions and purification conditions. Specifically, for example, the number average molecular weight and weight average molecular weight can be increased by lowering the polymerization temperature. Also, the number average molecular weight and weight average molecular weight can be increased by shortening the polymerization time. Furthermore, the molecular weight distribution can be narrowed by performing purification.
• the monomer composition used in the preparation of the copolymer may be, for example, a mixture of monomer components including monomer (a), monomer (b), and any monomer copolymerizable with these monomers, an optionally usable solvent, an optionally usable polymerization initiator, and an optionally added additive.
• the polymerization of the monomer composition may be carried out using a known method. Among them, it is preferable to use cyclopentanone, water, or the like as the solvent. It is also preferable to use, for example, azobisisobutyronitrile, dimethyl 2,2'-azobis(2-methylpropionate), or the like as the polymerization initiator.
• the polymer obtained by polymerizing the monomer composition can be recovered by adding a good solvent such as tetrahydrofuran to a solution containing the polymer, without any particular limitations, and then dripping the solution with the good solvent into a poor solvent such as methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, or hexane to solidify the polymer.
• a good solvent such as tetrahydrofuran
• a poor solvent such as methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, or hexane
• the purification method used for purifying the obtained polymer is not particularly limited, and examples thereof include known purification methods such as reprecipitation and column chromatography. Among them, the reprecipitation method is preferably used as the purification method. The purification of the polymer may be repeated several times.
• the purification of the polymer by the reprecipitation method is preferably carried out, for example, by dissolving the obtained polymer in a good solvent such as tetrahydrofuran, and then dripping the obtained solution into a mixed solvent of a good solvent such as tetrahydrofuran and a poor solvent such as methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, hexane, etc., to precipitate a part of the polymer.
• a good solvent such as tetrahydrofuran
• a poor solvent such as methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, hexane, etc.
• the molecular weight distribution, number average molecular weight, and weight average molecular weight of the obtained copolymer can be easily adjusted by changing the type and mixture ratio of the good solvent and poor solvent.
• the molecular weight of the copolymer precipitated in the mixed solvent can be increased by increasing the proportion of the good solvent in the mixed solvent.
• the polymer precipitated in a mixed solvent of a good solvent and a poor solvent may be used as the copolymer as long as it meets the desired properties, or the polymer that did not precipitate in the mixed solvent (i.e., the polymer that is dissolved in the mixed solvent) may be used.
• the polymer that did not precipitate in the mixed solvent can be recovered from the mixed solvent using known techniques such as concentration to dryness.
• the positive resist composition of the present invention comprises the copolymer of the present invention and a solvent. Because the positive resist composition of the present invention contains the copolymer of the present invention described above, it is possible to form a resist pattern having a good shape while increasing the exposure margin of the obtained resist.
• the above-mentioned copolymer of the present invention can be used.
• the content of the copolymer in the positive resist composition is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 1.5% by mass or more, and is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less, assuming that the total of all components of the positive resist composition is 100% by mass.
• the solvent is not particularly limited as long as it is a solvent that can dissolve the copolymer of the present invention, and it is possible to use known solvents such as those described in Japanese Patent No. 5938536.
• anisole propylene glycol monomethyl ether acetate (PGMEA), cyclopentanone, cyclohexanone, or isoamyl acetate as the solvent, and it is more preferable to use isoamyl acetate.
• the positive resist composition of the present invention may further contain, in addition to the above-mentioned components, any of known additives that can be blended into resist compositions. There are no particular limitations on the amount of additives blended, and an appropriate amount can be added depending on the application.
• the positive resist composition can be prepared by mixing the copolymer of the present invention, a solvent, and any known additives that may be used. There are no particular limitations on the mixing method, and the components may be mixed by a known method. Alternatively, the composition may be prepared by mixing the components and then filtering the mixture.
• the method of filtering the mixture is not particularly limited, and for example, the mixture can be filtered using a filter.
• the filter is not particularly limited, and examples thereof include fluorocarbon, cellulose, nylon, polyester, and hydrocarbon filtration membranes.
• the material constituting the filter is preferably polyfluorocarbon such as polyethylene, polypropylene, polytetrafluoroethylene, Teflon (registered trademark), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), nylon, and a composite membrane of polyethylene and nylon.
• polyfluorocarbon such as polyethylene, polypropylene, polytetrafluoroethylene, Teflon (registered trademark), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), nylon, and a composite membrane of polyethylene and nylon.
• PFA tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer
• nylon a composite membrane of polyethylene and nylon.
• the filter for example, one disclosed in U.S. Pat. No. 6,103,122 may be used.
• the filter may contain a strong cationic or weak cationic ion exchange resin.
• the average particle size of the ion exchange resin is not particularly limited, but is preferably 2 ⁇ m or more and 10 ⁇ m or less.
• cation exchange resins include sulfonated phenol-formaldehyde condensates, sulfonated phenol-benzaldehyde condensates, sulfonated styrene-divinylbenzene copolymers, sulfonated methacrylic acid-divinylbenzene copolymers, and other types of sulfonic or carboxylic acid group-containing polymers.
• the cation exchange resins are provided with H + counterions, NH 4 + counterions, or alkali metal counterions, such as K + and Na + counterions.
• the cation exchange resins preferably have hydrogen counterions.
• cation exchange resins examples include Microlite® PrCH from Purolite, which is a sulfonated styrene-divinylbenzene copolymer with H + counterions.
• Such cation exchange resins are commercially available as AMBERLYST® from Rohm and Haas.
• the pore size of the filter is preferably 0.001 ⁇ m or more and 1 ⁇ m or less. If the pore size of the filter is within the above range, it is possible to sufficiently prevent impurities such as metals from being mixed into the positive resist composition.
• the method of forming a resist pattern of the present invention includes at least a step of forming a resist film using the above-mentioned positive resist composition of the present invention (resist film forming step), a step of exposing the resist film (exposure step), and a step of developing the exposed resist film (development step). Furthermore, the resist pattern forming method of the present invention may include, for example, a step of forming an underlayer film on the substrate on which the resist film is to be formed (underlayer film forming step) before the resist film forming step.
• the resist pattern forming method of the present invention may further include a step of heating the resist film between the exposure step and the development step (post-exposure bake (PEB) step) and/or a step of removing the developer after the development step (developer removal step).
• the method may further include a step of etching the underlayer film and/or the substrate (etching step).
• a positive resist composition of the present invention is used as the positive resist composition, so that a resist pattern in a good shape can be formed with a wide exposure margin.
• an underlayer film is formed on a substrate.
• the surface of the substrate is made hydrophobic. This increases the affinity between the substrate and the resist film, and increases the adhesion between the substrate and the resist film.
• the underlayer film may be an inorganic underlayer film or an organic underlayer film.
• the inorganic underlayer film can be formed by applying an inorganic material onto a substrate and then baking it.
• inorganic materials include silicon-based materials.
• the organic underlayer film can be formed by applying an organic material onto a substrate to form a coating film and drying it.
• the organic material is not limited to those that are sensitive to light or electron beams, and can be, for example, a resist material or resin material that is commonly used in the semiconductor and liquid crystal fields.
• the organic material is preferably a material that can form an organic underlayer film that can be etched, particularly dry etched. With such an organic material, the organic underlayer film can be etched using a pattern formed by processing the resist film, thereby transferring the pattern to the underlayer film and forming a pattern in the underlayer film.
• the organic material is preferably a material that can form an organic underlayer film that can be etched by oxygen plasma etching or the like.
• An example of an organic material used to form an organic underlayer film is AL412 from Brewer Science.
• the organic material can be applied by a conventional method using spin coating or a spinner.
• the method for drying the coating film may be any method capable of volatilizing the solvent contained in the organic material, such as a baking method.
• the baking conditions are not particularly limited, but the baking temperature is preferably 80°C or higher and 300°C or lower, and more preferably 200°C or higher and 300°C or lower.
• the baking time is preferably 30 seconds or longer, more preferably 60 seconds or longer, preferably 500 seconds or shorter, more preferably 400 seconds or shorter, even more preferably 300 seconds or shorter, and particularly preferably 180 seconds or shorter.
• the thickness of the underlayer film after drying of the coating film is not particularly limited, but is preferably 10 nm or longer and 100 nm or shorter.
• the substrate on which the underlayer film or resist film can be formed in the resist pattern forming method is not particularly limited, and examples that can be used include a substrate having an insulating layer and a copper foil provided on the insulating layer, which is used in the manufacture of printed circuit boards, and a mask blank having a light-shielding layer formed on a substrate.
• the substrate material examples include inorganic substances such as metals (silicon, copper, chromium, iron, aluminum, etc.), glass, titanium oxide, silicon dioxide (SiO 2 ), silica, and mica; nitrides such as SiN; oxynitrides such as SiON; and organic substances such as acrylic, polystyrene, cellulose, cellulose acetate, and phenolic resin.
• metals are preferred as the substrate material.
• the size and shape of the substrate are not particularly limited.
• the surface of the substrate may be smooth, curved, or uneven, and may be a thin-plate shaped substrate.
• the surface of the substrate may be subjected to a surface treatment as necessary.
• the substrate in the case of a substrate having hydroxyl groups on the surface layer, the substrate can be surface treated using a silane coupling agent capable of reacting with the hydroxyl groups. This changes the surface layer of the substrate from hydrophilic to hydrophobic, thereby improving the adhesion between the substrate and the underlayer film, or between the substrate and the resist layer.
• the silane coupling agent is not particularly limited, but hexamethyldisilazane is preferred.
• the positive resist composition of the present invention is coated onto a workpiece such as a substrate to be processed using the resist pattern (or onto an underlayer film if an underlayer film has been formed) to obtain a coating layer (coating process), and then the solvent is removed from the obtained coating layer to form a resist film (drying process).
• the workpiece to which the positive resist composition of the present invention is applied in the coating step is not particularly limited, and examples of usable materials include semiconductor substrates used in the manufacture of semiconductor devices, etc.; substrates having an insulating layer and a copper foil provided on the insulating layer, used in the manufacture of printed circuit boards, etc.; and mask blanks in which a light-shielding layer is formed on a substrate.
• the method for applying the positive resist composition of the present invention is not particularly limited, and known methods can be used.
• the method for removing the solvent from the coating layer is not particularly limited, and any drying method generally used in forming a resist film can be used. However, it is preferable to form a resist film by heating (pre-baking) the positive resist composition.
• the temperature at which the coating layer is dried is preferably 100° C. or higher, more preferably 110° C. or higher, from the viewpoint of adhesion between the resist film formed through the drying process and the workpiece, and is preferably 250° C. or lower, more preferably 200° C. or lower, from the viewpoint of reducing the thermal influence on the workpiece and the resist film.
• the time at which the coating layer is dried is preferably more than 10 seconds, more preferably 30 seconds or higher, and even more preferably 1 minute or higher, from the viewpoint of sufficiently improving the adhesion between the resist film formed by carrying out the drying process in a lower temperature range and the workpiece, and is preferably 60 minutes or lower, more preferably 30 minutes or lower, from the viewpoint of reducing the change in molecular weight of the polymer in the resist film before and after the drying process.
• the resist film formed in the resist film forming process is irradiated with ionizing radiation or the like to draw a desired pattern.
• ionizing radiation is radiation that has enough energy to ionize atoms or molecules
• non-ionizing radiation is radiation that does not have enough energy to ionize atoms or molecules.
• ionizing radiation examples include electron beams, extreme ultraviolet rays, gamma rays, X-rays, alpha rays, heavy particle beams, proton beams, beta rays, and ion beams.
• electron beams or extreme ultraviolet rays are preferred as ionizing radiation, and electron beams are more preferred.
• the wavelength of extreme ultraviolet rays is not particularly limited and can be, for example, 1 nm or more and 30 nm or less, and is preferably 13.5 nm.
• non-ionizing radiation with a wavelength of 300 nm or less.
• the post-exposure bake step In the optional post-exposure bake step, the resist film exposed in the exposure step is heated, and the post-exposure bake step can reduce the surface roughness of the resist pattern.
• the heating temperature is preferably 70°C or higher, more preferably 80°C or higher, and even more preferably 90°C or higher, and is preferably 200°C or lower, more preferably 170°C or lower, and even more preferably 150°C or lower. If the heating temperature is within the above range, the clarity of the resist pattern can be improved while the surface roughness of the resist pattern can be effectively reduced.
• the time for heating the resist film in the post-exposure bake step is preferably 10 seconds or more, more preferably 20 seconds or more, and even more preferably 30 seconds or more. If the heating time is 10 seconds or more, the clarity of the resist pattern can be further improved while the surface roughness of the resist pattern can be sufficiently reduced. On the other hand, from the viewpoint of production efficiency, the heating time is, for example, preferably 10 minutes or less, more preferably 5 minutes or less, and even more preferably 3 minutes or less.
• the method for heating the resist film in the post-exposure bake step is not particularly limited, and examples include a method of heating the resist film on a hot plate, a method of heating the resist film in an oven, and a method of blowing hot air onto the resist film.
• the exposed resist film (or the exposed and heated resist film if a post-exposure bake step has been performed) is developed to form a developed film on the workpiece.
• the development of the resist film can be carried out, for example, by contacting the resist film with a developer.
• the method of contacting the resist film with the developer is not particularly limited, and known methods such as immersing the resist film in the developer or applying the developer to the resist film can be used.
• the developer can be appropriately selected depending on the properties of the copolymer of the present invention. Specifically, when selecting the developer, it is preferable to select a developer that does not dissolve the resist film before the exposure process, but can dissolve the exposed part of the resist film after the exposure process. In addition, the developer may be used alone or in combination of two or more kinds at any ratio.
• Examples of the developer include hydrofluorocarbons such as 1,1,1,2,3,4,4,5,5,5-decafluoropentane (CF 3 CFHCFHCF 2 CF 3 ), 1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorohexane, 1,1,1,2,2,3,4,5,5,5-decafluoropentane, 1,1,1,3,3-pentafluorobutane, and 1,1,1,2,2,3,3,4,4-nonafluorohexane; 2,2-dichloro-1,1,1-trifluoroethane, 1,1-dichloro-1-fluoroethane, and 1,1-dichloro-2,2,3,3,3-pentafluoropropane (CF 3 CF 2 CHCl 2 ), hydrochlorofluorocarbons such as 1,3-dichloro-1,1,2,2,3-pentafluoropropane (CClF 2 CF 2 CHClF), hydrofluoroethers
• the developer is removed from the developed resist film to form a resist pattern on the workpiece.
• the developer can be removed by air blowing using a gas such as nitrogen, or by rinsing using a rinsing liquid.
• the method of contacting the developed resist film with the rinsing liquid is not particularly limited, and known methods such as immersing the resist film in the rinsing liquid or applying the rinsing liquid to the resist film can be used.
• the rinsing liquid include, for example, the same developer as exemplified in the "developing process" section, as well as hydrocarbon solvents such as octane and heptane, and water.
• the rinsing liquid may contain a surfactant.
• the underlayer film and/or the substrate are etched using the resist pattern as a mask to form a pattern in the underlayer film and/or the substrate.
• the number of etchings is not particularly limited, and may be one or more times.
• the etching may be dry etching or wet etching, but dry etching is preferred. Dry etching can be performed using a known dry etching device.
• the etching gas used in dry etching can be appropriately selected depending on the elemental composition of the underlying film or substrate to be etched, etc.
• etching gas examples include fluorine-based gases such as CHF3 , CF4 , C2F6 , C3F8 , and SF6 ; chlorine-based gases such as Cl2 and BCl3 ; oxygen-based gases such as O2 , O3 , and H2O ; reducing gases such as H2 , NH3 , CO, CO2 , CH4 , C2H2 , C2H4, C2H6, C3H4 , C3H6 , C3H8 , HF , HI, HBr , HCl, NO, and BCl3 ; and inert gases such as He, N2 , and Ar. These gases may be used alone or in combination of two or more.
• oxygen-based gases are usually used.
• a fluorine-based gas is usually used, and a mixture of a fluorine-based gas and an inert gas is preferably used.
• the underlayer film remaining on the substrate may be removed before or after etching the substrate.
• the underlayer film may be a patterned underlayer film or an unpatterned underlayer film.
• examples of the method for removing the underlayer film include the above-mentioned dry etching.
• the underlayer film may be removed by contacting the underlayer film with a liquid such as a basic liquid or an acidic liquid, preferably a basic liquid.
• the basic liquid is not particularly limited, and examples thereof include alkaline hydrogen peroxide.
• the method for removing the underlayer film by wet stripping using alkaline hydrogen peroxide is not particularly limited as long as the underlayer film and alkaline hydrogen peroxide can be brought into contact with each other for a certain period of time under heated conditions, and examples thereof include a method of immersing the underlayer film in heated alkaline hydrogen peroxide, a method of spraying alkaline hydrogen peroxide onto the underlayer film in a heated environment, and a method of coating the underlayer film with heated alkaline hydrogen peroxide. After performing any of these methods, the substrate is washed with water and dried to obtain a substrate from which the underlayer film has been removed.
• a resist pattern forming method is a resist pattern forming method using an electron beam or EUV, which includes the above-mentioned underlayer film forming process, resist film forming process, exposure process, development process, and developer removal process.
• a etching method is one in which the resist pattern formed by the resist pattern forming method is used as a mask, and includes an etching process.
• the underlayer film forming step an inorganic material is applied onto a substrate and then baked to form an inorganic underlayer film.
• the positive resist composition of the present invention is applied onto the inorganic underlayer film formed in the underlayer film forming step, and then dried to form a resist film.
• the resist film formed in the resist film forming step is irradiated with EUV light to write a desired pattern.
• the developing step the resist film exposed in the exposure step is brought into contact with a developer to develop the resist film, thereby forming a resist pattern on the underlayer film.
• the resist film developed in the developing step is brought into contact with a rinsing solution to rinse the developed resist film.
• the underlying film is etched using the resist pattern as a mask to form a pattern in the underlying film.
• the substrate is etched using the underlayer film on which the pattern is formed as a mask to form a pattern on the substrate.
• the present invention will be specifically described below based on examples, but the present invention is not limited to these examples.
• the ratio of a monomer unit formed by polymerizing a certain monomer in the copolymer is usually the same as the ratio (feed ratio) of the certain monomer to the total monomers used in the polymerization of the copolymer, unless otherwise specified.
• the ratio of the monomer unit in the copolymer, the lowest unoccupied molecular orbital LUMO value and LogP value of the monomer unit (II) in the copolymer, the number average molecular weight, weight average molecular weight and molecular weight distribution of the copolymer were measured or calculated by the following methods.
• the exposure margin of the resist and the shape of the resist pattern were evaluated by the following methods.
• the copolymers obtained in the examples and comparative examples were dissolved in chloroform-d, 99.8% (manufactured by Fuji Film Wako Pure Chemical Industries, Ltd.) to a concentration of 10% by mass, and the proportion of each monomer unit in the copolymer was calculated using this solution with a nuclear magnetic resonance apparatus (manufactured by JEOL Ltd., 500 MHz).
• a nuclear magnetic resonance apparatus manufactured by JEOL Ltd., 500 MHz.
• the number average molecular weight (Mn) and weight average molecular weight (Mw) of the copolymer were determined in terms of standard polystyrene using a gel permeation chromatograph (HLC-8420, manufactured by Tosoh Corporation) and tetrahydrofuran as a developing solvent, and the molecular weight distribution (Mw/Mn) was calculated.
• HSC-8420 gel permeation chromatograph
• Mw/Mn molecular weight distribution
• Resist patterns were formed using the positive resist compositions obtained in the Examples and Comparative Examples, and the exposure margins were evaluated. Specifically, first, a positive resist composition was applied to a silicon wafer having a diameter of 4 inches to a thickness of 50 nm using a spin coater (MS-A150, manufactured by Mikasa).
• the applied positive resist composition was heated on a hot plate at a temperature of 170° C. for 1 minute to form a resist film on the silicon wafer (resist film formation process).
• the thickness of the resist film was 50 nm.
• ELS-S50 electron beam lithography device
• the resist film was exposed to light at 10 ⁇ C/cm 2 to 400 ⁇ C/cm 2 in increments of 10 ⁇ C/cm 2 to draw a pattern (exposure process).
• the resist film after the exposure process was subjected to a development process at a temperature of 23° C. for 1 minute using isopropyl alcohol (IPA) as a developer (development process).
• IPA isopropyl alcohol
• the resist pattern was then observed for pattern separation and pattern collapse.
• the resist pattern had lines (unexposed regions) and spaces (exposed regions) each of which was 30 nm wide.
• the exposure margin was evaluated according to the following criteria. The results are shown in Table 2.
• ⁇ Resist pattern shape> A resist pattern was formed using the positive resist compositions obtained in the examples and comparative examples, and the shape of the resist pattern was evaluated. Specifically, the shape of a pattern exposed at a median exposure dose within the range from pattern separation to pattern collapse when the exposure margin was evaluated was observed with a scanning electron microscope. The shape of the resist pattern was evaluated according to the following criteria. The results are shown in Table 2. A: The sidewall shape of the resist pattern is smooth. B: The sidewall shape of the resist pattern is rough.
• Example 1 Preparation of Copolymer> Monomer composition A1 containing 3.46 g of ⁇ -chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl (ACAFPh) as monomer (a), 1.55 g of 3-methoxy- ⁇ -methylstyrene (3-MOAMS) as monomer (b), 0.0019 g of V-601 (dimethyl 2,2′-azobis(2-methylpropionate) as a polymerization initiator, and 1.10 g of cyclopentanone as a solvent was placed in a glass container, the glass container was sealed and substituted with nitrogen, and the mixture was stirred in a constant temperature bath at 78° C.
• ACAFPh ⁇ -chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl
• 3-MOAMS 3-methoxy- ⁇ -methylstyrene
• V-601 dimethyl 2,2′-azobis(2-
• copolymer A1 was a copolymer containing 52 mol% of ⁇ -chloroacrylic acid-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units and 48 mol% of 3-methoxy- ⁇ -methylstyrene units.
• the number average molecular weight, weight average molecular weight and molecular weight distribution of the copolymer A1 thus obtained were then measured. The results are shown in Table 2.
• Example 2 In the preparation of the copolymer, instead of the monomer composition A1, a monomer composition A2 containing 3.46 g of 1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl ⁇ -chloroacrylate (ACAFPh) as monomer (a), 1.57 g of 4-methoxy- ⁇ -methylstyrene (4-MOAMS) as monomer (b), 0.0038 g of V-601 (dimethyl 2,2'-azobis(2-methylpropionate) as a polymerization initiator, and 3.36 g of cyclopentanone as a solvent was used to prepare copolymer A2.
• ACAFPh 1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl ⁇ -chloroacrylate
• 4-MOAMS 4-methoxy- ⁇ -methylstyrene
• V-601 dimethyl 2,2'-azobis(2-methylpropionate)
• copolymer A2 and a positive resist composition were prepared and various measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 2.
• the obtained copolymer A2 was a copolymer containing 52 mol % of ⁇ -chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units and 48 mol % of 4-methoxy- ⁇ -methylstyrene units.
• Example 3 In the preparation of the copolymer, instead of the monomer composition A1, a monomer composition A3 containing 3.26 g of 1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl ⁇ -chloroacrylate (ACAFPh) as monomer (a), 1.74 g of 3,4-dimethoxy- ⁇ -methylstyrene (3,4-diMOAMS) as monomer (b), 0.0018 g of V-601 (dimethyl 2,2'-azobis(2-methylpropionate) as a polymerization initiator, and 1.06 g of cyclopentanone as a solvent was used to prepare copolymer A3.
• ACAFPh 1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl ⁇ -chloroacrylate
• ACAFPh 1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl ⁇ -chloroacrylate
• copolymer A3 and a positive resist composition were prepared and various measurements and evaluations were carried out. The results are shown in Table 2.
• the monomer unit ratio of the obtained copolymer A3 was 54 mol % of ⁇ -chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units and 46 mol % of 3,4-dimethoxy- ⁇ -methylstyrene units.
• Example 4 In the preparation of the copolymer, instead of the monomer composition A1, a monomer composition A4 containing 3.07 g of ⁇ -chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl (ACAFPh) as monomer (a), 1.93 g of 3,4,5-trimethoxy- ⁇ -methylstyrene as monomer (b), 0.0017 g of V-601 (dimethyl 2,2'-azobis(2-methylpropionate) as a polymerization initiator, and 6.43 g of cyclopentanone as a solvent was used to prepare copolymer A4.
• ACAFPh ⁇ -chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl
• copolymer A4 was a copolymer containing 51 mol % of ⁇ -chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units and 49 mol % of 3,4,5-trimethoxy- ⁇ -methylstyrene units.
• Example 5 In the preparation of the copolymer, instead of the monomer composition A1, a monomer composition A5 containing 2.88 g of ⁇ -chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl (ACAFPh) as monomer (a), 2.53 g of 3,5-dimethoxy- ⁇ -methylstyrene as monomer (b), 0.0052 g of V-601 (dimethyl 2,2'-azobis(2-methylpropionate) as a polymerization initiator, and 3.61 g of cyclopentanone as a solvent was used to prepare copolymer A5.
• ACAFPh ⁇ -chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl
• copolymer A5 and a positive resist composition were prepared in the same manner as in Example 1, and various measurements and evaluations were carried out. The results are shown in Table 2.
• the copolymer A5 was a copolymer containing 53 mol % of ⁇ -chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units and 47 mol % of 3,5-dimethoxy- ⁇ -methylstyrene units.
• Example 6 In the preparation of the copolymer, instead of the monomer composition A1, 6.92 g of ⁇ -chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl (ACAFPh) as the monomer (a), 2.96 g of 3,4-dimethoxy- ⁇ -methylstyrene as the monomer (b), 0.492 g of ⁇ -methylstyrene as a monomer other than the monomer (a) and the monomer (b), 0.0103 g of V-70 (2,2'-azobis (4-methoxy-2,4-dimethoxyvaleronitrile) as a polymerization initiator, and 6.23 g of cyclopentanone as a solvent were placed in a glass container, the glass container was sealed and replaced with nitrogen, and the mixture was stirred in a constant temperature bath at 25°C for 24 hours under a nitrogen atmosphere.
• ACAFPh ⁇ -chloroacrylate-1-phenyl-1
• Copolymer A6 and a positive resist composition were prepared in the same manner as in Example 1, except that copolymer A6 was prepared using monomer composition A6, and various measurements and evaluations were performed. The results are shown in Table 2.
• the copolymer A6 was a copolymer containing 51 mol % of ⁇ -chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units, 40 mol % of 3,4-dimethoxy- ⁇ -methylstyrene units, and 9 mol % of ⁇ -methylstyrene units.
• Example 7 In the preparation of the copolymer, instead of the monomer composition A6, 6.92 g of ⁇ -chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl (ACAFPh) as monomer (a), 1.85 g of 3,4-dimethoxy- ⁇ -methylstyrene as monomer (b), 1.23 g of ⁇ -methylstyrene as a monomer other than monomer (a) and monomer (b), 0.00720 g of V-70 (2,2'-azobis(4-methoxy-2,4-dimethoxyvaleronitrile) as a polymerization initiator, and 5.96 g of cyclopentanone as a solvent were used to prepare copolymer A7.
• ACAFPh ⁇ -chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl
• copolymer A7 and a positive resist composition were prepared in the same manner as in Example 6, and various measurements and evaluations were carried out. The results are shown in Table 2.
• the copolymer A7 was a copolymer containing 49 mol % of ⁇ -chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units, 27 mol % of 3,4-dimethoxy- ⁇ -methylstyrene units, and 24 mol % of ⁇ -methylstyrene units.
• Example 8 In the preparation of the copolymer, instead of the monomer composition A6, 7.19 g of ⁇ -chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl (ACAFPh) as monomer (a), 0.770 g of 3,4-dimethoxy- ⁇ -methylstyrene as monomer (b), 2.04 g of ⁇ -methylstyrene as a monomer other than monomer (a) and monomer (b), 0.00750 g of V-70 (2,2'-azobis(4-methoxy-2,4-dimethoxyvaleronitrile) as a polymerization initiator, and 5.96 g of cyclopentanone as a solvent were used to prepare copolymer A8.
• ACAFPh ⁇ -chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl
• copolymer A8 and a positive resist composition were prepared in the same manner as in Example 6, and various measurements and evaluations were carried out. The results are shown in Table 2.
• the copolymer A8 was a copolymer containing 51 mol % of ⁇ -chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units, 11 mol % of 3,4-dimethoxy- ⁇ -methylstyrene units, and 38 mol % of ⁇ -methylstyrene units.
• copolymer A9 was a copolymer containing 52 mol % of ⁇ -chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units and 48 mol % of ⁇ -methylstyrene units.
• the copolymer A10 was a copolymer containing 54 mol % of ⁇ -chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units and 46 mol % of 4-methyl- ⁇ -methylstyrene units.
• EB electron beam
• ACAFPh ⁇ -chloroacrylic acid-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl
• AMS alpha-methylstyrene
• 3-MOAMS 3-methoxy- ⁇ -methylstyrene
• 4-MOAMS 4-methoxy- ⁇ -methylstyrene
• 3,4-diMOAMS refers to 3,4-dimethoxy- ⁇ -methylstyrene
• 3,4,5-triMOAMS refers to 3,4,5-trimethoxy- ⁇ -methylstyrene
• 3,5-diMOAMS refers to 3,5-dimethoxy- ⁇ -methylstyrene
• 4-MAMS 4-methyl- ⁇ -methylstyrene
• IPA refers to isopropyl alcohol.
• a copolymer and a positive resist composition which are capable of forming a resist pattern having a wide exposure margin and a good shape. Furthermore, according to the present invention, there can be provided a method for forming a resist pattern which has a wide exposure margin and is capable of forming a resist pattern having a good shape.

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