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

Abstract

Provided are: a radiation-sensitive composition capable of exhibiting excellent sensitivity, CDU performance, DOF performance, pattern circularity, LWR performance, pattern rectangularity, and development defect suppression when forming a pattern; a pattern formation method; and an onium salt. This radiation-sensitive composition contains an onium salt represented by formula (1) (hereinafter, also referred to as an "onium salt (1)"), a polymer containing a structural unit (I) having an acid-dissociable group, and a solvent. (In formula (1), Ar1 is an (a1 + b1 +1)-valent aromatic ring. Ar2 is an (a2 + b2 +1)-valent aromatic ring. X1 and X2 are each independently a monovalent organic group having 1-20 carbon atoms, a cyano group, a nitro group, or a halogen atom. When multiple X1 and multiple X2 are present, the multiple X1 and the multiple X2 are each identical to or different from each other. Y1 is a monovalent organic group having 4-20 carbon atoms and bonded via Ar1 and -O-, -S-, or-SO2-, or a monovalent perfluoroalkyl group having 1-20 carbon atoms. When multiple Y1 are present, the multiple Y1 are identical to or different from each other. Y2 is a monovalent organic group having 4-20 carbon atoms and bonded via Ar2 and -O-, -S-, or -SO2-, or a monovalent perfluoroalkyl group having 1-20 carbon atoms. When multiple Y2 are present, the multiple Y2 are identical to or different from each other. L is a single bond or a divalent linking group having 1-5 carbon atoms. a1, a2, b1, and b2 are each independently an integer of 0-5. When the aromatic ring of Ar2 is a benzene ring, b1 + b2 ≥ 1.)

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] As efforts toward further technological advances continue, a technology has been proposed in which a quencher (acid diffusion controller) is added to a resist composition to capture acid that has diffused to unexposed areas through a salt exchange reaction, thereby improving lithography performance (Japanese Patent No. 5706778).

[0005] Patent No. 5706778

[0006] However, it has been found that the above techniques lead to increased roughness and development defects in the resist pattern after development.

[0007] Therefore, even in efforts to develop next-generation technologies, resist compositions are required to have various resist performances that are equivalent to or better than conventional ones in terms of critical dimension uniformity (CDU) performance, which is an index of the uniformity of sensitivity, line width, and hole diameter, DOF (Depth Of Focus) performance, pattern circularity, which indicates the circularity of the hole shape, line width roughness (LWR), which indicates variations in the line width of the resist pattern, pattern rectangularity, which indicates the rectangularity of the cross-sectional shape of the resist pattern, and development defect suppression ability.

[0008] An object of the present invention is to provide a radiation-sensitive composition, a pattern formation method, and an onium salt that are capable of exhibiting excellent sensitivity, CDU performance, DOF performance, pattern circularity, LWR performance, pattern rectangularity, and development defect suppression during pattern formation.

[0009] 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.

[0010] That is, in one embodiment, the present invention relates to a radiation-sensitive composition comprising: an onium salt represented by the following formula (1) (hereinafter also referred to as “onium salt (1)”); a polymer including a structural unit (I) having an acid-dissociable group; and a solvent: (In formula (1), Ar １ is an aromatic ring with a valence of (a1+b1+1). ２ is an (a2+b2+1)-valent aromatic ring. １ and X ２ are each independently a monovalent organic group having 1 to 20 carbon atoms, a cyano group, a nitro group, or a halogen atom. １ and X ２ If there are multiple Xs, １ and X ２ are the same or different from each other. １ is Ar １ and -O-, -S- or -SO ２ Y is a monovalent organic group having 4 to 20 carbon atoms, or a monovalent perfluoroalkyl group having 1 to 20 carbon atoms, bonded via a -. １If there are multiple Y １ are the same or different. ２ is Ar ２ and -O-, -S- or -SO ２ Y is a monovalent organic group having 4 to 20 carbon atoms, or a monovalent perfluoroalkyl group having 1 to 20 carbon atoms, bonded via a -. ２ If there are multiple Y ２ are the same or different. L is a single bond or a divalent linking group having 1 to 5 carbon atoms. a1, a2, b1, and b2 are each independently an integer of 0 to 5. ２ When the aromatic ring is a benzene ring, b1+b2≧1.

[0011] The radiation-sensitive composition contains onium salt (1) as a quencher (acid diffusion controller), and therefore can exhibit various resist properties during pattern formation, such as excellent sensitivity, CDU performance, DOF performance, pattern circularity, LWR performance, pattern rectangularity, and development defect suppression. Without being bound by any theory, the reason for this is presumed to be as follows. The inventors believe that the above-mentioned problem is due to the low solubility of the quencher in solvents. That is, they speculate that a quencher having a highly polar intramolecular salt (zwitterion) structure has increased polarity throughout the structure, resulting in reduced solubility in solvents and insufficient solubility in organic solvents during organic solvent development, leading to increased development defects and roughness. The introduction of a relatively hydrophobic structure into onium salt (1) can increase the solubility of the entire molecule in solvents and developers. Furthermore, the use of a carboxylate salt provides strong basicity, allowing the composition to exhibit excellent quencher function. It is presumed that these synergistic effects enable the radiation-sensitive composition to exhibit the above-mentioned resist properties at a high level.

[0012] In this specification, the term "organic group" refers to a group containing at least one carbon atom, excluding groups that can be functional or characteristic groups by themselves (e.g., cyano, carboxy, or carbonyl groups).

[0013] In another embodiment, the present invention relates to a pattern forming method, comprising: a step of applying the radiation-sensitive composition directly or indirectly to a substrate to form a resist film; a step of exposing the resist film; and a step of developing the exposed resist film with a developer.

[0014] The pattern formation method uses the radiation-sensitive composition, which is capable of exhibiting excellent sensitivity, CDU performance, DOF performance, pattern circularity, LWR performance, pattern rectangularity, and development defect suppression during pattern formation, and therefore can form high-quality resist patterns with good yield.

[0015] In yet another embodiment, the present invention relates to an onium salt represented by the following formula (1): (In formula (1), Ar １ is an aromatic ring with a valence of (a1+b1+1). ２ is an (a2+b2+1)-valent aromatic ring. １ and X ２ are each independently a monovalent organic group having 1 to 20 carbon atoms, a cyano group, a nitro group, or a halogen atom. １ and X ２ If there are multiple Xs, １ and X ２ are the same or different from each other. １ is Ar １ and -O-, -S- or -SO ２ Y is a monovalent organic group having 4 to 20 carbon atoms, or a monovalent perfluoroalkyl group having 1 to 20 carbon atoms, bonded via a -. １ If there are multiple Y １ are the same or different. ２ is Ar ２ and -O-, -S- or -SO ２ Y is a monovalent organic group having 4 to 20 carbon atoms, or a monovalent perfluoroalkyl group having 1 to 20 carbon atoms, bonded via a -. ２ If there are multiple Y ２are the same or different. L is a single bond or a divalent linking group having 1 to 5 carbon atoms. a1, a2, b1, and b2 are each independently an integer of 0 to 5. ２ When the aromatic ring is a benzene ring, b1+b2≧1.

[0016] The onium salt (1) has good solubility in solvents and developers and can exhibit strong basicity in a resist film, and is therefore suitable for use in radiation-sensitive compositions that are required to exhibit high levels of the above-mentioned resist properties, including the ability to suppress development defects.

[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 in the embodiments are also preferred.

[0018] <Radiation-Sensitive Composition> The radiation-sensitive composition according to this embodiment (hereinafter also simply referred to as "composition") contains an onium salt (1), a polymer, and a solvent. If necessary, it may further contain a radiation-sensitive acid generator. The composition may contain other optional components as long as they do not impair the effects of the present invention.

[0019] (Onium Salt (1)) The onium salt (1) can function as a quencher (also called a "photodegradable base" or "acid diffusion controller") that captures acid in pre-exposed or unexposed areas. The onium salt (1) is represented by the above formula (1).

[0020] Ar １ and Ar ２The aromatic ring represented by the formula (I) is not particularly limited as long as it is a ring structure having aromaticity. Examples of the aromatic ring 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, a perylene ring, and a coronene ring, and 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, a triazine ring, a carbazole ring, and a dibenzofuran ring, and combinations thereof. Among these, the aromatic ring is preferably a benzene ring, a naphthalene ring, or an anthracene ring, more preferably a benzene ring or a naphthalene ring, and even more preferably a benzene ring. １ is a group obtained by removing (a1+b1+1) hydrogen atoms from the aromatic ring. ２ is a group obtained by removing (a2+b2+1) hydrogen atoms from the above aromatic ring.

[0021] The combination of ring structures is not limited to aromatic rings and is not particularly limited. The combination of ring structures may be any of a fused ring in which two adjacent rings share one side (two adjacent atoms), a ring assembly in which two adjacent rings are bonded by a single bond, a spiro ring in which two adjacent rings share one carbon atom, and a bridged ring in which two adjacent rings share three or more consecutive atoms.

[0022] X １ and X ２ The monovalent organic group having 1 to 20 carbon atoms represented by the formula (I) is not particularly limited, and includes a monovalent hydrocarbon group having 1 to 20 carbon atoms, -CO-, -CS-, -O-, -S-, -SO ２ Examples include -, -NR'-, or a group containing a combination of two or more of these (hereinafter also referred to as "group (α)"), the above hydrocarbon group or a group in which some or all of the hydrogen atoms contained in the above group (α) have been substituted with substituents (hereinafter also referred to as "group (β)"), or a combination thereof. R' is a hydrogen atom or a monovalent hydrocarbon group having 1 to 10 carbon atoms. However, X １ and X ２ As for Y １ and Y ２Excluding structures that fall under the following.

[0023] 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.

[0024] Examples of the monovalent chain hydrocarbon group having 1 to 20 carbon atoms include a linear or branched saturated hydrocarbon group having 1 to 20 carbon atoms, and a linear or branched unsaturated hydrocarbon group having 1 to 20 carbon atoms.

[0025] Examples of the monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms include monocyclic or polycyclic saturated hydrocarbon groups, and monocyclic or polycyclic unsaturated hydrocarbon groups. Preferred monocyclic saturated hydrocarbon groups are cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl groups. Preferred polycyclic cycloalkyl groups are bridged alicyclic hydrocarbon groups such as norbornyl, adamantyl, tricyclodecyl, and tetracyclododecyl groups. Preferred monocyclic unsaturated hydrocarbon groups include monocyclic cycloalkenyl groups such as cyclopropenyl, cyclobutenyl, cyclopentenyl, and cyclohexenyl groups. Preferred polycyclic unsaturated hydrocarbon groups include polycyclic cycloalkenyl groups such as norbornenyl, tricyclodecenyl, and tetracyclododecenyl groups.

[0026] Examples of the monovalent aromatic hydrocarbon group having 6 to 20 carbon atoms include aryl groups such as phenyl, tolyl, xylyl, naphthyl, and anthryl; and aralkyl groups such as benzyl, phenethyl, and naphthylmethyl.

[0027] The group (α) is also preferably a group containing a heterocyclic group containing a heteroatom between carbon atoms constituting the ring. Examples of the heterocyclic group include a group in which one hydrogen atom has been removed from an aromatic heterocyclic structure, a group in which one hydrogen atom has been removed from an aliphatic heterocyclic structure, and a group combining these. Examples of the heteroatom include an oxygen atom, a nitrogen atom, and a sulfur atom.

[0028] Examples of the aromatic heterocyclic structure include: oxygen atom-containing aromatic heterocyclic structures such as furan, benzofuran, and dibenzofuran; nitrogen atom-containing aromatic heterocyclic structures such as pyrrole, imidazole, pyridine, pyrimidine, pyrazine, indole, quinoline, isoquinoline, acridine, phenazine, and carbazole; sulfur atom-containing aromatic heterocyclic structures such as thiophene, benzothiophene, and dibenzothiophene; and aromatic heterocyclic structures containing multiple heteroatoms such as thiazole, benzothiazole, thiazine, and oxazine.

[0029] Examples of the aliphatic heterocyclic structure include: oxygen atom-containing aliphatic heterocyclic structures such as oxirane, tetrahydrofuran, tetrahydropyran, 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.

[0030] Examples of the aliphatic heterocyclic structure include a lactone structure, a cyclic carbonate structure, a sultone structure, and a structure containing a cyclic acetal, such as those represented by the following formulas (H-1) to (H-11).

[0031]

[0032] In the above formula, γ is an integer of 1 to 3.

[0033] Examples of the substituent that substitutes some or all of the hydrogen atoms of the organic group include halogen atoms such as fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms; hydroxy groups; carboxy groups; cyano groups; nitro groups; alkyl groups, alkoxy groups, alkoxycarbonyl groups, alkoxycarbonyloxy groups, acyl groups, acyloxy groups, and groups in which the hydrogen atoms of these groups are substituted with halogen atoms; and oxo groups (═O).

[0034] X １ and X ２Examples of the halogen atom represented by the formula (I) include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

[0035] X １ and X ２ As the alkyl group, a monovalent hydrocarbon group having 1 to 10 carbon atoms, a group containing -O-, -CO- or a combination thereof between carbon atoms of the hydrocarbon group or at the end of the hydrocarbon group, a group in which a hydrogen atom of the hydrocarbon group is substituted with a fluorine atom, or a halogen atom is preferred.

[0036] Y １ and Y ２ The monovalent organic group having 4 to 20 carbon atoms in １ and X ２ Among the monovalent organic groups having 1 to 20 carbon atoms, those having 4 to 20 carbon atoms, represented by the following formula, can be suitably used. １ and Y ２ When the monovalent organic group having 4 to 20 carbon atoms is represented by y, Y １ and Y ２ are each independently represented by the following formula:

[0037] (wherein * represents Ar １ or Ar ２ It is a bond with

[0038] Y １ is Ar １ and Y is preferably a monovalent organic group having 4 to 20 carbon atoms or a monovalent perfluoroalkyl group having 1 to 20 carbon atoms, which is bonded to Y via —O—; ２ is Ar ２ and a monovalent organic group having 4 to 20 carbon atoms, or a monovalent perfluoroalkyl group having 1 to 20 carbon atoms, which is bonded to the above via —O—.

[0039] Y １ and Y ２ The lower limit of the number of carbon atoms in the monovalent organic group is preferably 5, more preferably 6, and even more preferably 7. The upper limit of the number of carbon atoms is preferably 16, more preferably 12, and even more preferably 10. This allows the onium salt (1) to exhibit good solubility.

[0040] Y１ and Y ２ The monovalent perfluoroalkyl group having 1 to 20 carbon atoms represented by the formula (I) may be either linear or branched, and examples thereof include a trifluoromethyl group, a perfluoroethyl group, a perfluoro n-propyl group, a perfluoro i-propyl group, a perfluoro n-butyl group, a perfluoro i-butyl group, a perfluoro t-butyl group, a perfluoro n-pentyl group, and a perfluoro n-hexyl group.

[0041] Y １ and Y ２ As the monovalent perfluoroalkyl group having 1 to 20 carbon atoms represented by the formula (I), a monovalent perfluoroalkyl group having 1 to 10 carbon atoms is preferred, a monovalent linear perfluoroalkyl group having 1 to 5 carbon atoms is more preferred, and a trifluoromethyl group or a perfluoroethyl group is even more preferred.

[0042] The divalent linking group having 1 to 5 carbon atoms represented by L includes X １ and X ２ Among the monovalent organic groups having 1 to 20 carbon atoms, those in which one hydrogen atom has been removed from a group corresponding to 1 to 5 carbon atoms, represented by the following formula, can be suitably used.

[0043] L is preferably a single bond or an alkanediyl group having 1 to 3 carbon atoms, more preferably a single bond, a methanediyl group, or an ethanediyl group, and even more preferably a single bond. ＋ is preferably bonded to the ortho position of the carbon atom to which is bonded.

[0044] a1, a2, b1 and b2 are each independently preferably an integer of 0 to 4, more preferably an integer of 0 to 3, and even more preferably an integer of 0 to 2.

[0045] Ar ２ When the aromatic ring is a benzene ring, it is preferable that 1≦b1+b2≦3, more preferably 1≦b1+b2≦2, and even more preferably that b1+b2=1. Among these, it is preferable that b1 is 0 and b2 satisfies the above range, and it is more preferable that b1 is 0 and b2 is 1.

[0046] The onium salt is preferably represented by the following formula (1-1), (1-2) or (1-3). (In formula (1-1), X １ , X ２ , L, a1, a2, b1 and b2 are the same as in the formula (1). １１ and Y ２１ each independently represents an aromatic ring of formula (1-1) and —O—, —S— or —SO ２ In formula (1-2), X is a monovalent organic group having 4 to 20 carbon atoms, or a monovalent perfluoroalkyl group having 1 to 20 carbon atoms, bonded via a - group. c1 is 0 or 1. １ , X ２ , L, a1 and a2 have the same meanings as in the above formula (1). １ is an alicyclic hydrocarbon structure, an aromatic hydrocarbon structure, or an aliphatic heterocyclic structure that forms a condensed ring with the adjacent benzene ring of formula (1-2). １２ and Y ２２ each independently represents an aromatic ring of formula (1-2) and —O—, —S— or —SO ２ b1 and b2 are each independently an integer of 0 to 5. c1 is 0 or 1. In formula (1-3), L and X are each independently an integer of 0 to 5. １ , X ２ , a1 and a2 have the same meanings as in formula (1). ２３ is an aromatic heterocycle. １３ represents an aromatic ring of formula (1-3) and —O—, —S— or —SO ２ Y is a monovalent organic group having 4 to 20 carbon atoms, or a monovalent perfluoroalkyl group having 1 to 20 carbon atoms, bonded via a -. ２３ is Ar ２３ and -O-, -S- or -SO ２ b1 and b2 are each independently an integer of 0 to 5. c1 is 0 or 1.

[0047] In the above formula (1-1), Y １１ and Y２１ Each aromatic ring of formula (1-1) is represented by —O—, —S— or —SO ２ The monovalent organic group having 4 to 20 carbon atoms bonded via - is, for example, Y in the above formula (1). １ Ar represented by １ and -O-, -S- or -SO ２ a monovalent organic group having 4 to 20 carbon atoms bonded via -, and Y ２ Ar represented by ２ and -O-, -S- or -SO ２ A monovalent organic group having 4 to 20 carbon atoms and bonded via - can be preferably used. １２ and Y ２２ and Y in the above formula (1-3) １３ and Y ２３ For the monovalent organic group represented by the formula (1), １ Ar represented by １ and -O-, -S- or -SO ２ a monovalent organic group having 4 to 20 carbon atoms bonded via -, and Y ２ Ar represented by ２ and -O-, -S- or -SO ２ A monovalent organic group having 4 to 20 carbon atoms and bonded via a - bond can be preferably used.

[0048] In the above formula (1-1), Y １１ and Y ２１ The monovalent perfluoroalkyl group having 1 to 20 carbon atoms represented by the formula (1) includes Y １ and Y ２ Similarly, Y in the above formula (1-2) can be suitably used. １２ and Y ２２ and Y in the above formula (1-3) １３ and Y ２３ For the monovalent perfluoroalkyl group represented by the formula (1), １ and Y ２ A monovalent perfluoroalkyl group represented by the following formula can be suitably employed.

[0049] In the above formulas (1-1) to (1-3), c1 is preferably 0.

[0050] In the above formula (1-2), W １ The alicyclic hydrocarbon structure, aromatic hydrocarbon structure and aliphatic heterocyclic structure forming a condensed ring with the adjacent benzene ring in formula (1-2) represented by the formula (1-3) are, respectively, X in formula (1) １ and X ２ a structure corresponding to the monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms in the above formula (1), １ and X ２ and X in the above formula (1). １ and X ２ The aliphatic heterocyclic structure shown in the formula (I) can be preferably used. １ Even if W is an alicyclic hydrocarbon structure or an aliphatic heterocyclic structure, it exhibits aromaticity together with the adjacent benzene ring. １ The fused ring with Ar in the above formula (1) ２ Included in the aromatic ring of W １ When is an alicyclic hydrocarbon structure or an aliphatic heterocyclic structure, the carbon-carbon bond shared with the adjacent benzene ring is W １ When looking at , it is treated as a single bond.

[0051] In the above formula (1-2), W １ The alicyclic hydrocarbon structure represented by the formula (I) is preferably a cycloalkane structure having 3 to 10 carbon atoms, more preferably a cycloalkane structure having 4 to 7 carbon atoms, and further preferably a cyclopentane structure or a cyclohexane structure.

[0052] In the above formula (1-2), W １ The aromatic hydrocarbon structure represented by the formula (I) is preferably an aromatic hydrocarbon structure having 6 to 12 carbon atoms, more preferably a benzene ring structure.

[0053] In the above formula (1-2), W １ The aliphatic heterocyclic structure represented by the formula (I) is preferably an aliphatic heterocyclic structure containing an oxygen atom as a ring-constituting atom, and more preferably a lactone structure, a cyclic acetal structure, or a cyclic ether structure.

[0054] In the above formulas (1-2) to (1-3), b1 and b2 are each independently preferably an integer of 0 to 3, more preferably an integer of 0 to 2, and even more preferably 0 or 1.

[0055] In the above formula (1-3), Ar ２３ The aromatic heterocycle represented by the formula (1) is １ and X ２ The aromatic heterocyclic structures shown in the formula (I) can be preferably used. ２３ As the ring structure, a five-membered aromatic heterocyclic structure and a ring structure in which a five-membered aromatic heterocyclic structure and an aromatic hydrocarbon structure are condensed are preferred.

[0056] Specific examples of the onium salt (1) represented by the above formula (1) are not particularly limited, but include structures represented by the following formulas (C-1) to (C-72).

[0057]

[0058]

[0059]

[0060]

[0061] The lower limit of the content of onium salt (1) (when multiple types of onium salts are used in combination, the total of all of them) is preferably 0.1 parts by mass, more preferably 0.5 parts by mass, even more preferably 1 part by mass, and particularly preferably 3 parts by mass, per 100 parts by mass of the polymer described below. The upper limit of the content is preferably 80 parts by mass, more preferably 60 parts by mass, even more preferably 50 parts by mass, and particularly preferably 40 parts by mass. By keeping the content of onium salt (1) within the above range, the above-mentioned resist performances can be exhibited during resist pattern formation.

[0062] (Method for synthesizing onium salt (1)) The onium salt (1) can be synthesized according to the following scheme. １ and Ar ２is a benzene ring, a1, a2, and b1 are 0, and b2 is 1. An iodobenzoic acid analogue that provides the carboxylic acid anion of onium salt (1) is used as a starting material, and then this is reacted with an oxidizing agent and a predetermined substituent (Y ２ The desired onium salt (1a) can be synthesized by nucleophilically reacting the compound (1b) with benzene having the formula (1b) and finally treating it with a (weak) base. Other structures can also be synthesized by appropriately changing the raw materials and the reagents used in the reaction.

[0063] (In the scheme, L and Y ２ has the same meaning as the above formula (1).

[0064] (Polymer) The polymer is an aggregate of polymer chains having a structural unit (I) containing an acid-dissociable group (hereinafter, this polymer will also be referred to as a "base polymer"). 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).

[0065] In addition to the structural unit (I), the base polymer preferably has a structural unit (II) containing at least one selected from the group consisting of a lactone structure, a cyclic carbonate structure, a sultone structure, and a lactam structure, which will be described later, and may also have structural units other than the structural units (I) and (II). Each structural unit will be described below.

[0066] [Structural Unit (I)] The structural unit (I) is a structural unit having 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.

[0067]

[0068] 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 substituted or unsubstituted hydrocarbon group having 1 to 20 carbon atoms. １９ and R ２０ are each independently a monovalent substituted or unsubstituted chain hydrocarbon group having 1 to 10 carbon atoms or a monovalent substituted or unsubstituted 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 represents 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] L １１ａExamples 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.

[0073] The above R １８ Examples of the monovalent hydrocarbon group having 1 to 20 carbon atoms represented by the formula (I) include a monovalent chain hydrocarbon group having 1 to 10 carbon atoms, a monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms, and a monovalent aromatic hydrocarbon group having 6 to 20 carbon atoms.

[0074] The above R １８ ~R ２０ Examples of the monovalent chain hydrocarbon group having 1 to 10 carbon atoms represented by the formula (I) include a monovalent linear or branched saturated hydrocarbon group having 1 to 10 carbon atoms, and a monovalent linear or branched unsaturated hydrocarbon group having 1 to 10 carbon atoms.

[0075] The above R １８ ~R ２０ The monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms represented by the formula (1) is １ and X ２ A monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms in the above formula can be suitably used.

[0076] The above R １８ The monovalent aromatic hydrocarbon group having 6 to 20 carbon atoms represented by the formula (1) is １ and X ２ A monovalent aromatic hydrocarbon group having 6 to 20 carbon atoms in the above formula can be suitably used.

[0077] The above R １８ The substituents that the monovalent hydrocarbon group having 1 to 20 carbon atoms represented by the formula (1) may have include X １ and X ２ The substituents that can be possessed by the monovalent organic group having 1 to 20 carbon atoms, represented by the following formula, can be suitably employed.

[0078] 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.

[0079] The above R１９ and R ２０ The divalent alicyclic group having 3 to 20 carbon atoms formed by combining these together with the carbon atoms to which they are bonded is not particularly limited as long as it is a group formed by removing two hydrogen atoms from the same carbon atom constituting a carbon ring of a monocyclic or polycyclic alicyclic hydrocarbon having the above carbon number. Either a monocyclic hydrocarbon group or a polycyclic hydrocarbon group may be used, and the polycyclic hydrocarbon group may be either a bridged alicyclic hydrocarbon group or a fused alicyclic hydrocarbon group, and may be either a saturated hydrocarbon group or an unsaturated hydrocarbon group. Note that a fused alicyclic hydrocarbon group refers to a polycyclic alicyclic hydrocarbon group formed in such a way that multiple alicyclic rings share a side (a bond between two adjacent carbon atoms).

[0080] Among the monocyclic alicyclic hydrocarbon groups, preferred saturated hydrocarbon groups include cyclopentanediyl, cyclohexanediyl, cycloheptanediyl, and cyclooctanediyl groups, and preferred unsaturated hydrocarbon groups include cyclopentenediyl, cyclohexenediyl, cycloheptenediyl, cyclooctenediyl, and cyclodecenediyl groups. Preferred polycyclic alicyclic hydrocarbon groups are bridged alicyclic saturated hydrocarbon groups, such as bicyclo[2.2.1]heptane-2,2-diyl (norbornane-2,2-diyl), bicyclo[2.2.2]octane-2,2-diyl, and tricyclo[3.3.1.1]heptane-2,2-diyl. ３，７ ] Decane-2,2-diyl group (adamantane-2,2-diyl group) and the like are preferred.

[0081] Among these, R １８ is an alkyl group having 1 to 4 carbon atoms, and R １９ 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.

[0082] The above R １８ ~R ２０ Examples of the substituent that may be possessed by L include １１ａ Substituents that can be possessed by the arenediyl group represented by the following formula can be suitably employed.

[0083] 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)").

[0084]

[0085]

[0086] 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.

[0087] i and j are preferably 1. １８ R is preferably a methyl group, an ethyl group, an isopropyl group, a t-butyl group, an ethenyl group, a phenyl group, or an iodophenyl group. １９ and R ２０ R is preferably a methyl group, an ethyl group, or an isopropyl group. Ｌ１１ is preferably an iodine atom, a hydroxy group, or an alkoxy group. Ｌ１１ By employing an iodine atom as the aryl group, an iodine group can be suitably introduced into the structural unit (I).

[0088] Furthermore, the polymer may contain structural units represented by the following formulae (1f) to (2f) as the structural unit (I).

[0089]

[0090] In the above formulas (1f) to (2f), R αｆ R are each independently a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group. βｆare each independently a hydrogen atom or a chain alkyl group having 1 to 5 carbon atoms. h1 is an integer of 1 to 4.

[0091] The above R βｆ is preferably a hydrogen atom, a methyl group or an ethyl group. h1 is preferably 1 or 2.

[0092] The base polymer may contain one or more types of structural unit (I).

[0093] 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 5 mol%, more preferably 10 mol%, even more preferably 20 mol%, and particularly preferably 25 mol%. The upper limit of the content is preferably 80 mol%, more preferably 75 mol%, even more preferably 70 mol%, and particularly preferably 65 mol%. By setting the content of the structural unit (I) within the above range, the pattern formability of the radiation-sensitive composition can be further improved.

[0094] [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, a sultone structure, and a lactam 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.

[0095] Examples of the structural unit (II) include structural units represented by the following formulae (T-1) to (T-11).

[0096]

[0097] 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.

[0098] 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, examples include groups having 3 to 8 carbon atoms. One or more hydrogen atoms on this alicyclic group may be substituted with a hydroxy group.

[0099] 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-.

[0100] Of these, the structural unit (II) is preferably a structural unit containing a lactone structure, more preferably a structural unit containing a norbornane lactone structure, and even more preferably a structural unit derived from norbornane lactone-yl (meth)acrylate.

[0101] The lower limit of the content of the structural unit (II) is preferably 5 mol%, more preferably 10 mol%, and even more preferably 15 mol%, based on all structural units constituting the base polymer. 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.

[0102] [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.

[0103] Examples of the structural unit (III) include structural units represented by the following formula:

[0104]

[0105] In the above formula, R Ａ is a hydrogen atom, a fluorine atom, a methyl group or a trifluoromethyl group.

[0106] When the base polymer has the structural unit (III) having the polar group, the lower limit of the content of the structural unit (III) is preferably 1 mol%, more preferably 2 mol%, and even more preferably 4 mol%, based on the total structural units constituting the base polymer. The upper limit of the content is preferably 40 mol%, more preferably 30 mol%, and even more preferably 25 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.

[0107] [Structural Unit (IV)] The base polymer optionally has, 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. In particular, it is suitable for pattern formation using exposure to radiation having a wavelength of 50 nm or less, such as electron beams or EUV. In this case, it is preferable that the polymer has structural unit (I) in addition to structural unit (IV).

[0108] The structural unit having a phenolic hydroxyl group is represented by, for example, the following formulas (4-1) to (4-4).

[0109]

[0110] In the above formulas (4-1) to (4-4), R ４１ are each independently a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group. Q is each independently 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 Qs, the multiple Qs are the same or different. t is an integer of 0 to 4.

[0111] In order to obtain the structural unit (IV), it is preferable to carry out polymerization in a state in which the phenolic hydroxyl group of the monomer compound 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. Polymerization can also be carried out without protecting the phenolic hydroxyl group.

[0112] In the case of a polymer for exposure to radiation having a wavelength of 50 nm or less, the lower limit of the content of the structural unit (IV) is preferably 10 mol %, more preferably 20 mol %, based on all structural units constituting the polymer, and the upper limit of the content is preferably 70 mol %, more preferably 60 mol %.

[0113] [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.

[0114] In the above formula (6), R ２α The monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms represented by the formula (1) is １ and X ２ A monovalent alicyclic hydrocarbon group having 3 to 20 carbon atoms in the above formula can be suitably used.

[0115] 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 20 mol%, more preferably 15 mol%, and even more preferably 12 mol%.

[0116] (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.

[0117] 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. Of 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.

[0118] 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; polyhydric alcohol partial ether acetate solvents such as diethylene glycol mono-n-butyl ether acetate, propylene glycol monomethyl ether acetate, and dipropylene glycol monomethyl ether acetate; ketones such as acetone, methyl ethyl ketone, 2-butanone, 4-methyl-2-pentanone, 2-heptanone, and cyclohexanone; Examples of the solvent include ethers such as tetrahydrofuran, dimethoxyethanes, diethoxyethane, and 1,4-dioxanes; alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-methoxy-2-propanol, and 4-methyl-2-pentanol; and lactones such as γ-butyrolactone. These solvents used in the polymerization may be used alone or in combination of two or more.

[0119] 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.

[0120] 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 2,000, more preferably 3,000, and even more preferably 4,000. The upper limit of Mw is preferably 30,000, more preferably 20,000, and even more preferably 15,000. By setting the Mw of the base polymer within the above range, the resulting resist film can have good heat resistance and developability.

[0121] 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.

[0122] The Mw and Mn of the polymer in this specification are values ​​measured using gel permeation chromatography (GPC) under the following conditions.

[0123] 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

[0124] The content of the base polymer is preferably 50% by mass or more, more preferably 55% by mass or more, and even more preferably 60% by mass or more, based on the total solid content of the radiation-sensitive composition.

[0125] (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.

[0126] The high-fluorine content polymer preferably has, for example, a structural unit represented by the following formula (5) (hereinafter also referred to as "structural unit (V)"), and may also have the structural unit (I) or the structural unit (III) of the base polymer, as necessary.

[0127]

[0128] In the above formula (5), R １３ is a hydrogen atom, a methyl group, or a trifluoromethyl group. Ｌrepresents 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.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] The above R １４ Examples 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.

[0133] The above R １４ As the alkyl group, a fluorinated chain hydrocarbon group is preferred, a fluorinated alkyl group is more preferred, and a 2,2,2-trifluoroethyl group, a 2,2,3,3,3-pentafluoropropyl group, a 1,1,1,3,3,3-hexafluoropropan-2-yl group, and a 5,5,5-trifluoro-1,1-diethylpentyl group are even more preferred.

[0134] When the high-fluorine content polymer has the structural unit (V), the lower limit of the content of the structural unit (V) is preferably 2 mol%, more preferably 5 mol%, and even more preferably 8 mol%, based on all structural units constituting the high-fluorine content 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 (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.

[0135] 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.

[0136]

[0137] 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 simply referred to as an "alkali-dissociable group"). In both (x) and (y), R Ｃ is 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 At the end of the side, there is an oxygen atom, a sulfur atom, and -NR 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.

[0138] When the structural unit (VI) has an alkali-soluble group (x), R Ｆis 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.

[0139] 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-*. 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. １is 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.

[0140] 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.

[0141] 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 90 mol%, more preferably 80 mol%, and even more preferably 70 mol%. By setting the content of the structural unit (VI) within the above range, the water repellency of the resist film during immersion exposure can be further improved, and the occurrence of development defects can be suppressed.

[0142] [Other Structural Units] The high fluorine content polymer may contain a structural unit having an alicyclic structure represented by the above formula (6) as a structural unit other than the structural units listed above.

[0143] When the high-fluorine content polymer contains the structural unit having an alicyclic structure, the content of the structural unit having an alicyclic structure is preferably 10 mol %, more preferably 20 mol %, and even more preferably 30 mol %, based on all structural units constituting the high-fluorine content polymer. The upper limit of the content is preferably 60 mol %, more preferably 50 mol %, and even more preferably 45 mol %.

[0144] The lower limit of Mw of the high fluorine content polymer is preferably 3,000, more preferably 5,000, and even more preferably 7,000. The upper limit of Mw is preferably 30,000, more preferably 20,000, and even more preferably 12,000.

[0145] 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.

[0146] 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 2 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.

[0147] 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 increased water repellency of the surface of the resist film during immersion lithography, and control of the surface modification of the resist film and the distribution of composition within the film during EUV exposure. The radiation-sensitive composition may contain one or more high fluorine content polymers.

[0148] (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.

[0149] (Radiation-Sensitive Acid Generator) The radiation-sensitive composition of this embodiment preferably further contains a radiation-sensitive acid generator that generates an acid having a lower pKa than the acid generated from the onium salt (1), i.e., a relatively strong acid, upon irradiation (exposure) with radiation. The acid generated from the radiation-sensitive acid generator upon exposure can dissociate the acid-dissociable group contained in the structural unit (I) of the polymer, thereby generating a carboxyl group or the like. This function is different from the function of the onium salt (1), which, under pattern formation conditions using the radiation-sensitive composition, does not substantially dissociate the acid-dissociable group contained in the structural unit (I) of the polymer, thereby suppressing the diffusion of the acid generated from the radiation-sensitive acid generator in unexposed areas. The difference between the functions of the onium salt (1) and the radiation-sensitive acid generator is determined by the energy required to dissociate the acid-dissociable group contained in the structural unit (I) of the polymer, the acidity of the acid generated from the radiation-sensitive acid generator, and the like. The radiation-sensitive acid generator may be contained in the radiation-sensitive composition in a form in which it exists as a compound alone (isolated from a polymer), in which it is incorporated as part of a polymer, or in both of these forms. However, the form in which it exists as a compound alone is preferred.

[0150] When the radiation-sensitive composition contains the radiation-sensitive acid generator, the polarity of the polymer in the exposed area increases, and the polymer in the exposed area becomes soluble in the developer in the case of development with an aqueous alkaline solution, while becoming poorly soluble in the developer in the case of development with an organic solvent.

[0151] Examples of the radiation-sensitive acid generator include onium salts (excluding the onium salt (1)), sulfonimide compounds, halogen-containing compounds, and diazoketone compounds. Examples of the onium salt include sulfonium salts, tetrahydrothiophenium salts, iodonium salts, phosphonium salts, diazonium salts, and pyridinium salts. Of these, sulfonium salts and iodonium salts are preferred.

[0152] An example of an acid generated upon exposure is sulfonic acid. An example of a radiation-sensitive acid generator that generates such an acid is a compound in which one or more fluorine atoms or fluorinated hydrocarbon groups are substituted on the carbon atom adjacent to the sulfo group. Particularly preferred radiation-sensitive acid generators have, in addition to the sulfo group and the structure on the carbon atom adjacent thereto, a cyclic structure, —O—, —CO—, or a structure consisting of a combination of two or more of these. Preferred cyclic structures are polycyclic aliphatic hydrocarbon structures and polycyclic aliphatic heterocyclic structures.

[0153] These radiation-sensitive acid generators may be used alone or in combination of two or more. The lower limit of the content of the radiation-sensitive acid generator (when multiple types of radiation-sensitive acid generators are used in combination, the total amount of the radiation-sensitive acid generators) is preferably 2 parts by mass, more preferably 4 parts by mass, and even more preferably 6 parts by mass, per 100 parts by mass of the base polymer. The upper limit of the content is preferably 60 parts by mass, more preferably 50 parts by mass, and even more preferably 45 parts by mass, per 100 parts by mass of the base polymer. This allows the above-mentioned excellent resist performances to be exhibited during resist pattern formation.

[0154] (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) and the polymer, as well as the radiation-sensitive acid generator and other components that are optionally contained therein.

[0155] Examples of the solvent include alcohol-based solvents, ether-based solvents, ketone-based solvents, amide-based solvents, ester-based solvents, and hydrocarbon-based solvents.

[0156] Examples of alcohol-based solvents include monoalcohol-based solvents having 1 to 18 carbon atoms, such as i-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 partially etherified solvents in which some of the hydroxy groups in the above-mentioned polyhydric alcohol-based solvents have been etherified. In this embodiment, alcoholic acid esters 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 alcohol-based solvent.

[0157] 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 in which the hydroxy groups of the above-mentioned polyhydric alcohol-based solvents have been etherified, such as propylene glycol monomethyl ether.

[0158] Examples of the ketone solvent include chain ketone solvents such as acetone, butanone, and methyl-i-butyl ketone; cyclic ketone solvents such as cyclopentanone, cyclohexanone, and methylcyclohexanone; and 2,4-pentanedione, acetonylacetone, and acetophenone.

[0159] 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.

[0160] 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.

[0161] Examples of hydrocarbon solvents include aliphatic hydrocarbon solvents such as n-hexane, cyclohexane, and methylcyclohexane; and aromatic hydrocarbon solvents such as benzene, toluene, di-i-propylbenzene, and n-amylnaphthalene.

[0162] Among these, alcohol-based solvents and ester-based solvents are preferred, polyhydric alcohol partial ether-based solvents, polyhydric alcohol partial ether acetate-based solvents, lactone-based solvents, and monocarboxylic acid ester-based solvents are more preferred, and propylene glycol monomethyl ether, ethyl lactate, propylene glycol monomethyl ether acetate, and γ-butyrolactone are even more preferred. The radiation-sensitive composition may contain one or more solvents.

[0163] (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. The content of the other optional components is usually 5 parts by mass or less per 100 parts by mass of the polymer.

[0164] <Method for Preparing Radiation-Sensitive Composition> The radiation-sensitive composition can be prepared, for example, by mixing the onium salt (1), a polymer, and a solvent, and, if necessary, a radiation-sensitive acid generator and a high-fluorine-content polymer, etc., in predetermined ratios. After mixing, the radiation-sensitive composition is preferably filtered, for example, through a filter having a pore size of about 0.1 μm to 0.5 μm. The solids concentration of the radiation-sensitive composition is usually 0.1% to 50% by mass, preferably 0.5% to 30% by mass, and more preferably 1% to 20% by mass.

[0165] <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").

[0166] According to the pattern forming method, since the radiation-sensitive composition having excellent resist properties is used, a high-quality resist pattern can be formed with a good yield. Each step will be described below.

[0167] [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, pre-baking (PB) may be performed, if necessary, to volatilize the solvent in the coating film. The PB temperature is typically 60°C to 150°C, preferably 80°C to 140°C. The PB time is typically 5 seconds to 600 seconds, preferably 10 seconds to 300 seconds. The thickness of the resist film formed is preferably 10 nm to 1,000 nm, more preferably 10 nm to 500 nm.

[0168] 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 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.

[0169] 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.

[0170] [Exposure Step] In this step (the above step (2)), the resist film formed in the above step (1), the resist film formation step, is exposed by irradiating it with radiation through a photomask (or, in some cases, through an immersion medium 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 ArF excimer laser light or EUV being even more preferred.

[0171] 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.

[0172] 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.

[0173] [Development Step] In this step (step (3) above), the resist film exposed in the exposure step (step (2) above) is developed with a developer. 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.

[0174] In the case of alkaline development, examples of the developer used in the development include an alkaline aqueous solution containing at least one alkaline compound dissolved therein, such as sodium hydroxide, potassium hydroxide, sodium carbonate, sodium silicate, sodium metasilicate, aqueous ammonia, ethylamine, n-propylamine, diethylamine, di-n-propylamine, triethylamine, methyldiethylamine, ethyldimethylamine, triethanolamine, tetramethylammonium hydroxide (TMAH), pyrrole, piperidine, choline, 1,8-diazabicyclo-[5.4.0]-7-undecene, and 1,5-diazabicyclo-[4.3.0]-5-nonene. Among these, an aqueous TMAH solution is preferred, and a 2.38% by mass aqueous TMAH solution is more preferred.

[0175] 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 ether solvents, glycol ether solvents are preferred, with ethylene glycol monomethyl ether and propylene glycol monomethyl ether being more preferred. As ester solvents, acetate ester solvents are preferred, with n-butyl acetate and amyl acetate being more preferred. As ketone solvents, chain ketones are preferred, with 2-heptanone being 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.

[0176] As mentioned above, the developer may be either an alkaline developer or an organic solvent developer.

[0177] 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).

[0178] <Onium Salt (1)> An onium salt according to yet another embodiment of the present invention is represented by the following formula (1). In formula (1), L is a single bond or a divalent linking group having 1 to 5 carbon atoms. １ is an aromatic ring with a valence of (a1+b1+1). ２ is an (a2+b2+1)-valent aromatic ring. １ and X ２ are each independently a monovalent organic group having 1 to 20 carbon atoms. １ is Ar １ and -O-, -S- or -SO ２ Y is a monovalent organic group having 4 to 20 carbon atoms, or a monovalent perfluoroalkyl group having 1 to 20 carbon atoms, bonded via a -. ２ is Ar ２ and -O-, -S- or -SO ２ a1, a2, b1, and b2 are each independently an integer of 0 to 5. ２ When the aromatic ring is a benzene ring, b1+b2≧1.

[0179] As the onium salt represented by the formula (1) according to this embodiment, the onium salt (1) contained in the radiation-sensitive composition can be suitably used.

[0180] 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.

[0181] [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.

[0182] [ １３ C-NMR analysis of polymer １３ C-NMR analysis was carried out using a nuclear magnetic resonance spectrometer (JNM-Delta400 manufactured by JEOL Ltd.).

[0183] <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 %.

[0184]

[0185] Synthesis Example 1 Synthesis of Polymer (A-1) Monomer (M-1), monomer (M-2), monomer (M-5), monomer (M-11), and monomer (M-14) were dissolved in 2-butanone (200 parts by mass) to give a molar ratio of 40 / 10 / 20 / 25 / 5 (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 polymerized 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: 80%). 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-11) and (M-14) were 40.1 mol%, 9.0 mol%, 20.9 mol%, 24.8 mol% and 5.2 mol%, respectively.

[0186] Synthesis Examples 2 to 11 and 21 to 22 (Synthesis of Polymers (A-2) to (A-11) and Polymers (A-21) to (A-22)) Polymers (A-2) to (A-11) and Polymers (A-21) to (A-22) 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 property values ​​(Mw and Mw / Mn) of the obtained polymers are also shown in Table 1 below. In Table 1 below, "-" indicates that the corresponding monomer was not used (the same applies to the following tables).

[0187]

[0188] Synthesis Example 12 Synthesis of Polymer (A-12) Monomer (M-1), monomer (M-15), and monomer (M-18) were dissolved in 1-methoxy-2-propanol (200 parts by mass) to give a molar ratio of 40 / 10 / 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 time 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 separated by filtration. The white powder collected by filtration was washed twice with hexane, filtered, and then dissolved in 1-methoxy-2-propanol (300 parts by mass). Methanol (500 parts by mass), triethylamine (50 parts by mass), and ultrapure water (10 parts by mass) were then added, and a hydrolysis reaction was carried out at 70°C for 6 hours with stirring. After completion of the reaction, the residual 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 collected by filtration 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 5,700, and the Mw / Mn was 1.66. １３ As a result of C-NMR analysis, the contents of the structural units derived from (M-1), (M-15) and (M-18) were 39.8 mol %, 10.1 mol % and 50.1 mol %, respectively.

[0189] [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 that gives the structural unit (IV) is １３C-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 of the obtained polymer and its physical properties (Mw and Mw / Mn) are also shown in Table 2 below.

[0190]

[0191] Synthesis Example 16 Synthesis of High Fluorine Content Polymer (F-1) Monomer (M-2), monomer (M-4), monomer (M-15), monomer (M-16), monomer (M-20), and monomer (M-22) were dissolved in 2-butanone (200 parts by mass) to give a molar ratio of 10 / 20 / 5 / 5 / 40 / 20 (mol %), and AIBN (3 mol %) was added as an initiator to prepare a monomer solution. 2-Butanone (100 parts by mass) was placed in a reaction vessel, and the reaction vessel was purged with nitrogen for 30 minutes. The temperature inside the reaction vessel was then raised to 80°C, and the monomer solution was added dropwise over 3 hours with stirring. The start of the dropwise addition marked the start time of the polymerization reaction, and the polymerization reaction was carried out for 6 hours. After completion of the polymerization reaction, the polymerized 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 procedure 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 Mw of the high fluorine content polymer (F-1) was 9,800, and the Mw / Mn was 1.71. １３ As a result of C-NMR analysis, the contents of the structural units derived from (M-2), (M-4), (M-15), (M-16), (M-20) and (M-22) were 8.7 mol%, 19.3 mol%, 5.4 mol%, 6.1 mol%, 40.9 mol%, and 19.6 mol%, respectively.

[0192] 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 Table 3 below. 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 Table 3 below.

[0193]

[0194] <Synthesis of [C] Onium Salt (1)> [Example C1] (Synthesis of Onium Salt (C-1)) [C] Onium salt (C-1) as an acid diffusion controller was synthesized according to the following synthesis scheme.

[0195]

[0196] A reaction vessel was charged with 20.0 mmol of 2-iodobenzoic acid, 20.0 mmol of metachloroperbenzoic acid (m-CPBA), 25.0 mmol of sulfuric acid, and 50 g of dichloromethane, and the mixture was stirred for 1 hour under ice cooling. Subsequently, 30.0 mmol of n-octyloxybenzene was added, and the mixture was stirred for an additional 3 hours. Then, 100 g of saturated aqueous sodium bicarbonate solution was added, and the mixture was stirred at room temperature for an additional 24 hours. Methylene chloride was added to the resulting reaction solution for extraction, and the organic layer was separated. The resulting organic layer was dried over sodium sulfate, the solvent was distilled off, and the mixture was purified by recrystallization, yielding the onium salt (C-1) represented by the above formula (C-1) in good yield.

[0197] Examples C2 to C37 Synthesis of Onium Salts (C-2) to (C-37) Salt compounds as acid diffusion controllers represented by the following formulas (C-2) to (C-37) were synthesized in the same manner as in Example C1, except that the raw materials and precursors were appropriately changed.

[0198]

[0199]

[0200] The following compounds were used as components other than the components synthesized above.

[0201] [Acid diffusion controllers other than onium salts (C-1) to (C-37)] cc-1 to cc-7: Compounds represented by the following formulas (cc-1) to (cc-7) (hereinafter, the compounds represented by formulas (cc-1) to (cc-7) may be referred to as "compound (cc-1)" to "compound (cc-7)," respectively).

[0202]

[0203] [[B] Radiation-Sensitive Acid Generator] B-1 to B-7: Compounds represented by the following formulas (B-1) to (B-9).

[0204]

[0205] [[E] Solvent] E-1: Propylene glycol monomethyl ether acetate E-2: Propylene glycol monomethyl ether E-3: γ-butyrolactone E-4: Ethyl lactate

[0206] [Preparation of Negative Radiation-Sensitive Composition for ArF Exposure] [Example 1] 100 parts by mass of [A] polymer (A-1), [B] radiation-sensitive acid generator (B-1) 8.0 parts by mass, [C] onium salt (1) (C-1) 6.0 parts by mass, [F] high-fluorine content polymer (F-1) 5.0 parts by mass (solids content), and [E] solvent (E-1) / (E-2) / (E-3) mixed solvent (2,000 / 1,200 / 200 parts by mass) were mixed and filtered through a membrane filter having a pore size of 0.2 μm to prepare radiation-sensitive composition (J-1).

[0207] [Examples 2 to 67 and 96 to 97 and Comparative Examples 1 to 7] Radiation-sensitive compositions (J-2) to (J-67), (J-96) to (J-97), 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.

[0208]

[0209] <Formation of Resist Pattern Using Negative Radiation-Sensitive Composition for ArF Exposure> A composition for forming an underlayer film ("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 an underlayer film with an average thickness of 100 nm. The negative radiation-sensitive composition for ArF exposure prepared above was applied to this underlayer film 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 with an average thickness of 110 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 dipole (σ = 0.9 / 0.7) through a mask pattern with 40 nm holes and an 80 nm pitch. After exposure, a post-exposure bake (PEB) was performed at 100°C for 60 seconds. Thereafter, the resist film was developed using n-butyl acetate as an organic solvent developer, and dried to form a negative resist pattern (40 nm holes, 80 nm pitch).

[0210] <Evaluation> The resist patterns formed using the above-described negative radiation-sensitive compositions for ArF exposure were evaluated for sensitivity, CDU performance, DOF performance, pattern circularity, and the number of development defects 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).

[0211] [Sensitivity] In forming a resist pattern using the negative radiation-sensitive composition for ArF exposure, the exposure dose required to form a 40 nm hole, 80 nm pitch 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".

[0212] [CDU Performance] A total of 1,800 resist patterns with 40 nm holes and an 80 nm pitch were measured at arbitrary points from the top of the pattern using the above-mentioned scanning electron microscope. The dimensional variation (3σ) was determined and used as the CDU performance (nm). The smaller the CDU value, the smaller the variation in hole diameter over a long period, indicating better performance. CDU performance was evaluated as "good" when it was 3.0 nm or less, and "poor" when it exceeded 3.0 nm.

[0213] [DOF Performance] The depth of focus (DOF) range in which the diameter of the hole pattern formed was 30 nm to 50 nm in the resist pattern resolved at the optimum exposure dose obtained in the sensitivity evaluation was measured. The DOF performance was evaluated as "good" when it was 100 nm or more, and "poor" when it was less than 100 nm.

[0214] [Pattern circularity] The 40 nm holes and 80 nm pitch contact holes formed by irradiating with the optimum exposure dose obtained in the sensitivity evaluation were observed in plan view using the scanning electron microscope, and their vertical and horizontal sizes were measured. A ratio of vertical size to horizontal size of 0.95 or more and less than 1.05 was evaluated as "A" (very good), a ratio of 0.90 or more and less than 0.95, or 1.05 or more and less than 1.10 was evaluated as "B" (good), and a ratio of less than 0.90 or more than 1.10 was evaluated as "C" (poor).

[0215] [Number of Development Defects] A resist film was exposed to an optimum exposure dose to form a contact hole pattern with 40 nm holes and an 80 nm pitch, which was used as a wafer for defect inspection. The number of defects on this wafer for defect inspection was measured using a defect inspection device (KLA-Tencor's "KLA2810"). Defects with a diameter of 50 μm or less were determined to be derived from the resist film, and the number of defects was calculated. After development, the number of defects determined to be derived from the resist film was evaluated as "good" when the number of defects was 50 or less, and as "poor" when the number of defects was more than 50.

[0216]

[0217] As is clear from the results in Table 5, the radiation-sensitive compositions of Examples 1 to 67 and 96 to 97 were good in sensitivity, CDU performance, DOF performance, pattern circularity, and the number of development defects when used for ArF exposure. In contrast, the radiation-sensitive compositions of Comparative Examples 1 to 7 were inferior in sensitivity, CDU performance, DOF performance, pattern circularity, and the number of development defects compared to the Examples. Therefore, it can be said that when the radiation-sensitive compositions of Examples 1 to 67 and 96 to 97 were used for negative ArF exposure, they were able to exhibit good CDU performance, DOF performance, and pattern circularity while maintaining high sensitivity, and were also excellent in suppressing development defects.

[0218] <Preparation of positive-tone radiation-sensitive composition for ArF exposure> [Example 68] 100 parts by mass of [A] polymer (A-1), [B] 10.0 parts by mass of radiation-sensitive acid generator (B-7), [C] 8.0 parts by mass of onium salt (1) (C-2), [F] 3.0 parts by mass (solids content) of high-fluorine polymer (F-2), and [E] 3,230 parts by mass of a mixed solvent of (E-1) / (E-2) / (E-3) (2,200 / 1200 / 30 (parts by mass)) as a solvent were mixed and filtered through a membrane filter having a pore size of 0.2 μm to prepare radiation-sensitive composition (J-68).

[0219] Examples 69 to 81 and Comparative Examples 8 to 10 Radiation-sensitive compositions (J-69) to (J-81) and (CJ-8) to (CJ-10) were prepared in the same manner as in Example 68, except that the types and amounts of each component shown in Table 6 below were used.

[0220]

[0221] <Formation of Resist Pattern Using Positive Radiation-Sensitive Composition for ArF Exposure> A composition for forming an underlayer film ("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 an underlayer film with an average thickness of 100 nm. The positive radiation-sensitive composition for ArF exposure prepared as described above was applied to this underlayer film 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 with an average thickness of 120 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).

[0222] <Evaluation> The resist patterns formed using the positive radiation-sensitive compositions for ArF exposure were evaluated for sensitivity, LWR performance, and pattern rectangularity according to the methods described below. The results are shown in Table 7. A scanning electron microscope (CG-5000 manufactured by Hitachi High-Technologies Corporation) was used to measure the resist patterns.

[0223] [Sensitivity] In forming a resist pattern using a positive radiation-sensitive composition for ArF 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 used as the sensitivity (mJ / cm ２ The sensitivity was 30 mJ / cm ２ The following cases are evaluated as "good": 30 mJ / cm ２ If it exceeded this, it was evaluated as "poor".

[0224] [LWR Performance] 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. The LWR performance was evaluated as "good" when it was 3.0 nm or less, and as "poor" when it exceeded 3.0 nm.

[0225] [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.

[0226]

[0227] As is clear from the results in Table 7, when used for forming positive resist patterns by ArF exposure, the radiation-sensitive compositions of Examples 68 to 81 were all good in sensitivity, LWR performance, and pattern rectangularity. In contrast, the radiation-sensitive compositions of Comparative Examples 8 to 10 were inferior to the examples in each of the properties.

[0228] <Preparation of positive-tone radiation-sensitive composition for extreme ultraviolet (EUV) exposure> [Example 82] [A] 100 parts by mass of (A-12) as a polymer, [B] 30.0 parts by mass of (B-3) as a radiation-sensitive acid generator, [C] 20.0 parts by mass of (C-3) as an onium salt (1), [F] 6.0 parts by mass (solids content) of (F-5) as a high-fluorine content polymer, and [E] 6,100 parts by mass of a mixed solvent of (E-1) / (E-2) / (E-4) (2,000 / 4,000 / 100 (parts by mass)) 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-82).

[0229] Examples 83 to 94 and Comparative Examples 11 to 13 Radiation-sensitive compositions (J-83) to (J-94) and (CJ-11) to (CJ-13) were prepared in the same manner as in Example 83, except that the types and amounts of each component shown in Table 8 below were used.

[0230]

[0231] <Formation of Resist Pattern Using Positive Radiation-Sensitive Composition for EUV Exposure> A composition for forming an underlayer film (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 an underlayer film with an average thickness of 105 nm. The positive radiation-sensitive composition for EUV exposure prepared above was applied to this underlayer film 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 50 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: imecDEFECT32FFR02. After the exposure, PEB was performed for 60 seconds at 120° C. Thereafter, the resist film was subjected to alkaline development using a 2.38% by mass aqueous solution of TMAH as an alkaline developer, and after development, the resist film was washed with water and further dried to form a positive resist pattern (25 nm line and space pattern).

[0232] <Evaluation> The resist patterns formed using the positive radiation-sensitive compositions for EUV exposure were evaluated for sensitivity, LWR performance, and pattern rectangularity according to the methods described below. The results are shown in Table 9. A scanning electron microscope (CG-5000 manufactured by Hitachi High-Technologies Corporation) was used to measure the resist patterns.

[0233] [Sensitivity] In forming a resist pattern using a positive radiation-sensitive composition for EUV exposure, the exposure amount for forming a 25 nm line and space pattern is defined as the optimum exposure amount, and this optimum exposure amount is defined as the sensitivity (mJ / cm ２The sensitivity was 50 mJ / cm ２ The cases below were evaluated as "good", and the cases above 50 mJ / cm were evaluated as "poor".

[0234] [LWR Performance] 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 25 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. The LWR performance was evaluated as "good" when it was 3.0 nm or less, and as "poor" when it exceeded 3.0 nm.

[0235] [Pattern rectangularity] A 25 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.

[0236]

[0237] As is clear from the results in Table 9, when used for forming resist patterns by EUV exposure, the radiation-sensitive compositions of Examples 82 to 94 were all good in sensitivity, LWR performance, and pattern rectangularity. In contrast, the radiation-sensitive compositions of Comparative Examples 11 to 13 were inferior to the examples in each of the properties.

[0238] <Preparation of Negative Radiation-Sensitive Composition for EUV Exposure, and Formation and Evaluation of Resist Pattern Using This Composition> [Example 95] [A] 100 parts by mass of (A-15) as a polymer, [B] 40.0 parts by mass of (B-4) as a radiation-sensitive acid generator, [C] 35.0 parts by mass of (C-17) as an onium salt (1), [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-2) / (E-4) (4,280 / 1,830 (parts by mass)) 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-95).

[0239] A composition for forming an underlayer film (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 an underlayer film with an average thickness of 105 nm. The radiation-sensitive composition (J-95) prepared above was applied to this underlayer film using the spin coater, and post-baking was performed 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 45 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 exposure, post-baking was performed at 120°C for 60 seconds. Thereafter, the resist film was developed with n-butyl acetate as an organic solvent developer and dried to form a negative resist pattern (20 nm holes, 40 nm pitch).

[0240] The sensitivity and CDU performance of the resist pattern formed using the radiation-sensitive composition (J-95) were evaluated in the same manner as in the evaluation of the resist pattern formed using the negative-tone radiation-sensitive composition for ArF immersion exposure. As a result, the radiation-sensitive composition of Example 95 exhibited good sensitivity and CDU performance even when a negative-tone resist pattern was formed by EUV exposure.

[0241] The radiation-sensitive composition, pattern forming method, and onium salt described above can form a resist pattern that has good sensitivity to exposure light and is excellent in CDU performance, DOF performance, pattern circularity, LWR performance, pattern rectangularity, and development defect suppression. 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); a polymer containing a structural unit (I) having an acid-dissociable group; and a solvent. (In formula (1), Ar １ is an aromatic ring having a valence of (a1+b1+1). ２ is an aromatic ring having a valence of (a2+b2+1). １ and X ２ are each independently a monovalent organic group having 1 to 20 carbon atoms, a cyano group, a nitro group, or a halogen atom. １ and X ２ When there are multiple Xs, １ and X ２ are the same or different. １ is Ar １ and -O-, -S- or -SO ２ Y is a monovalent organic group having 4 to 20 carbon atoms, or a monovalent perfluoroalkyl group having 1 to 20 carbon atoms, bonded via a -. １ If there are multiple Y １ are the same or different. ２ is Ar ２ and -O-, -S- or -SO ２ Y is a monovalent organic group having 4 to 20 carbon atoms, or a monovalent perfluoroalkyl group having 1 to 20 carbon atoms, bonded via a -. ２ If there are multiple Y ２ are the same or different. L is a single bond or a divalent linking group having 1 to 5 carbon atoms. a1, a2, b1, and b2 are each independently an integer of 0 to 5. ２ When the aromatic ring is a benzene ring, b1+b2≧1.

2. The radiation-sensitive composition according to claim 1, wherein the onium salt is represented by the following formula (1-1), (1-2) or (1-3): (In formula (1-1), L, １ , X ２ , a1, a2, b1 and b2 are the same as those in formula (1). １１ and Y ２１ each independently represents an aromatic ring of formula (1-1) and —O—, —S— or —SO ２ In formula (1-2), L and X are each a monovalent organic group having 4 to 20 carbon atoms, or a monovalent perfluoroalkyl group having 1 to 20 carbon atoms, bonded via a -. c1 is 0 or 1. １ , X ２ , a1 and a2 are the same as those in formula (1). １ Y is an alicyclic hydrocarbon structure, an aromatic hydrocarbon structure, or an aliphatic heterocyclic structure which forms a condensed ring with the adjacent benzene ring of formula (1-2). １２ and Y ２２ each independently represents an aromatic ring of formula (1-2) and —O—, —S— or —SO ２ Each of b1 and b2 is independently an integer of 0 to 5. c1 is 0 or 1. In formula (1-3), L and X are each a monovalent organic group having 4 to 20 carbon atoms, or a monovalent perfluoroalkyl group having 1 to 20 carbon atoms, bonded via a -. １ , X ２ , a1 and a2 are the same as those in formula (1). ２３ is an aromatic heterocycle. １３ represents an aromatic ring of the formula (1-3) and -O-, -S- or -SO ２ Y is a monovalent organic group having 4 to 20 carbon atoms, or a monovalent perfluoroalkyl group having 1 to 20 carbon atoms, bonded via a -. ２３ is Ar ２３ and -O-, -S- or -SO ２ b1 and b2 are each independently an integer of 0 to 5. c1 is 0 or 1.

3. Y １ is Ar １ a monovalent organic group having 4 to 20 carbon atoms or a monovalent perfluoroalkyl group having 1 to 20 carbon atoms, which is bonded to Y via —O—; ２ is Ar ２ 2. The radiation-sensitive composition according to claim 1, wherein the alkyl group is a monovalent organic group having 4 to 20 carbon atoms, or a monovalent perfluoroalkyl group having 1 to 20 carbon atoms, which is bonded to the alkyl group via --O--.

4. Ar １ The radiation-sensitive composition according to claim 1 , wherein is a benzene ring.

5. L is a single bond, and I in the above formula (1) ＋ The radiation-sensitive composition according to any one of claims 1 to 4, wherein the carbon atom to which is bonded is an ortho-position.

6. The radiation-sensitive composition according to any one of claims 1 to 4, wherein the content of the onium salt is from 0.1 parts by mass to 80 parts by mass based on 100 parts by mass of the polymer.

7. The radiation-sensitive composition according to any one of claims 1 to 4, wherein the structural unit (I) is represented by the following formula (3): (In formula (3), R １７ R is a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group. １８ R is a monovalent substituted or unsubstituted hydrocarbon group having 1 to 20 carbon atoms. １９ and R ２０ are each independently a monovalent substituted or unsubstituted chain hydrocarbon group having 1 to 10 carbon atoms or a monovalent substituted or unsubstituted 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 together with the carbon atom 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.) 8. The radiation-sensitive composition according to any one of claims 1 to 4, wherein the content of the structural unit (I) in all structural units constituting the polymer is 5 mol % or more and 80 mol % or less.

9. The radiation-sensitive composition according to any one of claims 1 to 4, 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.

10. The radiation-sensitive composition according to claim 9, wherein the content of the structural unit (II) in all structural units constituting the polymer is 5 mol % or more and 80 mol % or less.

11. The radiation-sensitive composition according to any one of claims 1 to 4, further comprising a radiation-sensitive acid generator that generates an acid having a lower pKa than the acid generated from the onium salt upon exposure to radiation.

12. A method for forming a pattern, comprising the steps of: applying the radiation-sensitive composition according to any one of claims 1 to 4 directly or indirectly to a substrate to form a resist film; exposing the resist film to light; and developing the exposed resist film with a developer.

13. The pattern forming method according to claim 12, wherein the exposure is carried out with an ArF excimer laser or extreme ultraviolet light.

14. An onium salt represented by the following formula (1): (In formula (1), Ar １ is an aromatic ring having a valence of (a1+b1+1). ２ is an aromatic ring having a valence of (a2+b2+1). １ and X ２ are each independently a monovalent organic group having 1 to 20 carbon atoms, a cyano group, a nitro group, or a halogen atom. １ and X ２ When there are multiple Xs, １ and X ２ are the same or different. １ is Ar １ and -O-, -S- or -SO ２ Y is a monovalent organic group having 4 to 20 carbon atoms, or a monovalent perfluoroalkyl group having 1 to 20 carbon atoms, bonded via a -. １ If there are multiple Y １ are the same or different. ２ is Ar ２ and -O-, -S- or -SO ２ Y is a monovalent organic group having 4 to 20 carbon atoms, or a monovalent perfluoroalkyl group having 1 to 20 carbon atoms, bonded via a -. ２ If there are multiple Y ２ are the same or different. L is a single bond or a divalent linking group having 1 to 5 carbon atoms. a1, a2, b1, and b2 are each independently an integer of 0 to 5. ２ When the aromatic ring is a benzene ring, b1+b2≧1.

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