Copolymer, positive resist composition, and method for forming a resist pattern

Abstract

Provided is a copolymer including a monomer unit (A) represented by formula (I) and a monomer unit (B) represented by formula (II), the copolymer having a weight-average molecular weight of 230,000 or higher. In the formulae, L is a single bond or a divalent linking group, Ar is an optionally substituted aromatic ring group, R1 is an alkyl group, R2 is hydrogen, an alkyl group, a halogen atom, a halogenated alkyl group, a hydroxyl group, a carboxylic acid group, or a halogenated carboxylic acid group, and p is an integer of 0-5. In the case where there are two or more R2 moieties, the moieties may be the same or different.

Description

[Technical Field]

[0001] The present invention relates to a copolymer, a positive resist composition, and a method of forming a resist pattern. In particular, it relates to a copolymer that can be used favorably as a positive resist, a positive resist composition containing said copolymer, and a method of forming a resist pattern using such a positive resist composition. [Background technology]

[0002] BACKGROUND ART In the field of semiconductor manufacturing and the like, polymers whose main chains are scissed and whose molecular weight is reduced by irradiation with ionizing radiation such as electron beams or short-wavelength light such as ultraviolet light (hereinafter, ionizing radiation and short-wavelength light may be collectively referred to as "ionizing radiation, etc.") have conventionally been used as main-chain scission type positive resists.

[0003] For example, Patent Document 1 discloses a copolymer formed using a predetermined aromatic ring-containing monomer, the copolymer having a molecular weight distribution of 1.7 or less. The copolymer disclosed in Patent Document 1 enables the formation of a resist pattern that is excellent in heat resistance, resolution, and clarity. Patent Document 1 also discloses that the weight-average molecular weight of the predetermined copolymer can be preferably 10,000 or more and 80,000 or less. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2020 / 066806 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the positive resist made of the specified copolymer described in Patent Document 1 has room for improvement in terms of dry etching resistance. Furthermore, in recent years, with the demand for even finer resist patterns, positive resists are also required to enable the formation of resist patterns with even better clarity. Furthermore, when forming fine resist patterns using positive resists, it is also required to suppress the occurrence of defects.

[0006] Therefore, an object of the present invention is to provide a copolymer that can be used favorably as a main-chain scission type positive resist that exhibits excellent dry etching resistance and clarity and is capable of forming a resist pattern with few defects, and a positive resist composition containing the copolymer. Another object of the present invention is to provide a method for forming a resist pattern, which is capable of forming a resist pattern that has excellent dry etching resistance and clarity and has few defects. [Means for solving the problem]

[0007] The present inventors have conducted extensive research to achieve the above object, and have found that a positive resist comprising a copolymer formed from a predetermined aromatic ring-containing monomer and having a predetermined weight-average molecular weight can form a resist pattern that is excellent in dry etching resistance and clarity and has few defects, thereby completing the present invention.

[0008] That is, an object of the present invention is to advantageously solve the above-mentioned problems, and the copolymer of the present invention is a copolymer represented by the following formula (I): [ka] [In formula (I), L represents a single bond or a divalent linking group, and Ar represents an aromatic ring group which may have a substituent.] and a monomer unit (A) represented by the following formula (II): [ka] [In formula (II), R 1 is an alkyl group, and R 2 is a hydrogen atom, an alkyl group, a halogen atom, a halogenated alkyl group, a hydroxyl group, a carboxylic acid group, or a halogenated carboxylic acid group, p is an integer of 0 to 5, and R 2 When a plurality of are present, they may be the same or different. and a weight average molecular weight of 230,000 or more. The copolymer having the monomer units (A) and (B) can be used effectively as a main chain scission type positive resist. Furthermore, when the weight average molecular weight of the copolymer having the monomer units (A) and (B) is equal to or greater than the lower limit, it is possible to form a resist pattern that has excellent dry etching resistance and clarity and has few defects. In this specification, the "weight average molecular weight" can be measured using gel permeation chromatography as a value converted into standard polystyrene.

[0009] Here, the copolymer of the present invention preferably has a weight-average molecular weight of at least 280,000. When the weight-average molecular weight of a given copolymer is at least the above-mentioned lower limit, it is possible to form a resist pattern that has even more excellent dry etching resistance and clarity, and that has even fewer defects.

[0010] Furthermore, the copolymer of the present invention preferably contains 20% or less of components having a molecular weight of less than 50,000. If the copolymer contains 20% or less of components having a molecular weight of less than 50,000, the copolymer will have even more excellent dry etching resistance and clarity, and will be able to form a resist pattern with even fewer defects. In the present invention, the "proportion of components having a molecular weight of less than 50,000" can be determined by using a chromatogram obtained by gel permeation chromatography and calculating the ratio (=(B / A)×100%) of the total area of ​​peaks (B) of components having a molecular weight of less than 50,000 in the chromatogram to the total area (A) of peaks in the chromatogram. The "molecular weight" in this case is a value based on the weight average molecular weight of the standard substance (polystyrene in the examples of this specification) used to prepare the chromatogram.

[0011] Furthermore, the copolymer of the present invention preferably contains 30% or less of components having a molecular weight of less than 100,000. If the copolymer contains 30% or less of components having a molecular weight of less than 100,000, the copolymer will have even more excellent dry etching resistance and clarity, and will be able to form a resist pattern with even fewer defects. In the present invention, the "proportion of components having a molecular weight of less than 100,000" can be determined by using a chromatogram obtained by gel permeation chromatography and calculating the ratio (=(C / A)×100%) of the total area of ​​peaks (C) of components having a molecular weight of less than 100,000 in the chromatogram to the total area (A) of peaks in the chromatogram.

[0012] Furthermore, the copolymer of the present invention preferably contains 10% or more of components having a molecular weight of more than 500,000. If the copolymer contains 10% or more of components having a molecular weight of more than 500,000, the copolymer will have even more excellent dry etching resistance and clarity, and will be able to form a resist pattern with even fewer defects. In the present invention, the "proportion of components having a molecular weight of more than 500,000" can be determined by using a chromatogram obtained by gel permeation chromatography and calculating the ratio (=(D / A)×100%) of the total area of ​​peaks (D) of components having a molecular weight of more than 500,000 in the chromatogram to the total area (A) of the peaks in the chromatogram.

[0013] In the copolymer of the present invention, L is preferably a divalent linking group having an electron-withdrawing group, because when L is a divalent linking group having an electron-withdrawing group, sensitivity to ionizing radiation and the like can be improved.

[0014] The electron-withdrawing group of the copolymer of the present invention is preferably at least one selected from the group consisting of a fluorine atom, a fluoroalkyl group, a cyano group, and a nitro group, because the sensitivity to ionizing radiation and the like can be sufficiently improved when the electron-withdrawing group is at least one selected from the group consisting of a fluorine atom, a fluoroalkyl group, a cyano group, and a nitro group.

[0015] Furthermore, the copolymer of the present invention can be cured by electron beam irradiation at a dose of 20 μC / cm 2 Weight average molecular weight Mw when exposed to light 20 and an electron beam irradiation dose of 40 μC / cm 2 Weight average molecular weight Mw when exposed to light 40 It is preferable that the difference between the weight-average molecular weights is at least 12,100. If the difference between the weight-average molecular weights when the copolymer is exposed to the above two electron beam irradiation doses is at least 12,100, a resist pattern with even better clarity and fewer defects can be formed.

[0016] The present invention also aims to advantageously solve the above-mentioned problems, and provides a positive resist composition comprising any one of the copolymers described above and a solvent. By incorporating the copolymer described above as a positive resist, it is possible to form a resist pattern that is excellent in dry etching resistance and clarity, and that has few defects.

[0017] Furthermore, the present invention has an object to advantageously solve the above-mentioned problems, and is characterized by a method for forming a resist pattern of the present invention, comprising the steps of: (A) forming a resist film using the above-mentioned positive resist composition; (B) exposing the resist film; and (C) developing the exposed resist film using a developer. By exposing and developing the resist film formed using the above-mentioned positive resist composition, it is possible to form a resist pattern that has excellent dry etching resistance and clarity and has few defects.

[0018] In the method of forming a resist pattern of the present invention, the developer preferably contains an alcohol. By developing a resist film formed using the above-mentioned positive resist composition with a developer containing an alcohol, a resist pattern with even more excellent clarity can be formed. [Effects of the Invention]

[0019] The copolymer of the present invention can provide a main chain scission type positive resist that is excellent in dry etching resistance and clarity and is capable of forming a resist pattern with few defects. Furthermore, according to the positive resist composition of the present invention and the method of forming a resist pattern of the present invention using such a positive resist composition, it is possible to form a resist pattern that has excellent dry etching resistance and clarity, and also has few defects. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, embodiments of the present invention will be described in detail. In the present invention, the phrase "may have a substituent" means "unsubstituted or substituted".

[0021] The copolymer of the present invention can be suitably used as a main chain scission type positive resist in which the main chain is scissed and the molecular weight is reduced by irradiation with ionizing radiation such as an electron beam or short wavelength light such as ultraviolet light. Furthermore, the positive resist composition of the present invention comprises the copolymer of the present invention as a positive resist, and can be used, for example, when forming a resist pattern in the production processes of semiconductors, photomasks, molds, etc.

[0022] (copolymer) The copolymer of the present invention has the following formula (I): [ka] a monomer unit (A) represented by formula (I): wherein L is a single bond or a divalent linking group, and Ar is an aromatic ring group which may have a substituent; The following formula (II): [ka] [In formula (II), R 1 is an alkyl group, and R 2 is a hydrogen atom, an alkyl group, a halogen atom, a halogenated alkyl group, a hydroxyl group, a carboxylic acid group, or a halogenated carboxylic acid group, p is an integer of 0 to 5, and R 2 When a plurality of units are present, they may be the same or different. The copolymer of the present invention has a weight average molecular weight of 230,000 or more.

[0023] The copolymer of the present invention may contain any monomer unit other than the monomer unit (A) and the monomer unit (B). However, the proportion of the monomer unit (A) and the monomer unit (B) in the total monomer units constituting the copolymer is preferably 90 mol % or more, and more preferably 100 mol % (i.e., the copolymer contains only the monomer unit (A) and the monomer unit (B)).

[0024] Furthermore, since the copolymer of the present invention contains both the predetermined monomer unit (A) and the monomer unit (B), the main chain of the copolymer is more easily cleaved when irradiated with ionizing radiation or the like (e.g., electron beam, KrF laser, ArF laser, EUV laser, etc.) and has excellent heat resistance, compared to a homopolymer or the like containing only one of the monomer units. Furthermore, since the copolymer of the present invention has a weight average molecular weight of at least the above lower limit, it is possible to form a resist pattern that is excellent in dry etching resistance and clarity and has few defects.

[0025] <Monomer unit (A)> Here, the monomer unit (A) is represented by the following formula (III): [ka] [In formula (III), L and Ar are the same as in formula (I)].

[0026] The proportion of the monomer units (A) in all the monomer units constituting the copolymer is not particularly limited, and can be, for example, 30 mol % or more and 70 mol % or less.

[0027] Here, the divalent linking group that can constitute L in formula (I) and formula (III) is not particularly limited, and examples thereof include an alkylene group which may have a substituent and an alkenylene group which may have a substituent.

[0028] The alkylene group of the alkylene group which may have a substituent is not particularly limited and examples thereof include chain alkylene groups such as methylene, ethylene, propylene, n-butylene, and isobutylene, and cyclic alkylene groups such as 1,4-cyclohexylene. Among these, the alkylene group is preferably a chain alkylene group having 1 to 6 carbon atoms such as methylene, ethylene, propylene, n-butylene, and isobutylene, more preferably a linear alkylene group having 1 to 6 carbon atoms such as methylene, ethylene, propylene, and n-butylene, and even more preferably a linear alkylene group having 1 to 3 carbon atoms such as methylene, ethylene, and propylene.

[0029] The alkenylene group of the alkenylene group which may have a substituent is not particularly limited and examples thereof include chain alkenylene groups such as ethenylene, 2-propenylene, 2-butenylene, and 3-butenylene, and cyclic alkenylene groups such as cyclohexenylene. Of these, the alkenylene group is preferably a linear alkenylene group having 2 to 6 carbon atoms such as ethenylene, 2-propenylene, 2-butenylene, and 3-butenylene.

[0030] Among the above, from the viewpoint of sufficiently improving the sensitivity to ionizing radiation and the like and the heat resistance, the divalent linking group is preferably an alkylene group which may have a substituent, more preferably a chain alkylene group of 1 to 6 carbon atoms which may have a substituent, still more preferably a linear alkylene group of 1 to 6 carbon atoms which may have a substituent, and particularly preferably a linear alkylene group of 1 to 3 carbon atoms which may have a substituent.

[0031] Furthermore, from the viewpoint of further improving sensitivity to ionizing radiation, etc., the divalent linking group that can constitute L in formula (I) and formula (III) preferably has one or more electron-withdrawing groups. In particular, when the divalent linking group is an alkylene group having an electron-withdrawing group as a substituent or an alkenylene group having an electron-withdrawing group as a substituent, it is preferred that the electron-withdrawing group be bonded to the carbon that bonds to O adjacent to the carbonyl carbon in formula (I) and formula (III).

[0032] The electron-withdrawing group capable of sufficiently improving sensitivity to ionizing radiation and the like is not particularly limited, and examples thereof include at least one selected from the group consisting of a fluorine atom, a fluoroalkyl group, a cyano group, and a nitro group. The fluoroalkyl group is not particularly limited, and examples thereof include a fluoroalkyl group having 1 to 5 carbon atoms. Of these, the fluoroalkyl group is preferably a perfluoroalkyl group having 1 to 5 carbon atoms, and more preferably a trifluoromethyl group.

[0033] From the viewpoint of improving sensitivity to ionizing radiation and the like and dry etching resistance, L in formula (I) and formula (III) is preferably a methylene group, a cyanomethylene group, a trifluoromethylmethylene group, or a bis(trifluoromethyl)methylene group, and more preferably a bis(trifluoromethyl)methylene group.

[0034] Furthermore, Ar in the formula (I) and formula (III) includes an aromatic hydrocarbon ring group which may have a substituent and an aromatic heterocyclic group which may have a substituent.

[0035] 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 fluoranthene ring group, a pentacene ring group, a perylene ring group, a pentaphene ring group, a picene ring group, and a pyranthrene ring group.

[0036] Furthermore, the aromatic heterocyclic group is not particularly limited, and examples thereof include 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 ring group, and a carbazole ring group.

[0037] Furthermore, the substituent that Ar may have is not particularly limited, and examples thereof include an alkyl group, a fluorine atom, and a fluoroalkyl group. Examples of the alkyl group that Ar may have as a substituent include a chain alkyl group 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. Examples of the fluoroalkyl group that Ar may have as a substituent include a fluoroalkyl group having 1 to 5 carbon atoms, such as a trifluoromethyl group, a trifluoroethyl group, and a pentafluoropropyl group.

[0038] Among these, from the viewpoint of improving sensitivity to ionizing radiation and the like and dry etching resistance, Ar in formula (I) and formula (III) 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).

[0039] From the viewpoint of improving sensitivity to ionizing radiation and dry etching resistance, the monomer (a) represented by the above formula (III) capable of forming the monomer unit (A) represented by the above formula (I) is preferably benzyl α-chloroacrylate and 1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl α-chloroacrylate, more preferably 1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl α-chloroacrylate. That is, the copolymer preferably has at least one of 1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl α-chloroacrylate unit and benzyl α-chloroacrylate unit, more preferably 1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl α-chloroacrylate unit.

[0040] <Monomer unit (B)> The monomer unit (B) is represented by the following formula (IV): [ka] [In formula (IV), R 1 and R 2 and p is the same as in formula (II).

[0041] The proportion of the monomer units (B) in all the monomer units constituting the copolymer is not particularly limited, and can be, for example, 30 mol % or more and 70 mol % or less.

[0042] Here, R in formula (II) and formula (IV) 1 ~R 2 The alkyl group that can constitute R is not particularly limited, and examples thereof include unsubstituted alkyl groups having 1 to 5 carbon atoms. 1 ~R 2 The alkyl group that can constitute the group is preferably a methyl group or an ethyl group.

[0043] In addition, R in formula (II) and formula (IV)2 The halogen atom that can constitute the group is not particularly limited, and examples thereof include a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc. Among these, the halogen atom is preferably a fluorine atom or a chlorine atom, and more preferably a chlorine atom.

[0044] Furthermore, R in formula (II) and formula (IV) 2 The halogenated alkyl group that can constitute the above is not particularly limited, and examples thereof include fluoroalkyl groups having 1 to 5 carbon atoms. Among these, the halogenated alkyl group is preferably a perfluoroalkyl group having 1 to 5 carbon atoms, and more preferably a trifluoromethyl group.

[0045] Furthermore, R in formula (II) and formula (IV) 2 The halogenated carboxylic acid group that can constitute the above is not particularly limited, and examples thereof include a monochlorocarboxylic acid group, a dichlorocarboxylic acid group, a trichlorocarboxylic acid group, a monofluorocarboxylic acid group, a difluorocarboxylic acid group, and a trifluorocarboxylic acid group. Among these, the trifluorocarboxylic acid group is preferred as the halogenated carboxylic acid group.

[0046] From the viewpoint of facilitating the preparation of the copolymer and improving the scission property of the main chain when irradiated with ionizing radiation or the like, R 1 and R 2 However, it is preferably an alkyl group having 1 to 5 carbon atoms, and more preferably a methyl group.

[0047] Furthermore, from the viewpoint of easiness in preparing the copolymer and improving the severability of the main chain when irradiated with ionizing radiation or the like, p in formula (II) and formula (IV) is preferably 0 or 1.

[0048] The monomer (b) represented by the above formula (IV) which can form the monomer unit (B) represented by the above formula (II) is not particularly limited, and examples thereof include α-methylstyrene and its derivatives such as the following (b-1) to (b-12). [ka]

[0049] From the viewpoints of ease of preparation of the copolymer and improving the scission resistance of the main chain upon irradiation with ionizing radiation or the like and dry etching resistance, the monomer unit (B) is preferably a structural unit derived from α-methylstyrene (the above b-1), 4-isopropenyltoluene (the above b-2), or 4-chloro-α-methylstyrene (the above b-8), and from the viewpoint of further improving the clarity and dry etching resistance of the resulting resist pattern, the monomer unit (B) is more preferably a structural unit derived from α-methylstyrene. That is, from the viewpoint of further improving the clarity and dry etching resistance of the resulting resist pattern, the copolymer preferably contains an α-methylstyrene unit.

[0050] <Properties of copolymer> The copolymer must have a weight-average molecular weight of 230,000 or more, preferably greater than 230,000, more preferably greater than 240,010, even more preferably greater than 280,000, and even more preferably greater than 300,000. A weight-average molecular weight equal to or greater than the above-mentioned lower limit can improve the dry etching resistance and clarity of resist patterns formed using the copolymer. Furthermore, a weight-average molecular weight equal to or greater than the above-mentioned lower limit can prevent adjacent contact holes from interconnecting when forming a contact hole pattern using the copolymer, thereby improving resist pattern formability. Interconnection between adjacent contact holes can occur due to so-called open defects, which are caused by the copolymer in unexposed portions of the resist film dissolving in the developer. Furthermore, a weight-average molecular weight equal to or greater than the above-mentioned lower limit can prevent the top of the resist pattern from shrinking when forming a fine resist pattern using the copolymer. The upper limit of the weight-average molecular weight of the copolymer is not particularly limited, but from the viewpoint of ease of polymerization, it can be, for example, 900,000 or less.

[0051] Furthermore, the number-average molecular weight of the copolymer is preferably 70,000 or more, more preferably 80,000 or more, even more preferably 100,000 or more, and even more preferably 150,000 or more. When the number-average molecular weight of the copolymer is equal to or greater than the above-mentioned lower limit, the dry etching resistance and clarity of the resulting resist pattern can be improved, and the occurrence of interconnection between adjacent contact holes in the resulting resist pattern and reduction in the top of the resist pattern can be suppressed. The upper limit of the number-average molecular weight of the copolymer is not particularly limited, but from the viewpoint of ease of polymerization, it can be, for example, 500,000 or less. In this specification, the "number average molecular weight" can be measured using gel permeation chromatography as a value converted into standard polystyrene.

[0052] Furthermore, the molecular weight distribution of the copolymer is preferably 1.40 or more, more preferably 1.45 or more, and preferably 3.00 or less, more preferably 2.50 or less. If the molecular weight distribution of the copolymer is equal to or greater than the above lower limit, the ease of preparation of the polymer can be improved. Furthermore, if the molecular weight distribution of the copolymer is equal to or less than the above upper limit, the clarity of the obtained resist pattern can be further improved. In this specification, 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).

[0053] Furthermore, the copolymer preferably contains 20% or less of components having a molecular weight of less than 50,000, more preferably 15% or less, even more preferably 10% or less, and even more preferably 8% or less. The copolymer may contain no components having a molecular weight of less than 50,000. When the copolymer contains components having a molecular weight of less than 50,000 that are equal to or less than the upper limit mentioned above, the copolymer can have more excellent dry etching resistance and clarity, and can form a resist pattern with fewer defects.

[0054] Furthermore, the copolymer preferably has a proportion of components having a molecular weight of less than 100,000 of 30% or less, more preferably 28% or less, even more preferably 25% or less, even more preferably 20% or less, and particularly preferably 10% or less. The copolymer may contain no components having a molecular weight of less than 100,000. When the proportion of components having a molecular weight of less than 100,000 in the copolymer is equal to or less than the upper limit mentioned above, a resist pattern having even more excellent dry etching resistance and clarity and fewer defects can be formed.

[0055] Furthermore, the copolymer preferably contains 10% or more of components having a molecular weight of over 500,000, more preferably 16% or more, and even more preferably 19% or more. When the proportion of components having a molecular weight of over 500,000 in the copolymer is equal to or greater than the above-mentioned lower limit, the copolymer can have more excellent dry etching resistance and clarity, and can form a resist pattern with fewer defects. The proportion of components having a molecular weight of over 500,000 in the copolymer is not particularly limited, but from the viewpoint of ease of preparation, it can be 80% or less.

[0056] The copolymer was then subjected to electron beam irradiation at a dose of 20 μC / cm 2 Weight average molecular weight Mw when exposed to light 20 and an electron beam irradiation dose of 40 μC / cm 2 Weight average molecular weight Mw when exposed to light 40 The difference between the weight average molecular weight Mw and the copolymer is preferably 12,100 or more, more preferably 16,000 or more, and even more preferably 17,000 or more. If the sensitivity of the copolymer to electron beams satisfies the above conditions, a resist pattern with even better clarity and fewer defects can be formed. 20 and weight average molecular weight Mw 40 The upper limit of the difference between the weight average molecular weight Mw and the 20 and weight average molecular weight Mw 40 It is presumed that the difference between the weight average molecular weight Mw and the weight average molecular weight Mw is equal to or greater than the lower limit, which means that the copolymer has very high sensitivity to electron beams, the rate of molecular weight reduction when irradiated with electron beams is high, and the copolymer in the exposed portion of the resist film can be targeted and reliably reduced in molecular weight. 20 and weight average molecular weight Mw 40 It is presumed that a copolymer in which the difference between is equal to or greater than the above lower limit will enable the formation of a resist pattern with even better clarity and fewer defects.

[0057] Furthermore, when the metal content of the copolymer is measured according to the method described in the Examples, the potassium content is preferably 300 ppb or less, more preferably 200 ppb or less, and even more preferably 100 ppb or less, and the sodium content is preferably 1,000 ppb or less, more preferably 500 ppb or less, even more preferably 100 ppb or less, and even more preferably 50 ppb or less. When the metal content of the copolymer is below the above-mentioned upper limit, it is possible to form a resist pattern with even better dry etching resistance and clarity, and with fewer defects. By reducing the metal content of the copolymer, it is possible to suppress local absorption of ionizing radiation such as electron beams and short-wavelength light such as ultraviolet light in a resist composed of the copolymer. Therefore, by controlling the metal content of the copolymer below the above-mentioned upper limit, it is possible to prevent pattern defects in a resist pattern formed using such a copolymer. The copolymer may also be metal-free. Here, the metal content of the copolymer can be adjusted by purifying the polymer obtained by polymerizing the monomer composition according to a predetermined method, as described below. The metal content of the copolymer can also be measured according to the method described in the Examples.

[0058] (Method for preparing copolymer) The copolymer having the above-mentioned monomer unit (A) and monomer unit (B) can be prepared, for example, by polymerizing a monomer composition containing the monomer (a) and the monomer (b), recovering the obtained copolymer, and optionally purifying it. The composition, molecular weight distribution, weight-average molecular weight, and number-average molecular weight of the copolymer can be adjusted by changing the polymerization conditions and purification conditions. Specifically, for example, the weight-average molecular weight and number-average molecular weight can be reduced by increasing the polymerization temperature. The weight-average molecular weight and number-average molecular weight can also be reduced by shortening the polymerization time. Furthermore, the molecular weight distribution can be narrowed by performing purification.

[0059] <Polymerization of Monomer Composition> The monomer composition used to prepare the copolymer of the present invention can be a mixture of monomer components including monomer (a) and monomer (b), an optional solvent, a polymerization initiator, and optional additives. The emulsion polymerization method can be suitably employed for polymerizing the monomer composition. Water is a suitable solvent for use in emulsion polymerization. An anionic surfactant composed of an alkali salt of a higher fatty acid, such as partially hydrogenated beef tallow fatty acid potassium soap, can be suitably used as the surfactant for emulsion polymerization. A water-soluble initiator, such as potassium persulfate, can be suitably used as the polymerization initiator for emulsion polymerization. Furthermore, a buffer, such as sodium carbonate, can be optionally used for emulsion polymerization.

[0060] Furthermore, 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, and then dropping the solution to which the good solvent has been added into a poor solvent such as methanol to solidify the polymer, without any particular limitation.

[0061] <Purification of polymer> The purification method used to purify the obtained polymer is not particularly limited, and examples thereof include known purification methods such as reprecipitation and column chromatography. Purification by reprecipitation, column chromatography, or the like can remove at least a portion of various metal components, including potassium and sodium, that may be inevitably mixed in due to reagents, synthesis vessels, and the like when preparing the copolymer. Among these, reprecipitation is preferred as the purification method from the viewpoint of ease. The purification of the polymer may be repeated multiple times. By repeating the purification, the amount of various metal components that may be contained in the copolymer can be further reduced.

[0062] 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 dropping the obtained solution into a mixed solvent of a good solvent such as tetrahydrofuran and a poor solvent such as methanol to precipitate a portion of the polymer. In this way, by dropping the polymer solution into a mixed solvent of a good solvent and a poor solvent to perform purification, the molecular weight distribution, weight average molecular weight, and number average molecular weight of the obtained copolymer can be easily adjusted by changing the type and mixing ratio of the good solvent and poor solvent. Specifically, for example, 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.

[0063] When purifying a polymer by reprecipitation, the copolymer of the present invention may be a polymer precipitated in a mixed solvent of a good solvent and a poor solvent, or a polymer not precipitated in the mixed solvent (i.e., a polymer dissolved in the mixed solvent) as long as it has the desired properties. The polymer not precipitated in the mixed solvent can be recovered from the mixed solvent by a known method such as concentration to dryness.

[0064] (Positive resist composition) The positive resist composition of the present invention comprises the above-mentioned copolymer and a solvent, and optionally further contains known additives that can be incorporated into resist compositions. Because the positive resist composition of the present invention contains the above-mentioned copolymer as a positive resist, it can be suitably used to form a resist film, and when used to form a resist pattern, it is possible to form a resist pattern that has excellent dry etching resistance and clarity.

[0065] <Solvent> There are no particular restrictions on the solvent as long as it is capable of dissolving the copolymer described above, and it is possible to use known solvents such as those described in Japanese Patent No. 5938536. Among these, from the perspective of obtaining a positive resist composition with an appropriate viscosity and improving the coatability of the positive resist composition, it is preferable to use anisole, propylene glycol monomethyl ether acetate (PGMEA), cyclopentanone, cyclohexanone, or isoamyl acetate as the solvent.

[0066] <Preparation of Positive Resist Composition> The positive resist composition can be prepared by mixing the above-mentioned copolymer, solvent, and any known additives that can be used. The mixing method is not particularly limited, and the components can be mixed by any known method. Alternatively, the resist composition can be prepared by mixing the components and then filtering the mixture.

[0067] 〔filtration〕 The method for filtering the mixture is not particularly limited, and the mixture can be filtered using a filter, for example. The filter is not particularly limited, and examples include fluorocarbon, cellulose, nylon, polyester, and hydrocarbon-based filter membranes. Among these, from the perspective of effectively preventing impurities such as metals from being mixed into the positive resist composition from metal piping, etc., which may be used during the preparation of the copolymer, preferred filter materials include nylon, polyethylene, polypropylene, polytetrafluoroethylene, polyfluorocarbons such as Teflon (registered trademark), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers (PFA), nylon, and composite membranes of polyethylene and nylon. Filters such as those disclosed in U.S. Patent No. 6,103,122 may also be used. Filters are also commercially available, such as Zeta Plus (registered trademark) 40Q manufactured by CUNO Incorporated. Furthermore, the filter may contain a strong or weak cationic ion exchange resin. The average particle size of the ion exchange resin is not particularly limited, but is preferably 2 μm or more and 10 μm or less. Examples of 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 polymers containing sulfonic or carboxylic acid groups. + Counterion, NH4 + Counterions or alkali metal counterions, e.g., K + and Na + Counterions are provided. Preferably, the cation exchange resin has hydrogen counterions. Examples of such cation exchange resins include H + Sulfonated styrene-divinylbenzene copolymers with counterions, such as Microlite® PrCH from Purolite, are commercially available as AMBERLYST® from Rohm and Haas.

[0068] Furthermore, the pore size of the filter is preferably from 0.001 μm to 1 μm. If the pore size of the filter is within this range, it is possible to sufficiently prevent impurities such as metals from being mixed into the positive resist composition.

[0069] (Method for forming a resist pattern) The method for 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 using a developer (developing step).The method for forming a resist pattern of the present invention may further include a step of removing the developer after the developing step (developer removing step).The method for forming a resist pattern of the present invention may further include a step of heating the exposed resist film (post-exposure bake step) between the exposure step and the developing step.

[0070] Furthermore, in the method of forming a resist pattern of the present invention, a positive resist composition containing a specified copolymer is used as the positive resist, so a resist pattern with excellent dry etching resistance can be formed.

[0071] (Resist film formation process) In the resist film formation process, the positive resist composition described above is applied to a workpiece, such as a substrate, to be processed using the resist pattern (or to the underlayer film, if one is formed, to the underlayer film), and the applied positive resist composition is dried to form a resist film. The substrate is not particularly limited, and examples include substrates having an insulating layer and copper foil provided on the insulating layer, such as those used in the manufacture of printed circuit boards. The application and drying methods for the positive resist composition are also not particularly limited, and methods commonly used in the formation of resist films can be used. Among these, heating (prebaking) is preferred as the drying method. The prebaking temperature is preferably 100°C or higher, more preferably 120°C or higher, and even more preferably 140°C or higher, from the viewpoint of improving the film density of the resist film. From the viewpoint of reducing changes in the molecular weight and molecular weight distribution of the copolymer in the resist film before and after prebaking, the prebaking temperature is preferably 250°C or lower, more preferably 220°C or lower, and even more preferably 200°C or lower. Furthermore, from the viewpoint of improving the film density of the resist film formed after prebaking, the prebaking time is preferably 10 seconds or longer, more preferably 20 seconds or longer, and even more preferably 30 seconds or longer; from the viewpoint of reducing changes in the molecular weight and molecular weight distribution of Copolymer A and Copolymer B in the resist film before and after prebaking, the prebaking time is preferably 10 minutes or shorter, more preferably 5 minutes or shorter, and even more preferably 3 minutes or shorter.

[0072] -substrate- Here, the substrate on which a 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 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.

[0073] Examples of substrate materials include inorganic materials such as metals (silicon, copper, chromium, iron, aluminum, etc.), glass, titanium oxide, silicon dioxide (SiO2), silica, and mica; nitrides such as SiN; oxynitrides such as SiON; and organic materials such as acrylic, polystyrene, cellulose, cellulose acetate, and phenolic resin. Among these, metals are preferred as substrate materials. Examples of substrates that can be used include silicon substrates, silicon dioxide substrates, and copper substrates, and preferably silicon substrates or silicon dioxide substrates.

[0074] 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.

[0075] Furthermore, the surface of the substrate may be subjected to a surface treatment as necessary. For example, in the case of a substrate having hydroxyl groups on its surface layer, the surface of the substrate can be treated with 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 described below, or between the substrate and the resist film. In this case, the silane coupling agent is not particularly limited, but hexamethyldisilazane is preferred.

[0076] Optionally, an underlayer film forming step may be carried out prior to the resist film forming step. In the underlayer film forming step, an underlayer film is formed on a substrate. By providing the underlayer film on the substrate, the surface of the substrate is made hydrophobic. This increases the affinity between the substrate and the resist film, thereby improving the adhesion between the substrate and the resist film. The underlayer film may be an inorganic underlayer film or an organic underlayer film.

[0077] The inorganic underlayer film can be formed by applying an inorganic material onto a substrate and then baking it, etc. Examples of inorganic materials include silicon-based materials.

[0078] The organic underlayer film can be formed by applying an organic material to a substrate to form a coating film and drying it. The organic material is not limited to those sensitive to light or electron beams, and can include, for example, resist materials and resin materials commonly used in the semiconductor and liquid crystal fields. Among these, the organic material is preferably a material capable of forming 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 a resist film, thereby transferring the pattern to the underlayer film and forming a pattern in the underlayer film. Among these, the organic material is preferably a material capable of forming an organic underlayer film that can be etched by oxygen plasma etching or the like. Examples of organic materials used to form the organic underlayer film include AL412 from Brewer Science.

[0079] 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 baking. 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, and 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 the coating film is not particularly limited, but is preferably 10 nm or higher and 100 nm or lower.

[0080] (Exposure process) In the exposure step, the resist film formed in the resist film formation step is irradiated with ionizing radiation or light to write a desired pattern. Note that the ionizing radiation or light can be irradiated using a known writing device such as an electron beam writing device or a laser writing device.

[0081] (Post-exposure bake process) In the optional post-exposure bake step, the resist film exposed in the exposure step is heated. By performing the post-exposure bake step, the surface roughness of the resist pattern can be reduced. In the method for forming a resist pattern of the present invention, since the copolymer described above is used as a positive resist, the clarity of the resist pattern is significantly improved when the post-exposure bake step is performed.

[0082] Here, the heating temperature is preferably 85° C. or higher, more preferably 90° C. or higher, and is preferably 160° C. or lower, more preferably 140° C. or lower, even more preferably 130° C. or lower, and particularly preferably 120° C. or lower. When 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.

[0083] Furthermore, the time for heating the resist film in the post-exposure bake step (heating time) is preferably 30 seconds or longer, and more preferably 1 minute or longer. A heating time of 30 seconds or longer can sufficiently reduce the surface roughness of the resist pattern while improving the clarity of the resist pattern. On the other hand, from the viewpoint of production efficiency, the heating time is, for example, preferably 7 minutes or shorter, more preferably 6 minutes or shorter, and even more preferably 5 minutes or shorter.

[0084] The method for heating the resist film in the post-exposure bake step is not particularly limited, and examples thereof 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.

[0085] (Development process) In the development step, the exposed resist film is developed using a developer to form a developed film on the workpiece. Here, the development of the resist film can be carried out, for example, by bringing the resist film into contact with a developer. The method for bringing the resist film into contact 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.

[0086] <Developer> The developer can be appropriately selected depending on the properties of the copolymer described above. Specifically, when selecting a developer, it is preferable to select a developer that does not dissolve the resist film before the exposure step, but can dissolve the exposed portion of the resist film after the exposure step. Furthermore, one type of developer may be used alone, or two or more types may be mixed in any ratio. Examples of the developer include hydrofluorocarbons such as 1,1,1,2,3,4,4,5,5,5-decafluoropentane (CF3CFHCFHCF2CF3), 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-pentafluorohexane. Hydrochlorofluorocarbons such as propane (CF3CF2CHCl2) and 1,3-dichloro-1,1,2,2,3-pentafluoropropane (CClF2CF2CHClF), hydrofluoroethers such as methyl nonafluorobutyl ether (CF3CF2CF2CF2OCH3), methyl nonafluoroisobutyl ether, ethyl nonafluorobutyl ether (CF3CF2CF2CF2OC2H5), ethyl nonafluoroisobutyl ether, and perfluorohexyl methyl ether (CF3CF2CF(OCH3)C3F7), and CF4, C2F6, C3F8, C4F8, C4F 10 , C5F 12 , C6F 12 , C6F 14 , C7F 14 , C7F 16 , C8F 18, C9F 20 fluorine-based solvents such as perfluorocarbons such as methyl methacrylate, ...

[0087] The temperature of the developer during development is not particularly limited, but can be, for example, 21° C. to 25° C. The development time can be, for example, 30 seconds to 4 minutes.

[0088] (Developer removal process) In the method for forming a resist pattern of the present invention, a step of removing the developer may be carried out after the development step. The developer can be removed, for example, by air blowing using nitrogen or the like, or by rinsing using a rinse solution.

[0089] (etching process) In the etching step, which can be carried out optionally, the underlying film and / or the substrate are etched using the resist pattern as a mask to form a pattern in the underlying film and / or the substrate. The number of etching steps is not particularly limited and may be one or more. Etching may be either dry or wet, with dry etching being preferred. Dry etching can be performed using a known dry etching apparatus. The etching gas used in dry etching can be appropriately selected depending on the elemental composition of the underlying film and substrate to be etched. Examples of etching gases 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, NH3, and BCl3; and inert gases such as He, N2, and Ar. These gases may be used alone or in combination. For dry etching of inorganic underlying films, oxygen-based gases are typically used. Furthermore, for dry etching of the substrate, a fluorine-based gas is usually used, and a mixture of a fluorine-based gas and an inert gas is preferably used.

[0090] Furthermore, if necessary, the underlayer film remaining on the substrate may be removed before or after etching the substrate. When the underlayer film is removed before etching the substrate, the underlayer film may be a patterned or unpatterned underlayer film.

[0091] Here, examples of methods for removing the underlayer film include the above-mentioned dry etching. In the case of an inorganic underlayer film, the underlayer film may be removed by contacting the underlayer film with a liquid such as a basic or 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 it allows the underlayer film and alkaline hydrogen peroxide to come into contact with each other for a certain period of time under heated conditions. Examples 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.

[0092] Below, an example of a method for forming a resist pattern using a positive resist of the present invention and a method for etching an underlayer film and a substrate using the formed resist pattern will be described. However, since the substrate used in the following example and the conditions in each step can be the same as the substrate and conditions in each step described above, explanations will be omitted below. It should be noted that the method for forming a resist pattern of the present invention is not limited to the method shown in the following example.

[0093] An example of the resist pattern forming method is a resist pattern forming method using an electron beam or EUV, which includes the above-mentioned underlayer film forming step, resist film forming step, exposure step, development step, and rinsing step.An example of the etching method is a method in which a resist pattern formed by the resist pattern forming method is used as a mask, and includes an etching step.

[0094] Specifically, in the underlayer film forming step, an inorganic material is applied onto a substrate and then baked to form an inorganic underlayer film. Next, in the resist film forming step, 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. Then, in the exposure process, the resist film formed in the resist film formation process is irradiated with EUV light to draw a desired pattern. Furthermore, in 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. Then, in the rinsing step, the resist film developed in the developing step is brought into contact with a rinsing liquid to rinse the developed resist film.

[0095] Then, in an etching step, the underlying film is etched using the resist pattern as a mask to form a pattern in the underlying film. Next, the substrate is etched using the patterned underlayer film as a mask to form a pattern on the substrate. [Example]

[0096] The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. In the examples and comparative examples, the various attributes of the copolymers obtained were measured and evaluated according to the following methods.

[0097] <Weight average molecular weight, number average molecular weight and molecular weight distribution> The weight average molecular weight (Mw) and number average molecular weight (Mn) of the obtained copolymer were measured by gel permeation chromatography, and the molecular weight distribution (Mw / Mn) was calculated. Specifically, using a gel permeation chromatograph (Tosoh Corporation, HLC-8220) and tetrahydrofuran as a developing solvent, the weight-average molecular weight (Mw) and number-average molecular weight (Mn) of the copolymer were determined in terms of standard polystyrene, and the molecular weight distribution (Mw / Mn) was calculated. <Proportion of each molecular weight component in the copolymer> A chromatogram of the copolymer was obtained using a gel permeation chromatograph (Tosoh Corporation, HLC-8220) and tetrahydrofuran as the developing solvent. The molecular weight in the chromatogram was based on the weight-average molecular weight of standard polystyrene. From the obtained chromatogram, the total peak area (A), the sum of the peak areas of components with molecular weights less than 50,000 (B), the sum of the peak areas of components with molecular weights less than 100,000 (C), and the sum of the peak areas of components with molecular weights greater than 500,000 (D) were calculated. The proportion of each molecular weight component was calculated using the following formula. Percentage of components with molecular weight less than 50,000 (%) = (B / A) x 100 Percentage of components with molecular weight less than 100,000 (%) = (C / A) x 100 Percentage of components with molecular weights greater than 500,000 (%) = (D / A) x 100 <Weight average molecular weight and molecular weight difference after electron beam irradiation (Mw 20 -Mw 40 )> Using a spin coater (MS-A150 manufactured by Mikasa), the positive resist compositions (copolymer concentration: 8% by mass) prepared in the examples and comparative examples were applied to a silicon wafer with a diameter of 4 inches to a thickness of 500 nm. The applied positive resist composition was then heated on a hot plate at a temperature of 160°C for 5 minutes to form a resist film on the silicon wafer. The formed resist film was used as a sample, and the entire surface of each sample was coated with a 500 nm thick film under vacuum at an acceleration voltage of 50 kV and an irradiation dose of 20 μC / cm. 2 or 40 μC / cm 2 The entire surface was irradiated with an electron beam using a lithography system ("EB ENGINE" manufactured by Hamamatsu Photonics K.K.) under the following conditions. After irradiation, the resist film was subjected to gel permeation chromatography under the following conditions. 2 Weight average molecular weight Mw when exposed to light 20 and an electron beam irradiation dose of 40 μC / cm 2 Weight average molecular weight Mw when exposed to light 40In the gel permeation chromatography, a gel permeation chromatograph (HLC-8220, manufactured by Tosoh Corporation) was used, and tetrahydrofuran was used as a developing solvent, and the weight average molecular weight (Mw) was calculated as a value converted into standard polystyrene. And the electron beam irradiation dose was 20 μC / cm 2 Weight average molecular weight Mw when exposed to light 20 and an electron beam irradiation dose of 40 μC / cm 2 Weight average molecular weight Mw when exposed to light 40 The difference was calculated. <Metal content of copolymer> A 1.5% copolymer solution of isoamyl acetate prepared using the copolymers obtained in the Examples and Comparative Examples was heated on a hooded heater to dry the sample, which was then incinerated in an electric furnace. After cooling, the ash was completely dissolved in acid to prepare the test solution, which was then diluted appropriately and measured using an ICP mass spectrometer (Agilent Technologies, Inc., "Agilent 7900 ICP-MS"). The calibration curve was obtained using the absolute calibration curve method, with the measurement mode set to cool. <Sensitivity and gamma value> Using a spin coater (MS-A150, manufactured by Mikasa), the positive resist compositions (copolymer concentration: 8% by mass) prepared in the examples and comparative examples were applied to a silicon wafer with a diameter of 4 inches to a thickness of 500 nm. The applied positive resist composition was then heated on a hot plate at 160°C for 5 minutes to form a resist film on the silicon wafer. Then, using an electron beam lithography device (ELS-S50, manufactured by Elionix), multiple patterns (dimensions 500 μm × 500 μm) with different electron beam irradiation doses were written on the resist film. Development was carried out for 1 minute at 23°C using isopropyl alcohol as the resist developer, and the developer was then removed by nitrogen blowing. The electron beam irradiation dose was 4 μC / cm 2 to 200 μC / cm 2 Within the range of 4μC / cm 2Next, the thickness of the resist film in the written area was measured using an optical film thickness meter (Lambda Ace, manufactured by SCREEN Semiconductor Solutions), and a sensitivity curve was created showing the relationship between the common logarithm of the total electron beam dose and the remaining film ratio of the resist film after development (= film thickness of the resist film after development / film thickness of the resist film formed on the silicon wafer). Then, for the obtained sensitivity curve (horizontal axis: common logarithm of the total irradiation dose of the electron beam, vertical axis: remaining film ratio of the resist film (0≦remaining film ratio≦1.00)), the sensitivity curve was fitted to a quadratic function in the range of remaining film ratio 0.20 to 0.80, and a straight line (an approximation line of the slope of the sensitivity curve) connecting the point of remaining film ratio 0 and the point of remaining film ratio 0.50 on the obtained quadratic function (a function of remaining film ratio and common logarithm of the total irradiation dose) was created. In addition, the total irradiation dose E of the electron beam when the remaining film ratio of the obtained line (a function of remaining film ratio and common logarithm of the total irradiation dose) becomes 0 was calculated. th (μC / cm 2 ) was calculated. th The smaller the value of , the higher the sensitivity, indicating that the copolymer as a positive resist can be successfully cleaved with a small amount of irradiation. The γ value was calculated using the following formula. In the formula, E0 is the logarithm of the total irradiation dose obtained by fitting the sensitivity curve to a quadratic function over the range of film retention ratios of 0.20 to 0.80 and substituting a film retention ratio of 0 for the obtained quadratic function (a function of the film retention ratio and the common logarithm of the total irradiation dose). Furthermore, E1 is the logarithm of the total irradiation dose obtained by creating a line (an approximation line of the slope of the sensitivity curve) connecting the point of film retention ratio 0 and the point of film retention ratio 0.50 on the obtained quadratic function and substituting a film retention ratio of 1.00 for the obtained line (a function of the film retention ratio and the common logarithm of the total irradiation dose). The formula below represents the slope of the line between film retention ratios of 0 and 1.00. The larger the γ value, the steeper the slope of the sensitivity curve, indicating that clearer patterns can be formed.

number

[0098] Example 1 <Preparation of copolymer> [Preparation of an aqueous solution of partially hardened beef tallow fatty acid potassium soap with a solid content of 18%] 100 g of ion-exchanged water was prepared and heated to 70°C while stirring, and 8.40 g of potassium hydroxide (49% aqueous solution) was added. Next, 19.6 g of beef tallow 45° hydrogenated fatty acid HFA (NOF Corporation) was added at a rate of 1.28 g / min, followed by 0.126 g of potassium silicate. The mixture was then stirred at 80°C for more than 2 hours to obtain an aqueous solution of semi-hydrogenated beef tallow fatty acid potassium soap with a solids content of 18%. [Synthesis of polymers] A glass ampoule containing a stirrer was charged with 3.00 g of α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl (below formula) as monomer (a), 2.712 g of α-methylstyrene as monomer (b), and 0.0011 g of potassium persulfate as a polymerization initiator. Furthermore, a solution of 0.5463 g of the above-prepared semi-hardened beef tallow fatty acid potassium soap with an 18% solids content, 6.771 g of ion-exchanged water, and 0.0047 g of sodium carbonate was added to the same ampoule to prepare a monomer composition. The ampoule was then sealed, and the system was pressurized and depressurized with nitrogen gas 10 times to remove oxygen from the system. [ka] The system was then heated to 40°C and the polymerization reaction was carried out for 6 hours. Next, 10 g of tetrahydrofuran was added to the system, and the resulting solution was added dropwise to 300 mL of methanol to precipitate a polymer. The precipitated polymer was then recovered by filtration. The resulting polymer was a copolymer containing 50 mol% each of α-methylstyrene units and α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units. Various attributes of the resulting copolymer were measured. The results are shown in Table 1. <Preparation of Positive Resist Composition> The obtained copolymer was dissolved in isoamyl acetate as a solvent to prepare resist solutions (positive resist compositions) with copolymer concentrations of 8 mass % and 1.7 mass %, respectively. The sensitivity and γ value of the copolymer were evaluated using a positive resist composition consisting of a resist solution with a copolymer concentration of 8% by mass. Furthermore, the formability of the resist pattern was evaluated using a positive resist composition consisting of a resist solution with a copolymer concentration of 1.7% by mass. The results are shown in Table 1.

[0099] Examples 2 to 5 A copolymer and a positive resist composition were prepared in the same manner as in Example 1, except that the polymer was purified as follows during preparation of the copolymer. Various measurements and evaluations were then carried out in the same manner as in Example 1. The results are shown in Table 1. [Purification of polymer] The polymer recovered by filtration was dissolved in 10 g of tetrahydrofuran (THF), and the resulting solution was added dropwise to 100 g of a mixed solvent of THF and methanol (MeOH) to precipitate a white coagulate (a copolymer containing α-methylstyrene units and α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units). The solution containing the precipitated copolymer was then filtered through a Kiriyama funnel to obtain a white copolymer (a copolymer containing 50 mol% each of α-methylstyrene units and α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units). The composition (THF:MeOH (mass ratio)) of the mixed solvent used in each example was 33:67 (Example 2), 34:66 (Example 3), 35:65 (Example 4), and 36:64 (Example 5), respectively. Various attributes of the resulting copolymer were then measured. The results are shown in Table 1. The obtained copolymer contained 50 mol % each of α-methylstyrene units and α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units.

[0100] Example 6 A polymer was obtained in the same manner as in Example 1, except that potassium persulfate, a polymerization initiator, was not added to the monomer composition during the synthesis of the polymer, and the polymerization reaction time was changed to 11 hours. The obtained polymer was a copolymer containing 50 mol% each of α-methylstyrene units and α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units. Various attributes of the obtained copolymer were measured. The results are shown in Table 1. A positive resist composition was then prepared using the resulting copolymer in the same manner as in Example 1, and various evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0101] (Examples 7 to 13) A copolymer and a positive resist composition were prepared in the same manner as in Example 6, except that the polymer was purified as follows during preparation of the copolymer. Various measurements and evaluations were then carried out in the same manner as in Example 1. The results are shown in Table 1. [Purification of polymer] The polymer recovered by filtration was dissolved in 10 g of tetrahydrofuran (THF), and the resulting solution was added dropwise to 100 g of a mixed solvent of THF and methanol (MeOH) to precipitate a white coagulated product (a copolymer containing α-methylstyrene units and α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units). The solution containing the precipitated copolymer was then filtered through a Kiriyama funnel to obtain a white copolymer (a copolymer containing 50 mol% each of α-methylstyrene units and α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units). The composition of the mixed solvent (THF:MeOH (mass ratio)) used in each example was 32:68 (Example 7), 33:67 (Example 8), 34:66 (Example 9), 35:65 (Example 10), 36:64 (Example 11), and 37:63 (Example 12), respectively. The copolymer thus obtained was subjected to measurement of various properties, and the results are shown in Table 1. The obtained copolymer contained 50 mol % each of α-methylstyrene units and α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units.

[0102] Example 13 A copolymer and a positive resist composition were prepared in the same manner as in Example 8 (i.e., the polymerization reaction time was 11 hours, and the mixed solvent used during purification had a THF:MeOH (mass ratio) of 33:67), except that 3.034 g of 4-isopropenyltoluene (see formula below) was used as monomer (b) in the synthesis of the polymer. Various measurements and evaluations were then carried out in the same manner as in Example 1. The results are shown in Table 1. The obtained copolymer contained 50 mol% each of 4-isopropenyltoluene units and α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units. [ka]

[0103] Example 14 In synthesizing the polymer, various measurements and evaluations were carried out in the same manner as in Example 9 (i.e., the polymerization reaction time was 11 hours, and the composition of the mixed solvent used during purification was THF:MeOH (mass ratio) = 34:66), except that 3.502 g of 4-chloro-α-methylstyrene (see formula below) was used as monomer (b). The results are shown in Table 1. The obtained copolymer contained 50 mol% each of 4-chloro-α-methylstyrene units and α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units. [ka]

[0104] (Comparative Example 1) A positive resist composition was prepared in the same manner as in Example 1, except that a copolymer prepared as follows was used. Various measurements and evaluations were then carried out in the same manner as in Example 1. The results are shown in Table 1. <Preparation of copolymer> [Synthesis of polymers] 3.00 g of α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl as the monomer (a), 2.493 g of α-methylstyrene as the monomer (b), and 0.0039534 g of azobisisobutyronitrile as a polymerization initiator were placed in a glass ampoule containing a stirrer, and the ampoule was sealed. The system was then pressurized and depressurized with nitrogen gas 10 times to remove oxygen from the system. The system was then heated to 78°C and reacted for 3.5 hours. Next, 10 g of tetrahydrofuran was added to the system, and the resulting solution was added dropwise to 300 mL of methanol to precipitate a polymer. The precipitated polymer was then recovered by filtration. Various properties of the resulting copolymer were measured. The results are shown in Table 1. The obtained copolymer contained 50 mol % each of α-methylstyrene units and α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units.

[0105] (Comparative Example 2) A copolymer and a positive resist composition were prepared in the same manner as in Comparative Example 1, except that the polymer was purified as follows during preparation of the copolymer. Various measurements and evaluations were then carried out in the same manner as in Example 1. The results are shown in Table 1. [Purification of polymer] The polymer obtained in the same manner as in Comparative Example 1 was dissolved in 100 g of tetrahydrofuran (THF), and the resulting solution was added dropwise to a mixed solvent of 250 g of THF and 750 g of methanol (MeOH), resulting in the precipitation of a white coagulated product (a copolymer containing α-methylstyrene units and α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units). The solution containing the precipitated copolymer was then filtered through a Kiriyama funnel to obtain a white copolymer. The resulting copolymer contained 50 mol% each of α-methylstyrene units and α-chloroacrylate-1-phenyl-1-trifluoromethyl-2,2,2-trifluoroethyl units.

[0106] (Comparative Example 3) <Polymer synthesis> 0.5463 g of an 18% solids aqueous solution of semi-hardened beef tallow fatty acid potassium soap prepared in the same manner as in Example 1 was placed in a separable flask and dissolved in 6.771 g of ion-exchanged water. 3 g of methyl α-chloroacrylate and 7.227 g of α-methylstyrene were added as monomers and emulsified with vigorous stirring. After purging the flask with nitrogen, 0.0027 g of sodium dithionite, 0.001 g of sodium iron ethylenediaminetetraacetate trihydrate, 0.0025 g of tetrasodium ethylenediaminetetraacetate tetrahydrate, 0.0015 g of sodium formaldehyde sulfoxylate, and 0.00524 g of cumene hydroperoxide were added in that order and stirred at 5°C for 48 hours. 100 g of methanol was added dropwise to the reaction solution, and the precipitated solid was filtered off. The resulting solid was then dried to obtain a copolymer containing α-methylstyrene units and α-chloroacrylate methyl units. The resulting copolymer was subjected to measurement of various properties, and the results are shown in Table 1. The copolymer contained 47 mol % of α-methylstyrene units and 53 mol % of α-chloroacrylate methyl units. <Preparation of Positive Resist Composition> The obtained copolymer was dissolved in anisole as a solvent to prepare resist solutions (positive resist compositions) with copolymer concentrations of 8 mass % and 1.7 mass %, respectively. The sensitivity and γ value of the copolymer were evaluated using a positive resist composition consisting of a resist solution with a copolymer concentration of 8% by mass. Furthermore, the formability of the resist pattern was evaluated using a positive resist composition consisting of a resist solution with a copolymer concentration of 1.7% by mass. The results are shown in Table 1. When a developer was used in various evaluations, a developer consisting of hexyl acetate (N60, manufactured by Nippon Zeon Co., Ltd.) was used. After the development process in various evaluations, instead of removing the developer by nitrogen blowing, the sample was rinsed with isopropyl alcohol for 10 seconds.

[0107] [Table 1]

[0108] Table 1 shows that when the copolymers of Examples 1 to 14 were used, it was possible to form resist patterns that were superior in dry etching resistance and clarity and had fewer defects, compared to when the copolymers of Comparative Examples 1 and 2, which had a weight-average molecular weight of less than 230,000, were used, and when the copolymer of Comparative Example 3, which did not have the specified monomer unit (A), was used. [Industrial Applicability]

[0109] The copolymer of the present invention can provide a main chain scission type positive resist that is excellent in dry etching resistance and clarity and is capable of forming a resist pattern with few defects. Furthermore, according to the positive resist composition of the present invention and the method of forming a resist pattern of the present invention using such a positive resist composition, it is possible to form a resist pattern that has excellent dry etching resistance and clarity, and also has few defects.

Claims

1. The following formula (I): 【Chemistry 1】 [In formula (I), L represents a single bond or a divalent linking group, and Ar represents an aromatic ring group which may have a substituent.] A monomer unit (A) represented by the formula: The following formula (II): 【Chemistry 2】 [In formula (II), R １ is an alkyl group, and R ２ is an alkyl group, a halogen atom, a halogenated alkyl group, a hydroxyl group, a carboxylic acid group, or a halogenated carboxylic acid group, p is an integer of 0 to 5, and R ２ When a plurality of are present, they may be the same or different. and a monomer unit (B) represented by A copolymer having a weight average molecular weight of 230,000 or more and a molecular weight distribution of 2.50 or less.

2. The copolymer according to claim 1, having a weight average molecular weight of 280,000 or more.

3. 3. The copolymer according to claim 1, wherein the proportion of components having a molecular weight of less than 50,000 is 20% or less.

4. 4. The copolymer according to claim 1, wherein the proportion of components having a molecular weight of less than 100,000 is 30% or less.

5. 5. The copolymer according to claim 1, wherein the proportion of components having a molecular weight of more than 500,000 is 10% or more.

6. 6. The copolymer according to claim 1, wherein L is a divalent linking group having an electron-withdrawing group.

7. 7. The copolymer according to claim 6, wherein the electron-withdrawing group is at least one selected from the group consisting of a fluorine atom, a fluoroalkyl group, a cyano group, and a nitro group.

8. Electron beam irradiation amount 20μC / cm ２ Weight average molecular weight Mw ２０ and an electron beam irradiation dose of 40 μC / cm ２ Weight average molecular weight Mw ４０ The copolymer according to any one of claims 1 to 7, wherein the difference between

9. A positive resist composition comprising the copolymer according to any one of claims 1 to 8 and a solvent.

10. a step (A) of forming a resist film using the positive resist composition according to claim 9; a step (B) of exposing the resist film; (C) a step of developing the exposed resist film using a developer; A method for forming a resist pattern, comprising:

11. The method for forming a resist pattern according to claim 10 , wherein the developer contains an alcohol.

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