Radiation-sensitive composition, pattern forming method, and onium salt

Abstract

The present invention provides: a radiation-sensitive composition which has excellent storage stability and is capable of exhibiting sensitivity, LWR, pattern rectangularity, CDU, and pattern circularity at sufficient levels when a pattern is formed; a pattern forming method; and an onium salt. This radiation-sensitive composition contains: an onium salt that is represented by formula (1-1) or (1-2); a polymer that contains a structural unit (I) having an acid-dissociable group; and a solvent.　[Chemical formula 1] (In formulae (1-1) and (1-2), Ar11 and Ar21 are each independently an (m2 + 1)-valent aromatic ring having 5 to 20 ring atoms. Ar12 is an (m3 + 1)-valent aromatic ring having 5 to 20 ring atoms. Ar22 is an m3-valent aromatic ring having 5 to 20 ring atoms, the aromatic ring constituting a fused ring structure together with two carbon atoms in formula (1-2). m1, m2 and m3 are each independently an integer of 0 to 5. In cases where m1 is 1, R1 is a monovalent organic group having 1 to 20 carbon atoms, a hydroxy group, a nitro group, a cyano group, an amino group, a halogen atom, or a sulfanyl group; and in cases where m1 is 2 or more, the plurality of R1s are the same as the R1 in the cases where m1 is 1, or two among the plurality of R1s combine with each other to form a cyclic structure having 3 to 10 carbon atoms, together with two carbon atoms of the ring in the formula to which the moieties are bonded. The plurality of R1s are the same as or different from each other. In cases where m2 is 1, R2 is the same as the R1 in the cases where m1 is 1; and in cases where m2 is 2 or more, the plurality of R2s are the same as the R1s in the cases where m1 is 2 or more. In cases where m3 is 1, R3 is the same as the R1 in the cases where m1 is 1; and in cases where m3 is 2 or more, the plurality of R3s are the same as the R1s in the cases where m1 is 2 or more. X is -CH2-, -O-, or -S-. Y is a single bond or a divalent linking group. The bonds expressed by the formula are each independently a single bond or a double bond.　[Chemical formula 2] In the formula, Z- is an organic acid anion having 2 or more carbon atoms.)

Description

Radiation-sensitive composition, pattern forming method, and onium salt

[0001] The present invention relates to a radiation-sensitive composition, a pattern forming method, and an onium salt.

[0002] Photolithography techniques using resist compositions are used to form fine circuits in semiconductor elements. A typical procedure involves, for example, exposing a coating of the resist composition to radiation through a mask pattern to generate an acid, which is then catalyzed by a reaction that causes a difference in the solubility of the polymer in alkaline or organic developers between exposed and unexposed areas, thereby forming a resist pattern on a substrate.

[0003] The photolithography technology described above is promoting pattern miniaturization by using short-wavelength radiation such as ArF excimer lasers, and further by using liquid immersion lithography, in which exposure is performed with the space between the lens of the exposure device and the resist film filled with a liquid medium. Lithography using even shorter-wavelength radiation such as electron beams, X-rays, and EUV (extreme ultraviolet) is also being considered as a next-generation technology.

[0004] Regarding photoacid generators, which are photosensitive components that are the main components of resist compositions, various structures have been investigated from the perspective of cationic structures (see JP 2013-114085 A).

[0005] JP 2013-114085 A

[0006] As patterns become increasingly finer, resist compositions are required to have storage stability as well as various resist performance characteristics that are equal to or better than conventional ones in terms of sensitivity, line width, LWR (Line Width Roughness) which indicates variation in the line width of the resist pattern, pattern rectangularity which indicates the rectangularity of the cross-sectional shape of the resist pattern, critical dimension uniformity (CDU) which is an index of the uniformity of line width and hole diameter, and pattern circularity which indicates the circularity of the hole shape.

[0007] An object of the present invention is to provide a radiation-sensitive composition, a pattern formation method, and an onium salt that have excellent storage stability and are capable of exhibiting sufficient levels of sensitivity, LWR, pattern rectangularity, CDU, and pattern circularity during pattern formation.

[0008] As a result of extensive research into solving the above problem, the present inventors have found that the above object can be achieved by employing the following configuration, and have thus completed the present invention.

[0009] That is, in one embodiment, the present invention relates to a radiation-sensitive composition comprising: an onium salt represented by the following formula (1-1) or (1-2) (hereinafter also referred to as "onium salt (1)"); a polymer containing a structural unit (I) having an acid-dissociable group; and a solvent. (In the above formulas (1-1) and (1-2), Ar １１ and Ar ２１ are each independently a ring having 5 to 20 members (m ２ +1)-valent aromatic ring. １２ is a ring having 5 to 20 members (m ３ +1)-valent aromatic ring. ２２ represents m, a 5-20 ring-membered group which forms a fused ring structure together with the two carbon atoms in formula (1-2). ３ It is a 2-valent aromatic ring. １ , m ２ and m ３ are each independently an integer of 0 to 5. １ If is 1, R １ represents a monovalent organic group having 1 to 20 carbon atoms, a hydroxy group, a nitro group, a cyano group, an amino group, a halogen atom, or a sulfanyl group; m １ If is 2 or more, R １ is m １ R when is 1 １ or a plurality of R １ Two of the R's are combined together to form a ring structure having 3 to 10 carbon atoms together with the two carbon atoms of the ring in the formula to which they are attached. １ are the same or different. ２ If is 1, R ２ is m１ R when is 1 １ is synonymous with; m ２ If is 2 or more, R ２ is m １ R when is 2 or more １ It is synonymous with m ３ If is 1, R ３ is m １ R when is 1 １ is synonymous with; m ３ If is 2 or more, R ３ is m １ R when is 2 or more １ X is -CH ２ Y is -, -O-, or -S-. Y is a single bond or a divalent linking group. The bonds represented by the following formulae are each independently a single bond or a double bond. Z - is an organic acid anion having two or more carbon atoms.

[0010] Because the radiation-sensitive composition contains onium salt (1) as a radiation-sensitive acid generator or acid diffusion controller, it has good storage stability and can exhibit excellent sensitivity, LWR, pattern rectangularity, CDU, and pattern circularity during pattern formation. Without being bound by any theory, the reason for this is presumed to be as follows: The sulfonium cation of onium salt (1) contains an alicyclic norbornene structure or a structure similar thereto (hereinafter, these are collectively referred to as "norbornene-based structures"), which results in significant steric hindrance around the carbon atom located at the α-position of the sulfonium cation, making it less susceptible to nucleophilic attack by nucleophiles. This improves the chemical stability of the cation, and as a result, improves storage stability. The sulfonium cation of onium salt (1) has high transparency to radiation and high quantum efficiency due to its norbornene-based structure, allowing it to efficiently generate acid throughout the entire thickness of the resist film. It is presumed that these combined effects enable the desired storage stability and resist performance to be exhibited.

[0011] In another embodiment, the present invention relates to a pattern forming method, comprising the steps of: applying the radiation-sensitive composition directly or indirectly to a substrate to form a resist film; exposing the resist film; and developing the exposed resist film with a developer.

[0012] The pattern formation method uses the radiation-sensitive composition, which has good storage stability and is excellent in sensitivity, LWR, pattern rectangularity, CDU, and pattern circularity during pattern formation, and therefore can efficiently form a high-quality resist pattern.

[0013] In yet another embodiment, the present invention relates to an onium salt represented by the following formula (1-1) or (1-2): (In the above formulas (1-1) and (1-2), Ar １１ and Ar ２１ are each independently a ring having 5 to 20 members (m ２ +1)-valent aromatic ring. １２ is a ring having 5 to 20 members (m ３ +1)-valent aromatic ring. ２２ represents m, a 5-20 ring-membered group which forms a fused ring structure together with the two carbon atoms in formula (1-2). ３ It is a 2-valent aromatic ring. １ , m ２ and m ３ are each independently an integer of 0 to 5. １ If is 1, R １ represents a monovalent organic group having 1 to 20 carbon atoms, a hydroxy group, a nitro group, a cyano group, an amino group, a halogen atom, or a sulfanyl group; m １ If is 2 or more, R １ is m １ R when is 1 １ or a plurality of R １ Two of the R's are combined together to form a ring structure having 3 to 10 carbon atoms together with the two carbon atoms of the ring in the formula to which they are attached. １ are the same or different. ２ If is 1, R ２ is m １R when is 1 １ is synonymous with; m ２ If is 2 or more, R ２ is m １ R when is 2 or more １ It is synonymous with m ３ If is 1, R ３ is m １ R when is 1 １ is synonymous with; m ３ If is 2 or more, R ３ is m １ R when is 2 or more １ X is -CH ２ Y is -, -O-, or -S-. Y is a single bond or a divalent linking group. The bonds represented by the following formulae are each independently a single bond or a double bond. Z - is an organic acid anion having two or more carbon atoms.

[0014] The onium salt has the above-mentioned chemical stability and acid generation efficiency, and is therefore suitable as a radiation-sensitive acid generator or acid diffusion controller for a radiation-sensitive composition.

[0015] In this specification, "number of ring members" refers to the number of atoms constituting a ring. For example, a biphenyl ring has 12 ring members, a naphthalene ring has 10 ring members, a fluorene ring has 13 ring members, and a pyrrole ring has 5 ring members. A "fused ring structure" refers to a structure in which adjacent rings share one edge (two adjacent atoms). An "organic group" refers to a group containing at least one carbon atom.

[0016] In this specification, the term "hydrocarbon group" includes linear hydrocarbon groups, alicyclic hydrocarbon groups, and aromatic hydrocarbon groups. This "hydrocarbon group" includes saturated hydrocarbon groups and unsaturated hydrocarbon groups. The term "linear hydrocarbon group" refers to a hydrocarbon group that does not contain a ring structure and is composed only of a linear structure, and includes both linear hydrocarbon groups and branched hydrocarbon groups. The term "alicyclic hydrocarbon group" refers to a hydrocarbon group that contains only an alicyclic structure as a ring structure and does not contain an aromatic ring structure, and includes both monocyclic alicyclic hydrocarbon groups and polycyclic alicyclic hydrocarbon groups (however, it does not have to be composed only of an alicyclic structure and may contain a linear 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, it does not have to be composed only of an aromatic ring structure and may contain an alicyclic structure or a linear structure as part of it).

[0017] Hereinafter, the embodiments of the present invention will be described in detail, but the present invention is not limited to these embodiments. Combinations of preferred aspects are also preferred.

[0018] <Radiation-Sensitive Composition> The radiation-sensitive composition according to this embodiment (hereinafter also referred to simply as the "composition") contains an onium salt (1), a polymer (hereinafter also referred to as the "base polymer") containing a structural unit (I) having an acid-dissociable group, and a solvent. The composition may contain other optional components as long as the effects of the present invention are not impaired. By containing the onium salt (1) as a radiation-sensitive acid generator or an acid diffusion controller, the radiation-sensitive composition has improved storage stability and can impart high levels of sensitivity, LWR, pattern rectangularity, CDU, and pattern circularity during pattern formation.

[0019] (Onium Salt (1)) The onium salt (1) is represented by the above formula (1) and functions as a radiation-sensitive acid generator or an acid diffusion controller. The type of function is determined by the organic acid anion. First, the sulfonium cation will be explained, followed by the organic acid anion.

[0020] In the above formulas (1-1) and (1-2), Ar １１ , Ar １２ , Ar２１ and Ar ２２ Examples of the aromatic ring having 5 to 20 ring members in the above formula include aromatic hydrocarbon rings such as a benzene ring, a naphthalene ring, an anthracene ring, a phenalene ring, a phenanthrene ring, a pyrene ring, a fluorene ring, and a perylene ring, aromatic heterocycles such as a furan ring, a pyrrole ring, a thiophene ring, a phosphole ring, a pyrazole ring, an oxazole ring, an isoxazole ring, a thiazole ring, a pyridine ring, a pyrazine ring, a pyrimidine ring, a pyridazine ring, and a triazine ring, and combinations thereof. The combination of these rings may be either a condensed ring or a ring assembly (a structure in which two rings are bonded by a single bond). As the aromatic ring, a benzene ring or a naphthalene ring is preferred, and a benzene ring is more preferred.

[0021] Ar １１ and Ar ２１ The ring members are 5 to 20 (m ２ As the aromatic ring having a valence of (m +1), the aromatic ring ２ A group in which 1) hydrogen atoms have been removed can be suitably used. １２ The ring members are 5 to 20 (m ３ As the aromatic ring having a valence of (m +1), the aromatic ring ３ A group in which 1) hydrogen atoms have been removed can be suitably used. ２２ m having 5 to 20 carbon atoms which constitutes a condensed ring structure together with the two carbon atoms in the formula ３ The aromatic ring may be any of the above aromatic rings. ３ A group in which one hydrogen atom has been removed can be preferably used. ２２ The aromatic ring in the formula forms a fused ring structure with the ring structure containing the sulfur atom and two carbon atoms.

[0022] m1, m2, and m3 are each independently preferably an integer of 0 to 4, more preferably an integer of 0 to 3, even more preferably an integer of 0 to 2, and particularly preferably 0 or 1. ２ and m ３ is Ar １１ , Ar １２ , Ar ２１ and Ar ２２It should be understood that the upper limit is determined depending on the number of hydrogen atoms in the aromatic ring.

[0023] R １ , R ２ and R ３ Examples of the monovalent organic group having 1 to 20 carbon atoms and represented by the formula (I) include a monovalent hydrocarbon group having 1 to 20 carbon atoms, a group having a divalent heteroatom-containing group between carbon atoms of the hydrocarbon group (between two adjacent or non-adjacent carbon atoms) or at the end of the hydrocarbon group, a group in which some or all of the hydrogen atoms of the hydrocarbon group have been substituted with a monovalent heteroatom-containing group, and combinations thereof.

[0024] Examples of the monovalent hydrocarbon group having 1 to 20 carbon atoms include a monovalent chain hydrocarbon group having 1 to 20 carbon atoms, a monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms, a monovalent aromatic hydrocarbon group having 6 to 20 carbon atoms, and combinations thereof.

[0025] Examples of the monovalent chain hydrocarbon group having 1 to 20 carbon atoms include alkyl groups such as a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, a sec-butyl group, and a tert-butyl group; alkenyl groups such as an ethenyl group, a propenyl group, and a butenyl group; and alkynyl groups such as an ethynyl group, a propynyl group, and a butynyl group.

[0026] Examples of the monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms include cycloalkyl groups such as a cyclopentyl group and a cyclohexyl group; cycloalkenyl groups such as a cyclopropenyl group, a cyclopentenyl group and a cyclohexenyl group; bridged ring saturated hydrocarbon groups such as a norbornyl group, an adamantyl group and a tricyclodecyl group; and bridged ring unsaturated hydrocarbon groups such as a norbornenyl group and a tricyclodecenyl group.

[0027] Examples of the monovalent aromatic hydrocarbon group having 6 to 20 carbon atoms include Ar １ Among the aromatic hydrocarbon rings shown as aromatic rings in the above, groups in which one hydrogen atom has been removed from a structure corresponding to 6 to 20 carbon atoms can be suitably used.

[0028] Examples of heteroatoms constituting the divalent or monovalent heteroatom-containing group include oxygen atoms, nitrogen atoms, sulfur atoms, phosphorus atoms, silicon atoms, halogen atoms, etc. Examples of halogen atoms include fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms.

[0029] Examples of the divalent heteroatom-containing group include -CO-, -CS-, -NH-, -O-, -S-, and combinations of these groups.

[0030] Examples of the monovalent heteroatom-containing group include a hydroxy group, a sulfanyl group, a cyano group, a nitro group, and a halogen atom.

[0031] R １ , R ２ and R ３ The monovalent organic group having 1 to 20 carbon atoms represented by the formula (I) is preferably an alkyl group, an alkoxy group, an alkoxycarbonyl group, a cycloalkyloxycarbonylalkoxy group, a group in which a hydrogen atom of any of these groups is substituted with the above-mentioned monovalent heteroatom-containing group, or a combination thereof.

[0032] Two R's １ Examples of the cyclic structure having 3 to 10 carbon atoms formed by combining and bonding together with the two carbon atoms of the ring in the above formula include structures corresponding to the 3 to 10 carbon atoms of the above monovalent alicyclic hydrocarbon groups having 3 to 20 carbon atoms, structures corresponding to the 3 to 10 carbon atoms of the above monovalent aromatic hydrocarbon groups having 6 to 20 carbon atoms, structures having the above divalent heteroatom-containing group between carbon atoms (between two adjacent or non-adjacent carbon atoms) of these structures, and combinations thereof. A benzene ring is preferred as the cyclic structure having 3 to 10 carbon atoms.

[0033] X is -CH ２ - or -O- is preferred, ２ - is more preferable.

[0034] The divalent linking group represented by Y is the same as R １ A group in which one hydrogen atom has been removed from a monovalent organic group having 1 to 20 carbon atoms, represented by the following formula: or the above divalent heteroatom-containing group can be suitably used.

[0035] Y is a single bond, -CH ２ -, -CO- or -O- is preferred, and a single bond is more preferred.

[0036] The double bond represented by the formula below also includes a bond formed in a cyclic π-electron conjugated (resonant) system in an aromatic ring.

[0037] The onium salt is preferably represented by the following formula (1-1a) or (1-2a). (In the above formulas (1-1a) and (1-2a), R １ , R ２ , R ３ , m １ , m ２ , m ３ , X, Y, Z - and the bonds represented by the following formulae have the same meanings as those in the above formulae (1-1) and (1-2), respectively.

[0038] Specific examples of the sulfonium cation of the onium salt (1) include, but are not limited to, structures represented by the following formulae (a-1) to (a-30).

[0039]

[0040]

[0041] As described above, the onium salt (1) functions as either a radiation-sensitive acid generator or an acid diffusion controller depending on the structure of the organic acid anion. The radiation-sensitive acid generator is a compound that generates an acid that induces dissociation of the acid-dissociable group upon exposure. The acid diffusion controller is a compound that generates an acid that does not induce dissociation of the acid-dissociable group upon exposure, and has the function of suppressing the diffusion of the acid generated from the radiation-sensitive acid generator in unexposed areas. The acid generated from the acid diffusion controller can be said to be a relatively weaker acid (having a higher pKa) than the acid generated from the radiation-sensitive acid generator. Whether the onium salt (1) functions as a radiation-sensitive acid generator or an acid diffusion controller depends on the energy required to dissociate the acid-dissociable group in the base polymer and the acidity of the acid generated upon exposure. The onium salt (1) may be contained in the radiation-sensitive composition in the form of a compound (isolated from the polymer), incorporated as part of the polymer, or both, although the form of a compound present alone is preferred.

[0042] Acids that are generated upon exposure include those that generate sulfonic acid, sulfonimide, sulfonmethide, carboxylic acid, and sulfonamide. The organic acid anion can have a structure corresponding to these.

[0043] Examples of such acids include: (1) compounds in which one or more fluorine atoms, cyano groups, or fluorinated hydrocarbon groups are substituted on the carbon atom at the α- or β-position of a sulfo group, (2) compounds having a sulfonimide structure containing a fluorine atom, (3) compounds having a sulfonemethide structure containing a fluorine atom, and (4) compounds in which the carbon atom at the α- or β-position of a sulfo group is not substituted with a fluorine atom or a fluorinated hydrocarbon group. Examples of carboxylic acids generated by exposure include: (5) compounds in which one or more fluorine atoms or fluorinated hydrocarbon groups are substituted on the carbon atom adjacent to a carboxy group, (6) compounds in which the carbon atom adjacent to a carboxy group is not substituted with a fluorine atom or a fluorinated hydrocarbon group, and (7) compounds having a sulfonamide structure which may have a fluorine atom.

[0044] Among these, the radiation-sensitive acid generator is preferably one corresponding to the above (1) to (3), and more preferably one having a cyclic structure, and the acid diffusion controller is preferably one corresponding to the above (4) to (7), and more preferably one corresponding to (4) or (6).

[0045] When the onium salt (1) is a radiation-sensitive acid generator, the organic acid anion of the onium salt (1) is preferably represented by the following formula (za). (In formula (z-a), R ４ is a monovalent organic group having 2 to 40 carbon atoms. ３ - A fluorine atom, a cyano group, or a monovalent fluorinated hydrocarbon group is bonded to the carbon atom at the α- or β-position of

[0046] R ４ The monovalent organic group having 2 to 40 carbon atoms represented by the formula (1-1) and (1-2) includes R １ A group in which the monovalent organic group having 1 to 20 carbon atoms represented by the following formula (I) is extended to have 2 to 40 carbon atoms can be suitably used.

[0047] R ４ is preferably a monovalent organic group having 3 to 40 carbon atoms and containing a cyclic structure. The organic group is not particularly limited and may be either a group containing only a cyclic structure or a group combining a cyclic structure and a chain structure. The cyclic structure may be a monocyclic ring, a polycyclic ring, or a combination thereof. The cyclic structure may be an alicyclic structure, an aromatic ring structure, or a combination thereof. In the case of a combination, the cyclic structures may be linked in a chain structure, or two or more cyclic structures may form a fused ring structure. These structures are preferably included as the smallest basic skeleton of the cyclic structure. The number of cyclic structures as the basic skeleton in the organic group may be one or two or more. The divalent heteroatom-containing group may be present between the carbon atoms forming the skeleton of the cyclic structure or the chain structure or at the terminal of the carbon chain, and hydrogen atoms on the carbon atoms of the cyclic structure or the chain structure may be substituted with other substituents.

[0048] The alicyclic structure includes R １A structure corresponding to the monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms in the above formula can be suitably employed.

[0049] The aromatic ring structure includes Ar in the above formulas (1-1) and (1-2). １１ A structure corresponding to the aromatic ring in the following formula can be suitably employed.

[0050] The chain structure may be any of R １ A structure corresponding to the monovalent chain hydrocarbon group having 1 to 20 carbon atoms in the above formula can be suitably employed.

[0051] The alicyclic structure may also be an aliphatic heterocyclic structure. Examples of the aliphatic heterocyclic structure include oxygen atom-containing aliphatic heterocyclic structures such as oxirane, tetrahydrofuran, tetrahydropyrane, dioxolane, and dioxane; nitrogen atom-containing aliphatic heterocyclic structures such as aziridine, pyrrolidine, piperidine, and piperazine; sulfur atom-containing aliphatic heterocyclic structures such as thietane, thiolane, and thiane; and aliphatic heterocyclic structures containing multiple heteroatoms such as morpholine, 1,2-oxathiolane, and 1,3-oxathiolane.

[0052] The aliphatic heterocyclic structure includes a lactone structure, a cyclic carbonate structure, a sultone structure, a cyclic acetal structure, a cyclic imide structure, or a combination thereof.

[0053] R ４ Preferably, contains the above alicyclic structure.

[0054] Examples of the substituent substituting a hydrogen atom on a carbon atom of the cyclic structure or chain structure include a halogen atom such as a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom; a hydroxy group; a carboxy group; a cyano group; a nitro group; an alkyl group, an alkoxy group, an alkoxycarbonyl group, an alkoxycarbonyloxy group, an acyl group, an acyloxy group, or a group in which a hydrogen atom of any of these groups has been substituted with a halogen atom; and an oxo group (═O).

[0055] Examples of the monovalent fluorinated hydrocarbon group include a monovalent fluorinated chain hydrocarbon group having 1 to 20 carbon atoms and a monovalent fluorinated alicyclic hydrocarbon group having 3 to 20 carbon atoms.

[0056] Examples of the monovalent fluorinated chain hydrocarbon group having 1 to 20 carbon atoms include fluorinated alkyl groups such as trifluoromethyl, 2,2,2-trifluoroethyl, pentafluoroethyl, 2,2,3,3,3-pentafluoropropyl, 1,1,1,3,3,3-hexafluoropropyl, heptafluoro-n-propyl, heptafluoro-i-propyl, nonafluoro-n-butyl, nonafluoro-i-butyl, nonafluoro-t-butyl, 2,2,3,3,4,4,5,5-octafluoro-n-pentyl, tridecafluoro-n-hexyl, and 5,5,5-trifluoro-1,1-diethylpentyl; fluorinated alkenyl groups such as trifluoroethenyl and pentafluoropropenyl; and fluorinated alkynyl groups such as fluoroethynyl and trifluoropropynyl.

[0057] Examples of the monovalent fluorinated alicyclic hydrocarbon group having 3 to 20 carbon atoms include fluorinated cycloalkyl groups such as a fluorocyclopentyl group, a difluorocyclopentyl group, a nonafluorocyclopentyl group, a fluorocyclohexyl group, a difluorocyclohexyl group, an undecafluorocyclohexylmethyl group, a fluoronorbornyl group, a fluoroadamantyl group, a fluorobornyl group, a fluoroisobornyl group, and a fluorotricyclodecyl group; and fluorinated cycloalkenyl groups such as a fluorocyclopentenyl group and a nonafluorocyclohexenyl group.

[0058] The fluorinated hydrocarbon group is preferably a monovalent fluorinated chain hydrocarbon group having 1 to 8 carbon atoms, more preferably a monovalent fluorinated straight chain hydrocarbon group having 1 to 5 carbon atoms.

[0059] Specific examples of the organic acid anion when the onium salt (1) is a radiation-sensitive acid generator include, but are not limited to, structures represented by the following formulas (z-1-1) to (z-1-30) (including the structure represented by the above formula (za)).

[0060]

[0061]

[0062] The onium salt (1) as a radiation-sensitive acid generator can be obtained by any combination of the above-mentioned sulfonium cation and the above-mentioned organic acid anion when the onium salt (1) is used as a radiation-sensitive acid generator. Specific examples include, but are not limited to, structures represented by the following formulas (1B-1) to (1B-30).

[0063]

[0064]

[0065]

[0066] The lower limit of the content of the onium salt (1) as the radiation-sensitive acid generator (the total amount when multiple types are included) is preferably 1 part by mass, more preferably 2 parts by mass, even more preferably 3 parts by mass, and particularly preferably 4 parts by mass, per 100 parts by mass of the base polymer described below. The upper limit of the content is preferably 50 parts by mass, more preferably 40 parts by mass, and even more preferably 30 parts by mass. This improves the storage stability of the composition, and enables it to exhibit excellent sensitivity, LWR, pattern rectangularity, CDU, and pattern circularity during resist pattern formation.

[0067] The composition may contain a known radiation-sensitive acid generator other than the onium salt (1) as the radiation-sensitive acid generator, as long as the effect of the present invention is not impaired.

[0068] When the onium salt (1) is an acid diffusion controller, the organic acid anion of the onium salt (1) is preferably represented by the following formula (z-b) or (z-c). (In formulas (z-b) and (z-c), R ５ and R ６ are each independently a monovalent organic group having 2 to 40 carbon atoms. ３ -No fluorine atom, cyano group, or monovalent fluorinated hydrocarbon group is bonded to the carbon atom at the α- or β-position of

[0069] R ５ and R ６ The monovalent organic group having 2 to 40 carbon atoms represented by the formula (za) is R ４ A monovalent organic group having 2 to 40 carbon atoms and represented by the following formula can be suitably used.

[0070] R ５ and R ６ Preferably, R contains a cyclic structure. ５ and R ６ As the cyclic structure of the formula (z-a), R ４ The cyclic structure shown in the formula (I) can be preferably employed.

[0071] Specific examples of the organic acid anion when the onium salt (1) is an acid diffusion controller include, but are not limited to, structures represented by the following formulae (z-2-1) to (z-2-18) (including the structures represented by the above formulae (z-b) and (z-c)).

[0072]

[0073] The onium salt (1) as an acid diffusion controller can be obtained by arbitrarily combining the above-mentioned sulfonium cation with the above-mentioned organic acid anion when the onium salt (1) is used as an acid diffusion controller. Specific examples include, but are not limited to, structures represented by the following formulas (1D-1) to (1D-23).

[0074]

[0075]

[0076]

[0077] The lower limit of the content of the onium salt (1) as the acid diffusion controller (the total amount when multiple types are included) is preferably 1 part by mass, more preferably 2 parts by mass, and even more preferably 3 parts by mass, per 100 parts by mass of the base polymer described below. The upper limit of the content is preferably 30 parts by mass, more preferably 20 parts by mass, and even more preferably 15 parts by mass. This improves the storage stability of the composition, and enables it to exhibit excellent sensitivity, LWR, pattern rectangularity, CDU, and pattern circularity during resist pattern formation.

[0078] The composition may contain a known acid diffusion controller other than the onium salt (1) as the acid diffusion controller, as long as the effect of the present invention is not impaired.

[0079] (Method for synthesizing onium salt (1)) The onium salt (1) can be synthesized typically according to the following scheme: However, the synthesis is not limited thereto, and known methods can also be used.

[0080] (In the scheme, R is a monovalent organic group which may be fluorinated. Z - has the same meaning as the above formulas (1-1) and (1-2).

[0081] Benzothiophene is reacted with a salt of a diaryliodonium cation of a strong acid to form a sulfonium cation. This is then reacted with cyclopentadiene to form a norbornene, which is then reacted with a salt having the desired organic acid anion for salt exchange, thereby synthesizing the desired onium salt (1). Other structures can also be synthesized by appropriately changing the starting materials, intermediate components, etc.

[0082] (Polymer) The polymer (i.e., base polymer) is an aggregate of polymer chains containing a structural unit having an acid-dissociable group (hereinafter also referred to as "structural unit (I)"). The "acid-dissociable group" refers to a group that substitutes a hydrogen atom in a carboxy group, a phenolic hydroxyl group, an alcoholic hydroxyl group, a sulfo group, or the like, and that dissociates under the action of an acid. The radiation-sensitive composition has excellent pattern formability because the polymer contains the structural unit (I).

[0083] In addition to the structural unit (I), the base polymer preferably contains a structural unit (II) containing at least one selected from the group consisting of a lactone structure, a cyclic carbonate structure, and a sultone structure, which will be described later, and may contain structural units other than the structural units (I) and (II). Each structural unit will be described below.

[0084] [Structural Unit (I)] The structural unit (I) is a structural unit containing an acid-dissociable group. The structural unit (I) is not particularly limited as long as it contains an acid-dissociable group, and examples thereof include a structural unit having a tertiary alkyl ester moiety, a structural unit having a structure in which the hydrogen atom of a phenolic hydroxyl group is substituted with a tertiary alkyl group, and a structural unit having an acetal bond. From the viewpoint of improving the pattern formability of the radiation-sensitive composition, a structural unit represented by the following formula (3) (hereinafter also referred to as "structural unit (I-1)") is preferred.

[0085]

[0086] In the above formula (3), R １７ is a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group. １８ is a monovalent hydrocarbon group having 1 to 20 carbon atoms. １９ and R ２０ L each independently represents a monovalent chain hydrocarbon group having 1 to 10 carbon atoms, a monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms, or a divalent alicyclic group having 3 to 20 carbon atoms formed by combining these groups together with the carbon atoms to which they are bonded. １１ teeth, ＊ -COO-, ＊ -L １１ａ COO- or ＊ -COOL １１ａ COO-. １１ａ is a substituted or unsubstituted alkanediyl group or arenediyl group. * is R １７ is the bond to the carbon atom to which it is bonded.

[0087] The above R １７ From the viewpoint of copolymerizability of the monomer that gives the structural unit (I-1), a hydrogen atom or a methyl group is preferred, and a methyl group is more preferred.

[0088] L １１ａ Examples of the alkanediyl group represented by the formula (I) include alkanediyl groups having 1 to 10 carbon atoms, such as a methylene group, an ethanediyl group, a 1,3-propanediyl group, and a 2,2-propanediyl group. １１ａ As the alkyl group, a methylene group or an ethanediyl group is preferred.

[0089] L １１ａ Examples of the arenediyl group represented by the formula (I) include divalent aromatic hydrocarbon groups having 6 to 20 carbon atoms, such as benzenediyl and naphthalenediyl groups. １１ａ As the alkyl group, a benzenediyl group is preferred.

[0090] L １１ａ Examples of the substituent that the arenediyl group represented by the formula (I) may have include a halogen atom, a hydroxy group, a carboxy group, a cyano group, a nitro group, an alkyl group, a fluorinated alkyl group, an alkoxycarbonyloxy group, an acyl group, an acyloxy group, and an alkoxy group.

[0091] The above R １８ The monovalent hydrocarbon group having 1 to 20 carbon atoms represented by the formula (1-1) and (1-2) includes R １ , R ２ and R ３ A monovalent hydrocarbon group having 1 to 20 carbon atoms in the above formula can be suitably used.

[0092] The above R １８ As the alkyl group, a linear or branched saturated hydrocarbon group having 1 to 10 carbon atoms, or an alicyclic hydrocarbon group having 3 to 20 carbon atoms is preferred.

[0093] The above R １９ and R ２０ Examples of the divalent alicyclic group having 3 to 20 carbon atoms formed by combining these groups together with the carbon atoms to which they are bonded include R １ , R ２ and R ３ A group in which one hydrogen atom has been removed from a monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms can be suitably used.

[0094] Among these, R １８ is an alkyl group having 1 to 4 carbon atoms, and R１９ and R ２０ The alicyclic structure formed by combining these together with the carbon atoms to which they are bonded is preferably a polycyclic or monocyclic cycloalkane structure.

[0095] Examples of the structural unit (I-1) include structural units represented by the following formulas (3-1) to (3-15) (hereinafter also referred to as "structural units (I-1-1) to (I-1-15)").

[0096]

[0097]

[0098] In the above formulas (3-1) to (3-15), R １７ ~R ２０ has the same meaning as in formula (3). Ｌ１１ is a halogen atom, a hydroxy group, a carboxy group, a cyano group, a nitro group, an alkyl group, a fluorinated alkyl group, an alkoxycarbonyloxy group, an acyl group, an acyloxy group, or an alkoxy group. i and j are each independently an integer of 1 to 4. k and l are each 0 or 1. 3a are each independently an integer of 0 to 3. When 3a is 2 or more, multiple R Ｌ１１ are the same or different from each other. a4 is an integer of 1 to 3.

[0099] i and j are preferably 1 or 2. １８ R is preferably a methyl group, an ethyl group, an isopropyl group, a t-butyl group, a cyclopentyl group, an ethenyl group, a phenyl group, or an iodophenyl group. １９ and R ２０ is preferably a methyl group or an ethyl group. Ｌ１１ By employing an iodine atom as the aryl group, an iodine group can be suitably introduced into the structural unit (I).

[0100] Furthermore, the polymer may contain structural units represented by the following formulae (1f) to (2f) as the structural unit (I).

[0101]

[0102] In the above formulas (1f) to (2f), R αｆR are each independently a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group. βｆ are each independently a hydrogen atom or a chain alkyl group having 1 to 5 carbon atoms. h1 is an integer of 1 to 4.

[0103] The above R βｆ is preferably a hydrogen atom, a methyl group or an ethyl group. h1 is preferably 1 or 2.

[0104] The base polymer may contain one type of structural unit (I) or a combination of two or more types.

[0105] The lower limit of the content of the structural unit (I) (the total content when multiple types are contained) relative to all structural units constituting the base polymer is preferably 10 mol%, more preferably 20 mol%, and even more preferably 30 mol%. The upper limit of this content is preferably 80 mol%, more preferably 70 mol%, and even more preferably 60 mol%. By setting the content of the structural unit (I) within this range, the pattern formability of the radiation-sensitive composition can be further improved.

[0106] [Structural Unit (II)] The structural unit (II) is a structural unit containing at least one selected from the group consisting of a lactone structure, a cyclic carbonate structure, and a sultone structure. By further including the structural unit (II), the base polymer can adjust its solubility in a developer, thereby improving the lithography performance, such as resolution, of the radiation-sensitive composition. Furthermore, the adhesion between a resist pattern formed from the base polymer and a substrate can be improved.

[0107] Examples of the structural unit (II) include structural units represented by the following formulae (T-1) to (T-11).

[0108]

[0109] In the above formula, R Ｌ１ is a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group. Ｌ２ ~R Ｌ５are each independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a cyano group, a trifluoromethyl group, a methoxy group, a methoxycarbonyl group, a hydroxy group, a hydroxymethyl group, or a dimethylamino group. Ｌ４ and R Ｌ５ may be a divalent alicyclic group having 3 to 8 carbon atoms formed by combining together with the carbon atoms to which they are attached. ２ is a single bond or a divalent linking group. X is an oxygen atom or a methylene group. k is an integer of 0 to 3. m is an integer of 1 to 3.

[0110] The above R Ｌ４ and R Ｌ５ The divalent alicyclic group having 3 to 8 carbon atoms formed by combining these groups together with the carbon atoms to which they are bonded includes R １９ and R ２０ Among divalent alicyclic groups having 3 to 20 carbon atoms constituted by combining these together with the carbon atoms to which they are bonded, groups having 3 to 8 carbon atoms are exemplified. One or more hydrogen atoms on this alicyclic group may be substituted with a hydroxy group.

[0111] The above L ２ Examples of the divalent linking group represented by the formula (I) include a divalent linear or branched hydrocarbon group having 1 to 10 carbon atoms, a divalent alicyclic hydrocarbon group having 4 to 12 carbon atoms, or a group composed of one or more of these hydrocarbon groups and at least one group selected from -CO-, -O-, -NH-, and -S-.

[0112] Of these, as the structural unit (II), a structural unit containing a lactone structure is preferred, a structural unit containing a γ-butyrolactone structure or a norbornane lactone structure is more preferred, and a structural unit derived from γ-butyrolactone-yl (meth)acrylate or norbornane lactone-yl (meth)acrylate is even more preferred.

[0113] The lower limit of the content of the structural unit (II) (the total content when multiple types are contained) relative to all structural units constituting the base polymer is preferably 10 mol%, more preferably 20 mol%, and even more preferably 25 mol%. The upper limit of the content is preferably 80 mol%, more preferably 70 mol%, and even more preferably 65 mol%. By setting the content of the structural unit (II) within the above range, the radiation-sensitive composition can further improve lithography performance such as resolution and adhesion of the formed resist pattern to the substrate.

[0114] [Structural Unit (III)] The base polymer optionally has other structural units in addition to the structural units (I) and (II). Examples of the other structural units include a structural unit (III) containing a polar group (excluding those corresponding to the structural unit (II)). By further including the structural unit (III), the base polymer can adjust its solubility in a developer, thereby improving the lithography performance, such as the resolution, of the radiation-sensitive composition. Examples of the polar group include a hydroxy group, a carboxy group, a cyano group, a nitro group, and a sulfonamide group. Among these, a hydroxy group and a carboxy group are preferred, and a hydroxy group is more preferred.

[0115] Examples of the structural unit (III) include structural units represented by the following formula:

[0116]

[0117] In the above formula, R Ａ is a hydrogen atom, a fluorine atom, a methyl group or a trifluoromethyl group.

[0118] When the base polymer has the structural unit (III) having the polar group, the lower limit of the content of the structural unit (III) (the total content when multiple types are contained) is preferably 2 mol%, more preferably 5 mol%, and even more preferably 8 mol%, based on all structural units constituting the base polymer. The upper limit of the content is preferably 30 mol%, more preferably 20 mol%, and even more preferably 15 mol%. By setting the content of the structural unit (III) within the above range, the lithography performance such as resolution of the radiation-sensitive composition can be further improved.

[0119] [Structural Unit (IV)] The base polymer optionally contains, as another structural unit, a structural unit having a phenolic hydroxyl group (hereinafter also referred to as "structural unit (IV)") in addition to the structural unit (III) having the polar group. The structural unit (IV) contributes to improving etching resistance and improving the difference in developer solubility (dissolution contrast) between exposed and unexposed areas. This polymer is suitable for pattern formation using exposure to radiation having a wavelength of 50 nm or less, such as a KrF excimer laser, electron beam, or EUV. In this case, it is preferable that the polymer contains the structural unit (I) in addition to the structural unit (IV).

[0120] The structural unit having a phenolic hydroxyl group is represented by, for example, the following formulas (4-1) to (4-6).

[0121]

[0122] In the above formulas (4-1) to (4-6), R ４１ are each independently a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group. Y is a halogen atom, a trifluoromethyl group, a cyano group, an alkyl group or an alkoxy group having 1 to 6 carbon atoms, or an acyl group, acyloxy group, or alkoxycarbonyl group having 2 to 7 carbon atoms. When there are multiple Ys, the multiple Ys may be the same or different. t is an integer of 0 to 4.

[0123] In order to obtain the structural unit (IV), it is preferable to polymerize the corresponding monomer in a state in which the phenolic hydroxyl group is protected with a protecting group such as an alkali-dissociable group (e.g., an acyl group) during polymerization, and then to obtain the structural unit (IV) by deprotecting the phenolic hydroxyl group by hydrolysis. The monomer may also be polymerized without protecting the phenolic hydroxyl group.

[0124] In the case of a polymer for exposure to a KrF excimer laser or radiation having a wavelength of 50 nm or less, the lower limit of the content of the structural unit (IV) (the total content when multiple types are contained) is preferably 10 mol %, more preferably 20 mol %, based on all structural units constituting the base polymer, and the upper limit of the content is preferably 70 mol %, more preferably 60 mol %.

[0125] [Other Structural Units] The base polymer may contain a structural unit having an alicyclic structure represented by the following formula (6) (hereinafter also referred to as "structural unit (VII)") as a structural unit other than the structural units listed above. (In the above formula (6), R １α is a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group. ２α is a monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms.

[0126] In the above formula (6), R ２α The monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms represented by the formula (1-1) and (1-2) includes R １ , R ２ and R ３ A monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms in the above formula can be suitably used.

[0127] When the base polymer contains the structural unit (VII), the lower limit of the content of the structural unit (VII) is preferably 2 mol%, more preferably 5 mol%, and even more preferably 8 mol%, based on the total structural units constituting the base polymer, and the upper limit of the content is preferably 30 mol%, more preferably 20 mol%, and even more preferably 15 mol%.

[0128] (Method of Synthesizing Base Polymer) The base polymer can be synthesized, for example, by polymerizing monomers that provide each structural unit in an appropriate solvent using a radical polymerization initiator or the like.

[0129] Examples of the radical polymerization initiator include azo radical initiators such as azobisisobutyronitrile (AIBN), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(2-cyclopropylpropionitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), and dimethyl 2,2'-azobisisobutyrate; and peroxide radical initiators such as benzoyl peroxide, t-butyl hydroperoxide, and cumene hydroperoxide. Among these, AIBN and dimethyl 2,2'-azobisisobutyrate are preferred, and AIBN is more preferred. These radical initiators can be used alone or in combination of two or more.

[0130] Examples of the solvent used in the polymerization include alkanes such as n-pentane, n-hexane, n-heptane, n-octane, n-nonane, and n-decane; cycloalkanes such as cyclohexane, cycloheptane, cyclooctane, decalin, and norbornane; aromatic hydrocarbons such as benzene, toluene, xylene, ethylbenzene, and cumene; halogenated hydrocarbons such as chlorobutanes, bromohexanes, dichloroethanes, hexamethylene dibromide, and chlorobenzene; saturated carboxylic acid esters such as ethyl acetate, n-butyl acetate, i-butyl acetate, and methyl propionate; lactones such as γ-butyrolactone; ketones such as acetone, methyl ethyl ketone, 2-butanone, 4-methyl-2-pentanone, and 2-heptanone; ethers such as tetrahydrofuran, dimethoxyethanes, diethoxyethanes, and 1,4-dioxanes; Examples of suitable solvents include alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 4-methyl-2-pentanol, 1-methoxy-2-propanol (propylene glycol monomethyl ether), etc. These solvents may be used alone or in combination of two or more.

[0131] The reaction temperature in the polymerization is usually 40° C. to 150° C., preferably 50° C. to 120° C. The reaction time is usually 1 hour to 48 hours, preferably 1 hour to 24 hours.

[0132] The molecular weight of the base polymer is not particularly limited, but the lower limit of the weight average molecular weight (Mw) in terms of polystyrene measured by gel permeation chromatography (GPC) is preferably 3,000, more preferably 4,000, and even more preferably 5,000. The upper limit of Mw is preferably 20,000, more preferably 10,000, and even more preferably 8,000. By setting the Mw of the base polymer within the above range, the resulting resist film can have good heat resistance and developability.

[0133] The ratio (Mw / Mn) of Mw to the polystyrene-equivalent number average molecular weight (Mn) of the base polymer as determined by GPC is usually 1 or more and 5 or less, preferably 1 or more and 3 or less, and more preferably 1 or more and 2 or less.

[0134] The Mw and Mn of the polymer in this specification are values ​​measured using gel permeation chromatography (GPC) under the following conditions.

[0135] GPC columns: 2 G2000HXL, 1 G3000HXL, 1 G4000HXL (all manufactured by Tosoh Corporation) Column temperature: 40°C Elution solvent: tetrahydrofuran Flow rate: 1.0 mL / min Sample concentration: 1.0 mass% Sample injection volume: 100 μL Detector: differential refractometer Standard material: monodisperse polystyrene

[0136] The content of the base polymer is preferably 60% by mass or more, more preferably 65% ​​by mass or more, and even more preferably 70% by mass or more, based on the total solid content of the radiation-sensitive composition.

[0137] (Other Polymers) The radiation-sensitive composition of the present embodiment may contain, as another polymer, a polymer having a higher mass content of fluorine atoms than the base polymer (hereinafter also referred to as a "high-fluorine content polymer"). When the radiation-sensitive composition contains a high-fluorine content polymer, the high-fluorine content polymer can be unevenly distributed in the surface layer of the resist film relative to the base polymer. As a result, it is possible to increase the water repellency of the surface of the resist film during immersion exposure, and to modify the surface of the resist film during EUV exposure and control the distribution of composition within the film.

[0138] The high fluorine content polymer may have, for example, a structural unit represented by the following formula (5) (hereinafter also referred to as "structural unit (V)").

[0139]

[0140] In the above formula (5), R １３ is a hydrogen atom, a methyl group, or a trifluoromethyl group. Ｌ represents a single bond, an alkanediyl group having 1 to 5 carbon atoms, an oxygen atom, a sulfur atom, -COO-, or -SO ２ -ONH-, -CONH-, -OCONH- or a combination thereof. １４ is a monovalent fluorinated chain hydrocarbon group having 1 to 20 carbon atoms or a monovalent fluorinated alicyclic hydrocarbon group having 3 to 20 carbon atoms.

[0141] The above R １３ As the alkyl group, from the viewpoint of copolymerizability of the monomer that gives the structural unit (V), a hydrogen atom or a methyl group is preferred, and a methyl group is more preferred.

[0142] Above G Ｌ As the group, from the viewpoint of copolymerizability of the monomer that gives the structural unit (V), a single bond and -COO- are preferred, and -COO- is more preferred.

[0143] The above R １４ Examples of the monovalent fluorinated chain hydrocarbon group having 1 to 20 carbon atoms represented by the formula (I) include a linear or branched alkyl group having 1 to 20 carbon atoms in which some or all of the hydrogen atoms have been substituted with fluorine atoms.

[0144] The above R １４Examples of the monovalent fluorinated alicyclic hydrocarbon group having 3 to 20 carbon atoms represented by the formula (I) include monocyclic or polycyclic hydrocarbon groups having 3 to 20 carbon atoms in which some or all of the hydrogen atoms have been substituted with fluorine atoms.

[0145] The above R １４ As the alkyl group, a fluorinated chain hydrocarbon group is preferable, a fluorinated alkyl group is more preferable, and a 2,2,2-trifluoroethyl group, a 2,2,3,3,3-pentafluoropropyl group, a 1,1,1,3,3,3-hexafluoropropyl group, and a 5,5,5-trifluoro-1,1-diethylpentyl group are even more preferable.

[0146] When the high-fluorine content polymer has the structural unit (V), the lower limit of the content of the structural unit (V) is preferably 50 mol%, more preferably 60 mol%, and even more preferably 70 mol%, based on all structural units constituting the high-fluorine content polymer. The upper limit of the content is preferably 95 mol%, more preferably 90 mol%, and even more preferably 85 mol%. By setting the content of the structural unit (V) within the above range, the mass content of fluorine atoms in the high-fluorine content polymer can be more appropriately adjusted, further promoting uneven distribution of fluorine atoms in the surface layer of the resist film, and as a result, the water repellency of the resist film during immersion exposure can be further improved.

[0147] The high-fluorine content polymer may have a fluorine atom-containing structural unit represented by the following formula (f-2) (hereinafter also referred to as structural unit (VI)) in addition to or instead of the structural unit (V): By having the structural unit (f-2), the high-fluorine content polymer has improved solubility in an alkaline developer, and can suppress the occurrence of development defects.

[0148]

[0149] The structural unit (VI) is roughly classified into two types: (x) a case having an alkali-soluble group, and (y) a case having a group that dissociates under the action of an alkali to increase the solubility in an alkali developer (hereinafter, also simply referred to as an "alkali-dissociable group"). In both (x) and (y), R Ｃis a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group. Ｄ is a single bond, a hydrocarbon group having 1 to 20 carbon atoms and a valence of (s+1), and R Ｅ Oxygen atom, sulfur atom, -NR at the end of ｄｄ R has a structure in which -, a carbonyl group, -COO-, -OCO-, or -CONH- is bonded, or a structure in which some of the hydrogen atoms in this hydrocarbon group are substituted with an organic group having a hetero atom. ｄｄ is a hydrogen atom or a monovalent hydrocarbon group having 1 to 10 carbon atoms. s is an integer of 1 to 3.

[0150] When the structural unit (VI) has an alkali-soluble group (x), R Ｆ is a hydrogen atom, and A １ is an oxygen atom, -COO-* or -SO ２ O-*. * is R Ｆ The binding site of W is shown. １ represents a single bond, a hydrocarbon group having 1 to 20 carbon atoms, or a divalent fluorinated hydrocarbon group. １ is an oxygen atom, W １ is A １ is a fluorinated hydrocarbon group having a fluorine atom or a fluoroalkyl group on the carbon atom to which R is bonded. Ｅ is a single bond or a divalent organic group having 1 to 20 carbon atoms. When s is 2 or 3, multiple R Ｅ , W １ , A １ and R Ｆ may be the same or different. When the structural unit (VI) has an alkali-soluble group (x), it is possible to increase affinity for an alkaline developer and suppress development defects. As the structural unit (VI) having an alkali-soluble group (x), A １ is an oxygen atom and W １ It is particularly preferred that is a 1,1,1,3,3,3-hexafluoro-2,2-methanediyl group.

[0151] When the structural unit (VI) has an alkali-dissociable group (y), R Ｆ is a monovalent organic group having 1 to 30 carbon atoms, and A １ is an oxygen atom, -NR ａａ-, -COO-*, -OCO-* or -SO ２ O-*. R ａａ is a hydrogen atom or a monovalent hydrocarbon group having 1 to 10 carbon atoms. * is R Ｆ The binding site of W is shown. １ is a single bond or a divalent fluorinated hydrocarbon group having 1 to 20 carbon atoms. Ｅ is a single bond or a divalent organic group having 1 to 20 carbon atoms. １ is -COO-*, -OCO-* or -SO ２ If O-*, then W １ or R Ｆ is A １ A has a fluorine atom on the carbon atom bonded to or adjacent to the carbon atom. １ is an oxygen atom, W １ , R Ｅ is a single bond, and R Ｄ is a hydrocarbon group having 1 to 20 carbon atoms. Ｅ A carbonyl group is bonded to the end of the R Ｆ is an organic group having a fluorine atom. When s is 2 or 3, a plurality of R Ｅ , W １ , A １ and R Ｆ may be the same or different. When the structural unit (VI) has an alkali-dissociable group (y), the surface of the resist film changes from hydrophobic to hydrophilic in the alkali development step. As a result, affinity to the developer is significantly increased, and development defects can be more efficiently suppressed. Examples of the structural unit (VI) having an alkali-dissociable group (y) include A １ is -COO-*, and R Ｆ Or W １ It is particularly preferred that both of them have a fluorine atom.

[0152] R Ｃ As the alkyl group, from the viewpoint of copolymerizability of the monomer that gives the structural unit (VI), a hydrogen atom or a methyl group is preferred, and a methyl group is more preferred.

[0153] R ＥWhen is a divalent organic group, it is preferably a group having a lactone structure, more preferably a group having a polycyclic lactone structure, and even more preferably a group having a norbornane lactone structure.

[0154] When the high-fluorine-content polymer has the structural unit (VI), the lower limit of the content of the structural unit (VI) is preferably 40 mol%, more preferably 50 mol%, and even more preferably 55 mol%, based on all structural units constituting the high-fluorine-content polymer. The upper limit of the content is preferably 95 mol%, more preferably 90 mol%, and even more preferably 85 mol%. By setting the content of the structural unit (VI) within the above range, it is possible to increase the water repellency of the resist film during immersion exposure and to improve the solubility in an alkaline developer, thereby suppressing the occurrence of development defects.

[0155] [Other Structural Units] The high fluorine content polymer may, if necessary, contain structural units other than the structural units listed above, such as the structural unit (I), the structural unit (III), or the structural unit (VII) in the base polymer.

[0156] When the high-fluorine content polymer contains the structural unit (I), the lower limit of the content of the structural unit (I) is preferably 5 mol %, more preferably 8 mol %, based on all structural units constituting the high-fluorine content polymer, and the upper limit of the content is preferably 40 mol %, more preferably 30 mol %.

[0157] When the high-fluorine content polymer contains the structural unit (III), the lower limit of the content of the structural unit (III) is preferably 5 mol %, more preferably 8 mol %, based on all structural units constituting the high-fluorine content polymer, and the upper limit of the content is preferably 50 mol %, more preferably 40 mol %.

[0158] When the high-fluorine content polymer contains the structural unit (VII), the lower limit of the content of the structural unit (VII) is preferably 20 mol %, more preferably 30 mol %, based on all structural units constituting the high-fluorine content polymer, and the upper limit of the content is preferably 60 mol %, more preferably 50 mol %.

[0159] The lower limit of Mw of the high fluorine content polymer is preferably 3,000, more preferably 4,000, and even more preferably 5,000. The upper limit of Mw is preferably 20,000, more preferably 10,000, and even more preferably 8,000.

[0160] The lower limit of Mw / Mn of the high fluorine content polymer is usually 1, more preferably 1.1. The upper limit of Mw / Mn is usually 5, preferably 3, more preferably 2.

[0161] When the radiation-sensitive composition contains a high-fluorine-containing polymer, the lower limit of the content of the high-fluorine-containing polymer is preferably 0.5 parts by mass, more preferably 1 part by mass, and even more preferably 1.5 parts by mass, relative to 100 parts by mass of the base polymer, and the upper limit of the content is preferably 15 parts by mass, more preferably 10 parts by mass, and even more preferably 8 parts by mass.

[0162] By setting the content of the high fluorine content polymer within the above range, the high fluorine content polymer can be more effectively localized in the surface layer of the resist film, which results in improving the water repellency of the surface of the resist film during immersion lithography, and enabling control of the surface modification of the resist film and the distribution of the composition within the film during EUV exposure. The radiation-sensitive composition may contain one or more high fluorine content polymers.

[0163] (Method for synthesizing high fluorine content polymer) The high fluorine content polymer can be synthesized by the same method as the above-mentioned method for synthesizing the base polymer.

[0164] (Solvent) The radiation-sensitive composition according to this embodiment contains a solvent. The solvent is not particularly limited as long as it can dissolve or disperse at least the onium salt (1), the base polymer, and optional components that may be contained as desired.

[0165] Examples of the solvent include alcohol-based solvents, ether-based solvents, ketone-based solvents, amide-based solvents, ester-based solvents, and hydrocarbon-based solvents.

[0166] Examples of alcohol-based solvents include monoalcohol-based solvents having 1 to 18 carbon atoms, such as iso-propanol, 4-methyl-2-pentanol, 3-methoxybutanol, n-hexanol, 2-ethylhexanol, furfuryl alcohol, cyclohexanol, 3,3,5-trimethylcyclohexanol, and diacetone alcohol; polyhydric alcohol-based solvents having 2 to 18 carbon atoms, such as ethylene glycol, 1,2-propylene glycol, 2-methyl-2,4-pentanediol, 2,5-hexanediol, diethylene glycol, dipropylene glycol, triethylene glycol, and tripropylene glycol; and polyhydric alcohol partial ether-based solvents in which some of the hydroxy groups in the above-mentioned polyhydric alcohol-based solvents, such as 3-methoxybutanol and 1-methoxy-2-propanol (propylene glycol monomethyl ether), are etherified. In this embodiment, alcoholic acid ester solvents such as methyl lactate, ethyl lactate, propyl lactate, butyl lactate, methyl 2-hydroxyisobutyrate, i-propyl 2-hydroxyisobutyrate, i-butyl 2-hydroxyisobutyrate, and n-butyl 2-hydroxyisobutyrate are also included in the alcoholic solvents.

[0167] Examples of ether-based solvents include dialkyl ether-based solvents such as diethyl ether, dipropyl ether, and dibutyl ether; cyclic ether-based solvents such as tetrahydrofuran and tetrahydropyran; aromatic ring-containing ether-based solvents such as diphenyl ether and anisole (methyl phenyl ether); and polyhydric alcohol ether-based solvents obtained by etherifying the hydroxy groups of the above-mentioned polyhydric alcohol-based solvents.

[0168] Examples of ketone solvents include chain ketone solvents such as acetone, butanone, and methyl-iso-butyl ketone; cyclic ketone solvents such as cyclopentanone, cyclohexanone, and methylcyclohexanone; and 2,4-pentanedione, acetonylacetone, and acetophenone.

[0169] Examples of the amide solvent include cyclic amide solvents such as N,N'-dimethylimidazolidinone and N-methylpyrrolidone; and chain amide solvents such as N-methylformamide, N,N-dimethylformamide, N,N-diethylformamide, acetamide, N-methylacetamide, N,N-dimethylacetamide, and N-methylpropionamide.

[0170] Examples of ester-based solvents include monocarboxylic acid ester-based solvents such as n-butyl acetate; polyhydric alcohol partial ether acetate-based solvents such as diethylene glycol mono-n-butyl ether acetate, propylene glycol monomethyl ether acetate, and dipropylene glycol monomethyl ether acetate; lactone-based solvents such as γ-butyrolactone and valerolactone; carbonate-based solvents such as diethyl carbonate, ethylene carbonate, and propylene carbonate; and polyvalent carboxylic acid diester-based solvents such as propylene glycol diacetate, methoxytriglycol acetate, diethyl oxalate, ethyl acetoacetate, and diethyl phthalate.

[0171] Examples of hydrocarbon solvents include aliphatic hydrocarbon solvents such as n-hexane, cyclohexane, and methylcyclohexane; and aromatic hydrocarbon solvents such as benzene, toluene, di-isopropylbenzene, and n-amylnaphthalene.

[0172] Among these, alcohol-based solvents, ester-based solvents, and ketone-based solvents are preferred, alcohol acid ester-based solvents, polyhydric alcohol partial ether acetate-based solvents, lactone-based solvents, and cyclic ketone-based solvents are more preferred, and ethyl lactate, propylene glycol monomethyl ether acetate, γ-butyrolactone, and cyclohexanone are even more preferred. The radiation-sensitive composition may contain one or more solvents.

[0173] (Other Optional Components) The radiation-sensitive composition may contain other optional components in addition to the components described above. Examples of the other optional components include a crosslinking agent, a localization promoter, a surfactant, an alicyclic skeleton-containing compound, and a sensitizer. These other optional components may be used alone or in combination of two or more.

[0174] <Method for Preparing Radiation-Sensitive Composition> The radiation-sensitive composition can be prepared, for example, by mixing the onium salt (1), the polymer, and, if necessary, a high-fluorine-content polymer, and a solvent in a predetermined ratio. After mixing, the radiation-sensitive composition is preferably filtered, for example, through a filter having a pore size of about 0.05 μm to 0.40 μm. The solids concentration of the radiation-sensitive composition is usually 0.1% by mass to 50% by mass, preferably 0.5% by mass to 30% by mass, and more preferably 1% by mass to 20% by mass.

[0175] <Pattern Forming Method> A pattern forming method according to one embodiment of the present invention includes: a step (1) of applying the radiation-sensitive composition directly or indirectly to a substrate to form a resist film (hereinafter also referred to as a "resist film forming step"); a step (2) of exposing the resist film (hereinafter also referred to as an "exposure step"); and a step (3) of developing the exposed resist film with a developer (hereinafter also referred to as a "development step").

[0176] According to the pattern formation method, a high-quality resist pattern can be efficiently formed because the radiation-sensitive composition has good storage stability and is capable of exhibiting excellent sensitivity, LWR, pattern rectangularity, CDU, and pattern circularity during pattern formation.

[0177] [Resist Film Forming Step] In this step (step (1) above), a resist film is formed from the radiation-sensitive composition. Examples of substrates on which the resist film is formed include conventionally known substrates such as silicon wafers, silicon dioxide wafers, and aluminum-coated wafers. Alternatively, an organic or inorganic anti-reflective coating, such as those disclosed in JP-B-6-12452 and JP-A-59-93448, may be formed on the substrate. Examples of coating methods include spin coating, casting coating, and roll coating. After coating, if necessary, pre-baking (PB) may be performed to volatilize the solvent in the coating film. The PB temperature is typically 60°C to 140°C, and preferably 80°C to 120°C. The PB time is typically 5 to 600 seconds, and preferably 10 to 300 seconds.

[0178] The lower limit of the thickness of the resist film to be formed is preferably 10 nm, more preferably 15 nm, and even more preferably 20 nm, and the upper limit is preferably 300 nm, more preferably 200 nm, and even more preferably 100 nm.

[0179] When performing immersion exposure, regardless of whether the radiation-sensitive composition contains a water-repellent polymer additive such as a high-fluorine-content polymer, a protective film for immersion exposure that is insoluble in the immersion liquid may be provided on the formed resist film in order to prevent direct contact between the immersion liquid and the resist film. The protective film for immersion exposure may be either a solvent-peelable protective film that is peeled off with a solvent before the development step (see, for example, JP-A No. 2006-227632), or a developer-peelable protective film that is peeled off simultaneously with development in the development step (see, for example, WO 2005-069076 and WO 2006-035790). However, from the viewpoint of throughput, it is preferable to use a developer-peelable protective film for immersion exposure.

[0180] When the next exposure step is carried out using radiation having a wavelength of 50 nm or less, it is preferable to use a polymer having the structural units (I) and (IV) as the base polymer in the composition.

[0181] [Exposure Step] In this step (step (2) above), the resist film formed in the resist film formation step (1) above is exposed to radiation through a photomask (or, in some cases, through an immersion liquid such as water). Examples of radiation used for exposure include electromagnetic waves such as visible light, ultraviolet light, far ultraviolet light, EUV (extreme ultraviolet), X-rays, and gamma rays; and charged particle beams such as electron beams and alpha rays, depending on the line width of the desired pattern. Among these, far ultraviolet light, electron beams, and EUV are preferred, with ArF excimer laser light (wavelength 193 nm), KrF excimer laser light (wavelength 248 nm), electron beams, and EUV being more preferred, and electron beams and EUV with wavelengths of 50 nm or less, which are positioned as next-generation exposure technologies, being even more preferred.

[0182] When exposure is performed by immersion exposure, examples of the immersion liquid used include water and fluorine-based inert liquids. The immersion liquid is preferably a liquid that is transparent to the exposure wavelength and has as small a temperature coefficient of refractive index as possible so as to minimize distortion of the optical image projected onto the film. However, particularly when the exposure light source is an ArF excimer laser beam (wavelength 193 nm), water is preferred from the above-mentioned viewpoints, as well as from the viewpoints of ease of availability and ease of handling. When water is used, a small proportion of an additive that reduces the surface tension of water and increases its surfactant power may be added. It is preferable that this additive does not dissolve the resist film on the wafer and has negligible effect on the optical coating on the underside of the lens. Distilled water is preferred as the water used.

[0183] After the exposure, post-exposure baking (PEB) is preferably performed to promote dissociation of acid-dissociable groups in the polymer or the like in the exposed portions of the resist film by the acid generated from the radiation-sensitive acid generator upon exposure. This PEB results in a difference in solubility in a developer between the exposed and unexposed portions. The PEB temperature is typically 50°C to 180°C, preferably 80°C to 130°C. The PEB time is typically 5 seconds to 600 seconds, preferably 10 seconds to 300 seconds.

[0184] [Development Step] In this step (step (3) above), the resist film exposed in the exposure step (step (2) above) is developed. This allows a predetermined 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.

[0185] In the case of alkaline development, the developer used in the development may be, for example, 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, or 1,5-diazabicyclo-[4.3.0]-5-nonene. Among these, an aqueous TMAH solution is preferred, and a 2.38 mass % aqueous TMAH solution is more preferred.

[0186] In the case of organic solvent development, examples of the organic solvent include hydrocarbon solvents, ether solvents, ester solvents, ketone solvents, and alcohol solvents, as well as solvents containing an organic solvent. Examples of the organic solvent include one or more of the solvents listed above as solvents for the radiation-sensitive composition. Among these, ether solvents, ester solvents, and ketone solvents are preferred. As the ether solvent, glycol ether solvents are preferred, and ethylene glycol monomethyl ether and propylene glycol monomethyl ether are more preferred. As the ester solvent, acetate ester solvents are preferred, and n-butyl acetate and amyl acetate are more preferred. As the ketone solvent, chain ketones are preferred, and 2-heptanone is more preferred. The content of the organic solvent in the developer is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 99% by mass or more. Examples of components other than the organic solvent in the developer include water and silicone oil.

[0187] As mentioned above, the developer may be either an alkaline developer or an organic solvent developer, and can be appropriately selected depending on whether the desired pattern is a positive or negative pattern.

[0188] 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 a 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 rotating at a constant speed (dynamic dispense method).

[0189] <Onium Salt> The onium salt is represented by the above formula (1-1) or (1-2): As such an onium salt, the onium salt (1) in the radiation-sensitive composition can be suitably used.

[0190] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Measurement methods for various physical properties are shown below.

[0191] [Weight-average molecular weight (Mw) and number-average molecular weight (Mn)] The Mw and Mn of the polymer were measured under the conditions described above. The dispersity (Mw / Mn) was calculated from the measurement results of Mw and Mn.

[0192] [ １３ C-NMR analysis of polymers and high fluorine content polymers １３ C-NMR analysis was carried out using a nuclear magnetic resonance spectrometer (JNM-Delta400 manufactured by JEOL Ltd.).

[0193] <Synthesis of Polymer> The monomers used in the synthesis of each polymer in each Example and Comparative Example are shown below. In the following synthesis examples, unless otherwise specified, parts by mass refer to a value when the total mass of the monomers used is taken as 100 parts by mass, and mol % refers to a value when the total number of moles of the monomers used is taken as 100 mol %.

[0194]

[0195] Synthesis Example 1 Synthesis of Polymer (A-1) Monomer (M-1), monomer (M-2), monomer (M-5), monomer (M-10), and monomer (M-14) were dissolved in 2-butanone (200 parts by mass) to a molar ratio of 40 / 10 / 20 / 20 / 10 (mol %), and AIBN (azobisisobutyronitrile) (5 mol % relative to 100 mol % of the total monomers used) was added as an initiator to prepare a monomer solution. 2-butanone (100 parts by mass) was placed in a reaction vessel, and after purging with nitrogen for 30 minutes, the reaction vessel was heated to 80°C, and the monomer solution was added dropwise over 3 hours with stirring. The start of the dropwise addition marked the start of the polymerization reaction, and the polymerization reaction was carried out for 6 hours. After completion of the polymerization reaction, the polymerization solution was cooled to below 30°C with water. The cooled polymerization solution was poured into methanol (2,000 parts by mass), and the precipitated white powder was filtered off. The filtered white powder was washed twice with methanol, filtered off, and dried at 50°C for 24 hours to obtain a white powdery polymer (A-1) (yield: 85%). The Mw of the polymer (A-1) was 7,100, and the Mw / Mn was 1.61. １３ As a result of C-NMR analysis, the contents of the structural units derived from (M-1), (M-2), (M-5), (M-10) and (M-14) were 40.3 mol%, 9.2 mol%, 20.5 mol%, 19.8 mol% and 10.2 mol%, respectively.

[0196] Synthesis Examples 2 to 11 (Synthesis of Polymers (A-2) to (A-11)) Polymers (A-2) to (A-11) were synthesized in the same manner as in Synthesis Example 1, except that the types and blending ratios of monomers shown in Table 1 below were used. The content (mol %) of each structural unit and physical properties (Mw and Mw / Mn) of the resulting polymers are also shown in Table 1 below. In Table 1 below, "-" indicates that the corresponding component was not used (the same applies to the following tables).

[0197]

[0198] Synthesis Example 12 Synthesis of Polymer (A-12) Monomer (M-1) and monomer (M-18) were dissolved in 1-methoxy-2-propanol (200 parts by mass) to a molar ratio of 50 / 50 (mol %), and AIBN (5 mol %) was added as an initiator to prepare a monomer solution. 1-Methoxy-2-propanol (100 parts by mass) was placed in a reaction vessel, and after purging with nitrogen for 30 minutes, the reaction vessel was heated to 80°C and the monomer solution was added dropwise over 3 hours with stirring. The start of the dropwise addition marked the start of the polymerization reaction, and the polymerization reaction was carried out for 6 hours. After completion of the polymerization reaction, the polymerization solution was cooled with water to below 30°C. The cooled polymerization solution was poured into hexane (2,000 parts by mass), and the precipitated white powder was filtered off. The filtered white powder was washed twice with hexane, filtered off, and dissolved in 1-methoxy-2-propanol (300 parts by mass). Next, methanol (500 parts by mass), triethylamine (50 parts by mass), and ultrapure water (10 parts by mass) were added, and a hydrolysis reaction was carried out at 70°C for 6 hours while stirring. After completion of the reaction, the remaining solvent was distilled off, and the resulting solid was dissolved in acetone (100 parts by mass) and added dropwise to water (500 parts by mass) to coagulate the polymer. The resulting solid was filtered and dried at 50°C for 13 hours to obtain a white powdery polymer (A-12) (yield: 81%). The Mw of the polymer (A-12) was 5,500, and the Mw / Mn was 1.62. １３ As a result of C-NMR analysis, the content ratios of the structural units derived from (M-1) and (M-18) were 50.2 mol % and 49.8 mol %, respectively.

[0199] [Synthesis Examples 13 to 15] (Synthesis of Polymers (A-13) to (A-15)) Polymers (A-13) to (A-15) were synthesized in the same manner as in Synthesis Example 12, except that the types and blending ratios of monomers shown in Table 2 below were used. Note that the monomer providing the structural unit (IV) in the polymers was １３ C-NMR analysis confirmed that the peaks of the carbonyl groups of the acetyl groups had disappeared, and that substantially all of the alkali-dissociable groups had been hydrolyzed to phenolic hydroxyl groups. The content (mol %) of each structural unit and physical properties (Mw and Mw / Mn) of the obtained polymer are also shown in Table 2 below.

[0200]

[0201] Synthesis Example 16 Synthesis of High Fluorine-Content Polymer (F-1) Monomer (M-1) and monomer (M-20) were dissolved in 2-butanone (200 parts by mass) to a molar ratio of 20 / 80 (mol %), and AIBN (4 mol %) was added as an initiator to prepare a monomer solution. 2-Butanone (100 parts by mass) was placed in a reaction vessel, and after purging with nitrogen for 30 minutes, the reaction vessel was heated to 80°C and the monomer solution was added dropwise over 3 hours with stirring. The start of the dropwise addition marked the start of the polymerization reaction, and the polymerization reaction was carried out for 6 hours. After completion of the polymerization reaction, the polymerization solution was cooled with water to below 30°C. The solvent was replaced with acetonitrile (400 parts by mass), and then hexane (100 parts by mass) was added, stirred, and the acetonitrile layer was collected. This process was repeated three times. The solvent was replaced with propylene glycol monomethyl ether acetate, yielding a solution of high fluorine-content polymer (F-1) (yield: 75%). The high fluorine content polymer (F-1) had an Mw of 6,200 and an Mw / Mn ratio of 1.77. １３ As a result of C-NMR analysis, the content ratios of the structural units derived from (M-1) and (M-20) were 19.5 mol % and 80.5 mol %, respectively.

[0202] [Synthesis Examples 17 to 20] (Synthesis of high fluorine content polymer (F-2) to high fluorine content polymer (F-5)) High fluorine content polymer (F-2) to high fluorine content polymer (F-5) were synthesized in the same manner as in Synthesis Example 16, except for using monomers of the types and blending ratios shown in the following Table 3. The content (mol %) of each structural unit and physical properties (Mw and Mw / Mn) of the obtained high fluorine content polymers are also shown in the following Table 3.

[0203]

[0204] <Synthesis of Onium Salt (1) as Radiation-Sensitive Acid Generator [B]> [Example B1] (Synthesis of Compound (B-1)) Compound (B-1) was synthesized according to the following synthesis scheme.

[0205]

[0206] A reaction vessel was charged with 20.0 mmol of benzothiophene and diphenyliodonium trifluoromethanesulfonate (TfO - 20.0 mmol of methyl methylcellulose, 2.0 mmol of copper(II) acetate, and 50 g of toluene were added and reacted at 100°C for 12 hours. After that, saturated aqueous ammonium chloride solution was added to terminate the reaction, followed by extraction with dichloromethane and separation of the organic layer. After drying with sodium sulfate, the solvent was distilled off and the sulfonium compound was purified by column chromatography, yielding a good yield.

[0207] The sulfonium compound was added with 30.0 mmol of cyclopentadiene and 50 g of dichloromethane, and the mixture was stirred at room temperature for 4 hours. Thereafter, the solvent was distilled off, and the mixture was purified by column chromatography to obtain a norbornene compound in good yield.

[0208] 20.0 mmol of potassium nonafluoro-1-butanesulfonate was added to the norbornene compound, and a mixture of water and dichloromethane (1:3 (mass ratio)) was added to prepare a 0.5 M solution. After vigorously stirring at room temperature for 3 hours, dichloromethane was added for extraction, and the organic layer was separated. The obtained organic layer was dried over sodium sulfate, and the solvent was distilled off. The resulting mixture was purified by column chromatography to obtain compound (B-1) represented by formula (B-1) in good yield.

[0209] [Examples B2 to B16] (Synthesis of Compounds (B-2) to (B-16)) Radiation-sensitive acid generators represented by the following formulas (B-2) to (B-16) were synthesized in the same manner as in Example B1, except that the raw materials and precursors were appropriately changed.

[0210]

[0211]

[0212] Example B17 Synthesis of Compound (B-17) Compound (B-17) was synthesized according to the following synthesis scheme.

[0213]

[0214] 20.0 mmol of compound (B-1), 2.0 mmol of Pd / C, and 50 g of methanol were added to a reaction vessel and reacted at room temperature for 12 hours under a hydrogen atmosphere. The Pd / C in the reaction solution was then removed by filtration through Celite. The solvent in the resulting filtrate was evaporated, and the residue was purified by column chromatography to obtain compound (B-17) represented by formula (B-17) in good yield.

[0215] The following compounds were used as components other than the components synthesized above.

[0216] [Radiation-sensitive acid generators other than radiation-sensitive acid generators (B-1) to (B-17)] b-1 to b-14: compounds represented by the following formulas (b-1) to (b-14) (hereinafter, the compounds represented by formulas (b-1) to (b-14) may be referred to as "compound (b-1)" to "compound (b-14)," respectively).

[0217]

[0218]

[0219] [Synthesis of Onium Salt (1) as Acid Diffusion Controller [D]] [Example D1] (Synthesis of Compound (D-1)) Compound (D-1) was synthesized according to the following synthesis scheme.

[0220]

[0221] A reaction vessel was charged with 20.0 mmol of benzothiophene and diphenyliodonium trifluoromethanesulfonate (TfO - 20.0 mmol of methyl methylcellulose, 2.0 mmol of copper(II) acetate, and 50 g of toluene were added and reacted at room temperature for 12 hours. The reaction was then terminated by adding saturated aqueous ammonium chloride, followed by extraction with dichloromethane and separation of the organic layer. After drying with sodium sulfate, the solvent was removed by distillation, and the sulfonium compound was purified by column chromatography to obtain a good yield.

[0222] The sulfonium compound was added with 30.0 mmol of cyclopentadiene and 50 g of dichloromethane, and the mixture was stirred at room temperature for 4 hours. Thereafter, the solvent was distilled off, and the mixture was purified by column chromatography to obtain a norbornene compound in good yield.

[0223] 20.0 mmol of salicylic acid and 30.0 mmol of sodium bicarbonate were added to the norbornene compound, and a mixture of water and dichloromethane (1:3 (mass ratio)) was added to prepare a 0.5 M solution. After vigorously stirring at room temperature for 3 hours, dichloromethane was added for extraction, and the organic layer was separated. The obtained organic layer was dried over sodium sulfate, the solvent was distilled off, and the mixture was purified by column chromatography to obtain compound (D-1) represented by formula (D-1) in good yield.

[0224] [Examples D2 to D12] (Synthesis of Compounds (D-2) to (D-12)) Radiation-sensitive acid generators represented by the following formulas (D-2) to (D-12) were synthesized in the same manner as in Example D1, except that the raw materials and precursors were appropriately changed.

[0225]

[0226]

[0227] Example D13 Synthesis of Compound (D-13) Compound (D-13) was synthesized according to the following synthesis scheme.

[0228]

[0229] 20.0 mmol of compound (D-1), 2.0 mmol of Pd / C, and 50 g of methanol were added to a reaction vessel and reacted at room temperature for 12 hours under a hydrogen atmosphere. The Pd / C in the reaction solution was then removed by filtration through Celite. The solvent in the resulting filtrate was evaporated, and the residue was purified by column chromatography to obtain compound (D-13) represented by formula (D-13) in good yield.

[0230] The following compounds were used as components other than the components synthesized above.

[0231] [Acid diffusion controllers other than acid diffusion controllers (D-1) to (D-13)] d-1 to d-11: Compounds represented by the following formulas (d-1) to (d-11) (hereinafter, the compounds represented by formulas (d-1) to (d-11) may be referred to as "compound (d-1)" to "compound (d-11)," respectively.)

[0232]

[0233] [[E] Solvent] E-1: Propylene glycol monomethyl ether acetate E-2: Cyclohexanone E-3: γ-butyrolactone E-4: Ethyl lactate

[0234] [Preparation of positive-tone radiation-sensitive composition for ArF immersion exposure] [Example 1] [A] 100 parts by mass of (A-1) as a polymer, [B] 10.0 parts by mass of (B-2) as a radiation-sensitive acid generator, [D] 4.0 parts by mass of (D-1) as an acid diffusion controller, [F] 5.0 parts by mass (solids content) of (F-1) as a high-fluorine-content polymer, and [E] 3,400 parts by mass of a mixed solvent of (E-1) / (E-2) / (E-3) as a solvent were mixed and filtered through a membrane filter having a pore size of 0.2 μm to prepare a radiation-sensitive composition (J-1).

[0235] [Examples 2 to 56 and Comparative Examples 1 to 7] Radiation-sensitive compositions (J-2) to (J-56) and (CJ-1) to (CJ-7) were prepared in the same manner as in Example 1, except that the types and amounts of each component shown in Table 4 below were used.

[0236]

[0237] <Formation of Resist Pattern Using Positive Radiation-Sensitive Composition for ArF Immersion Exposure> A composition for forming a bottom antireflective coating ("ARC66" from Brewer Science) was applied to a 12-inch silicon wafer using a spin coater ("CLEAN TRACK ACT12" from Tokyo Electron Limited), and then heated at 205°C for 60 seconds to form a bottom antireflective coating having an average thickness of 100 nm. The positive radiation-sensitive composition for ArF immersion exposure prepared above was applied to this bottom antireflective coating using the spin coater, and prebaked at 100°C for 60 seconds. The wafer was then cooled at 23°C for 30 seconds to form a resist film having an average thickness of 90 nm. Next, this resist film was exposed to light through a 60 nm line-and-space mask pattern using an ArF excimer laser immersion exposure system (ASML's "TWINSCAN XT-1900i") under optical conditions of NA = 1.35 and dipole (σ = 0.9 / 0.7). After exposure, a PEB (post-exposure bake) was performed at 100°C for 60 seconds. Thereafter, the resist film was subjected to alkaline development using a 2.38 mass% aqueous TMAH solution as an alkaline developer, and after development, it was washed with water and further dried to form a positive resist pattern (60 nm line-and-space pattern).

[0238] <Evaluation> The storage stability of the positive-tone radiation-sensitive composition for ArF immersion exposure described above was evaluated, and the sensitivity, LWR, and pattern rectangularity of the resist patterns formed using the composition were evaluated according to the methods described below. The results are shown in Table 5 below. The resist patterns were measured using a scanning electron microscope (CG-5000 manufactured by Hitachi High-Technologies Corporation). The results are shown in Table 5 below.

[0239] [Sensitivity] In forming a resist pattern using the positive radiation-sensitive composition for ArF immersion exposure, the exposure dose required to form a 60 nm line and space pattern was defined as the optimum exposure dose, and this optimum exposure dose was defined as the sensitivity (mJ / cm ２ The sensitivity was 30 mJ / cm ２ The cases below are "good" and 30 mJ / cm ２ If it exceeded this, it was rated as "poor".

[0240] [LWR] A 60 nm line-and-space resist pattern was formed by irradiating the resist with the optimal exposure dose determined in the sensitivity evaluation. The formed resist pattern was observed from above the pattern using the scanning electron microscope described above. The line width variation was measured at a total of 500 points, and a 3 sigma value was calculated from the distribution of the measured values, and this 3 sigma value was taken as the LWR (nm). The smaller the LWR value, the smaller the line roughness and the better the result. LWR was evaluated as "good" when it was 3.0 nm or less, and as "poor" when it exceeded 3.0 nm.

[0241] [Pattern rectangularity] A 60 nm line-and-space resist pattern formed by irradiating with the optimum exposure dose obtained in the sensitivity evaluation was observed using the scanning electron microscope, and the cross-sectional shape of the line-and-space pattern was evaluated. The rectangularity of the resist pattern was evaluated as "A" (very good) if the ratio of the length of the bottom side to the length of the top side in the cross-sectional shape was 1.00 or more and 1.05 or less, "B" (good) if it was more than 1.05 and 1.10 or less, and "C" (poor) if it was more than 1.10.

[0242] [Storage Stability] The positive-working radiation-sensitive composition for ArF immersion exposure was stored at 35°C for 30 days, and then the optimum exposure dose for forming a 60 nm line and space, i.e., the sensitivity, was measured again. The sensitivity S before storage, which is represented by the following formula, ０ and sensitivity S after 30 days of storage ３０ If the rate of change in sensitivity was 0% or more and 1.0% or less, it was evaluated as "A" (very good), if it was more than 1.0% and 2.0% or less, it was evaluated as "B" (good), and if it was more than 2.0%, it was evaluated as "C" (poor). Rate of change in sensitivity (%) = (|S ３０ -S ０ | / S ０ ) x 100

[0243]

[0244] As is clear from the results in Table 5, the radiation-sensitive compositions of the Examples exhibited good sensitivity, LWR, pattern rectangularity, and storage stability when used in ArF immersion exposure, whereas the Comparative Examples were inferior in each property to the Examples. Therefore, the radiation-sensitive compositions of the Examples exhibited good storage stability, and when used in ArF immersion exposure, they were able to form resist patterns with optimal sensitivity and excellent LWR and pattern rectangularity.

[0245] [Preparation of positive-tone radiation-sensitive composition for extreme ultraviolet (EUV) exposure] [Example 57] [A] 100 parts by mass of (A-12) as a polymer, [B] 20.0 parts by mass of (B-1) as a radiation-sensitive acid generator, [D] 10.0 parts by mass of (D-2) as an acid diffusion controller, [F] 3.0 parts by mass (solids content) of (F-5) as a high fluorine content polymer, and [E] 6,110 parts by mass of a mixed solvent of (E-1) / (E-4) as a solvent were mixed and filtered through a membrane filter having a pore size of 0.2 μm, to prepare a radiation-sensitive composition (J-57).

[0246] Examples 58 to 76 and Comparative Examples 8 to 14 Radiation-sensitive compositions (J-57) to (J-76) and (CJ-8) to (CJ-14) were prepared in the same manner as in Example 57, except that the types and amounts of each component shown in Table 6 below were used.

[0247]

[0248] <Formation of Resist Pattern Using Positive Radiation-Sensitive Composition for EUV Exposure> A composition for forming a bottom antireflective coating ("ARC66" from Brewer Science) was applied to a 12-inch silicon wafer using a spin coater ("CLEAN TRACK ACT12" from Tokyo Electron Limited), and then heated at 205°C for 60 seconds to form a bottom antireflective coating with an average thickness of 105 nm. The positive radiation-sensitive composition for EUV exposure prepared above was applied to this bottom antireflective coating using the spin coater, and then subjected to PB at 130°C for 60 seconds. Subsequently, the wafer was cooled at 23°C for 30 seconds to form a resist film with an average thickness of 55 nm. Next, this resist film was exposed using an EUV exposure apparatus (ASML's "NXE3300") with NA = 0.33, illumination conditions: Conventional s = 0.89, and mask: imecDEFECT32FFR02. After exposure, PEB was performed at 120°C for 60 seconds. Thereafter, the resist film was subjected to alkaline development using a 2.38 mass% aqueous TMAH solution as an alkaline developer, and after development, the resist film was washed with water and further dried to form a positive resist pattern (20 nm line and space pattern).

[0249] <Evaluation> The storage stability of the positive-tone radiation-sensitive composition for EUV exposure was evaluated, and the sensitivity and LWR of the resist patterns formed using the composition were evaluated according to the methods described below. The results are shown in Table 7. The resist patterns were measured using a scanning electron microscope (CG-5000 manufactured by Hitachi High-Technologies Corporation).

[0250] [Sensitivity] In forming a resist pattern using the positive-working radiation-sensitive composition for EUV exposure, the exposure dose required to form a 20 nm line and space pattern was defined as the optimum exposure dose, and this optimum exposure dose was used as the sensitivity (mJ / cm ２ The sensitivity was 35 mJ / cm ２ The following cases are considered "good" and 35 mJ / cm ２ If it exceeded this, it was rated as "poor".

[0251] [LWR] A resist pattern was formed by irradiating the resist with the optimal exposure dose determined in the sensitivity evaluation above, and adjusting the mask size to form a 20 nm line-and-space pattern. The formed resist pattern was observed from above the pattern using the scanning electron microscope described above. The line width variation was measured at a total of 500 points, and a 3 sigma value was calculated from the distribution of the measured values, and this 3 sigma value was taken as the LWR (nm). The smaller the LWR value, the smaller the line chatter and the better the result. LWR was evaluated as "good" when it was 2.5 nm or less, and as "poor" when it exceeded 2.5 nm.

[0252] [Pattern rectangularity] A 20 nm line-and-space resist pattern formed by irradiating with the optimum exposure dose obtained in the sensitivity evaluation was observed using the scanning electron microscope, and the cross-sectional shape of the line-and-space pattern was evaluated. The rectangularity of the resist pattern was evaluated as "A" (very good) if the ratio of the length of the bottom side to the length of the top side in the cross-sectional shape was 1.00 or more and 1.05 or less, "B" (good) if it was more than 1.05 and 1.10 or less, and "C" (poor) if it was more than 1.10.

[0253] [Storage Stability] The positive-working radiation-sensitive composition for EUV exposure was stored at 35°C for 30 days, and then the optimum exposure dose for forming a 20 nm line and space, i.e., the sensitivity, was measured again. The sensitivity S before storage, which is represented by the following formula, ０ and sensitivity S after 30 days of storage ３０ If the rate of change in sensitivity was 0% or more and 1.0% or less, it was evaluated as "A" (very good), if it was more than 1.0% and 2.0% or less, it was evaluated as "B" (good), and if it was more than 2.0%, it was evaluated as "C" (poor). Rate of change in sensitivity (%) = (|S ３０ -S ０ | / S ０ ) x 100

[0254]

[0255] As is clear from the results in Table 7, the radiation-sensitive compositions of the Examples had good storage stability and, when used for EUV exposure, were excellent in sensitivity, LWR, and pattern rectangularity, whereas the Comparative Examples were inferior in each property to the Examples.

[0256] [Preparation of Negative Radiation-Sensitive Composition for ArF Exposure, and Formation and Evaluation of Resist Pattern Using This Composition] [Example 77] [A] 100 parts by mass of (A-1) as a polymer, [B] 12.0 parts by mass of (B-2) as a radiation-sensitive acid generator, [D] 10.0 parts by mass of (D-1) as an acid diffusion controller, [F] 2.0 parts by mass (solids content) of (F-3) as a high fluorine content polymer, and [E] 3,400 parts by mass (2,240 parts by mass / 960 parts by mass / 200 parts by mass) of a mixed solvent of (E-1) / (E-2) / (E-3) as a solvent were mixed and filtered through a membrane filter having a pore size of 0.2 μm, to prepare a radiation-sensitive composition (J-77).

[0257] A composition for forming a bottom antireflective coating ("ARC66" from Brewer Science) was applied to a 12-inch silicon wafer using a spin coater ("CLEAN TRACK ACT12" from Tokyo Electron Limited), and then heated at 205°C for 60 seconds to form a bottom antireflective coating with an average thickness of 100 nm. The negative radiation-sensitive composition for ArF exposure (J-77) prepared above was applied to this bottom antireflective coating using the spin coater, and prebaked at 100°C for 60 seconds. This was followed by cooling at 23°C for 30 seconds to form a resist film with an average thickness of 90 nm. Next, this resist film was exposed to light using an ArF excimer laser immersion exposure system (ASML's "TWINSCAN XT-1900i") under optical conditions of NA = 1.35 and annular (σ = 0.8 / 0.6) through a mask pattern with 50 nm holes and a 100 nm pitch. After exposure, a post-exposure bake (PEB) was performed at 100°C for 60 seconds. The resist film was then developed using n-butyl acetate as an organic solvent developer and dried to form a negative resist pattern (a contact hole pattern with 50 nm holes and a 100 nm pitch).

[0258] The resist patterns prepared using the negative-working radiation-sensitive composition for ArF exposure were evaluated for sensitivity in the same manner as the resist patterns prepared using the positive-working radiation-sensitive composition for ArF immersion exposure. The CDU, pattern circularity, and storage stability were also evaluated according to the following methods.

[0259] [CDU] A contact hole pattern with 50 nm holes and a 100 nm pitch was formed by irradiating the resist with the optimal exposure dose determined in the sensitivity evaluation. The formed resist pattern was observed from above using the scanning electron microscope described above. The variation in the contact hole pattern was measured at a total of 500 points, and a 3 sigma value was calculated from the distribution of the measured values, and this 3 sigma value was taken as CDU (nm). The smaller the CDU value, the smaller the hole roughness and the better the result. A CDU of less than 3.5 nm was evaluated as "good," and a CDU of 3.5 nm or more was evaluated as "poor."

[0260] [Pattern circularity] The contact hole patterns with 50 nm holes and 100 nm pitches formed by irradiating with the optimum exposure dose obtained in the sensitivity evaluation were observed in plan view using the scanning electron microscope, and the vertical and horizontal sizes were measured. If the ratio of the vertical size to the horizontal size was 0.95 or more and less than 1.05, the result was rated as "A" (very good); if it was 0.90 or more and less than 0.95, or 1.05 or more and less than 1.10, the result was rated as "B" (good); and if it was less than 0.90 or 1.10 or more, the result was rated as "C" (poor).

[0261] [Storage Stability] The negative radiation-sensitive composition for ArF exposure was stored at 35°C for 30 days, and then the optimum exposure dose for forming a contact hole pattern with 50 nm holes and a 100 nm pitch, i.e., the sensitivity, was measured again. The sensitivity S before storage, which is represented by the following formula: ０ and sensitivity S after 30 days of storage ３０ If the rate of change in sensitivity was 0% or more and 1.0% or less, it was evaluated as "A" (very good), if it was more than 1.0% and 2.0% or less, it was evaluated as "B" (good), and if it was more than 2.0%, it was evaluated as "C" (poor). Rate of change in sensitivity (%) = (|S ３０ -S ０ | / S ０ ) x 100

[0262] As a result, the radiation-sensitive composition of Example 77 had good storage stability, and was also excellent in sensitivity, CDU, and pattern circularity, even when a negative resist pattern was formed by ArF exposure.

[0263] [Preparation of Negative Radiation-Sensitive Composition for EUV Exposure, and Formation and Evaluation of Resist Pattern Using This Composition] [Example 78] 100 parts by mass of [A] (A-15) as a polymer, [B] 30.0 parts by mass of (B-12) as a radiation-sensitive acid generator, [D] 10.0 parts by mass of (D-4) as an acid diffusion controller, [F] 5.0 parts by mass (solids content) of (F-5) as a high fluorine content polymer, and [E] 6,110 parts by mass (4280 parts by mass / 1830 parts by mass) of a mixed solvent of (E-1) / (E-4) as a solvent were mixed and filtered through a membrane filter having a pore size of 0.2 μm, to prepare a radiation-sensitive composition (J-78).

[0264] A composition for forming a bottom antireflective coating (Brewer Science's ARC66) was applied to a 12-inch silicon wafer using a spin coater (Tokyo Electron Limited's CLEAN TRACK ACT12), and then heated at 205°C for 60 seconds to form a bottom antireflective coating with an average thickness of 105 nm. The negative radiation-sensitive composition for EUV exposure (J-78) prepared above was applied to this bottom antireflective coating using the spin coater, and baked at 130°C for 60 seconds. This was then cooled at 23°C for 30 seconds to form a resist film with an average thickness of 55 nm. Next, this resist film was exposed to light using an EUV exposure system (ASML's NXE3300) with NA=0.33, illumination conditions: Conventional s=0.89, and a mask: imecDEFECT32FFR15. After the exposure, PEB was performed for 60 seconds at 120° C. Thereafter, the resist film was developed with n-butyl acetate as an organic solvent developer and dried to form a negative resist pattern (a contact hole pattern with 20 nm holes and a 40 nm pitch).

[0265] The resist pattern formed using the negative radiation-sensitive composition for EUV exposure was evaluated in the same manner as the evaluation of the resist pattern formed using the negative radiation-sensitive composition for ArF exposure. As a result, the radiation-sensitive composition of Example 78 had good storage stability, and also had excellent sensitivity, CDU, and pattern circularity, even when a negative resist pattern was formed by EUV exposure.

[0266] The radiation-sensitive composition, pattern forming method, and onium salt described above have good storage stability and good sensitivity to exposure light, and can form resist patterns that are excellent in LWR, CDU, pattern rectangularity, and pattern circularity. Therefore, these can be suitably used in processing processes for semiconductor devices, which are expected to become even more miniaturized in the future.

Claims

1. A radiation-sensitive composition comprising: an onium salt represented by the following formula (1-1) or (1-2); a polymer containing a structural unit (I) having an acid-dissociable group; and a solvent. (In the above formulas (1-1) and (1-2), Ar １１ and Ar ２１ are each independently a ring having 5 to 20 members (m ２ +1)-valent aromatic ring. １２ is a ring having 5 to 20 members (m ３ +1)-valent aromatic ring. ２２ represents m, a 5-20 ring-membered group which forms a fused ring structure together with the two carbon atoms in formula (1-2). ３ It is a 2-valent aromatic ring. １ , m ２ and m ３ are each independently an integer of 0 to 5. １ If is 1, R １ represents a monovalent organic group having 1 to 20 carbon atoms, a hydroxy group, a nitro group, a cyano group, an amino group, a halogen atom, or a sulfanyl group; m １ If is 2 or more, R １ is m １ R when is 1 １ or a plurality of R １ Two of the R's are joined together to form a ring structure having 3 to 10 carbon atoms together with the two carbon atoms of the ring in the formula to which they are attached. １ are the same or different. ２ If is 1, R ２ is m １ R when is 1 １ is synonymous with; m ２ If is 2 or more, R ２ is m １ R when is 2 or more １ It is synonymous with m ３ If is 1, R ３ is m １ R when is 1 １ is synonymous with; m ３ If is 2 or more, R ３ is m １ R when is 2 or more １ X is -CH ２ Y is -, -O-, or -S-. Y is a single bond or a divalent linking group. The bonds represented by the following formulae are each independently a single bond or a double bond. Z - is an organic acid anion having two or more carbon atoms.

2. The radiation-sensitive composition according to claim 1, wherein the onium salt is represented by the following formula (1-1a) or (1-2a): (In the above formulas (1-1a) and (1-2a), R １ , R ２ , R ３ , m １ , m ２ , m ３ , X, Y, Z - and the bonds represented by the following formulae have the same meanings as those in the above formulae (1-1) and (1-2), respectively.

3. X is -CH ２ 3. The radiation-sensitive composition according to claim 1, wherein the aryl group is - or -O-.

4. Y is a single bond, -CH ２ 3. The radiation-sensitive composition according to claim 1, wherein the alkyl group is -, -CO-, or -O-.

5. The radiation-sensitive composition according to claim 1 or 2, wherein m1, m2, and m3 each independently represent 0 or 1.

6. The radiation-sensitive composition according to claim 1 or 2, wherein the onium salt is a radiation-sensitive acid generator that generates, upon exposure to light, an acid that induces dissociation of the acid-dissociable group.

7. The radiation-sensitive composition according to claim 6, wherein the content of the onium salt is 1 part by mass or more and 40 parts by mass or less per 100 parts by mass of the polymer.

8. The radiation-sensitive composition according to claim 1 or 2, wherein the onium salt is an acid diffusion controller that generates, upon exposure to light, an acid that does not induce dissociation of the acid-dissociable group.

9. The radiation-sensitive composition according to claim 8, wherein the content of the onium salt is 0.1 parts by mass or more and 20 parts by mass or less per 100 parts by mass of the polymer.

10. The radiation-sensitive composition according to claim 1 or 2, wherein the structural unit (I) is represented by the following formula (3): (In formula (3), R １７ is a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group. １８ is a monovalent hydrocarbon group having 1 to 20 carbon atoms. １９ and R ２０ are each independently a monovalent chain hydrocarbon group having 1 to 10 carbon atoms or a monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms, or R １９ and R ２０ L represents a divalent alicyclic group having 3 to 20 carbon atoms, which is formed by combining together with the carbon atom to which they are attached. １１ teeth, ＊ -COO-, ＊ -L １１ａ COO- or ＊ -COOL １１ａ COO-. １１ａ is a substituted or unsubstituted alkanediyl group or arenediyl group. * is R １７ is the bond to the carbon atom to which it is bonded.) 11. The radiation-sensitive composition according to claim 1 or 2, wherein the content of the structural unit (I) in all structural units constituting the polymer is 10 mol % or more and 80 mol % or less.

12. The radiation-sensitive composition according to claim 1 or 2, wherein the polymer further comprises a structural unit (II) containing at least one structure selected from the group consisting of a lactone structure, a cyclic carbonate structure, and a sultone structure.

13. The radiation-sensitive composition according to claim 12, wherein the content of the structural unit (II) in all structural units constituting the polymer is 5 mol % or more and 60 mol % or less.

14. The radiation-sensitive composition according to claim 1 or 2, further comprising a high-fluorine content polymer having a higher mass content of fluorine atoms than the polymer.

15. A pattern forming method comprising the steps of: applying the radiation-sensitive composition according to claim 1 or 2 directly or indirectly to a substrate to form a resist film; exposing the resist film; and developing the exposed resist film with a developer.

16. The pattern forming method according to claim 15, wherein the exposure is carried out with an ArF excimer laser or extreme ultraviolet light.

17. An onium salt represented by the following formula (1-1) or (1-2): (In the above formulas (1-1) and (1-2), Ar １１ and Ar ２１ are each independently a ring having 5 to 20 members (m ２ +1)-valent aromatic ring. １２ is a ring having 5 to 20 members (m ３ +1)-valent aromatic ring. ２２ represents m, a 5-20 ring-membered group which forms a fused ring structure together with the two carbon atoms in formula (1-2). ３ It is a 2-valent aromatic ring. １ , m ２ and m ３ are each independently an integer of 0 to 5. １ If is 1, R １ represents a monovalent organic group having 1 to 20 carbon atoms, a hydroxy group, a nitro group, a cyano group, an amino group, a halogen atom, or a sulfanyl group; m １ If is 2 or more, R １ is m １ R when is 1 １ or a plurality of R １ Two of the R's are joined together to form a ring structure having 3 to 10 carbon atoms together with the two carbon atoms of the ring in the formula to which they are attached. １ are the same or different. ２ If is 1, R ２ is m １ R when is 1 １ is synonymous with; m ２ If is 2 or more, R ２ is m １ R when is 2 or more １ It is synonymous with m ３ If is 1, R ３ is m １ R when is 1 １ is synonymous with; m ３ If is 2 or more, R ３ is m １ R when is 2 or more １ X is -CH ２ Y is -, -O-, or -S-. Y is a single bond or a divalent linking group. The bonds represented by the following formulae are each independently a single bond or a double bond. Z - is an organic acid anion having two or more carbon atoms.

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