Radiation-sensitive composition, resist pattern formation method, and compound

Abstract

A radiation-sensitive composition according to the present invention contains: a polymer (A) that has an acid-dissociable group; and an onium salt (Q) that comprises a carboxylic acid anion and an onium cation. The carboxylic acid anion has a (thio)acetal structure, and the onium cation is an iodonium cation or a quaternary ammonium cation or is a sulfonium cation that includes an aromatic ring and a functional group that is bonded to the aromatic ring, the functional group being at least one of a fluoro group (excluding a fluoro group of a fluoroalkyl group), an iodo group, and a fluoroalkyl group.

Description

Radiation-sensitive composition, method for forming resist pattern, and compound

[0001] [Cross-Reference to Related Applications] This application claims priority to Japanese Patent Application No. 2024-141645, filed on August 22, 2024, the entire contents of which are incorporated herein by reference. The present disclosure relates to a radiation-sensitive composition, a method for forming a resist pattern, and a compound.

[0002] In lithography techniques used in the manufacturing processes of various electronic devices such as semiconductor devices and liquid crystal devices, a radiation-sensitive composition is irradiated with far ultraviolet rays (such as an ArF excimer laser), extreme ultraviolet rays (EUV), electron beams, or the like to generate an acid in the exposed area, and a chemical reaction involving this acid causes a difference in the dissolution rate in a developer between the exposed area and the unexposed area, thereby forming a resist pattern on a substrate.

[0003]

[0003] Along with the miniaturization of various electronic device structures, there is a demand for further miniaturization of resist patterns in lithography processes. In addition, in response to the demand for further miniaturization of resist patterns, various studies have been conducted to improve the resolution and resist pattern shape of radiation-sensitive compositions used in microfabrication by lithography (see, for example, Patent Documents 1 and 2).

[0004] Patent Document 1 discloses that a radiation-sensitive composition containing a polymer containing a structural unit having a phenolic hydroxyl group, an acid generator consisting of a radiation-sensitive cation and a sulfonate anion, and an acid diffusion controller uses an onium salt having a sulfonate anion with a cyclic acetal skeleton as the acid generator. － and an onium salt having a structure in which two fluorine atoms are bonded to a carbon atom to which a fluorine atom is bonded.

[0005] JP 2021-071720 A JP 2017-203885 A

[0006] In recent years, attempts have been made to form finer patterns than ever before. Radiation-sensitive compositions for forming resist films are required to exhibit high sensitivity, while also further reducing LWR (Line Width Roughness), which is an index of pattern quality, and further improving resolution.

[0007] The present disclosure has been made in consideration of the above-mentioned problems, and has as its object to provide a radiation-sensitive composition that is excellent in sensitivity, LWR performance, and resolution, and a method of forming a resist pattern using the radiation-sensitive composition. Another object is to provide an onium salt that can provide a radiation-sensitive composition that is excellent in sensitivity, LWR performance, and resolution.

[0008] According to one aspect of the present disclosure, there is provided a radiation-sensitive composition comprising a polymer (A) having an acid-dissociable group and an onium salt (Q) composed of a carboxylate anion and an onium cation, wherein the carboxylate anion has a (thio)acetal structure and the onium cation is an iodonium cation or a quaternary ammonium cation, or a sulfonium cation having an aromatic ring and at least one functional group selected from the group consisting of a fluoro group (excluding a fluoro group in a fluoroalkyl group), an iodo group, and a fluoroalkyl group, and bonded to the aromatic ring.

[0009] According to another aspect of the present disclosure, there is provided a method for forming a resist pattern, the method including the steps of forming a resist film on a substrate using the radiation-sensitive composition described above, exposing the resist film to light, and developing the exposed resist film.

[0010] According to another aspect of the present disclosure, there is provided an onium salt comprising a carboxylate anion and an onium cation, wherein the carboxylate anion has a (thio)acetal structure, and the onium cation is an iodonium cation or a quaternary ammonium cation, or a sulfonium cation having an aromatic ring and at least one functional group selected from the group consisting of a fluoro group (excluding a fluoro group in a fluoroalkyl group), an iodo group, and a fluoroalkyl group, which is bonded to the aromatic ring.

[0011] According to the present disclosure, a radiation-sensitive composition having excellent sensitivity, LWR performance, and resolution can be obtained. Furthermore, according to the present disclosure, by using the radiation-sensitive composition of the present disclosure, a resist pattern having reduced LWR and excellent resolution can be obtained.

[0012] Matters relating to the embodiments will be described in detail below. In this specification, a numerical range described using "to" means that the numerical values ​​before and after "to" are included as the lower and upper limits.

[0013] In this specification, the term "hydrocarbon group" includes chain hydrocarbon groups, alicyclic hydrocarbon groups, and aromatic hydrocarbon groups. The term "chain hydrocarbon group" refers to a linear hydrocarbon group or a branched hydrocarbon group that does not contain a cyclic structure and is composed solely of a chain structure. However, the chain hydrocarbon group may be saturated or unsaturated. The term "alicyclic hydrocarbon group" refers to a hydrocarbon group that contains only an alicyclic hydrocarbon structure as a ring structure and does not contain an aromatic ring structure. However, the alicyclic hydrocarbon group does not necessarily have to be composed solely of an alicyclic hydrocarbon structure and may also contain a chain structure as part of it. The term "aromatic hydrocarbon group" refers to a hydrocarbon group that contains an aromatic ring structure as a ring structure. However, the aromatic hydrocarbon group does not necessarily have to be composed solely of an aromatic ring structure and may contain a chain structure or an alicyclic hydrocarbon structure as part of it. The term "organic group" refers to an atomic group formed by removing any hydrogen atom from a carbon-containing compound (i.e., an organic compound). The term "aromatic ring" refers to an aromatic hydrocarbon ring and an aromatic heterocycle.

[0014] The "main chain" of a polymer refers to the "backbone" portion of the polymer, which is the longest chain of atoms. It is acceptable for this "backbone" portion to contain a ring structure. For example, "having a specific structure in the main chain" means that the specific structure constitutes a part of the main chain of the polymer. A "side chain" refers to a portion branched from the "backbone" of the polymer. A "structural unit" refers to a unit that mainly constitutes the main chain structure, and at least two or more of which are contained in the main chain structure. A structural unit is typically a monomer unit. "(Meth)acrylate" is a term that includes "acrylate" and "methacrylate." "(Thio)acetal" is a term that includes "acetal" and "thioacetal."

[0015] The expression "substituted or unsubstituted p-valent hydrocarbon group (where p is an integer of 1 or more)" encompasses p-valent hydrocarbon groups (i.e., unsubstituted p-valent hydrocarbon groups) and groups in which p hydrogen atoms have been removed from the hydrocarbon structural portion of a substituted hydrocarbon group. Examples of substituted or unsubstituted p-valent hydrocarbon groups include alkyl groups and fluoroalkyl groups where p = 1, and alkanediyl groups and fluoroalkanediyl groups where p = 2. Of these, fluoroalkyl groups are "substituted monovalent hydrocarbon groups," and fluoroalkanediyl groups are "substituted divalent hydrocarbon groups." The same applies to other groups to which "substituted or unsubstituted" is attached.

[0016] <Radiation-Sensitive Composition> The radiation-sensitive composition of the present disclosure (hereinafter also referred to as "the composition") contains a polymer (A) having an acid-dissociable group and an onium salt (Q) composed of a carboxylate anion and an onium cation. The components contained in the composition and the components that may be optionally blended are specifically described below. Note that, unless otherwise specified, each component contained in the composition may be used alone or in combination of two or more.

[0017] <Polymer (A)> The acid-dissociable group contained in the polymer (A) is a group that substitutes a hydrogen atom contained in an acidic group such as a carboxyl group or a hydroxyl group, and is a group that dissociates under the action of an acid. By including a polymer having an acid-dissociable group in the composition, the acid-dissociable group is dissociated by the acid generated by exposing the composition to light to generate an acidic group, thereby changing the solubility of the polymer component in the developer in the exposed area. As a result, the composition can be endowed with good lithography properties. In order to sufficiently increase the difference in dissolution rate between the exposed area and the unexposed area in the developer, it is preferable that the polymer (A) contains a structural unit having an acid-dissociable group. Hereinafter, the structural unit having an acid-dissociable group contained in the polymer (A) is also referred to as the "first structural unit."

[0018] (First structural unit) The first structural unit is not particularly limited as long as it has an acid-dissociable group. Examples of the first structural unit include a structural unit represented by the following formula (2-1) (hereinafter also referred to as "structural unit (1A)"), a structural unit represented by the following formula (2-2) (hereinafter also referred to as "structural unit (1B)"), and a structural unit represented by the following formula (2-3) (hereinafter also referred to as "structural unit (1C)"): (In formula (2-1), R ３０ is a hydrogen atom, a fluoro group, a methyl group, or a trifluoromethyl group. ３ R is a divalent chain organic group or an alicyclic hydrocarbon group. ３１ is a hydrogen atom or a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms. ３２ and R ３３ are each independently a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms, a monovalent aromatic heterocyclic group, or R ３２ and R ３３ are combined together to form R ３２ and R ３３ represents an alicyclic hydrocarbon structure having 3 to 20 carbon atoms, which is formed together with the carbon atom to which R is bonded. ３１ When is a hydrogen atom, R ３２ and R ３３or both of which are, independently of each other, a substituted or unsubstituted monovalent alicyclic unsaturated hydrocarbon group, a substituted or unsubstituted monovalent aromatic hydrocarbon group, or a monovalent aromatic heterocyclic group, or R ３２ and R ３３ are combined together to form R ３２ and R ３３ represents an alicyclic unsaturated hydrocarbon structure having 3 to 20 carbon atoms, which is formed together with the carbon atom to which it is bonded. g1 is 0 or 1. In formula (2-2), R ３０ is a hydrogen atom, a fluoro group, a methyl group, or a trifluoromethyl group. ４ represents a single bond, -O-, -CO-, * ２ -COO- or * ２ -CONH-. ２ " represents a bond to the main chain. ３４ , R ３５ and R ３６ are each independently a hydrogen atom, a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms, or a substituted or unsubstituted monovalent oxyhydrocarbon group having 1 to 20 carbon atoms. ２８ is a monovalent substituent. g2 is an integer of 0 to 4. In formula (2-3), R ３０ is a hydrogen atom, a fluoro group, a methyl group, or a trifluoromethyl group. ５ represents a single bond, -O-, -CO-, * ３ -COO- or * ３ -CONH-. ３ " represents a bond to the main chain. ３７ R is a hydrogen atom, a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms, or a substituted or unsubstituted monovalent oxyhydrocarbon group having 1 to 20 carbon atoms. ３８ and R ３９ are each independently a hydrogen atom, a substituted or unsubstituted monovalent hydrocarbon group having 1 to 20 carbon atoms, or a substituted or unsubstituted monovalent oxyhydrocarbon group having 1 to 20 carbon atoms, or R ３８ and R ３９ are aligned with each other and R ３８ and R ３９ represents an alicyclic hydrocarbon structure having 3 to 20 carbon atoms formed together with the carbon atom to which R is bonded.２９ is a monovalent substituent. g3 is an integer of 0 to 4.

[0019] In the above formula (2-1), R ３０ In view of the copolymerizability of the monomer that gives the structural unit (1A), R is preferably a hydrogen atom or a methyl group, and more preferably a methyl group. ３０ is preferably a hydrogen atom from the viewpoint of copolymerizability of the monomer that gives the structural unit (1B). ３０ is preferably a hydrogen atom or a methyl group. ４ Or L in formula (2-3) ５ is preferably a single bond, —COO— or —CONH—.

[0020] L in the above formula (2-1) ３ The divalent chain organic group represented by the formula (I) includes a divalent saturated chain hydrocarbon group having 1 to 20 carbon atoms, a divalent saturated chain hydrocarbon group in which a methylene group is a heteroatom-containing group (for example, -O-, -S-, -CO-, -COO-, -NH-, -NHCO-, -SO ２ Examples of such a divalent group include a divalent group having 2 to 20 carbon atoms substituted with a substituted aryl group (-). The divalent saturated chain hydrocarbon group having 1 to 20 carbon atoms may be linear or branched.

[0021] R in the above formulas (2-1) to (2-3) ３１ ~R ３３ , R ３４ ~R ３６ or R ３７ ~R ３９ Examples of the monovalent hydrocarbon group having 1 to 20 carbon atoms represented by the formula (I) include a monovalent chain hydrocarbon group having 1 to 20 carbon atoms, a monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms, and a monovalent aromatic hydrocarbon group having 6 to 20 carbon atoms.

[0022] Examples of the monovalent chain hydrocarbon group having 1 to 20 carbon atoms include alkyl groups such as methyl, ethyl, n-propyl, i-propyl, n-butyl, and t-butyl; alkenyl groups such as ethenyl, propenyl, and butenyl; and alkynyl groups such as ethynyl, propynyl, and butynyl. ３１The monovalent chain hydrocarbon group having 1 to 20 carbon atoms, represented by the formula (I) or (II), is preferably an alkyl group, more preferably an alkyl group having 1 to 4 carbon atoms.

[0023] Examples of the monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms include monovalent monocyclic alicyclic saturated hydrocarbon groups such as a cyclopentyl group, a cyclohexyl group, a methylcyclopentyl group, an ethylcyclopentyl group, a methylcyclohexyl group, and an ethylcyclohexyl group; monovalent monocyclic unsaturated hydrocarbon groups such as a cyclopentenyl group, a cyclohexenyl group, a methylcyclopentenyl group, and a methylcyclohexenyl group; monovalent polycyclic alicyclic saturated hydrocarbon groups such as a norbornyl group, an adamantyl group, and a tricyclodecyl group; and monovalent polycyclic unsaturated alicyclic hydrocarbon groups such as a norbornenyl group, a tricyclodecenyl group, an indenyl group, and an indanyl group.

[0024] Examples of the monovalent aromatic hydrocarbon group having 6 to 20 carbon atoms include aryl groups such as phenyl, tolyl, xylyl, mesityl, vinylphenyl, naphthyl, methylnaphthyl, anthryl, and methylanthryl; and aralkyl groups such as benzyl, phenethyl, naphthylmethyl, and anthrylmethyl. Examples of the monovalent aromatic heterocyclic group include furyl and thienyl.

[0025] R ３２ and R ３３ are combined together to form R ３２ and R ３３ an alicyclic hydrocarbon structure having 3 to 20 carbon atoms formed together with the carbon atom to which R is bonded, and ３８ and R ３９ are combined together to form R ３８ and R ３９ Examples of the alicyclic hydrocarbon structure having 3 to 20 carbon atoms constituted together with the carbon atom to which it is bonded include monocyclic saturated alicyclic structures such as a cyclopropane structure, cyclobutane structure, cyclopentane structure, cyclohexane structure, cycloheptane structure, and cyclooctane structure; monocyclic unsaturated alicyclic structures such as cyclopentene and cyclohexene; and polycyclic alicyclic structures such as a norbornane structure, adamantane structure, tricyclodecane structure, and tetracyclododecane structure.

[0026] R３１ , R ３５ , R ３６ , R ３７ , R ３８ or R ３９ Examples of the monovalent oxyhydrocarbon group having 1 to 20 carbon atoms represented by the formula (I) include the above-mentioned R ３１ Examples of the monovalent hydrocarbon group having 1 to 20 carbon atoms include groups having an oxygen atom at the bond-side terminal of the groups exemplified as R ３４ Of these, the monovalent oxyhydrocarbon group represented by the following formula (I) is preferably an alkoxy group, a cycloalkoxy group, or a cycloalkylalkoxy group.

[0027] R ３１ ~R ３９ When the group represented by R has a substituent, examples of the substituent include a halogeno group (a fluoro group, a chloro group, a bromo group, an iodo group, etc.), a hydroxyl group, an alkoxy group having 1 to 3 carbon atoms, etc. ２８ or R ２９ Examples of the monovalent substituent represented by the formula (I) include a halogeno group (such as a fluoro group, a chloro group, a bromo group, or an iodo group), a substituted or unsubstituted monovalent hydrocarbon group, a substituted or unsubstituted monovalent oxyhydrocarbon group, an ester group (-COOR, where R is an alkyl group having 1 to 3 carbon atoms), an alkylsulfonyl group, a cycloalkylsulfonyl group, a hydroxyl group, a carboxy group, a cyano group, and a nitro group. When one or more hydrogen atoms of the monovalent hydrocarbon group or the monovalent oxyhydrocarbon group are substituted, examples of the substituent include a halogeno group, a hydroxyl group, a carboxy group, a cyano group, and a nitro group. g1 and g2 are preferably 0 to 2.

[0028] Specific examples of the first structural unit include structural units represented by the following formulas. However, the first structural unit is not limited to the following specific examples. In the following formulas, R ３０ is a hydrogen atom, a fluoro group, a methyl group, or a trifluoromethyl group. Structural unit (1A)

[0029] Structural unit (1B)

[0030] Structural unit (1C)

[0031] When the acid-dissociable group of the polymer (A) has an iodine atom, the introduction of the iodine atom increases the sensitivity of the composition before exposure, and the acid-dissociable group is eliminated together with the iodine atom by the action of an acid, thereby improving the solubility of the polymer (A) in a developer. This is preferable because it further enhances the contrast between exposed and unexposed areas. Furthermore, when the acid-dissociable group of the polymer (A) has an iodine atom, it is possible to improve the storage stability of the radiation-sensitive composition.

[0032] In the polymer (A), the content of the first structural unit is preferably 20 mol% or more, more preferably 25 mol% or more, and even more preferably 30 mol% or more, based on the total structural units constituting the polymer (A). The content of the first structural unit is preferably 85 mol% or less, more preferably 80 mol% or less, and even more preferably 75 mol% or less, based on the total structural units constituting the polymer (A). By setting the content of the first structural unit within the above range, the difference in dissolution rate in a developer between the exposed and unexposed areas can be sufficiently increased, which is advantageous in that a good pattern shape of the resist film can be obtained.

[0033] The polymer (A) may contain structural units (hereinafter also referred to as "other structural units") different from the first structural unit. Examples of the other structural units include the following second structural unit, third structural unit, fourth structural unit, and fifth structural unit.

[0034] (Second structural unit) The polymer (A) may further contain a structural unit having an aromatic ring and a hydroxyl group bonded to the aromatic ring (referred to as the "second structural unit"). By having the hydroxyl group bonded to the aromatic ring in the polymer (A), the LWR performance and CDU (Critical Dimension Uniformity) performance of the present composition can be further improved, and the effect of suppressing dissolution of unexposed areas into a developer can be highly effective, thereby sufficiently reducing defects. Furthermore, the polymer (A) containing the second structural unit can be preferably used in pattern formation using exposure to radiation with a wavelength of 50 nm or less, particularly electron beams or EUV.

[0035] The second structural unit differs from the first structural unit in that it does not have an acid-dissociable group. In this specification, a structural unit having a partial structure in which a hydroxyl group and an acid-dissociable group are bonded to the same aromatic ring is classified as a first structural unit.

[0036] A preferred example of the second structural unit is a structural unit represented by the following formula (3). (In formula (3), R ５０ is a hydrogen atom, a fluoro group, a methyl group, or a trifluoromethyl group. ２ represents a single bond, —O—, —COO—, or —CONH—. １１ is a group obtained by removing (n1+n2+1) hydrogen atoms from an aromatic ring. １４ is a substituent different from a hydroxyl group and does not have an acid-dissociable group. n1 is an integer of 1 or more. n2 is an integer of 0 or more. When n2 is 2 or more, a plurality of R ４ are the same or different.)

[0037] In the above formula (3), R ５０ is preferably a hydrogen atom or a methyl group from the viewpoint of copolymerizability of the monomer that provides the second structural unit. １１ The aromatic ring contained in A is preferably an aromatic hydrocarbon ring, and examples thereof include a benzene ring, a naphthalene ring, an anthracene ring, and a phenanthrene ring. １１ The aromatic ring contained in is preferably a benzene ring or a naphthalene ring, more preferably a benzene ring.

[0038] The position of the hydroxyl group bonded to the aromatic ring is not particularly limited. For example, when the second structural unit has a hydroxyl group bonded to a benzene ring, the bonding position of the hydroxyl group on the benzene ring in the second structural unit is not particularly limited. ２ ) may be at any of the ortho, meta and para positions.

[0039] R １４Specific examples of n1 include monovalent hydrocarbon groups, halogeno groups (fluoro, chloro, bromo, iodo, etc.), carboxy groups, ester groups, acyl groups, and monovalent oxyhydrocarbon groups. n1 is preferably 1 to 3, and more preferably 1 or 2. n2 is preferably 0 to 5, more preferably 0 to 2, and even more preferably 0 or 1.

[0040] Specific examples of the second structural unit include structural units represented by the following formulae: However, the second structural unit is not limited to these specific examples. (In the formula, R ５０ is a hydrogen atom, a fluoro group, a methyl group, or a trifluoromethyl group.

[0041] In the polymer (A), the content of the second structural unit is preferably 10 mol% or more, more preferably 20 mol% or more, and even more preferably 30 mol% or more, based on the total amount of structural units contained in the polymer (A). The content of the second structural unit is preferably 70 mol% or less, more preferably 65 mol% or less, and even more preferably 60 mol% or less, based on the total amount of structural units contained in the polymer (A). By setting the content of the second structural unit within the above range, the lithography properties of the composition, such as LWR performance and CDU performance, can be further improved, and defects can be sufficiently reduced. This is advantageous.

[0042] (Third Structural Unit) The polymer (A) may further contain a structural unit derived from a radiation-sensitive onium salt (referred to as the "third structural unit"). The third structural unit is typically a structural unit derived from a monomer comprising a radiation-sensitive onium cation and an organic anion. The third structural unit is thought to be formed by the radiation-induced decomposition of the radiation-sensitive onium cation to liberate an organic anion, which then bonds with hydrogen abstracted from components contained in the composition (e.g., a radiation-sensitive acid generator, an acid diffusion controller, a solvent, etc.), thereby generating an acid derived from the organic anion. Examples of the organic anion include a sulfonate anion, a carboxylate anion, and a sulfonimide anion.

[0043] When the organic anion in the third structural unit is a sulfonate anion or a sulfonimide anion, the third structural unit is considered to function primarily as a radiation-sensitive acid generator by generating a strong acid that induces dissociation of the acid-dissociable group under normal conditions. When the organic anion in the third structural unit is a carboxylate anion, the third structural unit is considered to function primarily as an acid diffusion controller by generating a weak acid that does not induce dissociation of the acid-dissociable group under normal conditions. Here, "normal conditions" refers to conditions in which post-exposure baking (PEB) is performed at 110°C for 60 seconds.

[0044] The third structural unit is typically a structural unit derived from a monomer having a radiation-sensitive onium cation, an organic anion, and a group participating in polymerization. ３ － Ya-COO － ) may be bonded to the main chain of the polymer via a linking group, and the radiation-sensitive onium cation may form a counter ion. Alternatively, the radiation-sensitive onium cation may be bonded to the main chain of the polymer via a linking group, and the organic anion may form a counter ion. In order to further improve the CDU performance of the present composition, it is preferable that the third structural unit be bonded to the main chain of the polymer via a linking group, and that the organic anion be a sulfonate anion (—SO ３ － ) is more preferably bonded to the main chain of the polymer via a linking group.

[0045] Examples of the radiation-sensitive cation in the third structural unit include a sulfonium cation, an iodonium cation, and a quaternary ammonium cation. From the viewpoint of increasing the sensitivity of the present composition, the radiation-sensitive cation in the third structural unit is preferably a sulfonium cation or an iodonium cation, and more preferably a triarylsulfonium cation or a diaryliodonium cation. From the viewpoint of further increasing the sensitivity of the present composition, the aromatic ring (i.e., S) possessed by the triarylsulfonium cation or diaryliodonium cation is preferably a cation having an aromatic ring (i.e., S) ＋ or I ＋Preferably, a total of one or more of an iodo group, a fluoro group (excluding the fluoro group in a fluoroalkyl group), and a fluoroalkyl group are bonded to the aromatic ring bonded to the aromatic ring. The fluoroalkyl group is preferably a trifluoromethyl group.

[0046] The third structural unit may have an iodine atom, which can contribute to further increasing the sensitivity of the present composition. When the third structural unit has an iodine atom, it is preferable that the third structural unit has an aromatic ring to which the iodine atom is bonded.

[0047] Specific examples of the third structural unit include structural units represented by the following formulas: However, the third structural unit is not limited to these specific examples. (In the formula, R ４０ is a hydrogen atom, a fluoro group, a methyl group, or a trifluoromethyl group. ＋ is a sulfonium cation or an iodonium cation. － is a sulfonate anion or a carboxylate anion.

[0048] When the polymer (A) contains a third structural unit, the content of the third structural unit in the polymer (A) is preferably 1 mol% or more, more preferably 5 mol% or more, and even more preferably 10 mol% or more, based on the total amount of structural units contained in the polymer (A).Furthermore, the content of the third structural unit in the polymer (A) is preferably 30 mol% or less, more preferably 25 mol% or less, based on the total amount of structural units contained in the polymer (A).By setting the content of the third structural unit within the above range, the effect of improving the sensitivity of the composition by introducing the third structural unit can be sufficiently obtained.

[0049] (Fourth Structural Unit) The polymer (A) may further contain a structural unit having a lactone structure, a cyclic carbonate structure, a sultone structure, or a ring structure comprising a combination of two or more of these (excluding those corresponding to the first to third structural units; hereinafter, also referred to as a "fourth structural unit"). When the polymer (A) contains the fourth structural unit, the solubility in a developer can be adjusted, and as a result, the lithography properties of the composition can be further improved. Furthermore, when the polymer (A) contains the fourth structural unit, the adhesion between a resist film obtained using the composition and a substrate can be improved.

[0050] Examples of the fourth structural unit include structural units represented by the following formula:

[0051]

[0052] (In the formula, R Ｌ１ is a hydrogen atom, a fluoro group, a methyl group, or a trifluoromethyl group.

[0053] When the polymer (A) contains a fourth structural unit, the content of the fourth structural unit is preferably 1 mol% or more, more preferably 3 mol% or more, based on the total structural units constituting the polymer (A). The content of the fourth structural unit is preferably 50 mol% or less, more preferably 30 mol% or less, and even more preferably 15 mol% or less, based on the total structural units constituting the polymer (A). Setting the content of the fourth structural unit within the above range is advantageous in that it can improve the lithography properties of the composition and can improve the adhesion of a resist film obtained using the composition to a substrate.

[0054] (Fifth structural unit) The polymer (A) may further contain a structural unit having an alcoholic hydroxyl group (excluding those corresponding to the first to fourth structural units; hereinafter, also referred to as the "fifth structural unit"). Herein, the "alcoholic hydroxyl group" refers to a group having a structure in which a hydroxyl group is directly bonded to a carbon atom constituting an aliphatic hydrocarbon group. The aliphatic hydrocarbon group may be a chain hydrocarbon group or an alicyclic hydrocarbon group. When the polymer (A) further contains the fifth structural unit, the solubility of the polymer (A) in a developer can be improved, and as a result, the lithography performance of the present composition can be further improved.

[0055] Specific examples of the fifth structural unit include structural units represented by the following formulas. (In the formula, R Ｌ２ is a hydrogen atom, a fluoro group, a methyl group, or a trifluoromethyl group.

[0056] When the polymer (A) contains the fifth structural unit, the content of the fifth structural unit is preferably 1 mol% or more, more preferably 3 mol% or more, based on all structural units constituting the polymer (A), and is preferably 30 mol% or less, more preferably 20 mol% or less, based on all structural units constituting the polymer (A).

[0057] In addition to the above, other structural units contained in the polymer (A) include, for example, structural units containing a cyano group, a nitro group, or a sulfonamide group (specifically, a structural unit derived from 2-cyanomethyladamantan-2-yl(meth)acrylate); structural units containing a non-acid-dissociable hydrocarbon group (specifically, a structural unit derived from styrene or a halogenated styrene (e.g., a styrene unit, a bromostyrene unit, an iodostyrene unit), a structural unit derived from vinylnaphthalene, a structural unit derived from n-pentyl(meth)acrylate, etc.). The content ratio of these structural units can be appropriately set depending on each structural unit, as long as the effects of the present invention are not impaired. The polymer (A) can be synthesized, for example, by polymerizing monomers that provide each structural unit in an appropriate solvent using a known radical polymerization initiator or the like.

[0058] The weight average molecular weight (Mw) of the polymer (A) measured by gel permeation chromatography (GPC) in terms of polystyrene is preferably 1,000 or more, more preferably 2,000 or more, even more preferably 3,000 or more, and even more preferably 4,000 or more. The Mw of the polymer (A) is preferably 50,000 or less, more preferably 30,000 or less, even more preferably 20,000 or less, and even more preferably 15,000 or less. By setting the Mw of the polymer (A) within the above range, the coatability of the composition can be improved and development defects can be sufficiently suppressed, which is advantageous.

[0059] The ratio of Mw to the polystyrene-equivalent number average molecular weight (Mn) of the polymer (A) measured by GPC (Mw / Mn, hereinafter also referred to as "dispersity") is preferably 5.0 or less, more preferably 3.0 or less, and even more preferably 2.0 or less. The Mw / Mn of the polymer (A) is usually 1.0 or more.

[0060] The polymer (A) is preferably blended into the composition as at least a part of the base resin, and the content of the polymer (A) in the composition is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 85% by mass or more, based on the total amount of solids contained in the composition.

[0061] <Onium Salt (Q)> The onium salt (Q) is a compound comprising a carboxylic acid anion and an onium cation. The onium salt (Q) generates a weak acid that does not induce dissociation of an acid-dissociable group under the above-mentioned normal conditions. This allows the onium salt (Q) to function mainly as an acid diffusion controller in the radiation-sensitive composition. The molecular weight of the onium salt (Q) is preferably 1,000 or less, more preferably 850 or less, and even more preferably 750 or less.

[0062] The carboxylic acid anion constituting the onium salt (Q) has a (thio)acetal structure. The onium cation constituting the onium salt (Q) is an iodonium cation or a quaternary ammonium cation, or a sulfonium cation having an aromatic ring and at least one functional group selected from the group consisting of a fluoro group (excluding the fluoro group in a fluoroalkyl group), an iodo group, and a fluoroalkyl group, which is bonded to the aromatic ring. In the following, when the onium cation constituting the onium salt (Q) is a sulfonium cation, the functional group of the onium cation, which is at least one selected from the group consisting of a fluoro group (excluding the fluoro group in a fluoroalkyl group), an iodo group, and a fluoroalkyl group, and which is bonded to the aromatic ring, is also referred to as a "specific functional group."

[0063] (Carboxylic Acid Anion) It is believed that the carboxylate anion constituting the onium salt (Q) generates a polar group through hydrolysis of the (thio)acetal structure by the acid generated from the radiation-sensitive acid generator upon exposure (preferably exposure and subsequent baking). By incorporating such an onium salt (Q) into the radiation-sensitive composition together with the polymer (A), the contrast between exposed and unexposed areas in the resist film can be improved.

[0064] The (thio)acetal structure may be linear or cyclic. In order to improve the resolution of the present composition, it is preferable that the (thio)acetal structure possessed by the carboxylate anion in the onium salt (Q) is cyclic. That is, it is preferable that the carboxylate anion constituting the onium salt (Q) has a (thio)acetal ring structure.

[0065] Here, the term "(thio)acetal ring" refers to a ring structure containing a ring in which two methylene groups constituting a monocyclic saturated aliphatic hydrocarbon ring (e.g., a cyclopentane ring, a cyclohexane ring, a cycloheptane ring, a cyclooctane ring, etc.) are each replaced with a (thio)ether bond, resulting in two oxygen atoms, two sulfur atoms, or one oxygen atom and one sulfur atom being bonded to the same carbon. Note that the term "(thio)acetal ring" does not include rings having heteroatoms other than oxygen and sulfur in the ring skeleton, or rings having a carbon atom directly bonded to a heteroatom (e.g., a carbon atom bonded to an oxo group) in the ring skeleton. Thus, for example, a ring having an ester bond (-C(=O)-O-) in the ring skeleton does not fall under the category of a "(thio)acetal ring."

[0066] From the viewpoint of ease of synthesis, the (thio)acetal ring in the carboxylate anion is preferably an acetal ring in which two methylene groups constituting a monocyclic saturated aliphatic hydrocarbon ring are both replaced with ether bonds.

[0067] When the carboxylic acid anion in the onium salt (Q) has a (thio)acetal ring structure, the number of ring members in the (thio)acetal ring is preferably 5 to 18, more preferably 5 to 10, and even more preferably 5 to 7. In particular, when the number of ring members in the (thio)acetal ring is 7, the LWR of the radiation-sensitive composition tends to be further reduced. In addition, when the (thio)acetal ring in the (thio)acetal ring structure is -CF ２ When the ring contains -, the LWR of the radiation-sensitive composition tends to be further reduced.

[0068] A preferred specific example of the (thio)acetal ring structure that the carboxylate anion may have is a ring structure (r is an integer of 1 or more) in which r hydrogen atoms have been removed from a structure represented by the following formula (4): (In formula (4), Y ２ and Y ３ are each independently an oxygen atom or a sulfur atom. ｇ１ and R ｇ２ are each independently a hydrogen atom or a monovalent organic group, or R ｇ１ and R ｇ２ are combined together to form R ｇ１ and Rｇ２ represents an aliphatic ring structure formed together with the carbon atom to which R is attached. ｆ１ and R ｆ２ are each independently a hydrogen atom, a fluoro group, or a fluoroalkyl group. m is an integer of 0 to 13. When m is 2 or more, multiple R ｆ１ and R ｆ２ are the same or different.)

[0069] In the above formula (4), Y ２ and Y ３ At least one of Y is preferably an oxygen atom, ２ and Y ３ It is more preferable that both of R are oxygen atoms. ｇ１ or R ｇ２ Examples of the monovalent organic group represented by the formula (I) include a substituted or unsubstituted monovalent hydrocarbon group; and a monovalent group in which a methylene group contained in a substituted or unsubstituted monovalent hydrocarbon group is substituted with a group containing at least one heteroatom selected from the group consisting of an oxygen atom, a sulfur atom, and a nitrogen atom.

[0070] R ｇ１ or R ｇ２ In the monovalent organic group represented by the formula (2-1), examples of the monovalent hydrocarbon group include a monovalent chain hydrocarbon group having 1 to 20 carbon atoms, a monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms, and a monovalent aromatic hydrocarbon group having 6 to 20 carbon atoms. Specific examples of these include R ３１ ~R ３８ is a monovalent hydrocarbon group, examples of which include the same groups as those given as specific examples. Examples of the group containing at least one heteroatom selected from the group consisting of an oxygen atom, a sulfur atom, and a nitrogen atom include -O-, -CO-, -NH ２ -, -SO-, -SO ２ or a divalent group consisting of a combination of two or more thereof.

[0071] Examples of the substituent include a halogeno group (a fluoro group, a chloro group, a bromo group, an iodo group, etc.), a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted cycloalkyloxy group, an ester group (-COOR, where R is an alkyl group having 1 to 3 carbon atoms), an alkylsulfonyl group, a cycloalkylsulfonyl group, a hydroxy group, a carboxy group, a cyano group, a nitro group, etc. When one or more hydrogen atoms of an alkyl group, an alkoxy group, a cycloalkyl group, or a cycloalkyloxy group are substituted, examples of the substituent include a halogeno group, a hydroxy group, a carboxy group, a cyano group, a nitro group, etc.

[0072] R ｆ１ or R ｆ２ When R is a fluoroalkyl group, examples of the fluoroalkyl group include linear or branched fluoroalkyl groups having 1 to 10 carbon atoms. Among these, linear or branched fluoroalkyl groups having 1 to 3 carbon atoms are preferred, and a trifluoromethyl group is more preferred. ｆ１ and R ｆ２ is preferably a hydrogen atom, a fluoro group, or a trifluoromethyl group, and more preferably a hydrogen atom or a fluoro group. ｆ１ and R ｆ２ A partial structure in which both are fluoro groups (i.e., -CF ２ When m has a group (-), it is preferred in that the LWR of the present composition tends to be further reduced. m is preferably 0 to 5, and more preferably 0 to 2. When m is 2, it is preferred in that the LWR of the present composition tends to be further reduced.

[0073] In the ring structure obtained by removing r hydrogen atoms from the structure represented by the formula (4), the positions of the r hydrogen atoms removed from the structure represented by the formula (4) are not particularly limited. In order to improve the LWR performance of the present composition, the carboxylate anion constituting the onium salt (Q) is selected from the carbon atoms constituting the (thio)acetal ring, and the carbon atoms Y in the formula (4) are selected from the carbon atoms constituting the (thio)acetal ring. ２ and Y ３ It is preferable that the ring structure has a hydrogen atom bonded to the carbon atom adjacent to at least one of Y ２ and Y３ It is more preferable that the ring structure has a ring structure in which the hydrogen atom bonded to the carbon atom between

[0074] The carboxylate anion constituting the onium salt (Q) may have a (thio)acetal structure, and the structure of the other moieties is not particularly limited. Examples of the carboxylate anion include an aliphatic dicarboxylic acid structure, an aromatic dicarboxylic acid structure, an oxalic acid structure, an oxalic acid amide structure, a difluoromethylcarboxylic acid structure, and a salicylic acid structure. In terms of improving the storage stability of the present composition, the carboxylate anion constituting the onium salt (Q) preferably has an aliphatic dicarboxylic acid structure, an aromatic dicarboxylic acid structure, an oxalic acid structure, an oxalic acid amide structure, or a difluoromethylcarboxylic acid structure.

[0075] (Onium Cation) Examples of the onium cation constituting the onium salt (Q) include a sulfonium cation, an iodonium cation, a quaternary ammonium cation, etc. Among these, the onium cation constituting the onium salt (Q) is preferably a sulfonium cation or an iodonium cation, in view of the ability to form a high-quality resist film with excellent LWR performance and CDU performance.

[0076] When the onium cation constituting the onium salt (Q) is an iodonium cation or a quaternary ammonium cation, the onium cation does not need to have a specific functional group and may be, for example, an unsubstituted diaryliodonium cation or an unsubstituted quaternary ammonium cation. Furthermore, the onium cation constituting the onium salt (Q) may have a substituent different from the specific functional group. Examples of the substituent include an alkyl group, an alkoxy group, a bromo group, a chloro group, a cycloalkyl group, a cycloalkyloxy group, an ester group, an alkylsulfonyl group, a cycloalkylsulfonyl group, a hydroxy group, a carboxy group, a cyano group, and a nitro group. These groups may be further substituted with a chloro group, a bromo group, an iodo group, a hydroxy group, a carboxy group, a cyano group, a nitro group, an alkoxy group having 1 to 5 carbon atoms, or the like.

[0077] In order to further increase the sensitivity of the radiation-sensitive composition, it is preferable that the onium cation constituting the onium salt (Q) has a specific functional group. ＋ or I ＋ and a specific functional group is bonded to the aromatic ring. That is, the onium cation is preferably an arylsulfonium cation or an aryliodonium cation. Examples of the aromatic ring include a benzene ring, a naphthalene ring, an anthracene ring, and a thiophene ring, and among these, a benzene ring or a naphthalene ring is preferred.

[0078] With regard to the specific functional group, an example of a trifluoroalkyl group is a group in which one or more hydrogen atoms in a linear or branched alkyl group having 1 to 10 carbon atoms have been replaced with a fluorine atom. Specific examples of these include a trifluoromethyl group, a 2,2,2-trifluoroethyl group, a pentafluoroethyl group, a 2,2,3,3,3-pentafluoropropyl group, and a 1,1,1,3,3,3-hexafluoropropyl group. The fluoroalkyl group as the specific functional group is preferably a linear or branched fluoroalkyl group having 1 to 3 carbon atoms, and more preferably a trifluoromethyl group.

[0079] The number of specific functional groups in the onium cation constituting the onium salt (Q) (the total number when two or more types are present) is preferably one or more per molecule. The number of specific functional groups in the onium cation is preferably two or more, from the viewpoint of further increasing the sensitivity of the radiation-sensitive composition. Furthermore, the number of specific functional groups in the onium cation is preferably 10 or less, more preferably 8 or less, from the viewpoint of balancing the ease of synthesis of the onium salt and the effect of introducing the specific functional groups.

[0080] When the number of specific groups bonded to the same aromatic ring in the onium cation is two or more, it is preferable in that a radiation-sensitive composition with higher sensitivity can be obtained. Furthermore, when the onium cation has two or more aromatic ring structures each having two or more specific groups bonded to the same aromatic ring, the sensitivity of the radiation-sensitive composition can be further increased. Examples of such onium cations include triarylsulfonium cations or diaryliodonium cations, which have multiple partial structures in which two or more specific functional groups are bonded to the same aromatic ring.

[0081] Preferred specific examples of the onium cation in the onium salt (Q) include cations represented by the following formula (5) and cations represented by the following formula (6). (In formula (5), R １ａ and R ２ａ are each independently a monovalent substituent, or R １ａ and R ２ａ are combined together to represent a single bond or a divalent group connecting the rings to which they are attached. ３ａ is a monovalent substituent. a1 and a2 are each independently an integer of 0 to 5. a3 is an integer of 0 to (2×r+5). r is 0 or 1. However, in formula (5), R １ａ , R ２ａ and R ３ａ In formula (6), one or more of R ４ａ and R ５ａ are each independently a monovalent substituent; a4 and a5 are each independently an integer of 0 to 5.

[0082] In the above formulas (5) and (6), R １ａ , R ２ａ , R ３ａ , R ４ａ and R ５ａ (Hereinafter referred to as “R １ａ ~R ５ａExamples of the monovalent substituent represented by R include a fluoro group, a chloro group, a bromo group, an iodo group, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted cycloalkyloxy group, an ester group, an alkylsulfonyl group, a cycloalkylsulfonyl group, a hydroxy group, a carboxy group, a cyano group, and a nitro group. １ａ ~R ５ａ When has a substituent, examples of the substituent include a fluoro group, a chloro group, a bromo group, an iodo group, a hydroxy group, a carboxy group, a cyano group, a nitro group, and an alkoxy group having 1 to 5 carbon atoms.

[0083] R １ａ and R ２ａ When taken together, they represent a divalent group connecting the rings to which they are attached, R １ａ and R ２ａ is preferably a single bond connecting the rings, or forms —O— or —S—.

[0084] Each of a1, a2, and a3 is preferably an integer of 0 to 2. １ａ , R ２ａ and R ３ａ At least one of the groups is a fluoro group, an iodo group, or a trifluoroalkyl group. The trifluoroalkyl group is preferably a trifluoromethyl group.

[0085] From the viewpoint of further increasing the sensitivity of the present composition, it is preferable that at least one of a1, a2, and a3 is 1 or 2, and it is more preferable that at least two of a1, a2, and a3 are 1 or 2. Furthermore, from the viewpoint of further increasing the sensitivity of the present composition, it is preferable that at least one of a1, a2, and a3 is 2.

[0086] Each of a4 and a5 is preferably an integer of 0 to 2. ４ａ and R ５ａ At least one of R in formula (6) is preferably a fluoro group, an iodo group, or a trifluoromethyl group. ４ａ and R ５ａPreferably, one or more of a4 and a5 are specific functional groups. The trifluoroalkyl group is preferably a trifluoromethyl group. From the viewpoint of further increasing the sensitivity of the present composition, it is preferable that at least one of a4 and a5 is 1 or 2, and it is more preferable that both a4 and a5 are 1 or 2.

[0087] Specific examples of the onium cation constituting the onium salt (Q) include cations represented by the following formulas: However, the onium cation constituting the onium salt (Q) is not limited to these specific examples.

[0088] A preferred specific example of the onium salt (Q) is a compound represented by the following formula (1). (In formula (1), A １ is a monovalent organic group having a (thio)acetal structure. １ is a monovalent anion represented by any one of the following formulas (1-1) to (1-5): ＋ is an onium cation having an aromatic ring and a functional group bonded to the aromatic ring, the functional group being at least one selected from the group consisting of a fluoro group (excluding a fluoro group in a fluoroalkyl group), an iodo group, and a fluoroalkyl group. (In formulas (1-1) to (1-5), X １ is -C(R ４ ) (R ５ ) -, -NR ６ - or a group in which two hydrogen atoms have been removed from the ring portion of a substituted or unsubstituted aromatic ring. ４ , R ５ and R ６ are each independently a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. １ is a group in which (n1+3) hydrogen atoms have been removed from an aromatic ring. － and -COOH is B １ are bonded to carbon atoms in the same benzene ring in － The carbon atom to which R is bonded and the carbon atom to which —COOH is bonded are adjacent to each other. １is a monovalent substituent. n is an integer of 0 or more. When n is 2 or more, multiple R １ are the same or different. ２ and R ３ is R ２ is an alkanediyl group, a substituted alkanediyl group, a cycloalkanediyl group, or a substituted cycloalkanediyl group, and R ３ is a hydrogen atom or an alkyl group, or R ２ and R ３ are combined together to form R ２ and R ３ represents an aliphatic ring structure formed together with the carbon atom to which X is attached. ２ and X ３ are each independently a single bond or a substituted or unsubstituted alkanediyl group. ２ is a group obtained by removing (r+1) hydrogen atoms from an aromatic ring. t is an integer from 1 to 5. "*" represents a bond.

[0089] In the above formula (1), A １ Examples of the monovalent organic group represented by the formula (4) include a group in which one hydrogen atom has been removed from the structure represented by the formula (4). More specifically, a group represented by the following formula (4-1) or formula (4-2) is preferred. (In formula (4-1) and formula (4-2), Y ２ , Y ３ , R ｇ１ , R ｇ２ , R ｆ１ , R ｆ２ and m are the same as in formula (4). １ and G ２ are each independently a single bond or a divalent linking group. １ represents a bond with .)

[0090] In the above formula (4-1) and formula (4-2), G １ or G ２ The divalent linking group represented by R in the above formula (4) is ｇ１ or R ｇ２ Examples of the monovalent organic group represented by the following formula include groups in which one hydrogen atom has been further removed from the groups exemplified above.

[0091] Y１ is a monovalent anion represented by any one of the above formulas (1-1) to (1-5). In the above formula (1-1), X １ -C(R ４ ) (R ５ ) - or -NR ６ -, then X １ Is A １ It is preferable that the hydrocarbon group in the —C(R ４ ) (R ５ ) - or -NR ６ Examples of hydrocarbon groups to which - is bonded include chain hydrocarbon groups, alicyclic hydrocarbon groups, and aromatic hydrocarbon groups.

[0092] In the above formula (1-3), B １ Examples of the aromatic ring include a benzene ring, a naphthalene ring, an anthracene ring, and a phenanthrene ring. Of these, a benzene ring or a naphthalene ring is preferred, and a benzene ring is more preferred. １ When the aromatic ring in the － It is bonded in the ortho position to R. １ Examples of the monovalent substituent represented by the formula (I) include a halogeno group (such as a fluoro group, a chloro group, a bromo group, or an iodo group), a hydroxyl group, an alkyl group having 1 to 3 carbon atoms, and an alkoxy group having 1 to 3 carbon atoms.

[0093] In the above formula (1-4), R ２ or R ３ When R has a substituent, examples of the substituent include a halogen atom, a hydroxyl group, and an alkoxy group having 1 to 3 carbon atoms. ２ and R ３ are bonded to each other to form R ２ and R ３ represents an aliphatic ring structure formed together with the carbon atom to which it is bonded, the aliphatic ring structure is ３２ and R ３３ are combined together to form R ３２ and R ３３ Examples of the alicyclic hydrocarbon structure having 3 to 20 carbon atoms constituted together with the carbon atom to which it is bonded include the same structures as those exemplified above.

[0094] In the above formula (1-5), B１ Examples of the aromatic ring represented by the formula (I) include a benzene ring and a naphthalene ring. １ The aromatic ring represented by the formula (I) is preferably a benzene ring.

[0095] Y is preferred in that it can improve the storage stability of the present composition. １ is preferably a monovalent anion represented by any one of the above formulas (1-1) to (1-4), and more preferably a monovalent anion represented by the above formula (1-2), formula (1-3) or formula (1-4).

[0096] M ＋ Specific examples of the cation include the same cations as those exemplified as cations constituting the onium salt (Q).

[0097] Further specific examples of the onium salt (Q) include compounds represented by the following formulas: However, the onium salt (Q) is not limited to the following specific examples.

[0098] In the present composition, the content of the onium salt (Q) is preferably 0.1 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 5 parts by mass or more, relative to 100 parts by mass of the polymer (A). Furthermore, the content of the onium salt (Q) is preferably 90 parts by mass or less, more preferably 80 parts by mass or less, relative to 100 parts by mass of the polymer (A). By setting the content of the onium salt (Q) within the above range, the sensitivity, LWR performance, and resolution of the present composition can be improved in a well-balanced manner.

[0099] When the present composition contains a so-called radiation-sensitive acid generator together with the onium salt (Q), when a structural unit exhibiting the function of a radiation-sensitive acid generator is introduced into the polymer (A) as a third structural unit, or when both of these are present in the present composition, the content of the onium salt (Q) in the present composition is preferably 1 mol % or more, more preferably 5 mol % or more, and even more preferably 10 mol % or more, based on the total amount of the radiation-sensitive acid generator contained in the present composition and the monomer that provides the structural unit exhibiting the function of a radiation-sensitive acid generator as the third structural unit in the polymer (A). Furthermore, the content of the onium salt (Q) is preferably 90 mol % or less, more preferably 80 mol % or less, based on the total amount of the radiation-sensitive acid generator contained in the present composition and the monomer that provides the structural unit exhibiting the function of a radiation-sensitive acid generator as the third structural unit in the polymer (A). By setting the content of the onium salt (Q) within the above range, the sensitivity, LWR performance, and resolution of the present composition can be improved in a well-balanced manner.

[0100] <Synthesis of Onium Salt (Q)> The onium salt (Q) can be synthesized by appropriately combining standard methods in organic chemistry. For example, the compound represented by the above formula (1) can be synthesized by １ -Y １ A compound having a structure corresponding to the formula (1-1) １ -X １ -CO-CO-O-CH ３ and compounds having a partial structure represented by the above formula (1-2): １ -X １ -CF ２ —CO—O—CH ３ The onium salt (Q) can be synthesized by hydrolyzing the intermediate product obtained and then reacting it with a sulfonium chloride or the like that provides an onium cation moiety. However, the synthesis method of the onium salt (Q) is not limited to the above.

[0101] The present composition containing the polymer (A) and the onium salt (Q) enables the formation of resist patterns that exhibit high sensitivity and high resolution while also exhibiting sufficiently reduced LWR. While the reason for this effect is unclear, the following may be one possible explanation: The anion moiety of the onium salt (Q) incorporates a (thio)acetal structure, and the cation moiety is an iodonium cation, a quaternary ammonium cation, or a sulfonium cation having a partial structure in which a specific functional group is bonded to an aromatic ring. When the onium salt (Q) having such a structure comes into contact with an acid generated from a radiation-sensitive acid generator during the exposure step (preferably during the exposure and bake steps), the (thio)acetal structure undergoes hydrolysis. This increases the contrast between exposed and unexposed areas, and the combination with the specific cation structure enhances sensitivity, resulting in improved LWR performance while achieving high sensitivity and high resolution. In particular, when the anion moiety of the onium salt (Q) is a weak base such as those of the above formulas (1-1) to (1-4), it is believed that the resolution is further improved and the storage stability of the radiation-sensitive composition is also improved. However, the above reasons are merely speculation and do not limit the present invention in any way.

[0102] <Other Components> The present composition may further contain, in addition to the polymer (A) and the onium salt (Q), a component different from the polymer (A) and the onium salt (Q) (hereinafter also referred to as "other component"). Examples of the other component include a radiation-sensitive acid generator, a high-fluorine-containing polymer, a solvent, etc.

[0103] (Radiation-Sensitive Acid Generator) The present composition may further contain a compound (i.e., a radiation-sensitive acid generator) that generates a strong acid that induces dissociation of the acid-dissociable group under the above-mentioned normal conditions. Preferred examples of strong acids include sulfonic acid, sulfonylimides, and sulfonylmethides. By containing a radiation-sensitive acid generator in the present composition, high sensitivity and good lithography performance can be ensured in the present composition. As the radiation-sensitive acid generator, a non-polymeric onium salt that generates an acid that is more acidic than the acid generated by the onium salt (Q) upon exposure can be preferably used.

[0104] The type of acid generator to be incorporated into the present composition is not particularly limited, and known radiation-sensitive acid generators used in resist pattern formation can be used as appropriate. Furthermore, an onium salt having an acid-dissociable group in either or both of the cation and anion moieties may also be used as the radiation-sensitive acid generator. Specific examples of radiation-sensitive acid generators include onium salts formed from the organic anions shown below and sulfonium cations, iodonium cations, or quaternary ammonium cations. However, the radiation-sensitive acid generator to be incorporated into the present composition is not limited to the following.

[0105] When a radiation-sensitive acid generator is contained in the present composition, the content of the radiation-sensitive acid generator is preferably 5 parts by mass or more, and more preferably 10 parts by mass or more, relative to 100 parts by mass of polymer (A), from the viewpoint of sufficiently obtaining the effect of improving the sensitivity of the present composition. Furthermore, from the viewpoint of suppressing the occurrence of defects due to the radiation-sensitive acid generator, the content of the radiation-sensitive acid generator is preferably 100 parts by mass or less, and more preferably 80 parts by mass or less, relative to 100 parts by mass of polymer (A).

[0106] (High-Fluorine Content Polymer) The high-fluorine content polymer (hereinafter also referred to as "polymer (F)") is a polymer having a higher mass content of fluorine atoms than polymer (A). Polymer (F) is contained in the present composition, for example, as a surface modifier that adjusts the hydrophilicity / hydrophobicity of the surface of the resist film, or as a modifier that further improves lithography performance.

[0107] The fluorine atom content of the polymer (F) is not particularly limited as long as it is larger than that of the polymer (A). The fluorine atom content of the polymer (F) is preferably 1% by mass or more, more preferably 4% by mass or more, and even more preferably 7% by mass or more. The fluorine atom content of the polymer (F) is preferably 60% by mass or less, more preferably 40% by mass or less. The fluorine atom content (% by mass) of the polymer is １３ The polymer structure can be determined by C-NMR spectrum measurement or the like, and the amount can be calculated from the structure.

[0108] When the composition contains polymer (F), the content of polymer (F) in the composition is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and even more preferably 0.5 parts by mass or more, relative to 100 parts by mass of polymer (A). The content of polymer (F) is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, relative to 100 parts by mass of polymer (A).

[0109] (Solvent) The solvent is preferably a solvent capable of dissolving or dispersing the components to be blended in the composition, and an organic solvent can be preferably used. Specific examples of the solvent include alcohols, ethers, ketones, amides, esters, and hydrocarbons.

[0110] Examples of alcohols include aliphatic monoalcohols having 1 to 18 carbon atoms, such as 4-methyl-2-pentanol and n-hexanol; alicyclic monoalcohols having 3 to 18 carbon atoms, such as cyclohexanol; polyhydric alcohols having 2 to 18 carbon atoms, such as 1,2-propylene glycol; and partial ethers of polyhydric alcohols having 3 to 19 carbon atoms, such as propylene glycol monomethyl ether. Examples of ethers include dialkyl ethers, such as diethyl ether, dipropyl ether, dibutyl ether, dipentyl ether, diisoamyl ether, dihexyl ether, and diheptyl ether; cyclic ethers, such as tetrahydrofuran and tetrahydropyran; and aromatic ring-containing ethers, such as diphenyl ether and anisole.

[0111] Examples of ketones include chain ketones such as acetone, methyl ethyl ketone, methyl n-propyl ketone, methyl n-butyl ketone, diethyl ketone, methyl isobutyl ketone, 2-heptanone, ethyl n-butyl ketone, methyl n-hexyl ketone, di-isobutyl ketone, and trimethylnonanone; cyclic ketones such as cyclopentanone, cyclohexanone, cycloheptanone, cyclooctanone, and methylcyclohexanone; 2,4-pentanedione, acetonylacetone, acetophenone, and diacetone alcohol. Examples of amides include cyclic amides such as N,N'-dimethylimidazolidinone and N-methylpyrrolidone; and chain amides such as N-methylformamide, N,N-dimethylformamide, N,N-diethylformamide, acetamide, N-methylacetamide, N,N-dimethylacetamide, and N-methylpropionamide.

[0112] Examples of esters include monocarboxylic acid esters such as n-butyl acetate, ethyl lactate, and methyl 2-hydroxyisobutyrate; polyhydric alcohol carboxylates such as propylene glycol diacetate; polyhydric alcohol partial ether carboxylates such as propylene glycol monomethyl ether acetate; polycarboxylic acid diesters such as diethyl oxalate; carbonates such as dimethyl carbonate and diethyl carbonate; and cyclic esters such as γ-butyrolactone. Examples of hydrocarbons include aliphatic hydrocarbons having 5 to 12 carbon atoms such as n-pentane and n-hexane; and aromatic hydrocarbons having 6 to 16 carbon atoms such as toluene and xylene.

[0113] Of these, the solvent preferably contains at least one selected from the group consisting of esters and ketones, and more preferably contains at least one selected from the group consisting of polyhydric alcohol partial ether carboxylates and cyclic ketones.

[0114] (Other Optional Components) The present composition may further contain, as other components, components other than the radiation-sensitive acid generator, the polymer (F), and the solvent (hereinafter also referred to as "other optional components"). Examples of the other optional components include an acid diffusion controller other than the onium salt (Q), aromatic carboxylic acids (e.g., benzoic acid, salicylic acid, benzenedicarboxylic acid, etc.), aliphatic carboxylic acids (e.g., acetic acid, oxalic acid, pyruvic acid, 1-adamantanecarboxylic acid, etc.), surfactants, alicyclic skeleton-containing compounds (e.g., 2-adamantanone, t-butyl deoxycholate, etc.), sensitizers, and uneven distribution promoters.

[0115] <Method for producing radiation-sensitive composition> The present composition can be produced, for example, by mixing the polymer (A) and onium salt (Q), as well as other components such as a solvent as needed, in desired proportions, and filtering the resulting mixture, preferably using a filter (for example, a filter with a pore size of about 0.2 μm). The solids concentration of the present composition is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1% by mass or more. The solids concentration of the present composition is preferably 50% by mass or less, more preferably 20% by mass or less, and even more preferably 5% by mass or less. By setting the solids concentration of the present composition within the above range, good coatability can be achieved, and a good resist pattern shape can be obtained, which is advantageous.

[0116] The composition thus obtained can be used as a positive pattern-forming composition for forming a pattern using an alkaline developer, or as a negative pattern-forming composition for forming a pattern using a developer containing an organic solvent.

[0117] <<Method of Forming Resist Pattern>> The method of forming a resist pattern according to the present disclosure includes a step of applying the present composition to one surface of a substrate (hereinafter also referred to as the "coating step"), a step of exposing the resist film obtained by the coating step (hereinafter also referred to as the "exposure step"), and a step of developing the resist film exposed by the exposure step (hereinafter also referred to as the "developing step"). Examples of patterns formed by the method of forming a resist pattern according to the present disclosure include line and space patterns and hole patterns. Because the method of forming a resist pattern according to the present disclosure uses the present composition to form a resist film, it is possible to form a resist pattern with good sensitivity, reduced LWR, and good resolution. Each step will be described below.

[0118] <Coating Step> In the coating step, the composition is applied to one side of a substrate to form a resist film on the substrate. Conventional substrates can be used as the substrate on which the resist film is formed, including, for example, silicon wafers, silicon dioxide wafers, and aluminum-coated wafers. Alternatively, an organic or inorganic anti-reflective coating, such as that disclosed in JP-A-59-93448, may be formed on the substrate. Examples of methods for applying the composition include spin coating, casting coating, and roll coating. After coating, a soft bake (also referred to as SB or pre-bake (PB)) may be performed to volatilize the solvent in the coating. The SB temperature is preferably 60°C or higher, more preferably 80°C or higher. The SB temperature is preferably 140°C or lower, more preferably 120°C or lower. The SB time is preferably 5 seconds or longer, more preferably 10 seconds or longer. The SB time is preferably 600 seconds or shorter, more preferably 300 seconds or shorter. The average thickness of the resist film formed is preferably 10 to 1,000 nm, and more preferably 20 to 500 nm.

[0119] <Exposure Step> In the exposure step, the resist film obtained in the coating step is exposed. This exposure is carried out by irradiating the resist film with radiation through a photomask, and optionally through an immersion medium such as water. Examples of radiation include electromagnetic waves such as visible light, ultraviolet light, far ultraviolet light, extreme ultraviolet light (EUV), X-rays, and gamma rays; charged particle beams such as electron beams and alpha rays, depending on the line width of the desired pattern. Among these, the radiation irradiated onto the resist film formed using the present composition is preferably far ultraviolet light, EUV, or electron beams, more preferably ArF excimer laser light (wavelength 193 nm), KrF excimer laser light (wavelength 248 nm), EUV, or electron beams, even more preferably ArF excimer laser light, EUV, or electron beams, even more preferably EUV or electron beams, and particularly preferably EUV.

[0120] After the exposure, post-exposure baking (PEB) is preferably performed to promote dissociation of acid-dissociable groups in the exposed portions of the resist film by acid generated from a compound that generates acid upon exposure (such as a radiation-sensitive acid generator, an acid diffusion controller, or a polymer (A) containing a second structural unit). This PEB can increase the difference in solubility in a developer between the exposed and unexposed portions. The PEB temperature is preferably 50°C or higher, more preferably 80°C or higher. The PEB temperature is preferably 180°C or lower, more preferably 130°C or lower. The PEB time is preferably 5 seconds or longer, more preferably 10 seconds or longer. The PEB time is preferably 600 seconds or shorter, more preferably 300 seconds or shorter.

[0121] <Developing Step> In the developing step, the exposed resist film is developed. This allows a desired resist pattern to be formed. After development, the resist film is generally washed with a rinse liquid such as water or alcohol, and then dried. The developing method in the developing step may be alkali development or organic solvent development.

[0122] In the case of alkaline development, examples of the developer used for development include an alkaline aqueous solution containing at least one alkaline compound dissolved therein, such as sodium hydroxide, potassium hydroxide, sodium carbonate, sodium silicate, sodium metasilicate, aqueous ammonia, ethylamine, n-propylamine, diethylamine, di-n-propylamine, triethylamine, methyldiethylamine, ethyldimethylamine, triethanolamine, tetramethylammonium hydroxide (TMAH), pyrrole, piperidine, choline, 1,8-diazabicyclo-[5.4.0]-7-undecene, and 1,5-diazabicyclo-[4.3.0]-5-nonene. Among these, an aqueous TMAH solution is preferred, and a 2.38% by mass TMAH solution is more preferred. In the case of organic solvent development, examples of the developer include one or more organic solvents such as hydrocarbons, ethers, esters, ketones, and alcohols, and solvents containing the above organic solvents.

[0123] Examples of the developing method include a method of immersing a substrate in a tank filled with a developer for a certain period of time (dip method), a method of developing by piling up the developer on the surface of the substrate by surface tension and leaving it to stand for a certain period of time (puddle method), a method of spraying the developer onto the surface of the substrate (spray method), and a method of continuously discharging the developer while scanning a developer discharging nozzle at a constant speed onto a substrate that is rotating at a constant speed (dynamic dispense method).

[0124] <Onium Salt> The present disclosure provides an onium salt comprising a carboxylate anion and an onium cation, wherein the carboxylate anion has a (thio)acetal structure and the onium cation has a specific functional group bonded to an aromatic ring. Such an onium salt can provide a radiation-sensitive composition with excellent sensitivity, LWR performance, and resolution. For details of the onium salt of the present disclosure, the description of the onium (Q) is incorporated herein by reference.

[0125] The present invention will be specifically described below with reference to synthesis examples, examples, and comparative examples, but the present invention is not limited to the following examples. In the following examples, "parts" and "%" are by mass unless otherwise specified.

[0126] 1. Synthesis of Base Resin [Synthesis Examples A-1 to A-36] The types of monomers shown in Table 1 were combined and copolymerized in a tetrahydrofuran (THF) solvent, crystallized in methanol, and repeatedly washed with hexane, followed by isolation and drying to obtain polymers (A-1) to (A-36) having the compositions shown in Table 1. The weight-average molecular weight (Mw) and dispersity (Mw / Mn) of the polymers were measured by gel permeation chromatography (GPC) using GPC columns manufactured by Tosoh Corporation (two "G2000HXL", one "G3000HXL", and one "G4000HXL") under the following conditions. [GPC Measurement Conditions] Eluent: tetrahydrofuran (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Flow rate: 1.0 mL / min Sample concentration: 1.0 mass% Sample injection amount: 100 μL Column temperature: 40°C Detector: differential refractometer Standard material: monodisperse polystyrene

[0127]

[0128] The monomers (M-1) to (M-37) used in the synthesis of the base resin are shown below.

[0129] 2. Synthesis of high fluorine content polymers [Synthesis Examples FP-1 to FP-21] The types of monomers shown in Table 2 were combined and copolymerized in tetrahydrofuran (THF) solvent. After polymerization, the solvent was replaced with acetonitrile and the resulting mixture was washed with hexane. The solvent was then replaced with propylene glycol monomethyl ether acetate to obtain high fluorine content polymers (FP-1) to (FP-21) having the compositions shown in Table 2.

[0130]

[0131] The monomers (M-38) to (M-41) and (F-1) to (F-10) used in the synthesis of the high fluorine content polymer are shown below. The monomers (M-7) and (M-9) are as described above.

[0132] 3. Synthesis of Acid Diffusion Controller [Synthesis Example Q-1] Synthesis of Acid Diffusion Controller (Q-1)

[0133] 50 mmol of methyl 2-(4-hydroxyphenyl)-2-oxoacetate, 60 mmol of potassium carbonate, 60 mmol of potassium iodide, and 100 mL of acetone were added to a reaction vessel and cooled to 0°C. Next, 60 mmol of bromoacetone was added dropwise, and the mixture was stirred at room temperature for 5 hours. After completion of the reaction, the mixture was filtered, and the filtrate was concentrated. The resulting residue was diluted with ethyl acetate, and the organic layer was washed with 1 M hydrochloric acid, ultrapure water, and saturated aqueous sodium chloride solution. After drying over sodium sulfate, the solvent was distilled off, and the mixture was purified by silica gel column chromatography to obtain (ppQ-1). 40 mmol of (ppQ-1), 48 mmol of 2,2,3,3-tetrafluorobutane-1,4-diol, 4 mmol of sulfuric acid, and 100 mL of toluene were added to a reaction vessel, connected to a Dean-Stark tube, and heated to reflux at 130°C for 12 hours. After completion of the reaction, the mixture was quenched with saturated aqueous sodium bicarbonate solution, and the organic layer was washed with ultrapure water and saturated aqueous sodium chloride solution. After drying with sodium sulfate, the solvent was distilled off and the residue was purified by silica gel column chromatography to obtain (pQ-1). 20 mmol of (pQ-1), 40 mL of 1 M aqueous sodium hydroxide solution, and 40 mL of tetrahydrofuran were added to a reaction vessel and stirred at room temperature for 12 hours. Next, 20 mL of 1 M hydrochloric acid, 20 mmol of bis(3,4-difluorophenyl)(4-iodophenyl)sulfonium chloride, and 80 mL of dichloromethane were added and stirred vigorously for 5 hours. After completion of the reaction, the mixture was extracted with dichloromethane, and the organic layer was washed twice with ultrapure water. The solvent was distilled off to obtain acid diffusion controller (Q-1).

[0134] Synthesis Examples Q-2 to Q-6, Q-9, and Q-10 Acid diffusion controllers (Q-2) to (Q-6), (Q-9), and (Q-10) were obtained in the same manner as in Synthesis Example Q-1, except that the substrate was appropriately selected.

[0135] [Synthesis Example Q-7] Synthesis of Acid Diffusion Controller (Q-7)

[0136] 132 mmol of copper was suspended in 60 mL of tetrahydrofuran, and 60 mmol of methyl 2-bromo-2,2-difluoroacetate and 20 mmol of acrolein were added, followed by stirring at room temperature for 1 hour. Next, 18 mmol of tetramethylethylenediamine was added, and the mixture was stirred at room temperature for 5 hours. After completion of the reaction, the mixture was quenched with 60 mL of 2 M hydrochloric acid and extracted twice with 50 mL of ethyl acetate. The organic layer was then washed with saturated aqueous sodium chloride solution and dried over sodium sulfate. The solvent was distilled off, and the product was purified by silica gel column chromatography to obtain (ppQ-7). 10 mmol of (ppQ-7), 12 mmol of 2,2,3,3-tetrafluorobutane-1,4-diol, 1 mmol of sulfuric acid, and 50 mL of toluene were added to a reaction vessel, connected to a Dean-Stark tube, and heated to reflux at 130°C for 12 hours. After completion of the reaction, the mixture was quenched with saturated aqueous sodium bicarbonate solution, and the organic layer was washed with ultrapure water and saturated aqueous sodium chloride solution. After drying with sodium sulfate, the solvent was distilled off and the residue was purified by silica gel column chromatography to obtain (pQ-7). 7 mmol of (pQ-7), 14 mL of a 1 M aqueous sodium hydroxide solution, and 10 mL of tetrahydrofuran were added to a reaction vessel and stirred at room temperature for 12 hours. Next, 7 mL of 1 M hydrochloric acid, 7 mmol of phenylbis(4-(trifluoromethyl)phenyl)sulfonium chloride, and 20 mL of dichloromethane were added, and the mixture was vigorously stirred for 5 hours. After completion of the reaction, the mixture was extracted with dichloromethane, and the organic layer was washed twice with ultrapure water. The solvent was distilled off to obtain acid diffusion controller (Q-7).

[0137] Synthesis Example Q-8 An acid diffusion controller (Q-8) was obtained in the same manner as in Synthesis Example Q-7, except that the substrate was appropriately selected.

[0138] The structural formulae of the acid diffusion controllers (Q-1) to (Q-10) are as follows:

[0139] 4. Preparation of Radiation-Sensitive Compositions Among the components used in preparing the radiation-sensitive compositions of Examples 1 to 83 and Comparative Examples 1 to 6, those other than those mentioned above are listed below.

[0140] [Radiation-sensitive acid generators] B-1 to B-19

[0141] [Acid diffusion controller] cQ-1 to cQ-6

[0142] [Additives] D-1 to D-9

[0143] [Organic solvent] E-1: Propylene glycol monomethyl ether acetate E-2: Propylene glycol 1-monomethyl ether E-3: 4-hydroxy-4-methyl-2-pentanone E-4: Methyl 2-hydroxyisobutyrate

[0144] Example 1 100 parts by mass of polymer (A-1), 30 parts by mass of radiation-sensitive acid generator (B-1), 30 mol% of acid diffusion controller (Q-7) based on (B-1), 5 parts by mass of high fluorine content polymer (FP-1), 2,000 parts by mass of organic solvent (E-1), and 4,800 parts by mass of organic solvent (E-2) were blended together. The resulting mixture was filtered through a membrane filter with a pore size of 0.20 μm to prepare radiation-sensitive composition (R-1).

[0145] Examples 2 to 85 and Comparative Examples 1 to 6 Radiation-sensitive compositions (R-2) to (R-85) and (cR-1) to (cR-6) were prepared in the same manner as in Example 1, except that the types and amounts of each component shown in Tables 3 to 5 below were used. However, in Examples 21 to 27, which used polymers (A-21) to (A-27), the amount of acid diffusion controller (Q-7) was 30 mol % relative to the amount of the monomer (monomers (M-24) to (M-30)) providing the third structural unit contained in each of polymers (A-21) to (A-27). In Examples 28 and 29, which used polymers (A-28) and (A-29), the amount of acid diffusion controller (Q-7) was 10 mol % relative to the amount of the sulfonate anion-containing onium salt (monomers (M-24) and (M-31)) contained in each of polymers (A-28) and (A-29). In Examples 34 to 36, in which polymers (A-34) to (A-36) were used, the amount of acid diffusion controller (Q-7) was adjusted to 30 mol % based on the total amount of the monomer (monomer (M-24)) that provides the third structural unit contained in polymers (A-34) to (A-36) and the radiation-sensitive acid generator (B-1).

[0146]

[0147]

[0148]

[0149] 5. Formation and Evaluation of Resist Pattern <Formation of Resist Pattern> (EUV Exposure, Alkali Development) The radiation-sensitive composition prepared above was applied to the surface of a 12-inch silicon wafer on which a 50-nm-thick underlayer film (AL412 (Brewer Science)) had been formed using a spin coater (CLEAN TRACK ACT12, Tokyo Electron Ltd.), followed by spin-back baking at 130°C for 60 seconds and then cooling at 23°C for 30 seconds to form a 50-nm-thick resist film. Next, this resist film was irradiated with EUV light using an EUV exposure machine (model "NXE3400," ASML, NA=0.33, illumination conditions: Conventional s=0.89, mask imecDEFECT32FFR02). The resist film was subjected to PEB at 110°C for 60 seconds. Next, development was carried out using a 2.38 wt % aqueous solution of TMAH at 23° C. for 30 seconds to form a positive 32 nm line and space pattern.

[0150] <Evaluation> The sensitivity, LWR performance, minimum CD, and storage stability of each radiation-sensitive composition were evaluated by measuring each of the resist patterns formed above according to the methods described below. A scanning electron microscope (Hitachi High-Technologies Corporation's "CG-5000") was used to measure the resist patterns. The evaluation results are shown in Tables 6 to 8 below.

[0151] [Sensitivity] In forming the EUV resist pattern, the exposure amount for forming a 32 nm line and space pattern was defined as the optimum exposure amount, and this optimum exposure amount was used as the sensitivity (mJ / cm ２ The sensitivity was 40 mJ / cm ２ "A" if less than 40 mJ / cm ２ 45mJ / cm or more ２ "B" if less than 45 mJ / cm ２ More than 47mJ / cm ２ "C" if less than 47 mJ / cm ２ In the above cases, the result was judged as "D".

[0152] [LWR Performance] The resist pattern formed by EUV was observed from above using the scanning electron microscope. Line widths were measured at 50 random locations, and the 3 sigma value was calculated from the distribution of the measured values, which was designated as the LWR (unit: nm). The smaller the LWR value, the smaller the line chatter and the better the LWR performance. An LWR value of less than 2.6 nm was designated "A," a value of 2.6 nm or more but less than 2.8 nm was designated "B," and a value of 2.8 nm or more was designated "C."

[0153] [Minimum CD] The resist pattern formed by EUV was observed from above using the scanning electron microscope. In the pattern, the minimum value of the width of the space pattern that can be resolved without bridge defects or residue defects was defined as the minimum CD (nm). The smaller the minimum CD, the better the performance. A minimum CD value of less than 12.5 nm was rated "A," 12.5 nm or more but less than 13.0 nm was rated "B," and 13.0 nm or more was rated "C."

[0154] [Storage Stability] After preparing the radiation-sensitive compositions, they were stored for 30 days at two temperature levels: -15°C and 35°C. Thereafter, each radiation-sensitive composition was applied to the surface of a 12-inch silicon wafer on which a 20-nm-thick underlayer film (DUV42 (Nissan Chemicals)) had been formed using a spin coater (CLEAN TRACK ACT12, Tokyo Electron Ltd.). After SB at 110°C for 60 seconds, the wafer was cooled at 23°C for 30 seconds to form a 50-nm-thick resist film. Next, this resist film was irradiated with KrF light using a KrF exposure machine (model "S210D," Nikon, NA = 0.55, illumination conditions: Annular s = 0.8, mask 150 nm LS). The resist film was subjected to PEB at 110°C for 60 seconds. Next, a 2.38 wt% aqueous solution of TMAH was used for development at 23°C for 30 seconds to form a positive 150 nm line and space pattern. The exposure dose for forming this 150 nm line and space pattern was determined to be the optimal exposure dose. A sensitivity difference of ±0.5% or less between storage at -15°C and storage at 35°C was evaluated as "A," greater than ±0.5% and less than ±1.0% as "B," greater than ±1.0% and less than ±1.5% as "C," and greater than ±1.5% as "D."

[0155] [Overall Evaluation] In each evaluation, a total score was calculated with "A" being 3 points, "B" being 2 points, "C" being 1 point, and "D" being 0 point. The higher the total score, the better the result.

[0156]

[0157]

[0158]

[0159] As is clear from the results in Tables 6 to 8, the radiation-sensitive compositions of the Examples all showed well-balanced improvements in sensitivity, LWR, Minimum CD, and storage stability compared to the radiation-sensitive compositions of the Comparative Examples, and showed favorable results.

[0160]

[0023] The above results demonstrate that the radiation-sensitive composition and method for forming a resist pattern according to the present disclosure can improve sensitivity, LWR, minimum CD, and storage stability in a well-balanced manner. Therefore, the radiation-sensitive composition and method for forming a resist pattern according to the present disclosure can be suitably used in processes for fabricating semiconductor devices, which are expected to become even more miniaturized in the future.

Claims

1. A radiation-sensitive composition comprising: a polymer (A) having an acid-dissociable group; and an onium salt (Q) consisting of a carboxylate anion and an onium cation, wherein the carboxylate anion has a (thio)acetal structure; and the onium cation is an iodonium cation or a quaternary ammonium cation, or a sulfonium cation having an aromatic ring and at least one functional group selected from the group consisting of a fluoro group (excluding fluoro groups in fluoroalkyl groups), an iodo group, and a fluoroalkyl group, which is bonded to the aromatic ring.

2. The radiation-sensitive composition according to claim 1, wherein the onium salt (Q) is represented by the following formula (1): (In formula (1), A １ is a monovalent organic group having a (thio)acetal structure. １ is a monovalent anion represented by any one of the following formulas (1-1) to (1-5): ＋ is the onium cation. (In formulas (1-1) to (1-5), X １ is -C(R ４ ) (R ５ ) -, -NR ６ - or a group in which two hydrogen atoms have been removed from the ring portion of a substituted or unsubstituted aromatic ring. ４ , R ５ and R ６ are each independently a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. １ is a group in which (n1+3) hydrogen atoms have been removed from an aromatic ring. － and -COOH is B １ are bonded to carbon atoms in the same benzene ring in － The carbon atom to which R is bonded and the carbon atom to which —COOH is bonded are adjacent to each other. １ is a monovalent substituent. n is an integer of 0 or more. When n is 2 or more, multiple R １ are the same or different. ２ and R ３ is R ２ is an alkanediyl group, a substituted alkanediyl group, a cycloalkanediyl group, or a substituted cycloalkanediyl group, and R ３ is a hydrogen atom or an alkyl group, or R ２ and R ３ are combined together to form R ２ and R ３ represents an aliphatic ring structure formed together with the carbon atom to which X is attached. ２ and X ３ are each independently a single bond or a substituted or unsubstituted alkanediyl group. ２ is a group obtained by removing (r+1) hydrogen atoms from an aromatic ring. t is an integer from 1 to 5. "*" represents a bond.

3. The radiation-sensitive composition according to claim 1, wherein the carboxylic acid anion has a (thio)acetal ring structure.

4. The (thio)acetal ring structure is —CF ２ The radiation-sensitive composition according to claim 3, wherein the ring contains -.

5. The radiation-sensitive composition according to claim 1, wherein the polymer (A) contains a structural unit having an aromatic ring and a hydroxyl group bonded to the aromatic ring.

6. The radiation-sensitive composition according to claim 1, further comprising a non-polymeric onium salt that generates an acid stronger in acidity than the acid generated by said onium salt (Q) upon exposure.

7. The radiation-sensitive composition according to claim 1, wherein the polymer (A) contains a structural unit derived from an onium salt.

8. The radiation-sensitive composition according to claim 1, wherein the acid-dissociable group of the polymer (A) has an iodine atom.

9. The radiation-sensitive composition according to claim 1, wherein the onium cation is a sulfonium cation or an iodonium cation.

10. The onium cation is S ＋ or I ＋ and at least one selected from the group consisting of a fluoro group (excluding a fluoro group in a fluoroalkyl group), an iodo group, and a fluoroalkyl group is bonded to the aromatic ring.

11. A method for forming a resist pattern, comprising: forming a resist film on a substrate using the radiation-sensitive composition according to any one of claims 1 to 10; exposing the resist film; and developing the exposed resist film.

12. An onium salt comprising a carboxylate anion and an onium cation, wherein the carboxylate anion has a (thio)acetal structure, and the onium cation is an iodonium cation or a quaternary ammonium cation, or a sulfonium cation having an aromatic ring and at least one functional group selected from the group consisting of a fluoro group (excluding fluoro groups in fluoroalkyl groups), an iodo group, and a fluoroalkyl group, which is bonded to the aromatic ring.

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