Patent Publication Number: US-11385542-B2

Title: Salt, quencher, resist composition and method for producing resist pattern

Description:
TECHNICAL FIELD 
     The present invention relates to a salt, a quencher and a resist composition which contain the salt, and a method for producing a resist pattern using the resist composition. 
     BACKGROUND ART 
     Patent Document 1 mentions a resist composition including a salt of the following structural formula, a resin including a structural unit having an acid-labile group, and an acid generator. 
     
       
         
         
             
             
         
       
     
     Patent Document 2 mentions a resist composition including a salt of the following structural formula, a resin including a structural unit having an acid-labile group, and an acid generator. 
     
       
         
         
             
             
         
       
     
     PRIOR ART DOCUMENT 
     Patent Document 
     Patent Document 1: JP 2017-202993 A 
     Patent Document 2: JP 2018-066985 A 
     DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention 
     An object of the present invention is to provide a salt capable of producing a resist pattern with CD uniformity (CDU) which is better than that of a resist pattern formed from the resist composition including the above-mentioned salts. 
     Means for Solving the Problems 
     The present invention includes the following inventions. 
     [1] A salt represented by formula (I): 
                         
wherein, in formula (I),
 
     R 1 , R 2  and R 3  each independently represent a halogen atom, a perfluoroalkyl group having 1 to 6 carbon atoms or a hydrocarbon group having 1 to 12 carbon atoms, and —CH 2 — included in the hydrocarbon group may be replaced by —O— or —CO—, 
     m1 represents an integer of 0 to 4, and when m1 is 2 or more, a plurality of R 1  may be the same or different from each other, 
     m2 represents an integer of 0 to 4, and when m2 is 2 or more, a plurality of R 2  may be the same or different from each other, and 
     m3 represents an integer of 0 to 4, and when m3 is 2 or more, a plurality of R 3  may be the same or different from each other. 
     [2] A quencher comprising the salt according to [1]. 
     [3] A resist composition comprising the quencher according to [2], a resin including a structural unit having an acid-labile group, and an acid generator. 
     [4] The resist composition according to [3], wherein the resin including a structural unit having an acid-labile group is a resin including at least one selected from the group consisting of a structural unit represented by formula (a1-1) and a structural unit represented by formula (a1-2): 
                         
wherein, in formula (a1-1) and formula (a1-2),
 
     L a1  and L a2  each independently represent —O— or *—O—(CH 2 ) k1 —CO—O—, k1 represents an integer of 1 to 7, and * represents a bond to —CO—,
         R a4  and R a5  each independently represent a hydrogen atom or a methyl group,   R a6  and R a7  each independently represent an alkyl group having 1 to 8 carbon atoms, an alicyclic hydrocarbon group having 3 to 18 carbon atoms, or a group obtained by combining these groups,   m1 represents an integer of 0 to 14,   n1 represents an integer of 0 to 10, and   n1′ represents an integer of 0 to 3.
 
[5] The resist composition according to [4], wherein the resin including a structural unit having an acid-labile group includes a structural unit represented by formula (a2-A):
       

                         
wherein, in formula (a2-A),
 
     R a50  represents a hydrogen atom, a halogen atom, or an alkyl group having 1 to 6 carbon atoms which may have a halogen atom, 
     R a51  represents a halogen atom, a hydroxy group, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an alkylcarbonyl group having 2 to 4 carbon atoms, an alkylcarbonyloxy group having 2 to 4 carbon atoms, an acryloyloxy group or a methacryloyloxy group, 
     A a50  represents a single bond or *—X a51 -(A a52 -X a52 ) nb —, and * represents a bond to a carbon atom to which —R a50  is bonded, 
     A a52  represents an alkanediyl group having 1 to 6 carbon atoms, 
     X a51  and X a52  each independently represent —O—, —CO—O— or —O—CO—, 
     nb represents 0 or 1, 
     mb represents an integer of 0 to 4, and when mb is an integer of 2 or more, a plurality of R a51  may be the same or different from each other. 
     [6] The resist composition according to any one of [3] to [5], wherein the acid generator is a salt represented by formula (B1): 
                         
wherein, in formula (B1),
 
     Q b1  and Q b2  each independently represent a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms, 
     L b1  represents a divalent saturated hydrocarbon group having 1 to 24 carbon atoms, —CH 2 — included in the divalent saturated hydrocarbon group may be replaced by —O— or —CO—, and a hydrogen atom included in the divalent saturated hydrocarbon group may be substituted with a fluorine atom or a hydroxy group, 
     Y represents a methyl group which may have a substituent, or an alicyclic hydrocarbon group having 3 to 18 carbon atoms which may have a substituent, and —CH 2 — included in the alicyclic hydrocarbon group may be replaced by —O—, —S(O) 2 — or —CO—, and 
     Z +  represents an organic cation. 
     [7] The resist composition according to any one of [3] to [6], further comprising a salt generating an acid having an acidity lower than that of an acid generated from the acid generator. 
     [8] A method for producing a resist pattern, which comprises: 
     (1) a step of applying the resist composition according to any one of [3] to [7] on a substrate, 
     (2) a step of drying the applied composition to form a composition layer, 
     (3) a step of exposing the composition layer, 
     (4) a step of heating the exposed composition layer, and 
     (5) a step of developing the heated composition layer. 
     Effects of the Invention 
     It is possible to produce a resist pattern with satisfactory CD uniformity (CDU) by using a resist composition containing a salt of the present invention. 
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     As used herein, “(meth)acrylate” each mean “at least one of acrylate and methacrylate”. The terms such as “(meth)acrylic acid” and “(meth)acryloyl” have the same meanings. 
     Unless otherwise specified, regarding groups capable of having linear, branched and/or ring structures such as “aliphatic hydrocarbon group” include any one of them. “Aromatic hydrocarbon group” also includes groups in which a hydrocarbon group is bonded to an aromatic ring. When stereoisomers exist, all stereoisomers are included. 
     As used herein, “solid component of resist composition” means the total of components excluding the below-mentioned solvent (E) from the total amount of the resist composition. 
     [Salt Represented by Formula (I)] 
     The salt of the present invention relates to a salt represented by formula (I) (hereinafter sometimes referred to as “salt (I)”). 
     In formula (I), examples of the halogen atom of R 1 , R 2  and R 3  include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom. 
     Examples of the perfluoroalkyl group having 1 to 6 carbon atoms of R 1 , R 2  and R 3  include a trifluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluoroisopropyl group, a perfluorobutyl group, a perfluorosec-butyl group, a perfluorotert-butyl group, a perfluoropentyl group and a perfluorohexyl group. 
     Examples of the hydrocarbon group having 1 to 12 carbon atoms of R 1 , R 2  and R 3  include a chain hydrocarbon group such as an alkyl group, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, and a group obtained by combining these groups. 
     Examples of the alkyl group include alkyl groups such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, a pentyl group, a hexyl group, an octyl group and a nonyl group. The number of carbon atoms of the alkyl group is preferably 1 to 9, and more preferably 1 to 4. 
     The alicyclic hydrocarbon group may be either monocyclic, polycyclic or spiro ring, or may be either saturated or unsaturated. Examples of the alicyclic hydrocarbon group include monocyclic cycloalkyl groups such as a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cyclooctyl group, a cyclononyl group, a cyclodecyl group and a cyclododecyl group; and polycyclic cycloalkyl groups such as a norbornyl group and an adamantyl group. The number of carbon atoms of the alicyclic hydrocarbon group is preferably 3 to 12, and more preferably 3 to 10. 
     Examples of the aromatic hydrocarbon group include aryl groups such as a phenyl group, a naphthyl group and a biphenyl group. The number of carbon atoms of the aromatic hydrocarbon group is preferably 6 to 12, and more preferably 6 to 10. 
     Examples of the group combined include a group obtained by combining the above-mentioned alkyl group and alicyclic hydrocarbon group (a cycloalkylalkyl group, etc.), an aralkyl group (benzyl group, etc.), an aromatic hydrocarbon group having an alkyl group (a p-methylphenyl group, a p-tert-butylphenyl group, a tolyl group, a xylyl group, a cumenyl group, a mesityl group, a 2,6-diethylphenyl group, a 2-methyl-6-ethylphenyl group, etc.), an aromatic hydrocarbon group having an alicyclic hydrocarbon group (a p-cyclohexylphenyl group, etc.), an aryl-cycloalkyl group (a phenylcyclohexyl group, etc.) and the like. 
     When —CH 2 — included in the hydrocarbon group represented by R 1 , R 2  and R 3  is replaced by —O— or —CO—, the number of carbon atoms before replacement is taken as the number of carbon atoms of the hydrocarbon group. 
     Examples of the group replaced include a hydroxy group (a group in which —CH 2 — included in a methyl group is replaced by —O—), a carboxy group (a group in which —CH 2 —CH 2 -included in an ethyl group is replaced by —O—CO—), an alkoxy group having 1 to 11 carbon atoms (a group in which —CH 2 -included in an alkyl group having 2 to 12 carbon atoms is replaced by —O—), an alkoxycarbonyl group having 2 to 11 carbon atoms (a group in which —CH 2 —CH 2 — included in an alkyl group having 3 to 12 carbon atoms is replaced by —O—CO—), an alkylcarbonyl group having 2 to 12 carbon atoms (a group in which —CH 2 — included in an alkyl group having 2 to 12 carbon atoms is replaced by —CO—), an alkylcarbonyloxy group having 2 to 11 carbon atoms (a group in which —CH 2 —CH 2 — included in an alkyl group having 3 to 12 carbon atoms is replaced by —CO—O—) and the like. 
     Examples of the alkoxy group include a methoxy group, an ethoxy group, a propoxy group, a butoxy group, a pentyloxy group, a hexyloxy group, a heptyloxy group, an octyloxy group, a nonyloxy group, a decyloxy group and an undecyloxy group. 
     Examples of the alkoxycarbonyl group include a methoxycarbonyl group, an ethoxycarbonyl group, a propoxycarbonyl group and a butoxycarbonyl group. 
     Examples of the alkylcarbonyl group include an acetyl group, a propionyl group and a butyryl group. 
     Examples of the alkylcarbonyloxy group include a methylcarbonyloxy group, an ethylcarbonyloxy group, a propylcarbonyloxy group and a butylcarbonyloxy group. 
     m1 is preferably an integer of 0 to 3, more preferably an integer of 1 to 3, and still more preferably 2 or 3. 
     Preferably, m2 and m3 each independently represent an integer of 0 to 2, and more preferably 0 or 1. 
     R 1  is preferably a fluorine atom, trifluoromethyl group or a hydrocarbon group having 1 to 10 carbon atoms (—CH 2 — included in the hydrocarbon group may be replaced by —O— or —CO—), more preferably a fluorine atom or an alkyl group having 1 to 6 carbon atoms (—CH 2 — included in the alkyl group may be replaced by —O— or —CO—), and still more preferably an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, an alkylcarbonyloxy group having 1 to 4 carbon atoms or a hydroxy group. 
     Preferably, R 2  and R 3  each independently represent a fluorine atom, a trifluoromethyl group or a hydrocarbon group having 1 to 10 carbon atoms (—CH 2 — included in the hydrocarbon group may be replaced by —O— or —CO—), more preferably a fluorine atom, an alkyl group having 1 to 6 carbon atoms or an alicyclic hydrocarbon group having 3 to 10 carbon atoms (—CH 2 — included in the alkyl group and the alicyclic hydrocarbon group may be replaced by —O— or —CO—), and still more preferably a fluorine atom, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms or a monocyclic cycloalkyl group having 3 to 6 carbon atoms. 
     Examples of the salt (I) include salts represented by the following formulas. 
                                                                                                 
&lt;Method for Producing Salt (I)&gt;
 
     The salt (I) can be produced by reacting a salt represented by formula (I-a) with silver oxide in a solvent: 
                         
wherein all symbols are the same as defined above.
 
     Examples of the solvent include methanol and the like. 
     The reaction is usually performed at a temperature in a range of 15 to 80° C. for 0.5 to 24 hours. 
     The salt represented by formula (I-a) can be produced by reacting a compound represented by formula (I-b) with a compound represented by formula (I-c) in the presence of phosphorus pentoxide and methanesulfonic acid in a solvent, followed by contacting with sodium iodide: 
                         
wherein all symbols are the same as defined above.
 
     Examples of the solvent include chloroform, acetonitrile and the like. 
     The reaction is usually performed at a temperature in a range of 0 to 60° C. for 0.5 to 24 hours. 
     Examples of the compound represented by formula (I-b) include compounds represented by the following formulas, which are easily available on the market. 
     
       
         
         
             
             
         
       
     
     Examples of the compound represented by formula (I-c) include compounds represented by the following formulas, which are easily available on the market. 
     
       
         
         
             
             
         
       
     
     The salt (I) can also be obtained by mixing a salt represented by formula (I-d) under a base catalyst in a solvent: 
                         
wherein all symbols are the same as defined above.
 
     Examples of the base include triethylamine and the like. 
     Examples of the solvent include chloroform and the like. 
     The reaction is usually performed at a temperature in a range of 0 to 80° C. for 0.5 to 24 hours. 
     The salt represented by formula (I-d) can be obtained by reacting a compound represented by formula (I-b) with a compound represented by formula (I-c) in the presence of trifluoromethanesulfonic acid and trifluoroacetic anhydride in a solvent: 
                         
wherein all symbols are the same as defined above.
 
     Examples of the solvent include chloroform, acetonitrile and the like. 
     The reaction is usually performed at a temperature in a range of 0 to 60° C. for 0.5 to 24 hours. 
     The salt (I) can also be obtained by mixing a salt represented by formula (I-e) under a base catalyst in a solvent: 
                         
wherein all symbols are the same as defined above.
 
     Examples of the base include sodium hydroxide and the like. 
     Examples of the solvent include chloroform and the like. 
     The reaction is usually performed at a temperature in a range of 0 to 80° C. for 0.5 to 24 hours. 
     The salt represented by formula (I-e) can be obtained by reacting a compound represented by formula (I-b) with a compound represented by formula (I-f) in the presence of trifluoromethanesulfonic acid and trifluoroacetic anhydride in a solvent: 
                         
wherein all symbols are the same as defined above.
 
     Examples of the solvent include chloroform, acetonitrile and the like. 
     The reaction is usually performed at a temperature in a range of 0 to 60° C. for 0.5 to 24 hours. 
     Examples of the compound represented by formula (I-f) include compounds represented by the following formulas, which are easily available on the market. 
                         
&lt;Quencher&gt;
 
     The quencher of the present invention includes a salt (I). The quencher may include one salt (I), or two or more salts (I). 
     The quencher of the present invention may include, in addition to the salt (I), a quencher known in the resist field (hereinafter sometimes referred to as “quencher (C)”). The quencher (C) may be used alone, or two or more quenchers may be used in combination. 
     When including the salt (I) and the quencher (C) as the quencher, a ratio of the content of the salt (I) to that of the quencher (C) (mass ratio; salt (I):quencher (C)) is usually 1:99 to 99:1, preferably 2:98 to 98:2, more preferably 5:95 to 95:5, still more preferably 10:90 to 90:10, and particularly preferably 15:85 to 85:15. 
     &lt;Resist Composition&gt; 
     The resist composition of the present invention includes a quencher containing a salt (I), a resin including a structural unit having an acid-labile group (hereinafter sometimes referred to as “resin (A)”) and an acid generator (hereinafter sometimes referred to as “acid generator (B)”). The “acid-labile group” means a group having a leaving group which is eliminated by contact with an acid, thus forming a hydrophilic group (e.g. a hydroxy group or a carboxy group). 
     The resist composition of the present invention preferably includes a solvent (hereinafter sometimes referred to as “solvent (E)”). 
     The resist composition of the present invention may further include a quencher other than the salt (I) (hereinafter sometimes referred to as “quencher (C)”), and preferably includes a salt generating an acid having low acidity, such as a weak acid inner salt (D) (hereinafter sometimes referred to as “weak acid inner salt (D)”). The resist composition of the present invention may have a resin other than the resin (A). 
     The content of the salt (I) is usually 0.001 to 20% by mass, preferably 0.005 to 15% by mass, and more preferably 0.01 to 10% by mass, based on the amount of the solid component of a resist composition. 
     The salt (I) has a function as the quencher in the resist composition. 
     &lt;Resin (A)&gt; 
     The resin (A) includes a structural unit having an acid-labile group (hereinafter sometimes referred to as “structural unit (a1)”). It is preferable that the resin (A) further includes a structural unit other than the structural unit (a1). Examples of the structural unit other than the structural unit (a1) include a structural unit having no acid-labile group (hereinafter sometimes referred to as “structural unit (s)”), a structural unit other than the structural unit (a1) and the structural unit (s) (e.g. a structural unit having a halogen atom mentioned later (hereinafter sometimes referred to as “structural unit (a4)”), a structural unit having a non-leaving hydrocarbon group mentioned later (hereinafter sometimes referred to as “structural unit (a5))) and other structural units derived from monomers known in the art. 
     &lt;Structural Unit (a1)&gt; 
     The structural unit (a1) is derived from a monomer having an acid-labile group (hereinafter sometimes referred to as “monomer (a1)”). 
     The acid-labile group contained in the resin (A) is preferably a group represented by formula (1) (hereinafter also referred to as group (1)) and/or a group represented by formula (2) (hereinafter also referred to as group (2)): 
                         
wherein, in formula (1), R a1 , R a2  and R a3  each independently represent an alkyl group having 1 to 8 carbon atoms, an alicyclic hydrocarbon group having 3 to 20 carbon atoms or groups obtained by combining these groups, or R a1  and R a2  are bonded to each other to form an alicyclic hydrocarbon group having 3 to 20 carbon atoms together with carbon atoms to which R a1  and R a2  are bonded,
 
     ma and na each independently represent 0 or 1, and at least one of ma and na represents 1, and 
     * represents a bond: 
                         
wherein, in formula (2), R a1 ′ and R a2 ′ each independently represent a hydrogen atom or a hydrocarbon group having 1 to 12 carbon atoms, R a3 ′ represents a hydrocarbon group having 1 to 20 carbon atoms, or R a2 ′ and R a3 ′ are bonded to each other to form a heterocyclic group having 3 to 20 carbon atoms together with carbon atoms and X to which R a2 ′ and R a3 ′ are bonded, and —CH 2 — included in the hydrocarbon group and the heterocyclic group may be replaced by —O— or —S—,
 
     X represents an oxygen atom or a sulfur atom, 
     na′ represents 0 or 1, and 
     * represents a bond. 
     Examples of the alkyl group in R a1 , R a2  and R a3  include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group and the like. 
     The alicyclic hydrocarbon group in R a1 , R a2  and R a3  may be either monocyclic or polycyclic. Examples of the monocyclic alicyclic hydrocarbon group include cycloalkyl groups such as a cyclopentyl group, a cyclohexyl group, a cycloheptyl group and a cyclooctyl group. Examples of the polycyclic alicyclic hydrocarbon group include a decahydronaphthyl group, an adamantyl group, a norbornyl group and the following groups (* represents a bond). The number of carbon atoms of the alicyclic hydrocarbon group of R a1 , R a2  and R a3  is preferably 3 to 16. 
     
       
         
         
             
             
         
       
     
     The group obtained by combining an alkyl group with an alicyclic hydrocarbon group includes, for example, a methylcyclohexyl group, a dimethylcyclohexyl group, a methylnorbornyl group, a cyclohexylmethyl group, an adamantylmethyl group, an adamantyldimethyl group, a norbornylethyl group and the like. 
     Preferably, ma is 0 and na is 1. 
     When R a1  and R a2  are bonded to each other to form an alicyclic hydrocarbon group, examples of —C(R a1 )(R a2 )(R a3 ) include the following groups. The alicyclic hydrocarbon group preferably has 3 to 12 carbon atoms. * represents a bond to —O—. 
     
       
         
         
             
             
         
       
     
     Examples of the hydrocarbon group in R a1 ′, R a2 ′ and R a3 ′ include an alkyl group, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, and groups obtained by combining these groups. 
     Examples of the alkyl group and the alicyclic hydrocarbon group include those which are the same as mentioned in R a1 , R a2  and R d3 . 
     Examples of the aromatic hydrocarbon group include aryl groups such as a phenyl group, a naphthyl group, an anthryl group, a biphenyl group and a phenanthryl group. 
     Examples of the group combined include a group obtained by combining the above-mentioned alkyl group and alicyclic hydrocarbon group (e.g., a cycloalkylalkyl group), an aralkyl group such as a benzyl group, an aromatic hydrocarbon group having an alkyl group (a p-methylphenyl group, a p-tert-butylphenyl group, a tolyl group, a xylyl group, a cumenyl group, a mesityl group, a 2,6-diethylphenyl group, a 2-methyl-6-ethylphenyl group, etc.), an aromatic hydrocarbon group having an alicyclic hydrocarbon group (a p-cyclohexylphenyl group, a p-adamantylphenyl group, etc.), an aryl-cycloalkyl group such as a phenylcyclohexyl group, and the like. 
     Examples of a heterocyclic group, which is formed by bonding R a2 ′ and R a3 ′ to each other together with carbon atoms and X to which R a2 ′ and R a3 ′ are bonded, include the following groups. * represents a bond. 
     
       
         
         
             
             
         
       
     
     Of R a1 ′ and R a2 ′, at least one is preferably a hydrogen atom. 
     na′ is preferably 0. 
     Examples of the group (1) include the following groups. 
     A group wherein, in formula (1), R a1 , R a2  and R a3  are alkyl groups, ma=0 and na=1. The group is preferably a tert-butoxycarbonyl group. 
     A group wherein, in formula (1), R a1  and R a2  are bonded to each other to form an adamantyl group together with carbon atoms to which R a1  and R a2  are bonded, R a3  is an alkyl group, ma=0 and na=1. 
     A group wherein, in formula (1), R a1  and R a2  are each independently an alkyl group, R a3  is an adamantyl group, ma=0 and na=1. 
     Specific examples of the group (1) include the following groups. * represents a bond. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Specific examples of the group (2) include the following groups. * represents a bond. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     The monomer (a1) is preferably a monomer having an acid-labile group and an ethylenic unsaturated bond, and more preferably a (meth)acrylic monomer having an acid-labile group. 
     Of the (meth)acrylic monomers having an acid-labile group, those having an alicyclic hydrocarbon group having 5 to 20 carbon atoms are preferably exemplified. When a resin (A) including a structural unit derived from a monomer (a1) having a bulky structure such as an alicyclic hydrocarbon group is used in a resist composition, it is possible to improve the resolution of a resist pattern. 
     The structural unit derived from a (meth)acrylic monomer having a group (1) is preferably a structural unit represented by formula (a1-0) (hereinafter sometimes referred to as structural unit (a1-0)), a structural unit represented by formula (a1-1) (hereinafter sometimes referred to as structural unit (a1-1)) or a structural unit represented by formula (a1-2) (hereinafter sometimes referred to as structural unit (a1-2)). The structural unit is more preferably at least one structural unit selected from the group consisting of a structural unit (a1-1) and a structural unit (a1-2). These structural units may be used alone, or two or more structural units may be used in combination. 
     
       
         
         
             
             
         
       
     
     In formula (a1-0), formula (a1-1) and formula (a1-2), 
     L a01 , L a1  and L a2  each independently represent —O— or *—O—(CH 2 ) k1 —CO—O—, k1 represents an integer of 1 to 7, and * represents a bond to —CO—, 
     R a01 , R a4  and R a5  each independently represent a hydrogen atom or a methyl group, 
     R a02 , R a03  and R a04  each independently represent an alkyl group having 1 to 8 carbon atoms, an alicyclic hydrocarbon group having 3 to 18 carbon atoms or groups obtained by combining these groups, 
     R a6  and R a7  each independently represent an alkyl group having 1 to 8 carbon atoms, an alicyclic hydrocarbon group having 3 to 18 carbon atoms or groups obtained by combining these groups, 
     m1 represents an integer of 0 to 14, 
     n1 represents an integer of 0 to 10, and 
     n1′ represents an integer of 0 to 3. 
     R a01 , R a4  and R a5  are preferably a methyl group. 
     L a01 , L a1  and L a2  are preferably an oxygen atom or *—O—(CH 2 ) k01 —CO—O— (in which k01 is preferably an integer of 1 to 4, and more preferably 1), and more preferably an oxygen atom. 
     Examples of the alkyl group, the alicyclic hydrocarbon group and groups obtained by combining these groups in R a02 , R a03 , R a04 , R a6  and R a7  include the same groups as mentioned for R a1 , R a2  and R a3  of formula (1). 
     The alkyl group in R a02 , R a03  and R a04  is preferably an alkyl group having 1 to 6 carbon atoms, more preferably a methyl group or an ethyl group, and still more preferably a methyl group. 
     The alkyl group in R a6  and R a7  is preferably an alkyl group having 1 to 6 carbon atoms, more preferably a methyl group, an ethyl group or an isopropyl group, and still more preferably an ethyl group or an isopropyl group. 
     The number of carbon atoms of the alicyclic hydrocarbon group of R a02 , R a03 , R a04 , R a6  and R a7  is preferably 5 to 12, and more preferably 5 to 10. 
     The total number of carbon atoms of the group obtained by combining the alkyl group with the alicyclic hydrocarbon group is preferably 18 or less. 
     R a02  and R a03  are preferably an alkyl group having 1 to 6 carbon atoms, and more preferably a methyl group or an ethyl group. 
     R a04  is preferably an alkyl group having 1 to 6 carbon atoms or an alicyclic hydrocarbon group having 5 to 12 carbon atoms, and more preferably a methyl group, an ethyl group, a cyclohexyl group or an adamantyl group. 
     Preferably, R a6  and R a7  are each independently an alkyl group having 1 to 6 carbon atoms, more preferably a methyl group, an ethyl group or an isopropyl group, and still more preferably an ethyl group or an isopropyl group. 
     m1 is preferably an integer of 0 to 3, and more preferably 0 or 1. 
     n1 is preferably an integer of 0 to 3, and more preferably 0 or 1. 
     n1′ is preferably 0 or 1. 
     The structural unit (a1-0) includes, for example, a structural unit represented by any one of formula (a1-0-1) to formula (a1-0-12) and a structural unit in which a methyl group corresponding to R a01  in the structural unit (a1-0) is substituted with a hydrogen atom and is preferably a structural unit represented by any one of formula (a1-0-1) to formula (a1-0-10). 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     The structural unit (a1-1) includes, for example, structural units derived from the monomers mentioned in JP 2010-204646 A. Of these structural units, a structural unit represented by any one of formula (a1-1-1) to formula (a1-1-4) and a structural unit in which a methyl group corresponding to R a4  in the structural unit (a1-1) is substituted with a hydrogen atom are preferable, and a structural unit represented by any one of formula (a1-1-1) to formula (a1-1-4) is more preferable. 
     
       
         
         
             
             
         
       
     
     Examples of the structural unit (a1-2) include a structural unit represented by any one of formula (a1-2-1) to formula (a1-2-6) and a structural unit in which a methyl group corresponding to R a5  in the structural unit (a1-2) is substituted with a hydrogen atom, and structural units represented by formula (a1-2-2), formula (a1-2-5) and formula (a1-2-6) are preferable. 
     
       
         
         
             
             
         
       
     
     When the resin (A) includes a structural unit (a1-0) and/or a structural unit (a1-1) and/or a structural unit (a1-2), the total content thereof is usually 10 to 95 mol %, preferably 15 to 90 mol %, more preferably 20 to 85 mol %, still more preferably 25 to 70 mol %, and yet more preferably 30 to 70 mol %, based on all structural units of the resin (A). 
     In the structural unit (a1), examples of the structural unit having a group (2) include a structural unit represented by formula (a1-4) (hereinafter sometimes referred to as “structural unit (a1-4)”): 
                         
wherein, in formula (a1-4),
 
     R a32  represents a hydrogen atom, a halogen atom or an alkyl group having 1 to 6 carbon atoms which may have a halogen atom, 
     R a33  represents a halogen atom, a hydroxy group, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an alkylcarbonyl group having 2 to 4 carbon atoms, an alkylcarbonyloxy group having 2 to 4 carbon atoms, an acryloyloxy group or a methacryloyloxy group, 
     la represents an integer of 0 to 4, and when la is 2 or more, a plurality of R a33  may be the same or different from each other, and 
     R a34  and R a35  each independently represent a hydrogen atom or a hydrocarbon group having 1 to 12 carbon atoms, R a36  represents a hydrocarbon group having 1 to 20 carbon atoms, or R a35  and R a36  are bonded to each other to form a divalent hydrocarbon group having 2 to 20 carbon atoms together with —C—O— to which R a35  and R d36  are bonded, and —CH 2 — included in the hydrocarbon group and the divalent hydrocarbon group may be replaced by —O— or —S—. 
     Examples of the alkyl group in R a32  and R a33  include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a pentyl group and a hexyl group. The alkyl group is preferably an alkyl group having 1 to 4 carbon atoms, more preferably a methyl group or an ethyl group, and still more preferably a methyl group. 
     Examples of the halogen atom in R a32  and R a33  include a fluorine atom, a chlorine atom and a bromine atom. 
     Examples of the alkyl group having 1 to 6 carbon atoms which may have a halogen atom include a trifluoromethyl group, a difluoromethyl group, a methyl group, a perfluoroethyl group, a 2,2,2-trifluoroethyl group, a 1,1,2,2-tetrafluoroethyl group, an ethyl group, a perfluoropropyl group, a 2,2,3,3,3-pentafluoropropyl group, a propyl group, a perfluorobutyl group, a 1,1,2,2,3,3,4,4-octafluorobutyl group, a butyl group, a perfluoropentyl group, a 2,2,3,3,4,4,5,5,5-nonafluoropentyl group, a pentyl group, a hexyl group, a perfluorohexyl group and the like. 
     Examples of the alkoxy group include a methoxy group, an ethoxy group, a propoxy group, a butoxy group, a pentyloxy group and a hexyloxy group. Of these groups, an alkoxy group having 1 to 4 carbon atoms is preferable, a methoxy group or an ethoxy group are more preferable, and a methoxy group is still more preferable. 
     Examples of the alkylcarbonyl group include an acetyl group, a propionyl group and a butyryl group. 
     Examples of the alkylcarbonyloxy group include an acetyloxy group, a propionyloxy group, a butyryloxy group and the like. 
     Examples of the hydrocarbon group in R a34 , R a35  and R a36  include an alkyl group, an alicyclic hydrocarbon group and an aromatic hydrocarbon group. 
     Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group and the like. 
     The alicyclic hydrocarbon group may be either monocyclic or polycyclic, and examples of the monocyclic alicyclic hydrocarbon group include cycloalkyl groups such as a cyclopentyl group, a cyclohexyl group, a cycloheptyl group and a cyclooctyl group. Examples of the polycyclic alicyclic hydrocarbon group include a decahydronaphthyl group, an adamantyl group, a norbornyl group and the following groups (* represents a bonding site). 
     
       
         
         
             
             
         
       
     
     Examples of the aromatic hydrocarbon group include aryl groups such as a phenyl group, a naphthyl group, an anthryl group, a biphenyl group and a phenanthryl group. 
     Examples of the group combined include a group obtained by combining the above-mentioned alkyl group and alicyclic hydrocarbon group (e.g., a cycloalkylalkyl group), an aralkyl group such as a benzyl group, an aromatic hydrocarbon group having an alkyl group (a p-methylphenyl group, a p-tert-butylphenyl group, a tolyl group, a xylyl group, a cumenyl group, a mesityl group, a 2,6-diethylphenyl group, a 2-methyl-6-ethylphenyl group, etc.), an aromatic hydrocarbon group having an alicyclic hydrocarbon group (a p-cyclohexylphenyl group, a p-adamantylphenyl group, etc.), an aryl-cycloalkyl group such as a phenylcyclohexyl group and the like. Particularly, examples of R a36  include an alkyl group having 1 to 18 carbon atoms, an alicyclic hydrocarbon group having 3 to 18 carbon atoms, an aromatic hydrocarbon group having 6 to 18 carbon atoms or groups obtained by combining these groups. 
     In formula (a1-4), R a32  is preferably a hydrogen atom, 
     R a33  is preferably an alkoxy group having 1 to 4 carbon atoms, more preferably a methoxy group and an ethoxy group, and still more preferably a methoxy group, 
     la is preferably 0 or 1, and more preferably 0, 
     R a34  is preferably a hydrogen atom, and 
     R a35  is preferably an alkyl group having 1 to 12 carbon atoms or an alicyclic hydrocarbon group, and more preferably a methyl group or an ethyl group. 
     The hydrocarbon group of R a36  is preferably an alkyl group having 1 to 18 carbon atoms, an alicyclic hydrocarbon group having 3 to 18 carbon atoms, an aromatic hydrocarbon group having 6 to 18 carbon atoms or groups formed by combining these groups, and more preferably an alkyl group having 1 to 18 carbon atoms, an alicyclic aliphatic hydrocarbon group having 3 to 18 carbon atoms or an aralkyl group having 7 to 18 carbon atoms. The alkyl group and the alicyclic hydrocarbon group in R a36  are preferably unsubstituted. The aromatic hydrocarbon group in R a36  is preferably an aromatic ring having an aryloxy group having 6 to 10 carbon atoms. 
     —OC(R a34 ) (R a35 )—O—R a36  in the structural unit (a1-4) is eliminated by contacting with an acid (e.g., p-toluenesulfonic acid) to form a hydroxy group. 
     The structural unit (a1-4) includes, for example, structural units derived from the monomers mentioned in JP 2010-204646 A. The structural unit preferably includes structural units represented by formula (a1-4-1) to formula (a1-4-12) and a structural unit in which a hydrogen atom corresponding to R a32  is substituted with a methyl group, and more preferably structural units represented by formula (a1-4-1) to formula (a1-4-5) and formula (a1-4-10). 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     When the resin (A) includes the structural unit (a1-4), the content is preferably 10 to 95 mol %, more preferably 15 to 90 mol %, still more preferably 20 to 85 mol %, yet more preferably 20 to 70 mol %, and particularly preferably 20 to 60 mol %, based on the total of all structural units of the resin (A). 
     The structural unit derived from a (meth)acrylic monomer having a group (2) also includes a structural unit represented by formula (a1-5) (hereinafter sometimes referred to as “structural unit (a1-5)”). 
     
       
         
         
             
             
         
       
     
     In formula (a1-5), 
     R a8  represents an alkyl group having 1 to 6 carbon atoms which may have a halogen atom, a hydrogen atom or a halogen atom, 
     Z a1  represents a single bond or *—(CH 2 ) h3 —CO-L 54 -, h3 represents an integer of 1 to 4, and * represents a bond to L 51 , 
     L 51 , L 52 , L 53  and L 54  each independently represent —O— or —S—, 
     s1 represents an integer of 1 to 3, and 
     s1′ represents an integer of 0 to 3. 
     The halogen atom includes a fluorine atom and a chlorine atom and is preferably a fluorine atom. Examples of the alkyl group having 1 to 6 carbon atoms which may have a halogen atom include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a fluoromethyl group and a trifluoromethyl group. 
     In formula (a1-5), R a8  is preferably a hydrogen atom, a methyl group or a trifluoromethyl group, 
     L 51  is preferably an oxygen atom, 
     one of L 52  and L 53  is preferably —O— and the other one is preferably —S—, 
     s1 is preferably 1, 
     s1′ is preferably an integer of 0 to 2, and 
     Z a1  is preferably a single bond or *—CH 2 —CO—O—. 
     The structural unit (a1-5) includes, for example, structural units derived from the monomers mentioned in JP 2010-61117 A. Of these structural units, structural units represented by formula (a1-5-1) to formula (a1-5-4) are preferable, and structural units represented by formula (a1-5-1) or formula (a1-5-2) are more preferable. 
     
       
         
         
             
             
         
       
     
     When the resin (A) includes the structural unit (a1-5), the content is preferably 1 to 50 mol %, more preferably 3 to 45 mol %, still more preferably 5 to 40 mol %, and yet more preferably 5 to 30 mol %, based on all structural units of the resin (A). 
     The structural unit (a1) also includes the following structural units. 
     
       
         
         
             
             
         
       
     
     When the resin (A) includes the above-mentioned structural units such as (a1-3-1) to (a1-3-7), the content is preferably 10 to 95 mol %, more preferably 15 to 90 mol %, still more preferably 20 to 85 mol %, yet more preferably 20 to 70 mol %, and particularly preferably 20 to 60 mol %, based on all structural units of the resin (A). 
     &lt;Structural Unit (s)&gt; 
     The structural unit (s) is derived from a monomer having no acid-labile group (hereinafter sometimes referred to as “monomer (s)”). It is possible to use, as the monomer from which the structural unit (s) is derived, a monomer having no acid-labile group known in the resist field. 
     The structural unit (s) preferably has a hydroxy group or a lactone ring. When a resin including a structural unit having a hydroxy group and having no acid-labile group (hereinafter sometimes referred to as “structural unit (a2)”) and/or a structural unit having a lactone ring and having no acid-labile group (hereinafter sometimes referred to as “structural unit (a3)”) is used in the resist composition of the present invention, it is possible to improve the resolution of a resist pattern and the adhesion to a substrate. 
     &lt;Structural Unit (a2)&gt; 
     The hydroxy group possessed by the structural unit (a2) may be either an alcoholic hydroxy group or a phenolic hydroxy group. 
     When a resist pattern is produced from the resist composition of the present invention, in the case of using, as an exposure source, high energy rays such as KrF excimer laser (248 nm), electron beam or extreme ultraviolet light (EUV), it is preferable to use a structural unit (a2) having a phenolic hydroxy group as the structural unit (a2). When using ArF excimer laser (193 nm) or the like, a structural unit (a2) having an alcoholic hydroxy group is preferably used as the structural unit (a2), and the below-mentioned structural unit (a2-1) is more preferably used. The structural unit (a2) may be included alone, or two or more structural units may be included. 
     In the structural unit (a2), examples of the structural unit having a phenolic hydroxy group include a structural unit represented by formula (a2-A) (hereinafter sometimes referred to as “structural unit (a2-A)”) 
                         
wherein, in formula (a2-A),
 
     R a50  represents a hydrogen atom, a halogen atom or an alkyl group having 1 to 6 carbon atoms which may have a halogen atom, 
     R a51  represents a halogen atom, a hydroxy group, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an alkylcarbonyl group having 2 to 4 carbon atoms, an alkylcarbonyloxy group having 2 to 4 carbon atoms, an acryloyloxy group or a methacryloyloxy group, 
     A a50  represents a single bond or *—X a51 -(A a52 -X a52 ) nb —, and * represents a bond to carbon atoms to which —R a50  is bonded, 
     A a52  represents an alkanediyl group having 1 to 6 carbon atoms, 
     X a51  and X a52  each independently represent —O—, —CO—O— or —O—CO—, 
     nb represents 0 or 1, and 
     mb represents an integer of 0 to 4, and when mb is an integer of 2 or more, a plurality of R a51  may be the same or different from each other. 
     Examples of the halogen atom in R a50  include a fluorine atom, a chlorine atom and a bromine atom. 
     Examples of the alkyl group having 1 to 6 carbon atoms which may have a halogen atom in R a50  include a trifluoromethyl group, a difluoromethyl group, a methyl group, a perfluoroethyl group, a 2,2,2-trifluoroethyl group, a 1,1,2,2-tetrafluoroethyl group, an ethyl group, a perfluoropropyl group, a 2,2,3,3,3-pentafluoropropyl group, a propyl group, a perfluorobutyl group, a 1,1,2,2,3,3,4,4-octafluorobutyl group, a butyl group, a perfluoropentyl group, a 2,2,3,3,4,4,5,5,5-nonafluoropentyl group, a pentyl group, a hexyl group and a perfluorohexyl group. 
     R a50  is preferably a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, more preferably a hydrogen atom, a methyl group or an ethyl group, and still more preferably a hydrogen atom or a methyl group. 
     Examples of the alkyl group in R a51  include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a sec-butyl group, a tert-butyl group, a pentyl group and a hexyl group. 
     Examples of the alkoxy group in R a51  include a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, a sec-butoxy group and a tert-butoxy group. An alkoxy group having 1 to 4 carbon atoms is preferable, a methoxy group or an ethoxy group is more preferable, and a methoxy group is still more preferable. 
     Examples of the alkylcarbonyl group in R a51  include an acetyl group, a propionyl group and a butyryl group. 
     Examples of the alkylcarbonyloxy group in R a51  include an acetyloxy group, a propionyloxy group and a butyryloxy group. 
     R a51  is preferably a methyl group. 
     Examples of *—X a51 -(A a52 -X a52 ) nb — include *—O—, *—CO—O—, *—O—CO—, *—CO—O-A a52 -CO—O—, *—O—CO-A a52 -O—, *—O-A a52 -CO—O—, *—CO—O-A a52 -O—CO— and *—O—CO-A a52 -O—CO—. Of these, *—CO—O—, *—CO—O-A a2 -CO—O— or *—O-A a52 -CO—O— is preferable. 
     Examples of the alkanediyl group include a methylene group, an ethylene group, a propane-1,3-diyl group, a propane-1,2-diyl group, a butane-1,4-diyl group, a pentane-1,5-diyl group, a hexane-1,6-diyl group, a butane-1,3-diyl group, a 2-methylpropane-1,3-diyl group, a 2-methylpropane-1,2-diyl group, a pentane-1,4-diyl group and a 2-methylbutane-1,4-diyl group. 
     A a52  is preferably a methylene group or an ethylene group. 
     A a50  is preferably a single bond, *—CO—O— or *—CO—O-A a52 -CO—O—, more preferably a single bond, *—CO—O— or *—CO—O—CH 2 —CO—O—, and still more preferably a single bond or *—CO—O—. 
     mb is preferably 0, 1 or 2, more preferably 0 or 1, and particularly preferably 0. 
     The hydroxy group is preferably bonded to the ortho-position or the para-position of a benzene ring, and more preferably the para-position. 
     Examples of the structural unit (a2-A) include structural units derived from the monomers mentioned in JP 2010-204634 A and JP 2012-12577 A. 
     Examples of the structural unit (a2-A) include structural units represented by formula (a2-2-1) to formula (a2-2-6), and a structural unit in which a methyl group corresponding to R a50  in the structural unit (a2-A) is substituted with a hydrogen atom in structural units represented by formula (a2-2-1) to formula (a2-2-6). The structural unit (a2-A) is preferably a structural unit represented by formula (a2-2-1), a structural unit represented formula (a2-2-3), a structural unit represented by formula (a2-2-6) and a structural unit in which a methyl group corresponding to R a50  in the structural unit (a2-A) is substituted with a hydrogen atom in the structural unit represented by formula (a2-2-1), the structural unit represented by formula (a2-2-3) or the structural unit represented by formula (a2-2-6). 
     
       
         
         
             
             
         
       
     
     When the structural unit (a2-A) is included in the resin (A), the content of the structural unit (a2-A) is preferably 5 to 80 mol %, more preferably 10 to 70 mol %, still more preferably 15 to 65 mol %, and yet more preferably 20 to 65 mol %, based on all structural units. 
     The structural unit (a2-A) can be included in a resin (A) by treating a resin including a structural unit (a1-4) with an acid such as p-toluenesulfonic acid. The structural unit (a2-A) can also be included in the resin (A) by polymerizing with acetoxystyrene and treating with an alkali such as tetramethylammonium hydroxide. 
     Examples of the structural unit having an alcoholic hydroxy group in the structural unit (a2) include a structural unit represented by formula (a2-1) (hereinafter sometimes referred to as “structural unit (a2-1)”). 
     
       
         
         
             
             
         
       
     
     In formula (a2-1), 
     L a3  represents —O— or *—O—(CH 2 ) k2 —CO—O—, 
     k2 represents an integer of 1 to 7, and * represents a bond to —CO—, 
     R a14  represents a hydrogen atom or a methyl group, 
     R a15  and R a16  each independently represent a hydrogen atom, a methyl group or a hydroxy group, and 
     o1 represents an integer of 0 to 10. 
     In formula (a2-1), L a3  is preferably —O— or —O—(CH 2 ) f1 —CO—O— (f1 represents an integer of 1 to 4), and more preferably —O—, 
     R a14  is preferably a methyl group, 
     R a15  is preferably a hydrogen atom, 
     R a16  is preferably a hydrogen atom or a hydroxy group, and 
     ol is preferably an integer of 0 to 3, and more preferably 0 or 1. 
     The structural unit (a2-1) includes, for example, structural units derived from the monomers mentioned in JP 2010-204646 A. A structural unit represented by any one of formula (a2-1-1) to formula (a2-1-6) is preferable, a structural unit represented by any one of formula (a2-1-1) to formula (a2-1-4) is more preferable, and a structural unit represented by formula (a2-1-1) or formula (a2-1-3) is still more preferable. 
     
       
         
         
             
             
         
       
     
     When the resin (A) includes the structural unit (a2-1), the content is usually 1 to 45 mol %, preferably 1 to 40 mol %, more preferably 1 to 35 mol %, still more preferably 1 to 20 mol %, and yet more preferably 1 to 10 mol %, based on all structural units of the resin (A). 
     &lt;Structural Unit (a3)&gt; 
     The lactone ring possessed by the structural unit (a3) may be a monocyclic ring such as a β-propiolactone ring, a γ-butyrolactone ring or a δ-valerolactone ring, or a condensed ring of a monocyclic lactone ring and the other ring. Preferably, a γ-butyrolactone ring, an adamantanelactone ring or a bridged ring including a γ-butyrolactone ring structure (e.g. a structural unit represented by the following formula (a3-2)) is exemplified. 
     The structural unit (a3) is preferably a structural unit represented by formula (a3-1), formula (a3-2), formula (a3-3) or formula (a3-4). These structural units may be included alone, or two or more structural units may be included: 
                         
wherein, in formula (a3-1), formula (a3-2), formula (a3-3) and formula (a3-4),
 
     L a4 , L a5  and L a6  each independently represent —O— or a group represented by *—O—(CH 2 ) k3 —CO—O— (k3 represents an integer of 1 to 7), 
     L a7  represents —O—, *—O-L a8 -O—, *—O-L a8 -CO—O—, *—O-L a8 -CO—O-L a9 -CO—O— or *—O-L a8 -O—CO-L a9 -O—, 
     L a8  and L a9  each independently represent an alkanediyl group having 1 to 6 carbon atoms, 
     * represents a bonding site to a carbonyl group, 
     R a18 , R a19  and R a20  each independently represent a hydrogen atom or a methyl group, 
     R a24  represents an alkyl group having 1 to 6 carbon atoms which may have a halogen atom, a hydrogen atom or a halogen atom, 
     X a3  represents —CH 2 — or an oxygen atom, 
     R a21  represents an aliphatic hydrocarbon group having 1 to 4 carbon atoms, 
     R d22 , R a23  and R d25  each independently represent a carboxy group, a cyano group or an aliphatic hydrocarbon group having 1 to 4 carbon atoms, 
     p1 represents an integer of 0 to 5, 
     q1 represents an integer of 0 to 3, 
     r1 represents an integer of 0 to 3, 
     w1 represents an integer of 0 to 8, and 
     when p1, q1, r1 and/or w1 is/are 2 or more, a plurality of R a21 , R a22 , R a23  and/or R a25  may be the same or different from each other. 
     Examples of the aliphatic hydrocarbon group in R a21 , R a22 , R a23  and R a25  include alkyl groups such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a sec-butyl group and a tert-butyl group. 
     Examples of the halogen atom in R a24  include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom. 
     Examples of the alkyl group in R a24  include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a sec-butyl group, a tert-butyl group, a pentyl group and a hexyl group, and the alkyl group is preferably an alkyl group having 1 to 4 carbon atoms, and more preferably a methyl group or an ethyl group. 
     Examples of the alkyl group having a halogen atom in R a24  include a trifluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluoroisopropyl group, a perfluorobutyl group, a perfluorosec-butyl group, a perfluorotert-butyl group, a perfluoropentyl group, a perfluorohexyl group, a trichloromethyl group, a tribromomethyl group, a triiodomethyl group and the like. 
     Examples of the alkanediyl group in L a8  and L a9  include a methylene group, an ethylene group, a propane-1,3-diyl group, a propane-1,2-diyl group, a butane-1,4-diyl group, a pentane-1,5-diyl group, a hexane-1,6-diyl group, a butane-1,3-diyl group, a 2-methylpropane-1,3-diyl group, a 2-methylpropane-1,2-diyl group, a pentane-1,4-diyl group and a 2-methylbutane-1,4-diyl group. 
     In formula (a3-1) to formula (a3-3), preferably, L a4  to L a6  are each independently —O— or a group in which k3 is an integer of 1 to 4 in *—O—(CH 2 ) k3 —CO—O—, more preferably —O— and *—O—CH 2 —CO—O—, and still more preferably an oxygen atom, 
     R a18  to R a21  are preferably a methyl group, 
     preferably, R a22  and R a23  are each independently a carboxy group, a cyano group or a methyl group, and preferably, p1, q1 and r1 are each independently an integer of 0 to 2, and more preferably 0 or 1. 
     In formula (a3-4), R a24  is preferably a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, more preferably a hydrogen atom, a methyl group or an ethyl group, and still more preferably a hydrogen atom or a methyl group, 
     R a25  is preferably a carboxy group, a cyano group or a methyl group, 
     L a7  is preferably —O— or *—O-L a8 -CO—O—, and more preferably —O—, —O—CH 2 —CO—O— or —O—C 2 H 4 —CO—O—, and 
     w1 is preferably an integer of 0 to 2, and more preferably 0 or 1. 
     Particularly, formula (a3-4) is preferably formula (a3-4)′: 
                         
wherein R a24  and L a7  are the same as defined above.
 
     Examples of the structural unit (a3) include structural units derived from the monomers mentioned in JP 2010-204646 A, the monomers mentioned in JP 2000-122294 A and the monomers mentioned in JP 2012-41274 A. The structural unit (a3) is preferably a structural unit represented by any one of formula (a3-1-1), formula (a3-1-2), formula (a3-2-1), formula (a3-2-2), formula (a3-3-1), formula (a3-3-2) and formula (a3-4-1) to formula (a3-4-12), and structural units in which methyl groups corresponding to R a18 , R a19 , R a20  and R a24  in formula (a3-1) to formula (a3-4) are substituted with hydrogen atoms in the above structural units. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     When the resin (A) includes the structural unit (a3), the total content is usually 5 to 70 mol %, preferably 10 to 65 mol %, and more preferably 10 to 60 mol %, based on all structural units of the resin (A). 
     Each content of the structural unit (a3-1), the structural unit (a3-2), the structural unit (a3-3) or the structural unit (a3-4) is preferably 5 to 60 mol %, more preferably 5 to 50 mol %, and still more preferably 10 to 50 mol %, based on all structural units of the resin (A). 
     &lt;Structural Unit (a4)&gt; 
     Examples of the structural unit (a4) include the following structural units: 
                         
wherein, in formula (a4),
 
     R 41  represents a hydrogen atom or a methyl group, and 
     R 42  represents a saturated hydrocarbon group having 1 to 24 carbon atoms which has a fluorine atom, and —CH 2 — included in the saturated hydrocarbon group may be replaced by —O— or —CO. 
     Examples of the saturated hydrocarbon group represented by R 42  include a chain hydrocarbon group and a monocyclic or polycyclic alicyclic hydrocarbon group, and groups formed by combining these groups. 
     Examples of the chain hydrocarbon group include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a decyl group, a dodecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group and an octadecyl group. Examples of the monocyclic or polycyclic alicyclic hydrocarbon group include cycloalkyl groups such as a cyclopentyl group, a cyclohexyl group, a cycloheptyl group and a cyclooctyl group; and polycyclic alicyclic saturated hydrocarbon groups such as a decahydronaphthyl group, an adamantyl group, a norbornyl group and the following groups (* represents a bond). 
     
       
         
         
             
             
         
       
     
     Examples of the group formed by combination include groups formed by combining one or more alkyl groups or one or more alkanediyl groups with one or more alicyclic hydrocarbon groups, and include an alkanediyl group-alicyclic hydrocarbon group, an alicyclic hydrocarbon group-alkyl group, an alkanediyl group-alicyclic hydrocarbon group-alkyl group and the like. 
     Examples of the structural unit (a4) include a structural unit represented by at least one selected from the group consisting of formula (a4-0), formula (a4-1), formula (a4-2), formula (a4-3) and formula (a4-4): 
                         
wherein, in formula (a4-0),
 
     R 5  represents a hydrogen atom or a methyl group, 
     L 4a  represents a single bond or a divalent aliphatic saturated hydrocarbon group having 1 to 4 carbon atoms, 
     L 3 a represents a perfluoroalkanediyl group having 1 to 8 carbon atoms or a perfluorocycloalkanediyl group having 3 to 12 carbon atoms, and 
     R 6  represents a hydrogen atom or a fluorine atom. 
     Examples of the divalent aliphatic saturated hydrocarbon group in L 4a  include linear alkanediyl groups such as a methylene group, an ethylene group, a propane-1,3-diyl group and a butane-1,4-diyl group; and branched alkanediyl groups such as an ethane-1,1-diyl group, a propane-1,2-diyl group, a butane-1,3-diyl group, a 2-methylpropane-1,3-diyl group and a 2-methylpropane-1,2-diyl group. 
     Examples of the perfluoroalkanediyl group in L 3a  include a difluoromethylene group, a perfluoroethylene group, a perfluoropropane-1,3-diyl group, a perfluoropropane-1,2-diyl group, a perfluoropropane-2,2-diyl group, a perfluorobutane-1,4-diyl group, a perfluorobutane-2,2-diyl group, a perfluorobutane-1,2-diyl group, a perfluoropentane-1,5-diyl group, a perfluoropentane-2,2-diyl group, a perfluoropentane-3,3-diyl group, a perfluorohexane-1,6-diyl group, a perfluorohexane-2,2-diyl group, a perfluorohexane-3,3-diyl group, a perfluoroheptane-1,7-diyl group, a perfluoroheptane-2,2-diyl group, a perfluoroheptane-3,4-diyl group, a perfluoroheptane-4,4-diyl group, a perfluorooctane-1,8-diyl group, a perfluorooctane-2,2-diyl group, a perfluorooctane-3,3-diyl group, a perfluorooctane-4,4-diyl group and the like. 
     Examples of the perfluorocycloalkanediyl group in L 3a  include a perfluorocyclohexanediyl group, a perfluorocyclopentanediyl group, a perfluorocycloheptanediyl group, a perfluoroadamantanediyl group and the like. 
     L 4a  is preferably a single bond, a methylene group or an ethylene group, and more preferably a single bond or a methylene group. 
     L 3a  is preferably a perfluoroalkanediyl group having 1 to 6 carbon atoms, and more preferably a perfluoroalkanediyl group having 1 to 3 carbon atoms. 
     Examples of the structural unit (a4-0) include the following structural units, and structural units in which a methyl group corresponding to R 5  in the structural unit (a4-0) in the following structural units is substituted with a hydrogen atom: 
                                                             
wherein, in formula (a4-1),
 
     R a41  represents a hydrogen atom or a methyl group, 
     R a42  represents a hydrocarbon group having 1 to 20 carbon atoms which may have a substituent, and —CH 2 — included in the saturated hydrocarbon group may be replaced by —O— or —CO—, 
     A a41  represents an alkanediyl group having 1 to 6 carbon atoms which may have a substituent or a group represented by formula (a-g1), in which at least one of A a41  and R a42  has, as a substituent, a halogen atom (preferably a fluorine atom): 
     
       
         
         
             
             
         
       
     
     [in which, in formula (a-g1), 
     s represents 0 or 1, 
     A a42  and A a44  each independently represent a divalent saturated hydrocarbon group having 1 to 5 carbon atoms which may have a substituent, 
     A a43  represents a single bond or a divalent hydrocarbon group having 1 to 5 carbon atoms which may have a substituent, 
     X a41  and X a42  each independently represent —O—, —CO—, —CO—O— or —O—CO—, in which the total number of carbon atoms of A a42 , A a43 , A a44 , X a41  and X a42  is 7 or less], and 
     * is a bond and * at the right side is a bond to —O—CO—R a42 . 
     Examples of the saturated hydrocarbon group in R a42  include a chain saturated hydrocarbon group and a monocyclic or polycyclic alicyclic saturated hydrocarbon group, and groups formed by combining these groups. 
     Examples of the chain saturated hydrocarbon group include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a decyl group, a dodecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group and an octadecyl group. 
     Examples of the monocyclic or polycyclic alicyclic hydrocarbon group include cycloalkyl groups such as a cyclopentyl group, a cyclohexyl group, a cycloheptyl group and a cyclooctyl group; and polycyclic alicyclic saturated hydrocarbon groups such as a decahydronaphthyl group, an adamantyl group, a norbornyl group and the following groups (* represents a bond). 
     
       
         
         
             
             
         
       
     
     Examples of the group formed by combination include groups formed by combining one or more alkyl groups or one or more alkanediyl groups with one or more alicyclic saturated hydrocarbon groups, and include an alkanediyl group-alicyclic saturated hydrocarbon group, an alicyclic saturated hydrocarbon group-alkyl group, an alkanediyl group-alicyclic saturated hydrocarbon group-alkyl group and the like. 
     Examples of the substituent which may be possessed by R a42  include at least one selected from the group consisting of a halogen atom and a group represented by formula (a-g3). Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is preferred:
 
*—X a43 -A a45   (a-g3)
 
wherein, in formula (a-g3),
 
     X a43  represents an oxygen atom, a carbonyl group, **—O—CO— or **—CO—O— (** represents a bond to R a42 ), 
     A a45  represents an aliphatic hydrocarbon group having 1 to 17 carbon atoms which may have a halogen atom, and 
     * represents a bond. 
     In R a42 —X a43 -A a45 , when R a42  has no halogen atom, A a45  represents an aliphatic hydrocarbon group having 1 to 17 carbon atoms having at least one halogen atom. 
     Examples of the aliphatic hydrocarbon group in A a45  include alkyl groups such as a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a decyl group, a dodecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group and an octadecyl group; monocyclic alicyclic hydrocarbon groups such as a cyclopentyl group, a cyclohexyl group, a cycloheptyl group and a cyclooctyl group; and polycyclic alicyclic hydrocarbon groups such as a decahydronaphthyl group, an adamantyl group, a norbornyl group and the following groups (* represents a bond): 
     
       
         
         
             
             
         
       
     
     Examples of the group formed by combination include a group obtained by combining one or more alkyl groups or one or more alkanediyl groups with one or more alicyclic hydrocarbon groups, and include an -alkanediyl group-alicyclic hydrocarbon group, an -alicyclic hydrocarbon group-alkyl group, an -alkanediyl group-alicyclic hydrocarbon group-alkyl group and the like. 
     R a42  is preferably an aliphatic hydrocarbon group which may have a halogen atom, and more preferably an alkyl group having a halogen atom and/or an aliphatic hydrocarbon group having a group represented by formula (a-g3). 
     When R a42  is an aliphatic hydrocarbon group having a halogen atom, an aliphatic hydrocarbon group having a fluorine atom is preferred, a perfluoroalkyl group or a perfluorocycloalkyl group is more preferred, a perfluoroalkyl group having 1 to 6 carbon atoms is still more preferred, and a perfluoroalkyl group having 1 to 3 carbon atoms is particularly preferred. Examples of the perfluoroalkyl group include a perfluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluorobutyl group, a perfluoropentyl group, a perfluorohexyl group, a perfluoroheptyl group and a perfluorooctyl group. Examples of the perfluorocycloalkyl group include a perfluorocyclohexyl group and the like. 
     When R a42  is an aliphatic hydrocarbon group having a group represented by formula (a-g3), the total number of carbon atoms of R a42  is preferably 15 or less, and more preferably 12 or less, including the number of carbon atoms included in the group represented by formula (a-g3). When having the group represented by formula (a-g3) as the substituent, the number thereof is preferably 1. 
     When R a42  is an aliphatic hydrocarbon group having the group represented by formula (a-g3), Ra4 2  is still more preferably a group represented by formula (a-g2):
 
*-A a46 -X a44 -A a47   (a-g2)
 
wherein, in formula (a-g2),
 
     A a46  represents a divalent aliphatic hydrocarbon group having 1 to 17 carbon atoms which may have a halogen atom, 
     X a44  represents **—O—CO— or **—CO—O— (** represents a bond to A a46 ), 
     A a47  represents an aliphatic hydrocarbon group having 1 to 17 carbon atoms which may have a halogen atom, 
     the total number of carbon atoms of A a46 , A a47  and X a44  is 18 or less, and at least one of A a46  and A a47  has at least one halogen atom, and 
     * represents a bonding to a carbonyl group. 
     The number of carbon atoms of the aliphatic hydrocarbon group of A a46  is preferably 1 to 6, and more preferably 1 to 3. 
     The number of carbon atoms of the aliphatic hydrocarbon group of A a47  is preferably 4 to 15, and more preferably 5 to 12, and A a47  is still more preferably a cyclohexyl group or an adamantyl group. 
     Preferred structure of the group represented by formula (a-g2) is the following structure (* represents a bond to a carbonyl group). 
     
       
         
         
             
             
         
       
     
     Examples of the alkanediyl group in A a41  include linear alkanediyl groups such as a methylene group, an ethylene group, a propane-1,3-diyl group, a butane-1,4-diyl group, a pentane-1,5-diyl group and a hexane-1,6-diyl group; and branched alkanediyl groups such as a propane-1,2-diyl group, a butane-1,3-diyl group, a 2-methylpropane-1,2-diyl group, a 1-methylbutane-1,4-diyl group and a 2-methylbutane-1,4-diyl group. 
     Examples of the substituent in the alkanediyl group represented by A a41  include a hydroxy group and an alkoxy group having 1 to 6 carbon atoms. 
     A a41  is preferably an alkanediyl group having 1 to 4 carbon atoms, more preferably an alkanediyl group having 2 to 4 carbon atoms, and still more preferably an ethylene group. 
     Examples of the divalent saturated hydrocarbon group represented by A a42 , A a43  and A a44  in the group represented by formula (a-g1) include a linear or branched alkanediyl group and a monocyclic divalent alicyclic hydrocarbon group, and groups formed by combining an alkanediyl group and a divalent alicyclic hydrocarbon group. Specific examples thereof include a methylene group, an ethylene group, a propane-1,3-diyl group, a propane-1,2-diyl group, a butane-1,4-diyl group, a 1-methylpropane-1,3-diyl group, a 2-methylpropane-1,3-diyl group, a 2-methylpropane-1,2-diyl group and the like. 
     Examples of the substituent of the divalent saturated hydrocarbon group represented by A a42 , A a43  and A a44  include a hydroxy group and an alkoxy group having 1 to 6 carbon atoms. 
     s is preferably 0. 
     In the group represented by formula (a-g1), examples of the group in which X a42  is —O—, —CO—, —CO—O— or —O—CO-include the following groups. In the following exemplification, * and ** each represent a bond, and ** represents a bond to —O—CO—R a42 . 
     
       
         
         
             
             
         
       
     
     Examples of the structural unit represented by formula (a4-1) include the following structural units, and structural units in which a methyl group corresponding to A a41  in the structural unit represented by formula (a4-1) in the following structural units is substituted with a hydrogen atom. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     The structural unit represented by formula (a4-1) is preferably a structural unit represented by formula (a4-2): 
                         
wherein, in formula (a4-2),
 
     R f3  represents a hydrogen atom or a methyl group, 
     L 44  represents an alkanediyl group having 1 to 6 carbon atoms, and —CH 2 — included in the alkanediyl group may be replaced by —O— or —CO—, 
     R f6  represents a saturated hydrocarbon group having 1 to 20 carbon atoms having a fluorine atom, and 
     the upper limit of the total number of carbon atoms of L 44  and R f6  is 21. 
     Examples of the alkanediyl group having 1 to 6 carbon atoms of L 44  include the same groups as mentioned for the alkanediyl group in A a41 . 
     Examples of the saturated hydrocarbon group of R f6  include the same groups as mentioned for R 42 . 
     The alkanediyl group having 1 to 6 carbon atoms in L 44  is preferably an alkanediyl group having 2 to 4 carbon atoms, and more preferably an ethylene group. 
     The structural unit represented by formula (a4-2) includes, for example, structural units represented by formula (a4-1-1) to formula (a4-1-11). A structural unit in which a methyl group corresponding to R f5  in the structural unit (a4-2) is substituted with a hydrogen atom is also exemplified as the structural unit represented by formula (a4-2). 
     Examples of the structural unit (a4) include a structural unit represented by formula (a4-3): 
                         
wherein, in formula (a4-3),
 
     R f7  represents a hydrogen atom or a methyl group, 
     L 5  represents an alkanediyl group having 1 to 6 carbon atoms, 
     A f13  represents a divalent saturated hydrocarbon group having 1 to 18 carbon atoms which may have a fluorine atom, 
     X f12  represents *—O—CO— or *—CO—O— (* represents a bond to A f13 ), 
     A f14  represents a saturated hydrocarbon group having 1 to 17 carbon atoms which may have a fluorine atom, and 
     at least one of A f13  and A f14  has a fluorine atom, and the upper limit of the total number of carbon atoms of L 5 , A f13  and A f14  is 20. 
     Examples of the alkanediyl group in L 5  include those which are the same as mentioned for the alkanediyl group in the divalent saturated hydrocarbon group of A a41 . 
     The divalent saturated hydrocarbon group which may have a fluorine atom in A f13  is preferably a divalent aliphatic saturated hydrocarbon group which may have a fluorine atom and a divalent alicyclic saturated hydrocarbon group which may have a fluorine atom, and more preferably a perfluoroalkanediyl group. 
     Examples of the divalent aliphatic saturated hydrocarbon group which may have a fluorine atom include alkanediyl groups such as a methylene group, an ethylene group, a propanediyl group, a butanediyl group and a pentanediyl group; and perfluoroalkanediyl groups such as a difluoromethylene group, a perfluoroethylene group, a perfluoropropanediyl group, a perfluorobutanediyl group and a perfluoropentanediyl group. 
     The divalent alicyclic hydrocarbon group which may have a fluorine atom may be either monocyclic or polycyclic. Examples of the monocyclic group include a cyclohexanediyl group and a perfluorocyclohexanediyl group. Examples of the polycyclic group include an adamantanediyl group, a norbornanediyl group, a perfluoroadamantanediyl group and the like. 
     Examples of the saturated hydrocarbon group and the saturated hydrocarbon group which may have a fluorine atom for A f14  include the same groups as mentioned for R a42 . Of these groups, preferred are fluorinated alkyl groups such as a trifluoromethyl group, a difluoromethyl group, a methyl group, a perfluoroethyl group, a 2,2,2-trifluoroethyl group, a 1,1,2,2-tetrafluoroethyl group, an ethyl group, a perfluoropropyl group, a 2,2,3,3,3-pentafluoropropyl group, a propyl group, a perfluorobutyl group, a 1,1,2,2,3,3,4,4-octafluorobutyl group, a butyl group, a perfluoropentyl group, a 2,2,3,3,4,4,5,5,5-nonafluoropentyl group, a pentyl group, a hexyl group, a perfluorohexyl group, a heptyl group, a perfluoroheptyl group, an octyl group and a perfluorooctyl group; a cyclopropylmethyl group, a cyclopropyl group, a cyclobutylmethyl group, a cyclopentyl group, a cyclohexyl group, a perfluorocyclohexyl group, an adamantyl group, an adamantylmethyl group, an adamantyldimethyl group, a norbornyl group, a norbornylmethyl group, a perfluoroadamantyl group, a perfluoroadamantylmethyl group and the like. 
     In formula (a4-3), L 5  is preferably an ethylene group. 
     The divalent saturated hydrocarbon group of A f13  is preferably a group including a chain hydrocarbon group having 1 to 6 carbon atoms and a divalent alicyclic hydrocarbon group having 3 to 12 carbon atoms, and more preferably a divalent chain hydrocarbon group having 2 to 3 carbon atoms. 
     The saturated hydrocarbon group of A f14  is preferably a group including a chain hydrocarbon group having 3 to 12 carbon atoms and an alicyclic hydrocarbon group having 3 to 12 carbon atoms, and more preferably a group including a chain hydrocarbon group having 3 to 10 carbon atoms and an alicyclic hydrocarbon group having 3 to 10 carbon atoms. Of these groups, A 1f4  is preferably a group including an alicyclic hydrocarbon group having 3 to 12 carbon atoms, and more preferably a cyclopropylmethyl group, a cyclopentyl group, a cyclohexyl group, a norbornyl group and an adamantyl group. 
     The structural unit represented by formula (a4-3) includes, for example, structural units represented by formula (a4-1′-1) to formula (a4-1′-11). A structural unit in which a methyl group corresponding to R f7  in the structural unit (a4-3) is substituted with a hydrogen atom is also exemplified as the structural unit represented by formula (a4-3). 
     It is also possible to exemplify, as the structural unit (a4), a structural unit represented by formula (a4-4): 
                         
wherein, in formula (a4-4),
 
     R f21  represents a hydrogen atom or a methyl group, 
     A f21  represents —(CH 2 ) j1 —, —(CH 2 ) j2 —O—(CH 2 ) j3 — or —(CH 2 ) j4 —CO—O—(CH 2 ) j5 —, 
     j1 to j5 each independently represent an integer of 1 to 6, and 
     R f22  represents a saturated hydrocarbon group having 1 to 10 carbon atoms having a fluorine atom. 
     Examples of the saturated hydrocarbon group of R f22  include those which are the same as the saturated hydrocarbon group represented by R a42 . R f22  is preferably an alkyl group having 1 to 10 carbon atoms having a fluorine atom or an alicyclic hydrocarbon group having 1 to 10 carbon atoms having a fluorine atom, more preferably an alkyl group having 1 to 10 carbon atoms having a fluorine atom, and still more preferably an alkyl group having 1 to 6 carbon atoms which has a fluorine atom. 
     In formula (a4-4), A f21  is preferably —(CH 2 ) j1 —, more preferably an ethylene group or a methylene group, and still more preferably a methylene group. 
     The structural unit represented by formula (a4-4) includes, for example, the following structural units and structural units in which a methyl group corresponding to R f21  in the structural unit (a4-4) is substituted with a hydrogen atom in structural units represented by the following formulas. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     When the resin (A) includes the structural unit (a4), the content is preferably 1 to 20 mol %, more preferably 2 to 15 mol %, and still more preferably 3 to 10 mol %, based on all structural units of the resin (A). 
     &lt;Structural Unit (a5)&gt; 
     Examples of a non-leaving hydrocarbon group possessed by the structural unit (a5) include groups having a linear, branched or cyclic hydrocarbon group. Of these, the structural unit (a5) is preferably a group having an alicyclic hydrocarbon group. 
     The structural unit (a5) includes, for example, a structural unit represented by formula (a5-1): 
                         
wherein, in formula (a5-1),
 
     R 51  represents a hydrogen atom or a methyl group, 
     R 52  represents an alicyclic hydrocarbon group having 3 to 18 carbon atoms, and a hydrogen atom included in the alicyclic hydrocarbon group may be substituted with an aliphatic hydrocarbon group having 1 to 8 carbon atoms, and 
     L 55  represents a single bond or a divalent saturated hydrocarbon group having 1 to 18 carbon atoms, and —CH 2 -included in the saturated hydrocarbon group may be replaced by —O— or —CO—. 
     The alicyclic hydrocarbon group in R 52  may be either monocyclic or polycyclic. The monocyclic alicyclic hydrocarbon group includes, for example, a cyclopropyl group, a cyclobutyl group, a cyclopentyl group and a cyclohexyl group. The polycyclic alicyclic hydrocarbon group includes, for example, an adamantyl group and a norbornyl group. 
     The aliphatic hydrocarbon group having 1 to 8 carbon atoms includes, for example, alkyl groups such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a sec-butyl group, a tert-butyl group, a pentyl group, a hexyl group, an octyl group and a 2-ethylhexyl group. 
     Examples of the alicyclic hydrocarbon group having a substituent includes a 3-methyladamantyl group and the like. 
     R 52  is preferably an unsubstituted alicyclic hydrocarbon group having 3 to 18 carbon atoms, and more preferably an adamantyl group, a norbornyl group or a cyclohexyl group. 
     Examples of the divalent saturated hydrocarbon group in L 55  include a divalent chain saturated hydrocarbon group and a divalent alicyclic saturated hydrocarbon group, and a divalent chain saturated hydrocarbon group is preferred. 
     The divalent chain saturated hydrocarbon group includes, for example, alkanediyl groups such as a methylene group, an ethylene group, a propanediyl group, a butanediyl group and a pentanediyl group. 
     The divalent alicyclic saturated hydrocarbon group may be either monocyclic or polycyclic. Examples of the monocyclic alicyclic saturated hydrocarbon group include cycloalkanediyl groups such as a cyclopentanediyl group and a cyclohexanediyl group. Examples of the polycyclic divalent alicyclic saturated hydrocarbon group include an adamantanediyl group and a norbornanediyl group. 
     The group in which —CH 2 — included in the divalent saturated hydrocarbon group represented by L 55  is replaced by —O— or —CO— includes, for example, groups represented by formula (L1-1) to formula (L1-4). In the following formulas, * and ** each represent a bond, and * represents a bond to an oxygen atom. 
     
       
         
         
             
             
         
       
     
     In formula (L1-1), 
     X x1  represents *—O—CO— or *—CO—O— (* represents a bond to L x1 ), 
     L x1  represents a divalent aliphatic saturated hydrocarbon group having 1 to 16 carbon atoms, 
     L x2  represents a single bond or a divalent aliphatic saturated hydrocarbon group having 1 to 15 carbon atoms, and 
     the total number of carbon atoms of L x1  and L x2  is 16 or less. 
     In formula (L1-2), 
     L x3  represents a divalent aliphatic saturated hydrocarbon group having 1 to 17 carbon atoms, 
     L x4  represents a single bond or a divalent aliphatic saturated hydrocarbon group having 1 to 16 carbon atoms, and the total number of carbon atoms of L x3  and L x4  is 17 or less. 
     In formula (L1-3), 
     L x5  represents a divalent aliphatic saturated hydrocarbon group having 1 to 15 carbon atoms, 
     L x6  and L x7  each independently represent a single bond or a divalent aliphatic saturated hydrocarbon group having 1 to 14 carbon atoms, and 
     the total number of carbon atoms of L x5 , L x6  and L x7  is 15 or less. 
     In formula (L1-4), 
     L x8  and L x9  represents a single bond or a divalent aliphatic saturated hydrocarbon group having 1 to 12 carbon atoms, 
     W x1  represents a divalent alicyclic saturated hydrocarbon group having 3 to 15 carbon atoms, and 
     the total number of carbon atoms of L x8 , L x9  and W x1  is 15 or less. 
     L x1  is preferably a divalent aliphatic saturated hydrocarbon group having 1 to 8 carbon atoms, and more preferably a methylene group or an ethylene group. 
     L x2  is preferably a single bond or a divalent aliphatic saturated hydrocarbon group having 1 to 8 carbon atoms, and more preferably a single bond. 
     L x3  is preferably a divalent aliphatic saturated hydrocarbon group having 1 to 8 carbon atoms. 
     L x4  is preferably a single bond or a divalent aliphatic saturated hydrocarbon group having 1 to 8 carbon atoms. 
     L x5  is preferably a divalent aliphatic saturated hydrocarbon group having 1 to 8 carbon atoms, and more preferably a methylene group or an ethylene group. 
     L x6  is preferably a single bond or a divalent aliphatic saturated hydrocarbon group having 1 to 8 carbon atoms, and more preferably a methylene group or an ethylene group. 
     L x7  is preferably a single bond or a divalent aliphatic saturated hydrocarbon group having 1 to 8 carbon atoms. 
     L x8  is preferably a single bond or a divalent aliphatic saturated hydrocarbon group having 1 to 8 carbon atoms, and more preferably a single bond or a methylene group. 
     L x9  is preferably a single bond or a divalent aliphatic saturated hydrocarbon group having 1 to 8 carbon atoms, and more preferably a single bond or a methylene group. 
     W x1  is preferably a divalent alicyclic saturated hydrocarbon group having 3 to 10 carbon atoms, and more preferably a cyclohexanediyl group or an adamantanediyl group. 
     The group represented by formula (L1-1) includes, for example, the following divalent groups. 
     
       
         
         
             
             
         
       
     
     The group represented by formula (L1-2) includes, for example, the following divalent groups. 
     
       
         
         
             
             
         
       
     
     The group represented by formula (L1-3) includes, for example, the following divalent groups. 
     
       
         
         
             
             
         
       
     
     The group represented by formula (L1-4) includes, for example, the following divalent groups. 
     
       
         
         
             
             
         
       
     
     L 55  is preferably a single bond or a group represented by formula (L1-1). 
     Examples of the structural unit (a5-1) include the following structural units and structural units in which a methyl group corresponding to R 51  in the structural unit (a5-1) in the following structural units is substituted with a hydrogen atom. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     When the resin (A) includes the structural unit (a5), the content is preferably 1 to 30 mol %, more preferably 2 to 20 mol %, and still more preferably 3 to 15 mol %, based on all structural units of the resin (A). 
     &lt;Structural Unit (II)&gt; 
     The resin (A) may further include a structural unit which is decomposed upon exposure to radiation to generate an acid (hereinafter sometimes referred to as “structural unit (II)”). Specific examples of the structural unit (II) include the structural units mentioned in JP 2016-79235 A, and a structural unit having a sulfonate group or a carboxylate group and an organic cation in a side chain or a structural unit having a sulfonio group and an organic anion in a side chain are preferred. 
     The structural unit having a sulfonate group or a carboxylate group in a side chain is preferably a structural unit represented by formula (II-2-A′): 
                         
wherein, in formula (II-2-A′),
 
     X III3  represents a divalent saturated hydrocarbon group having 1 to 18 carbon atoms, —CH 2 — included in the saturated hydrocarbon group may be replaced by —O—, —S— or —CO—, and a hydrogen atom included in the saturated hydrocarbon group may be substituted with a halogen atom, an alkyl group having 1 to 6 carbon atoms which may have a halogen atom, or a hydroxy group, 
     A x1  represents an alkanediyl group having 1 to 8 carbon atoms, and a hydrogen atom included in the alkanediyl group may be substituted with a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms, 
     RA −  represents a sulfonate group or a carboxylate group, 
     R III3  represents a hydrogen atom, a halogen atom or an alkyl group having 1 to 6 carbon atoms which may have a halogen atom, and 
     ZA +  represents an organic cation. 
     Examples of the halogen atom represented by R III3  include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom. 
     Examples of the alkyl group having 1 to 6 carbon atoms which may have a halogen atom represented by R III3  include those which are the same as the alkyl group having 1 to 6 carbon atoms which may have a halogen atom represented by R a8 . 
     Examples of the alkanediyl group having 1 to 8 carbon atoms represented by A x1  include a methylene group, an ethylene group, a propane-1,3-diyl group, a butane-1,4-diyl group, a pentane-1,5-diyl group, a hexane-1,6-diyl group, an ethane-1,1-diyl group, a propane-1,1-diyl group, a propane-1,2-diyl group, a propane-2,2-diyl group, a pentane-2,4-diyl group, a 2-methylpropane-1,3-diyl group, a 2-methylpropane-1,2-diyl group, a pentane-1,4-diyl group, a 2-methylbutane-1,4-diyl group and the like. 
     Examples of the perfluoroalkyl group having 1 to 6 carbon atoms which may be substituted in AxI include a trifluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluoroisopropyl group, a perfluorobutyl group, a perfluorosec-butyl group, a perfluorotert-butyl group, a perfluoropentyl group, a perfluorohexyl group and the like. 
     Examples of the divalent saturated hydrocarbon group having 1 to 18 carbon atoms represented by X III3  include a linear or branched alkanediyl group, a monocyclic or a polycyclic divalent alicyclic saturated hydrocarbon group, or a combination thereof. 
     Specific examples thereof include linear alkanediyl groups such as a methylene group, an ethylene group, a propane-1,3-diyl group, a propane-1,2-diyl group, a butane-1,4-diyl group, a pentane-1,5-diyl group, a hexane-1,6-diyl group, a heptane-1,7-diyl group, an octane-1,8-diyl group, a nonane-1,9-diyl group, a decane-1,10-diyl group, an undecane-1,11-diyl group and a dodecane-1,12-diyl group; branched alkanediyl groups such as a butane-1,3-diyl group, a 2-methylpropane-1,3-diyl group, a 2-methylpropane-1,2-diyl group, a pentane-1,4-diyl group and a 2-methylbutane-1,4-diyl group; cycloalkanediyl group such as a cyclobutane-1,3-diyl group, a cyclopentane-1,3-diyl group, a cyclohexane-1,4-diyl group and a cyclooctane-1,5-diyl group; and divalent polycyclic alicyclic saturated hydrocarbon groups such as a norbornane-1,4-diyl group, a norbornane-2,5-diyl group, an adamantane-1,5-diyl group and an adamantane-2,6-diyl group. 
     Those in which —CH 2 — included in the saturated hydrocarbon group is replaced by —O—, —S— or —CO— include, for example, divalent groups represented by formula (X1) to formula (X53). Before replacing —CH 2 — included in the saturated hydrocarbon group by —O—, —S— or —CO—, the number of carbon atoms is 17 or less. In the following formulas, * and ** represent a bonding site, and * represents a bond to A x1 . 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     X 3  represents a divalent saturated hydrocarbon group having 1 to 16 carbon atoms. 
     X 4  represents a divalent saturated hydrocarbon group having 1 to 15 carbon atoms. 
     X 5  represents a divalent saturated hydrocarbon group having 1 to 13 carbon atoms. 
     X 6  represents a divalent saturated hydrocarbon group having 1 to 14 carbon atoms. 
     X 7  represents a trivalent saturated hydrocarbon group having 1 to 14 carbon atoms. 
     X 8  represents a divalent saturated hydrocarbon group having 1 to 13 carbon atoms. 
     Examples of the organic cation of ZA +  include an organic onium cation, an organic sulfonium cation, an organic iodonium cation, an organic ammonium cation, a benzothiazolium cation and an organic phosphonium cation. Of these, an organic sulfonium cation and an organic iodonium cation are preferable, and an arylsulfonium cation is more preferable. Specific examples thereof include a cation represented by any one of formula (b2-1) to formula (b2-4) (hereinafter sometimes referred to as “cation (b2-1)” according to the number of formula). 
     
       
         
         
             
             
         
       
     
     In formula (b2-1) to formula (b2-4), 
     R b4  to R b6  each independently represent a chain hydrocarbon group having 1 to 30 carbon atoms, an alicyclic hydrocarbon group having 3 to 36 carbon atoms or an aromatic hydrocarbon group having 6 to 36 carbon atoms, a hydrogen atom included in the chain hydrocarbon group may be substituted with a hydroxy group, an alkoxy group having 1 to 12 carbon atoms, an alicyclic hydrocarbon group having 3 to 12 carbon atoms or an aromatic hydrocarbon group having 6 to 18 carbon atoms, a hydrogen atom included in the alicyclic hydrocarbon group may be substituted with a halogen atom, an aliphatic hydrocarbon group having 1 to 18 carbon atoms, an alkylcarbonyl group having 2 to 4 carbon atoms or a glycidyloxy group, and a hydrogen atom included in the aromatic hydrocarbon group may be substituted with a halogen atom, a hydroxy group or an alkoxy group having 1 to 12 carbon atoms, 
     R b4  and R b5  may be bonded to each other to form a ring together with sulfur atoms to which R b4  and R b5  are bonded, and —CH 2 — included in the ring may be replaced by —O—, —S— or —CO—, 
     R b7  and R b8  each independently represent a hydroxy group, an aliphatic hydrocarbon group having 1 to 12 carbon atoms or an alkoxy group having 1 to 12 carbon atoms, 
     m2 and n2 each independently represent an integer of 0 to 5, 
     when m2 is 2 or more, a plurality of R b7  may be the same or different, and when n2 is 2 or more, a plurality of R b8  may be the same or different, 
     R b9  and R b10  each independently represent a chain hydrocarbon group having 1 to 36 carbon atoms or an alicyclic hydrocarbon group having 3 to 36 carbon atoms, 
     R b9  and R b10  may be bonded to each other to form a ring together with sulfur atoms to which R b9  and R b10  are bonded, and —CH 2 — included in the ring may be replaced by —O—, —S— or —CO—, 
     R b11  represents a hydrogen atom, a chain hydrocarbon group having 1 to 36 carbon atoms, an alicyclic hydrocarbon group having 3 to 36 carbon atoms or an aromatic hydrocarbon group having 6 to 18 carbon atoms, 
     R b12  represents a chain hydrocarbon group having 1 to 12 carbon atoms, an alicyclic hydrocarbon group having 3 to 18 carbon atoms or an aromatic hydrocarbon group having 6 to 18 carbon atoms, a hydrogen atom included in the chain hydrocarbon may be substituted with an aromatic hydrocarbon group having 6 to 18 carbon atoms, and a hydrogen atom included in the aromatic hydrocarbon group may be substituted with an alkoxy group having 1 to 12 carbon atoms or an alkylcarbonyloxy group having 1 to 12 carbon atoms, 
     R b11  and R b12  may be bonded to each other to form a ring, including —CH—CO— to which R b11  and R b12  are bonded, and —CH 2 — included in the ring may be replaced by —O—, —S— or —CO—, 
     R b13  to R b18  each independently represent a hydroxy group, an aliphatic hydrocarbon group having 1 to 12 carbon atoms or an alkoxy group having 1 to 12 carbon atoms, 
     L b31  represents a sulfur atom or an oxygen atom, 
     o2, p2, s2 and t2 each independently represent an integer of 0 to 5, 
     q2 and r2 each independently represent an integer of 0 to 4, 
     u2 represents 0 or 1, and 
     when o2 is 2 or more, a plurality of R b13  are the same or different from each other, when p2 is 2 or more, a plurality of R b14  are the same or different from each other, when q2 is 2 or more, a plurality of R b15  are the same or different from each other, when r2 is 2 or more, a plurality of R b16  are the same or different from each other, when s2 is 2 or more, a plurality of R b17  are the same or different from each other, and when t2 is 2 or more, a plurality of R b18  are the same or different from each other. 
     The aliphatic hydrocarbon group represents a chain hydrocarbon group and an alicyclic hydrocarbon group. 
     Examples of the chain hydrocarbon group include alkyl groups such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a sec-butyl group, a tert-butyl group, a pentyl group, a hexyl group, an octyl group and a 2-ethylhexyl group. Particularly, the chain hydrocarbon group of R b9  to R b12  preferably has 1 to 12 carbon atoms. 
     The alicyclic hydrocarbon group may be either monocyclic or polycyclic, and examples of the monocyclic alicyclic hydrocarbon group include cycloalkyl groups such as a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group and a cyclodecyl group. Examples of the polycyclic alicyclic hydrocarbon group include a decahydronaphthyl group, an adamantyl group, a norbornyl group and the following groups. 
     
       
         
         
             
             
         
       
     
     Particularly, the alicyclic hydrocarbon group of R b9  to R b12  preferably has 3 to 18 carbon atoms, and more preferably 4 to 12 carbon atoms. 
     Examples of the alicyclic hydrocarbon group in which a hydrogen atom is substituted with an aliphatic hydrocarbon group include a methylcyclohexyl group, a dimethylcyclohexyl group, a 2-methyladamantan-2-yl group, a 2-ethyladamantan-2-yl group, a 2-isopropyladamantan-2-yl group, a methylnorbornyl group, an isobornyl group and the like. In the alicyclic hydrocarbon group in which a hydrogen atom is substituted with an aliphatic hydrocarbon group, the total number of carbon atoms of the alicyclic hydrocarbon group and the aliphatic hydrocarbon group is preferably 20 or less. 
     Examples of the aromatic hydrocarbon group include aryl groups such as a phenyl group, a biphenyl group, a naphthyl group and a phenanthryl group. The aromatic hydrocarbon group may have a chain hydrocarbon group or an alicyclic hydrocarbon group, and examples thereof include an aromatic hydrocarbon group which has a chain hydrocarbon group having 1 to 18 carbon atoms (a tolyl group, a xylyl group, a cumenyl group, a mesityl group, a p-ethylphenyl group, a p-tert-butylphenyl group, a 2,6-diethylphenyl group, a 2-methyl-6-ethylphenyl group, etc.), and an aromatic hydrocarbon group which has an alicyclic hydrocarbon group having 3 to 18 carbon atoms (a p-cyclohexylphenyl group, a p-adamantylphenyl group, etc.). When the aromatic hydrocarbon group has a chain hydrocarbon group or an alicyclic hydrocarbon group, a chain hydrocarbon group having 1 to 18 carbon atoms and an alicyclic hydrocarbon group having 3 to 18 carbon atoms are preferable. 
     Examples of the aromatic hydrocarbon group in which a hydrogen atom is substituted with an alkoxy group include a p-methoxyphenyl group and the like. 
     Examples of the chain hydrocarbon group in which a hydrogen atom is substituted with an aromatic hydrocarbon group include aralkyl groups such as a benzyl group, a phenethyl group, a phenylpropyl group, a trityl group, a naphthylmethyl group and a naphthylethyl group. 
     Examples of the alkoxy group include a methoxy group, an ethoxy group, a propoxy group, a butoxy group, a pentyloxy group, a hexyloxy group, a heptyloxy group, an octyloxy group, a decyloxy group and a dodecyloxy group. 
     Examples of the alkylcarbonyl group include an acetyl group, a propionyl group and a butyryl group. 
     Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom. 
     Examples of the alkylcarbonyloxy group include a methylcarbonyloxy group, an ethylcarbonyloxy group, a propylcarbonyloxy group, an isopropylcarbonyloxy group, a butylcarbonyloxy group, a sec-butylcarbonyloxy group, a tert-butylcarbonyloxy group, a pentylcarbonyloxy group, a hexylcarbonyloxy group, an octylcarbonyloxy group and a 2-ethylhexylcarbonyloxy group. 
     The ring formed by bonding R b4  and R b5  each other, together with sulfur atoms to which R b4  and R b5  are bonded, may be a monocyclic, polycyclic, aromatic, nonaromatic, saturated or unsaturated ring. This ring includes a ring having 3 to 18 carbon atoms and is preferably a ring having 4 to 18 carbon atoms. The ring containing a sulfur atom includes a 3-membered to 12-membered ring and is preferably a 3-membered to 7-membered ring and includes, for example, the following rings. * represents a bonding site. 
     
       
         
         
             
             
         
       
     
     The ring formed by combining R b9  and R b10  together may be a monocyclic, polycyclic, aromatic, nonaromatic, saturated or unsaturated ring. This ring includes a 3-membered to 12-membered ring and is preferably a 3-membered to 7-membered ring. The ring includes, for example, a thiolan-1-ium ring (tetrahydrothiophenium ring), a thian-1-ium ring, a 1,4-oxathian-4-ium ring and the like. 
     The ring formed by combining R b11  and R b12  together may be a monocyclic, polycyclic, aromatic, nonaromatic, saturated or unsaturated ring. This ring includes a 3-membered to 12-membered ring and is preferably a 3-membered to 7-membered ring. Examples thereof include an oxocycloheptane ring, an oxocyclohexane ring, an oxonorbornane ring, an oxoadamantane ring and the like. 
     Of cation (b2-1) to cation (b2-4), a cation (b2-1) is preferable. 
     Examples of the cation (b2-1) include the following cations. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Examples of the cation (b2-2) include the following cations. 
     
       
         
         
             
             
         
       
     
     Examples of the cation (b2-3) include the following cations. 
     
       
         
         
             
             
         
       
     
     Examples of the cation (b2-4) include the following cations. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     The structural unit represented by formula (II-2-A′) is preferably a structural unit represented by formula (II-2-A): 
                         
wherein, in formula (II-2-A), R III3 , X III3  and ZA +  are the same as defined above,
 
     z2A represents an integer of 0 to 6, 
     R III2  and R III4  each independently represent a hydrogen atom, a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms, and when z2A is 2 or more, a plurality of R III2  and R III4  may be the same or different from each other, and 
     Q a  and Q b  each independently represent a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms. 
     Examples of the perfluoroalkyl group having 1 to 6 carbon atoms represented by R III2 , R III4 , Q a  and Q b  include those which are the same as the perfluoroalkyl group having 1 to 6 carbon atoms represented by Q b1  mentioned below. 
     The structural unit represented by formula (II-2-A) is preferably a structural unit represented by formula (II-2-A-1): 
                         
wherein, in formula (II-2-A-1),
 
     R III2 , R III3 , R III4 , Q a , Q b  and ZA +  are the same as defined above, 
     R III5  represents a saturated hydrocarbon group having 1 to 12 carbon atoms, 
     z2A1 represents an integer of 0 to 6, and 
     X 12  represents a divalent saturated hydrocarbon group having 1 to 11 carbon atoms, —CH 2 — included in the saturated hydrocarbon group may be replaced by —O—, —S— or —CO—, and a hydrogen atom included in the saturated hydrocarbon group may be substituted with a halogen atom or a hydroxy group. 
     Examples of the saturated hydrocarbon group having 1 to 12 carbon atoms represented by R III5  include linear or branched alkyl groups such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a sec-butyl group, a tert-butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group and a dodecyl group. 
     Examples of the divalent saturated hydrocarbon group represented by X I2  include those which are the same as the divalent saturated hydrocarbon group represented by X III3 . 
     The structural unit represented by formula (II-2-A-1) is more preferably a structural unit represented by formula (II-2-A-2): 
                         
wherein, in formula (II-2-A-2), R III3 , R III5  and ZA +  are the same as defined above, and
 
     m and n each independently represent 1 or 2. 
     The structural unit represented by formula (II-2-A′) includes, for example, the following structural units, structural units in which a group corresponding to a methyl group of R III3  is substituted with a hydrogen atom, a halogen atom (e.g., fluorine atom) or an alkyl group having 1 to 6 carbon atoms which may have a halogen atom (e.g., trifluoromethyl group, etc.) and the structural units mentioned in WO 2012/050015 A. ZA +  represents an organic cation. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     The structural unit having a sulfonio group and an organic anion in a side chain is preferably a structural unit represented by formula (II-1-1): 
                         
wherein, in formula (II-1-1),
 
     A II1  represents a single bond or a divalent linking group, 
     R II1  represents a divalent aromatic hydrocarbon group having 6 to 18 carbon atoms, 
     R II2  and R II3  each independently represent a hydrocarbon group having 1 to 18 carbon atoms, and R II2  and R II3  may be bonded to each other to form a ring together with sulfur atoms to which R II2  and R II3  are bonded, 
     R II4  represents a hydrogen atom, a halogen atom or an alkyl group having 1 to 6 carbon atoms which may have a halogen atom, and 
     A −  represents an organic anion. 
     Examples of the divalent aromatic hydrocarbon group having 6 to 18 carbon atoms represented by R II1  include a phenylene group and a naphthylene group. 
     Examples of the hydrocarbon group represented by R II2  and R II3  include an alkyl group, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, and groups formed by combining these groups. 
     Examples of the halogen atom represented by R II4  include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom. 
     Examples of the alkyl group having 1 to 6 carbon atoms which may have a halogen atom represented by R II4  include those which are the same as the alkyl group having 1 to 6 carbon atoms which may have a halogen atom represented by R a8 . 
     Examples of the divalent linking group represented by A II1  include a divalent saturated hydrocarbon group having 1 to 18 carbon atoms, and —CH 2 — included in the divalent saturated hydrocarbon group may be replaced by —O—, —S— or —CO—. Specific examples thereof include those which are the same as the divalent saturated hydrocarbon group having 1 to 18 carbon atoms represented by X III3 . 
     Examples of the structural unit including a cation in formula (II-1-1) include the following structural units and structural units in which a group corresponding to R II4  is substituted with a hydrogen atom, a fluorine atom, trifluoromethyl or the like. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Examples of the organic anion represented by A −  include a sulfonic acid anion, a sulfonylimide anion, a sulfonylmethide anion and a carboxylic acid anion. The organic anion represented by A −  is preferably a sulfonic acid anion, and the sulfonic acid anion is more preferably an anion contained in a slat represented by the below-mentioned formula (B1). 
     Examples of the sulfonylimide anion represented by A-include the following. 
     
       
         
         
             
             
         
       
     
     Examples of the sulfonylmethide anion include the following. 
     
       
         
         
             
             
         
       
     
     Examples of the carboxylic acid anion include the following. 
     
       
         
         
             
             
         
       
     
     Examples of the structural unit represented by formula (II-1-1) include structural units represented by the following formulas. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     When the structural unit (II) is included in the resin (A), the content of the structural unit (II) is preferably 1 to 20 mol %, more preferably 2 to 15 mol %, and still more preferably 3 to 10 mol %, based on all structural units of the resin (A). 
     The resin (A) may include structural units other than the structural units mentioned above, and examples of such structural unit include structural units well-known in the art. 
     The resin (A) is preferably a resin composed of a structural unit (a1) and a structural unit (s), i.e., a copolymer of a monomer (a1) and a monomer (s). 
     The structural unit (a1) is preferably at least one selected from the group consisting of a structural unit (a1-0), a structural unit (a1-1) and a structural unit (a1-2) (preferably the structural unit having a cyclohexyl group, and a cyclopentyl group), more preferably at least two, and still more preferably at least two selected from the group consisting of a structural unit (a1-1) and a structural unit (a1-2). 
     The structural unit (s) is preferably at least one selected from the group consisting of a structural unit (a2) and a structural unit (a3). The structural unit (a2) is preferably a structural unit (a2-1) or a structural unit (a2-A). The structural unit (a3) is preferably at least one selected from the group consisting of a structural unit represented by formula (a3-1), a structural unit represented by formula (a3-2) and a structural unit represented by formula (a3-4). 
     The respective structural units constituting the resin (A) may be used alone, or two or more structural units may be used in combination. Using a monomer from which these structural units are derived, it is possible to produce by a known polymerization method (e.g. radical polymerization method). The content of the respective structural units included in the resin (A) can be adjusted according to the amount of the monomer used in the polymerization. 
     The weight-average molecular weight of the resin (A) is preferably 2,000 or more (more preferably 2,500 or more, and still more preferably 3,000 or more), and 50,000 or less (more preferably 30,000 or less, and still more preferably 15,000 or less). In the present specification, the weight-average molecular weight is a value determined by gel permeation chromatography under the conditions mentioned in Examples. 
     &lt;Resin Other than Resin (A)&gt; 
     In the resist composition of the present invention, a resin other than the resin (A) may be used in combination. 
     The resin other than the resin (A) includes, for example, a resin including a structural unit (a4) or a structural unit (a5) (hereinafter sometimes referred to as resin (X)). 
     The resin (X) is preferably a resin including a structural unit (a4), particularly. 
     In the resin (X), the content of the structural unit (a4) is preferably 30 mol % or more, more preferably 40 mol % or more, and still more preferably 45 mol % or more, based on the total of all structural units of the resin (X). 
     Examples of the structural unit, which may be further included in the resin (X), include a structural unit (a1), a structural unit (a2), a structural unit (a3) and structural units derived from other known monomers. Particularly, the resin (X) is preferably a resin composed only of a structural unit (a4) and/or a structural unit (a5). 
     The respective structural unit constituting the resin (X) may be used alone, or two or more structural units may be used in combination. Using a monomer from which these structural units are derived, it is possible to produce by a known polymerization method (e.g. radical polymerization method). The content of the respective structural units included in the resin (X) can be adjusted according to the amount of the monomer used in the polymerization. 
     The weight-average molecular weight of the resin (X) is preferably 6,000 or more (more preferably 7,000 or more) and 80,000 or less (more preferably 60,000 or less). The measurement means of the weight-average molecular weight of the resin (X) is the same as in the case of the resin (A). 
     When the resist composition of the present invention includes the resin (X), the content is preferably 1 to 60 parts by mass, more preferably 1 to 50 parts by mass, still more preferably 1 to 40 parts by mass, particularly preferably 1 to 30 parts by mass, and particularly preferably 1 to 8 parts by mass, based on 100 parts by mass of the resin (A). 
     The content of the resin (A) in the resist composition is preferably 80% by mass or more and 99% by mass or less, and more preferably 90% by mass or more and 99% by mass or less, based on the solid component of the resist composition. When including resins other than the resin (A), the total content of the resin (A) and resins other than the resin (A) is preferably 80% by mass or more and 99% by mass or less, and more preferably 90% by mass or more and 99% by mass or less, based on the solid component of the resist composition. In the present specification, “solid component of the resist composition” means the total amount of components obtained by removing a solvent (E) mentioned later from the total amount of the resist composition. The solid component of the resist composition and the content of the resin thereto can be measured by a known analysis means such as liquid chromatography or gas chromatography. 
     &lt;Acid Generator (B)&gt; 
     Either nonionic or ionic acid generator may be used as the acid generator (B). Examples of the nonionic acid generator include sulfonate esters (e.g., 2-nitrobenzyl ester, aromatic sulfonate, oxime sulfonate, N-sulfonyloxyimide, sulfonyloxyketone, diazonaphthoquinone 4-sulfonate), sulfones (e.g., disulfone, ketosulfone, sulfonyldiazomethane) and the like. Typical examples of the ionic acid generator include onium salts containing an onium cation (e.g., diazonium salt, phosphonium salt, sulfonium salt, iodonium salt). Examples of the anion of the onium salt include sulfonic acid anion, sulfonylimide anion, sulfonylmethide anion and the like. 
     Specific examples of the acid generator (B) include compounds generating an acid upon exposure to radiation mentioned in JP 63-26653 A, JP 55-164824 A, JP 62-69263 A, JP 63-146038 A, JP 63-163452 A, JP 62-153853 A, JP 63-146029 A, U.S. Pat. Nos. 3,779,778, 3,849,137, DE Patent No. 3914407 and EP Patent No. 126,712. Compounds produced by a known method may also be used. Two or more acid generators (B) may also be used in combination. 
     The acid generator (B) is preferably a fluorine-containing acid generator, and more preferably a salt represented by formula (B1) (hereinafter sometimes referred to as “acid generator (B1)”): 
                         
wherein, in formula (B1),
 
     Q b1  and Q b2  each independently represent a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms, 
     L b1  represents a divalent saturated hydrocarbon group having 1 to 24 carbon atoms, —CH 2 — included in the divalent saturated hydrocarbon group may be replaced by —O— or —CO—, and a hydrogen atom included in the divalent saturated hydrocarbon group may be substituted with a fluorine atom or a hydroxy group, 
     Y represents a methyl group which may have a substituent or an alicyclic hydrocarbon group having 3 to 18 carbon atoms which may have a substituent, and —CH 2 — included in the alicyclic hydrocarbon group may be replaced by —O—, —S(O) 2 — or —CO—, and 
     Z +  represents an organic cation. 
     Examples of the perfluoroalkyl group represented by Q b1  and Q b2  include a trifluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluoroisopropyl group, a perfluorobutyl group, a perfluorosec-butyl group, a perfluorotert-butyl group, a perfluoropentyl group and a perfluorohexyl group. 
     Preferably, Q b1  and Q b2  are each independently a fluorine atom or a trifluoromethyl group, and more preferably, both are fluorine atoms. 
     Examples of the divalent saturated hydrocarbon group in Lb1 include a linear alkanediyl group, a branched alkanediyl group, and a monocyclic or polycyclic divalent alicyclic saturated hydrocarbon group, or the divalent saturated hydrocarbon group may be a group formed by combining two or more of these groups. 
     Specific examples thereof include linear alkanediyl groups such as a methylene group, an ethylene group, a propane-1,3-diyl group, a butane-1,4-diyl group, a pentane-1,5-diyl group, a hexane-1,6-diyl group, a heptane-1,7-diyl group, an octane-1,8-diyl group, a nonane-1,9-diyl group, a decane-1,10-diyl group, an undecane-1,11-diyl group, a dodecane-1,12-diyl group, a tridecane-1,13-diyl group, a tetradecane-1,14-diyl group, a pentadecane-1,15-diyl group, a hexadecane-1,16-diyl group and a heptadecane-1,17-diyl group; 
     branched alkanediyl groups such as an ethane-1,1-diyl group, a propane-1,1-diyl group, a propane-1,2-diyl group, a propane-2,2-diyl group, a pentane-2,4-diyl group, a 2-methylpropane-1,3-diyl group, a 2-methylpropane-1,2-diyl group, a pentane-1,4-diyl group and a 2-methylbutane-1,4-diyl group; 
     monocyclic divalent alicyclic saturated hydrocarbon groups which are cycloalkanediyl groups such as a cyclobutane-1,3-diyl group, a cyclopentane-1,3-diyl group, a cyclohexane-1,4-diyl group and a cyclooctane-1,5-diyl group; and 
     polycyclic divalent alicyclic saturated hydrocarbon groups such as a norbornane-1,4-diyl group, a norbornane-2,5-diyl group, an adamantane-1,5-diyl group and an adamantane-2,6-diyl group. 
     The group in which —CH 2 — included in the divalent saturated hydrocarbon group represented by L b1  is replaced by —O— or —CO— includes, for example, a group represented by any one of formula (b1-1) to formula (b1-3). In groups represented by formula (b1-1) to formula (b1-3) and groups represented by formula (b1-4) to formula (b1-11) which are specific examples thereof, * and ** represent a bonding site, and * represents a bond to —Y. 
     
       
         
         
             
             
         
       
     
     In formula (b1-1), 
     L b2  represents a single bond or a divalent saturated hydrocarbon group having 1 to 22 carbon atoms, and a hydrogen atom included in the saturated hydrocarbon group may be substituted with a fluorine atom, 
     L b3  represents a single bond or a divalent saturated hydrocarbon group having 1 to 22 carbon atoms, a hydrogen atom included in the saturated hydrocarbon group may be substituted with a fluorine atom or a hydroxy group, and —CH 2 — included in the saturated hydrocarbon group may be replaced by —O— or —CO—, and 
     the total number of carbon atoms of L b2  and L b3  is 22 or less. 
     In formula (b1-2), 
     L b4  represents a single bond or a divalent saturated hydrocarbon group having 1 to 22 carbon atoms, and a hydrogen atom included in the saturated hydrocarbon group may be substituted with a fluorine atom, 
     L b5  represents a single bond or a divalent saturated hydrocarbon group having 1 to 22 carbon atoms, a hydrogen atom included in the saturated hydrocarbon group may be substituted with a fluorine atom or a hydroxy group, and —CH 2 — included in the saturated hydrocarbon group may be replaced by —O— or —CO—, and 
     the total number of carbon atoms of L b4  and L b5  is 22 or less. 
     In formula (b1-3), 
     L b6  represents a single bond or a divalent saturated hydrocarbon group having 1 to 23 carbon atoms, a hydrogen atom included in the saturated hydrocarbon group may be substituted with a fluorine atom or a hydroxy group, 
     L b7  represents a single bond or a divalent saturated hydrocarbon group having 1 to 23 carbon atoms, a hydrogen atom included in the saturated hydrocarbon group may be substituted with a fluorine atom or a hydroxy group, and —CH 2 — included in the saturated hydrocarbon group may be replaced by —O— or —CO—, and 
     the total number of carbon atoms of L b6  and L b7  is 23 or less. 
     In groups represented by formula (b1-1) to formula (b1-3), when —CH 2 — included in the saturated hydrocarbon group is replaced by —O— or —CO—, the number of carbon atoms before replacement is taken as the number of carbon atoms of the saturated hydrocarbon group. 
     Examples of the divalent saturated hydrocarbon group include those which are the same as the divalent saturated hydrocarbon group of L b1 . 
     L b2  is preferably a single bond. 
     L b3  is preferably a divalent saturated hydrocarbon group having 1 to 4 carbon atoms. 
     L b4  is preferably a divalent saturated hydrocarbon group having 1 to 8 carbon atoms, and a hydrogen atom included in the divalent saturated hydrocarbon group may be substituted with a fluorine atom. 
     L b5  is preferably a single bond or a divalent saturated hydrocarbon group having 1 to 8 carbon atoms. 
     L b6  is preferably a single bond or a divalent saturated hydrocarbon group having 1 to 4 carbon atoms, and a hydrogen atom included in the saturated hydrocarbon group may be substituted with a fluorine atom. 
     L b7  is preferably a single bond or a divalent saturated hydrocarbon group having 1 to 18 carbon atoms, a hydrogen atom included in the saturated hydrocarbon group may be substituted with a fluorine atom or a hydroxy group, and —CH 2 — included in the divalent saturated hydrocarbon group may be replaced by —O— or —CO—. 
     The group in which —CH 2 — included in the divalent saturated hydrocarbon group represented by L b1  is replaced by —O— or —CO— is preferably a group represented by formula (b1-1) or formula (b1-3). 
     Examples of the group represented by formula (b1-1) include groups represented by formula (b1-4) to formula (b1-8). 
     
       
         
         
             
             
         
       
     
     In formula (b1-4), 
     L b8  represents a single bond or a divalent saturated hydrocarbon group having 1 to 22 carbon atoms, and a hydrogen atom included in the saturated hydrocarbon group may be substituted with a fluorine atom or a hydroxy group. 
     In formula (b1-5), 
     L b9  represents a divalent saturated hydrocarbon group having 1 to 20 carbon atoms, and —CH 2 — included in the divalent saturated hydrocarbon group may be replaced by —O— or —CO—. 
     L b10  represents a single bond or a divalent saturated hydrocarbon group having 1 to 19 carbon atoms, and a hydrogen atom included in the divalent saturated hydrocarbon group may be substituted with a fluorine atom or a hydroxy group, and 
     the total number of carbon atoms of L b9  and L b10  is 20 or less. 
     In formula (b1-6), 
     L b11  represents a divalent saturated hydrocarbon group having 1 to 21 carbon atoms, 
     L b12  represents a single bond or a divalent saturated hydrocarbon group having 1 to 20 carbon atoms, and a hydrogen atom included in the divalent saturated hydrocarbon group may be substituted with a fluorine atom or a hydroxy group, and 
     the total number of carbon atoms of L b11  and L b12  is 21 or less. 
     In formula (b1-7), 
     L b13  represents a divalent saturated hydrocarbon group having 1 to 19 carbon atoms, 
     L b14  represents a single bond or a divalent saturated hydrocarbon group having 1 to 18 carbon atoms, and —CH 2 — included in the divalent saturated hydrocarbon group may be replaced by —O— or —CO—, 
     L b15  represents a single bond or a divalent saturated hydrocarbon group having 1 to 18 carbon atoms, and a hydrogen atom included in the divalent saturated hydrocarbon group may be substituted with a fluorine atom or a hydroxy group, and 
     the total number of carbon atoms of L b13  to L b15  is 19 or less. 
     In formula (b1-8), 
     L b16  represents a divalent saturated hydrocarbon group having 1 to 18 carbon atoms, and —CH 2 — included in the divalent saturated hydrocarbon group may be replaced by —O— or —CO—, 
     L b17  represents a divalent saturated hydrocarbon group having 1 to 18 carbon atoms, 
     L b18  represents a single bond or a divalent saturated hydrocarbon group having 1 to 17 carbon atoms, and a hydrogen atom included in the divalent saturated hydrocarbon group may be substituted with a fluorine atom or a hydroxy group, and 
     the total number of carbon atoms of L b16  to L b18  is 19 or less. 
     L b8  is preferably a divalent saturated hydrocarbon group having 1 to 4 carbon atoms. 
     L b9  is preferably a divalent saturated hydrocarbon group having 1 to 8 carbon atoms. 
     L b10  is preferably a single bond or a divalent saturated hydrocarbon group having 1 to 19 carbon atoms, and more preferably a single bond or a divalent saturated hydrocarbon group having 1 to 8 carbon atoms. 
     L b11  is preferably a divalent saturated hydrocarbon group having 1 to 8 carbon atoms. 
     L b12  is preferably a single bond or a divalent saturated hydrocarbon group having 1 to 8 carbon atoms. 
     L b13  is preferably a divalent saturated hydrocarbon group having 1 to 12 carbon atoms. 
     L b14  is preferably a single bond or a divalent saturated hydrocarbon group having 1 to 6 carbon atoms. 
     L b15  is preferably a single bond or a divalent saturated hydrocarbon group having 1 to 18 carbon atoms, and more preferably a single bond or a divalent saturated hydrocarbon group having 1 to 8 carbon atoms. 
     L b16  is preferably a divalent saturated hydrocarbon group having 1 to 12 carbon atoms. 
     L b17  is preferably a divalent saturated hydrocarbon group having 1 to 6 carbon atoms. 
     L b18  is preferably a single bond or a divalent saturated hydrocarbon group having 1 to 17 carbon atoms, and more preferably a single bond or a divalent saturated hydrocarbon group having 1 to 4 carbon atoms. 
     Examples of the group represented by formula (b1-3) include groups represented by formula (b1-9) to formula (b1-11). 
     
       
         
         
             
             
         
       
     
     In formula (b1-9), 
     L b19  represents a single bond or a divalent saturated hydrocarbon group having 1 to 23 carbon atoms, and a hydrogen atom included in the saturated hydrocarbon group may be substituted with a fluorine atom, 
     L b20  represents a single bond or a divalent saturated hydrocarbon group having 1 to 23 carbon atoms, and a hydrogen atom included in the saturated hydrocarbon group may be substituted with a fluorine atom, a hydroxy group or an alkylcarbonyloxy group, —CH 2 — included in the alkylcarbonyloxy group may be replaced by —O— or —CO—, and a hydrogen atom included in the alkylcarbonyloxy group may be substituted with a hydroxy group, and 
     the total number of carbon atoms of L b19  and L b20  is 23 or less. 
     In formula (b1-10), 
     L b21  represents a single bond or a divalent saturated hydrocarbon group having 1 to 21 carbon atoms, and a hydrogen atom included in the saturated hydrocarbon group may be substituted with a fluorine atom, 
     L b22  represents a single bond or a divalent saturated hydrocarbon group having 1 to 21 carbon atoms, 
     L b23  represents a single bond or a divalent saturated hydrocarbon group having 1 to 21 carbon atoms, and a hydrogen atom included in the saturated hydrocarbon group may be substituted with a fluorine atom, a hydroxy group or an alkylcarbonyloxy group, —CH 2 — included in the alkylcarbonyloxy group may be replaced by —O— or —CO—, and a hydrogen atom included in the alkylcarbonyloxy group may be substituted with a hydroxy group, and 
     the total number of carbon atoms of L b21 , L b22  and L b23  is 21 or less. 
     In formula (b1-11), 
     L b24  represents a single bond or a divalent saturated hydrocarbon group having 1 to 20 carbon atoms, and a hydrogen atom included in the saturated hydrocarbon group may be substituted with a fluorine atom, 
     L b25  represents a divalent saturated hydrocarbon group having 1 to 21 carbon atoms, 
     L b26  represents a single bond or a divalent saturated hydrocarbon group having 1 to 20 carbon atoms, a hydrogen atom included in the saturated hydrocarbon group may be substituted with a fluorine atom, a hydroxy group or an alkylcarbonyloxy group, —CH 2 — included in the alkylcarbonyloxy group may be replaced by —O— or —CO—, and a hydrogen atom included in the alkylcarbonyloxy group may be substituted with a hydroxy group, and 
     the total number of carbon atoms of L b24 , L b25  and L b26  is 21 or less. 
     In groups represented by formula (b1-9) to formula (b1-1), when a hydrogen atom included in the saturated hydrocarbon group is substituted with an alkylcarbonyloxy group, the number of carbon atoms before substitution is taken as the number of carbon atoms of the saturated hydrocarbon group. 
     Examples of the alkylcarbonyloxy group include an acetyloxy group, a propionyloxy group, a butyryloxy group, a cyclohexylcarbonyloxy group, an adamantylcarbonyloxy group and the like. 
     Examples of the group represented by formula (b1-4) include the followings. 
     
       
         
         
             
             
         
       
     
     Examples of the group represented by formula (b1-5) include the followings: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Examples of the group represented by formula (b1-6) include the followings. 
     
       
         
         
             
             
         
       
     
     Examples of the group represented by formula (b1-7) include the followings. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Examples of the group represented by formula (b1-8) include the followings. 
     
       
         
         
             
             
         
       
     
     Examples of the group represented by formula (b1-2) include the followings. 
     
       
         
         
             
             
         
       
     
     Examples of the group represented by formula (b1-9) include the followings. 
     
       
         
         
             
             
         
       
     
     Examples of the group represented by formula (b1-10) include the followings. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Examples of the group represented by formula (b1-11) include the followings. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Examples of the alicyclic hydrocarbon group represented by Y include groups represented by formula (Y1) to formula (Y11) and formula (Y36) to formula (Y38). 
     When —CH 2 — included in the alicyclic hydrocarbon group represented by Y is replaced by —O—, —S(O) 2 — or —CO—, the number may be 1, or 2 or more. Examples of such group include groups represented by formula (Y12) to formula (Y35) and formula (Y39) to formula (Y41). 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     The alicyclic hydrocarbon group represented by Y is preferably a group represented by any one of formula (Y1) to formula (Y20), formula (Y26), formula (Y27), formula (Y30), formula (Y31) and formula (Y39) to formula (Y41), more preferably a group represented by formula (Y11), formula (Y15), formula (Y16), formula (Y20), formula (Y26), formula (Y27), formula (Y30), formula (Y31), formula (Y39) or formula (Y40), and still more preferably a group represented by formula (Y11), formula (Y15), formula (Y20), formula (Y26), formula (Y27), formula (Y30), formula (Y31), formula (Y39) or formula (Y40). 
     The alicyclic hydrocarbon group represented by Y is a spiro ring including an oxygen atom in formula (Y28) to formula (Y35), formula (Y39) or formula (Y40), the alkanediyl group between two oxygen atoms preferably has one or more fluorine atoms. Of alkanediyl groups included in a ketal structure, it is preferable that a methylene group adjacent to the oxygen atom is not substituted with a fluorine atom. 
     Examples of the substituent of the methyl group represented by Y include a halogen atom, a hydroxy group, an alicyclic hydrocarbon group having 3 to 16 carbon atoms, an aromatic hydrocarbon group having 6 to 18 carbon atoms, a glycidyloxy group, a —(CH 2 ) ja —CO—O—R b1  group or a —(CH 2 ) ja —O—CO—R b1  group (wherein R b1  represents an alkyl group having 1 to 16 carbon atoms, an alicyclic hydrocarbon group having 3 to 16 carbon atoms, an aromatic hydrocarbon group having 6 to 18 carbon atoms, or groups obtained by combining these groups, —CH 2 — included in the alkyl group and the alicyclic hydrocarbon group may be replaced by —O—, —SO 2 — or —CO—, a hydrogen atom included in the alkyl group, the alicyclic hydrocarbon group and the aromatic hydrocarbon group may be substituted with a hydroxy group or a fluorine atom, and ja represents an integer of 0 to 4) and the like. 
     Examples of the substituent of the alicyclic hydrocarbon group represented by Y include a halogen atom, a hydroxy group, an alkyl group having 1 to 12 carbon atoms which may be substituted with a hydroxy group, an alicyclic hydrocarbon group having 3 to 16 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an aromatic hydrocarbon group having 6 to 18 carbon atoms, an aralkyl group having 7 to 21 carbon atoms, an alkylcarbonyl group having 2 to 4 carbon atoms, a glycidyloxy group, a —(CH 2 ) ja —CO—O—R b1  group or —(CH 2 ) ja —O—CO—R b1  group (wherein R b1  represents an alkyl group having 1 to 16 carbon atoms, an alicyclic hydrocarbon group having 3 to 16 carbon atoms, an aromatic hydrocarbon group having 6 to 18 carbon atoms, or groups obtained by combining these groups, —CH 2 — included in the alkyl group and the alicyclic hydrocarbon group may be replaced by —O—, —SO 2 — or —CO—, a hydrogen atom included in the alkyl group, the alicyclic hydrocarbon group and the aromatic hydrocarbon group may be substituted with a hydroxy group or a fluorine atom, and ja represents an integer of 0 to 4) and the like. 
     Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom. 
     The alicyclic hydrocarbon group includes, for example, a cyclopentyl group, a cyclohexyl group, a methylcyclohexyl group, a dimethylcyclohexyl group, a cycloheptyl group, a cyclooctyl group, a norbornyl group, an adamantyl group and the like. 
     Examples of the aromatic hydrocarbon group include aryl groups such as a phenyl group, a naphthyl group, an anthryl group, a biphenyl group and a phenanthryl group. The aromatic hydrocarbon group may have a chain hydrocarbon group or an alicyclic hydrocarbon group, examples of the aromatic hydrocarbon group having a chain hydrocarbon group include a tolyl group, a xylyl group, a cumenyl group, a mesityl group, a p-ethylphenyl group, a p-tert-butylphenyl group, a 2,6-diethylphenyl group, a 2-methyl-6-ethylphenyl group and the like, and examples of the aromatic hydrocarbon group having an alicyclic hydrocarbon group include a p-cyclohexylphenyl group, a p-adamantylphenyl group and the like. 
     The alkyl group includes, for example, a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a sec-butyl group, a tert-butyl group, a pentyl group, a hexyl group, a heptyl group, a 2-ethylhexyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group and the like. 
     Examples of the alkyl group substituted with a hydroxy group include hydroxyalkyl groups such as a hydroxymethyl group and a hydroxyethyl group. 
     Examples of the alkoxy group include a methoxy group, an ethoxy group, a propoxy group, a butoxy group, a pentyloxy group, a hexyloxy group, a heptyloxy group, an octyloxy group, a decyloxy group and a dodecyloxy group. 
     Examples of the aralkyl group include a benzyl group, a phenethyl group, a phenylpropyl group, a naphthylmethyl group and a naphthylethyl group. 
     The alkylcarbonyl group includes, for example, an acetyl group, a propionyl group and a butyryl group. 
     Examples of Y include the followings. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Y is preferably an alicyclic hydrocarbon group having 3 to 18 carbon atoms which may have a substituent, more preferably an adamantyl group which may have a substituent, and —CH 2 — constituting the alicyclic hydrocarbon group or the adamantyl group may be replaced by —CO—, —S(O) 2 — or —CO—. Y is still more preferably an adamantyl group, a hydroxyadamantyl group, an oxoadamantyl group, or groups represented by the following formulas. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     The anion in the salt represented by formula (B1) is preferably anions represented by formula (B1-A-1) to formula (B1-A-55) [hereinafter sometimes referred to as “anion (B1-A-1)” according to the number of formula], and more preferably an anion represented by any one of formula (B1-A-1) to formula (B1-A-4), formula (B1-A-9), formula (B1-A-10), formula (B1-A-24) to formula (B1-A-33), formula (B1-A-36) to formula (B1-A-40) and formula (B1-A-47) to formula (B1-A-55). 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     R i2  to R i7  each independently represent, for example, an alkyl group having 1 to 4 carbon atoms, and preferably a methyl group or an ethyl group. R i8  is, for example, an aliphatic hydrocarbon group having 1 to 12 carbon atoms, preferably an alkyl group having 1 to 4 carbon atoms, an alicyclic hydrocarbon group having 5 to 12 carbon atoms or groups formed by combining these groups, and more preferably a methyl group, an ethyl group, a cyclohexyl group or an adamantyl group. L A4  is a single bond or an alkanediyl group having 1 to 4 carbon atoms. 
     Q b1  and Q b2  are the same as defined above. 
     Specific examples of the anion in the salt represented by formula (B1) include anions mentioned in JP 2010-204646 A. 
     Preferable anions in the salt represented by formula (B1) are anions represented by formula (B1a-1) to formula (B1a-34). 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Of these, an anion represented by any one of formula (B1a-1) to formula (B1a-3) and formula (B1a-7) to formula (B1a-16), formula (B1a-18), formula (B1a-19) and formula (B1a-22) to formula (B1a-30) is preferable. 
     Examples of the organic cation of Z +  include an organic onium cation, an organic sulfonium cation, an organic iodonium cation, an organic ammonium cation, a benzothiazolium cation and an organic phosphonium cation, and include those which are the same as the organic cation ZA +  in the structural formula represented by formula (II-2-A′). Of these, an organic sulfonium cation and an organic iodonium cation are preferable, and an arylsulfonium cation is more preferable. 
     The acid generator (B) is a combination of the anion mentioned above and the organic cation mentioned above, and these can be optionally combined. The acid generator (B) preferably includes a combination of an anion represented by any one of formula (B1a-1) to formula (B1a-3) and formula (B1a-7) to formula (B1a-16), formula (B1a-18), formula (B1a-19) and formula (B1a-22) to formula (B1a-34) with a cation (b2-1) or a cation (b2-3). 
     The acid generator (B) preferably includes those represented by formula (B1-1) to formula (B1-48). Of these acid generators, those containing an arylsulfonium cation are preferable and those represented by formula (B1-1) to formula (B1-3), formula (B1-5) to formula (B1-7), formula (B1-11) to formula (B1-14), formula (B1-20) to formula (B1-26), formula (B1-29) and formula (B1-31) to formula (B1-48) are particularly preferable. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In the resist composition of the present invention, the content of the acid generator is preferably 1 part by mass or more and 40 parts by mass or less, and more preferably 3 parts by mass or more and 35 parts by mass or less, based on 100 parts by mass of the resin (A). The resist composition of the present invention may include one acid generator (B) or a plurality of acid generators. 
     &lt;Solvent (E)&gt; 
     The content of the solvent (E) in the resist composition is usually 90% by mass or more and 99.9% by mass or less, preferably 92% by mass or more and 99% by mass or less, and more preferably 94% by mass or more and 99% by mass or less. The content of the solvent (E) can be measured, for example, by a known analysis means such as liquid chromatography or gas chromatography. 
     Examples of the solvent (E) include glycol ether esters such as ethylcellosolve acetate, methylcellosolve acetate and propylene glycol monomethyl ether acetate; glycol ethers such as propylene glycol monomethyl ether; esters such as ethyl lactate, butyl acetate, amyl acetate and ethyl pyruvate; ketones such as acetone, methyl isobutyl ketone, 2-heptanone and cyclohexanone; and cyclic esters such as γ-butyrolactone. The solvent (E) may be used alone, or two or more solvents may be used. 
     &lt;Quencher (C)&gt; 
     Examples of the quencher (C) include a basic nitrogen-containing organic compound, and a salt generating an acid having an acidity lower than that of an acid generated from an acid generator (B) (excluding a salt represented by formula (I)). When the resist composition includes the quencher (C), the content of the quencher (C) is preferably about 0.01 to 5% by mass, and more preferably about 0.01 to 3% by mass, based on the amount of the solid component of the resist composition. 
     Examples of the basic nitrogen-containing organic compound include amine and an ammonium salt. Examples of the amine include an aliphatic amine and an aromatic amine. Examples of the aliphatic amine include a primary amine, a secondary amine and a tertiary amine. 
     Examples of the amine include 1-naphthylamine, 2-naphthylamine, aniline, diisopropylaniline, 2-, 3- or 4-methylaniline, 4-nitroaniline, N-methylaniline, N,N-dimethylaniline, diphenylamine, hexylamine, heptylamine, octylamine, nonylamine, decylamine, dibutylamine, dipentylamine, dihexylamine, diheptylamine, dioctylamine, dinonylamine, didecylamine, triethylamine, trimethylamine, tripropylamine, tributylamine, tripentylamine, trihexylamine, triheptylamine, trioctylamine, trinonylamine, tridecylamine, methyldibutylamine, methyldipentylamine, methyldihexylamine, methyldicyclohexylamine, methyldiheptylamine, methyldioctylamine, methyldinonylamine, methyldidecylamine, ethyldibutylamine, ethyldipentylamine, ethyldihexylamine, ethyldiheptylamine, ethyldioctylamine, ethyldinonylamine, ethyldidecylamine, dicyclohexylmethylamine, tris[2-(2-methoxyethoxy)ethyl]amine, triisopropanolamine, ethylenediamine, tetramethylenediamine, hexamethylenediamine, 4,4′-diamino-1,2-diphenylethane, 4,4′-diamino-3,3′-dimethyldiphenylmethane, 4,4′-diamino-3,3′-diethyldiphenylmethane, 2,2′-methylenebisaniline, imidazole, 4-methylimidazole, pyridine, 4-methylpyridine, 1,2-di(2-pyridyl)ethane, 1,2-di(4-pyridyl)ethane, 1,2-di(2-pyridyl)ethene, 1,2-di(4-pyridyl)ethene, 1,3-di(4-pyridyl)propane, 1,2-di(4-pyridyloxy)ethane, di(2-pyridyl)ketone, 4,4′-dipyridyl sulfide, 4,4′-dipyridyl disulfide, 2,2′-dipyridylamine, 2,2′-dipicolylamine, bipyridine and the like, preferably diisopropylaniline, and more preferably 2,6-diisopropylaniline. 
     Examples of the ammonium salt include tetramethylammonium hydroxide, tetraisopropylammonium hydroxide, tetrabutylammonium hydroxide, tetrahexylammonium hydroxide, tetraoctylammonium hydroxide, phenyltrimethylammonium hydroxide, 3-(trifluoromethyl)phenyltrimethylammonium hydroxide, tetra-n-butylammonium salicylate and choline. 
     The acidity in a salt generating an acid having an acidity lower than that of an acid generated from the acid generator (B) is indicated by the acid dissociation constant (pKa). Regarding the salt generating an acid having an acidity lower than that of an acid generated from the acid generator (B), the acid dissociation constant of an acid generated from the salt usually meets the following inequality: −3&lt;pKa, preferably −1&lt;pKa&lt;7, and more preferably 0&lt;pKa&lt;5. 
     Examples of the salt generating an acid having an acidity lower than that of an acid generated from the acid generator (B) include salts represented by the following formulas, a salt represented by formula (D) mentioned in JP 2015-147926 A (hereinafter sometimes referred to as “weak acid inner salt (D)”, and salts mentioned in JP 2012-229206 A, JP 2012-6908 A, JP 2012-72109 A, JP 2011-39502 A and JP 2011-191745 A. The salt generating an acid having an acidity lower than that of an acid generated from the acid generator (B) is preferably a weak acid inner salt (D). 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Examples of the weak acid inner salt (D) include the following salts. 
                                                             
&lt;Other Components&gt;
 
     The resist composition of the present invention may also include components other than the components mentioned above (hereinafter sometimes referred to as “other components (F)”). The other components (F) are not particularly limited and it is possible to use various additives known in the resist field, for example, sensitizers, dissolution inhibitors, surfactants, stabilizers and dyes. 
     &lt;Preparation of Resist Composition&gt; 
     The resist composition of the present invention can be prepared by mixing a quencher containing a salt (I), a resin (A) and an acid generator (B), and if necessary, resins other than the resin (A) used, a solvent (E), a quencher (C) and other components (F). The order of mixing these components is any order and is not particularly limited. It is possible to select, as the temperature during mixing, appropriate temperature from 10 to 40° C., according to the type of the resin, the solubility in the solvent (E) of the resin and the like. It is possible to select, as the mixing time, appropriate time from 0.5 to 24 hours according to the mixing temperature. The mixing means is not particularly limited and it is possible to use mixing with stirring. 
     After mixing the respective components, the mixture is preferably filtered through a filter having a pore diameter of about 0.003 to 0.2 μm. 
     (Method for Producing Resist Pattern) 
     The method for producing a resist pattern of the present invention include: 
     (1) a step of applying the resist composition of the present invention on a substrate, 
     (2) a step of drying the applied composition to form a composition layer, 
     (3) a step of exposing the composition layer, 
     (4) a step of heating the exposed composition layer, and 
     (5) a step of developing the heated composition layer. 
     The resist composition can be usually applied on a substrate using a conventionally used apparatus, such as a spin coater. Examples of the substrate include inorganic substrates such as a silicon wafer. Before applying the resist composition, the substrate may be washed, and an organic antireflection film may be formed on the substrate. 
     The solvent is removed by drying the applied composition to form a composition layer. Drying is performed by evaporating the solvent using a heating device such as a hot plate (so-called “prebake”), or a decompression device. The heating temperature is preferably 50 to 200° C. and the heating time is preferably 10 to 180 seconds. The pressure during drying under reduced pressure is preferably about 1 to 1.0×10 5  Pa. 
     The composition layer thus obtained is usually exposed using an aligner. The aligner may be a liquid immersion aligner. It is possible to use, as an exposure source, various exposure sources, for example, exposure sources capable of emitting laser beam in an ultraviolet region such as KrF excimer laser (wavelength of 248 nm), ArF excimer laser (wavelength of 193 nm) and F 2  excimer laser (wavelength of 157 nm), an exposure source capable of emitting harmonic laser beam in a far-ultraviolet or vacuum ultra violet region by wavelength-converting laser beam from a solid-state laser source (YAG or semiconductor laser), an exposure source capable of emitting electron beam or EUV and the like. In the present specification, such exposure to radiation is sometimes collectively referred to as “exposure”. The exposure is usually performed through a mask corresponding to a pattern to be required. When electron beam is used as the exposure source, exposure may be performed by direct writing without using the mask. 
     The exposed composition layer is subjected to a heat treatment (so-called “post-exposure bake”) to promote the deprotection reaction in an acid-labile group. The heating temperature is usually about 50 to 200° C., and preferably about 70 to 150° C. 
     The heated composition layer is usually developed with a developing solution using a development apparatus. Examples of the developing method include a dipping method, a paddle method, a spraying method, a dynamic dispensing method and the like. The developing temperature is preferably, for example, 5 to 60° C. and the developing time is preferably, for example, 5 to 300 seconds. It is possible to produce a positive resist pattern or negative resist pattern by selecting the type of the developing solution as follows. 
     When the positive resist pattern is produced from the resist composition of the present invention, an alkaline developing solution is used as the developing solution. The alkaline developing solution may be various aqueous alkaline solutions used in this field. Examples thereof include aqueous solutions of tetramethylammonium hydroxide and (2-hydroxyethyl)trimethylammonium hydroxide (commonly known as choline). The surfactant may be contained in the alkaline developing solution. 
     It is preferred that the developed resist pattern is washed with ultrapure water and then water remaining on the substrate and the pattern is removed. 
     When the negative resist pattern is produced from the resist composition of the present invention, a developing solution containing an organic solvent (hereinafter sometimes referred to as “organic developing solution”) is used as the developing solution. 
     Examples of the organic solvent contained in the organic developing solution include ketone solvents such as 2-hexanone and 2-heptanone; glycol ether ester solvents such as propylene glycol monomethyl ether acetate; ester solvents such as butyl acetate; glycol ether solvents such as propylene glycol monomethyl ether; amide solvents such as N,N-dimethylacetamide; and aromatic hydrocarbon solvents such as anisole. 
     The content of the organic solvent in the organic developing solution is preferably 90% by mass or more and 100% by mass or less, more preferably 95% by mass or more and 100% by mass or less, and still more preferably the organic developing solution is substantially composed of the organic solvent. 
     Particularly, the organic developing solution is preferably a developing solution containing butyl acetate and/or 2-heptanone. The total content of butyl acetate and 2-heptanone in the organic developing solution is preferably 50% by mass or more and 100% by mass or less, more preferably 90% by mass or more and 100% by mass or less, and still more preferably the organic developing solution is substantially composed of butyl acetate and/or 2-heptanone. 
     The surfactant may be contained in the organic developing solution. A trace amount of water may be contained in the organic developing solution. 
     During development, the development may be stopped by replacing by a solvent with the type different from that of the organic developing solution. 
     The developed resist pattern is preferably washed with a rinsing solution. The rinsing solution is not particularly limited as long as it does not dissolve the resist pattern, and it is possible to use a solution containing an ordinary organic solvent which is preferably an alcohol solvent or an ester solvent. 
     After washing, the rinsing solution remaining on the substrate and the pattern is preferably removed. 
     (Application) 
     The resist composition of the present invention is suitable as a resist composition for exposure of KrF excimer laser, a resist composition for exposure of ArF excimer laser, a resist composition for exposure of electron beam (EB) or a resist composition for exposure of EUV, particularly a resist composition for exposure of electron beam (EB) or a resist composition for exposure of EUV, and the resist composition is useful for fine processing of semiconductors. 
     EXAMPLES 
     The present invention will be described more specifically by way of Examples. Percentages and parts expressing the contents or amounts used in the Examples are by mass unless otherwise specified. 
     The weight-average molecular weight is a value determined by gel permeation chromatography under the following conditions. 
     Apparatus: Model HLC-8120GPC (manufactured by TOSOH CORPORATION) 
     Column: TSKgel Multipore IIXL-M×3+guardcolumn (manufactured by TOSOH CORPORATION) 
     Eluent: tetrahydrofuran 
     Flow rate: 1.0 mL/min 
     Detector: RI detector 
     Column temperature: 40° C. 
     Injection amount: 100 μl 
     Molecular weight standards: polystyrene standard (manufactured by TOSOH CORPORATION) 
     Structures of compounds were confirmed by measuring a molecular ion peak using mass spectrometry (Liquid Chromatography: Model 1100, manufactured by Agilent Technologies, Inc., Mass Spectrometry: Model LC/MSD, manufactured by Agilent Technologies, Inc.). The value of this molecular ion peak in the following Examples is indicated by “MASS”. 
     Example 1: Synthesis of Salt Represented by Formula (I-3) 
     
       
         
         
             
             
         
       
     
     5.00 Parts of a compound represented by formula (I-3-a), 20 parts of chloroform and 4.56 parts of a compound represented by formula (I-3-b) were mixed, followed by stirring at 23° C. for 30 minutes and further cooling to 5° C. To the mixture thus obtained, a mixed solution of 5.32 parts of methanesulfonic acid and 1.77 parts of phosphorus pentaoxide was added dropwise over 15 minutes, followed by stirring at 23° C. for 18 hours. To the mixture thus obtained, 40 parts of ion-exchanged water and 30 parts of ethyl acetate were added and, after stirring at 23° C. for 30 minutes, an aqueous layer was isolated through separation. To the aqueous layer thus obtained, 30 parts of ethyl acetate was added and, after stirring at 23° C. for 30 minutes, an aqueous layer containing a salt represented by formula (I-3-c) was isolated through separation. This washing operation with ethyl acetate was performed three times. After the aqueous layer thus obtained was filtered, 14.97 parts of sodium iodide and 15 parts of ion-exchanged water were added to the filtrate thus obtained, followed by stirring at 23° C. for 30 minutes and further filtration to obtain 5.50 parts of a salt represented by formula (I-3-d). 
     
       
         
         
             
             
         
       
     
     1.50 Parts of a salt represented by formula (I-3-d) and 45 parts of methanol were mixed, followed by stirring at 23° C. for 30 minutes, the addition of 0.36 part of silver oxide and further stirring at 23° C. for 18 hours. The mixture thus obtained was filtered and the filtrate thus obtained was concentrated. To the concentrated residue, 1.30 parts of methanol, 5.20 parts of acetonitrile and 40 parts of t-butyl methyl ether were added, followed by stirring at 23° C. for 30 minutes and further filtration to obtain 0.94 part of a salt represented by formula (I-3). 
     MASS (ESI (+) Spectrum): 349.1 [M+H] +   
     Example 2: Synthesis of Salt Represented by Formula (I-12) 
     
       
         
         
             
             
         
       
     
     2.50 Parts of a compound represented by formula (I-12-a), 20 parts of chloroform, 1.93 parts of a compound represented by formula (I-3-b) and 1.91 parts of trifluoromethanesulfonic acid were mixed, followed by stirring at 23° C. for 30 minutes and further cooling to 5° C. To the mixture thus obtained, 3.33 parts of trifluoroacetic anhydride was added dropwise over 15 minutes, followed by stirring at 23° C. for 2 hours. To the mixture thus obtained, 3.86 parts of triethylamine and 7.71 parts of ion-exchanged water were added and, after stirring at 23° C. for 30 minutes, an organic layer was isolated through separation. To the organic layer thus obtained, 50 parts of an aqueous 5% oxalic acid solution was added and, after stirring at 23° C. for 30 minutes, an organic layer was isolated through separation. To the organic layer thus obtained, 50 parts of ion-exchanged water was added and, after stirring at 23° C. for 30 minutes, an organic layer was isolated through separation. This water washing operation was performed five times. After the organic layer thus obtained was concentrated, 30 parts of t-butyl methyl ether was added to the residue thus obtained, followed by stirring at 23° C. for 30 minutes and further filtration to obtain 0.41 part of a salt represented by formula (I-12). 
     MASS (ESI (+) Spectrum): 385.1 [M+H] +   
     Example 3: Synthesis of Salt Represented by Formula (I-13) 
     
       
         
         
             
             
         
       
     
     4.43 Parts of a compound represented by formula (I-3-a), 20 parts of chloroform, 5.00 parts of a compound represented by formula (I-13-b) and 6.63 parts of trifluoromethanesulfonic acid were mixed, followed by stirring at 23° C. for 30 minutes and further cooling to 5° C. To the mixture thus obtained, 9.28 parts of trifluoroacetic anhydride was added dropwise over 15 minutes, followed by stirring at 23° C. for 12 hours. To the mixture thus obtained, 50 parts of an aqueous 10% sodium hydroxide solution was added and, after stirring at 23° C. for 2 hours, an organic layer was isolated through separation. This washing operation was performed three times. To the organic layer thus obtained, 50 parts of an aqueous 5% oxalic acid solution was added and, after stirring at 23° C. for 30 minutes, an organic layer was isolated through separation. To the organic layer thus obtained, 50 parts of ion-exchanged water was added and, after stirring at 23° C. for 30 minutes, an organic layer was isolated through separation. This water washing operation was performed five times. After the organic layer thus obtained was concentrated, 30 parts of t-butyl methyl ether was added to the residue thus obtained, followed by stirring at 23° C. for 30 minutes and further filtration to obtain 6.23 parts of a salt represented by formula (I-13). 
     MASS (ESI (+) Spectrum): 395.1 [M+H] +   
     Example 4: Synthesis of Salt Represented by Formula (I-14) 
     
       
         
         
             
             
         
       
     
     5.20 Parts of a compound represented by formula (I-12-a), 20 parts of chloroform, 5.00 parts of a compound represented by formula (I-13-b) and 6.63 parts of trifluoromethanesulfonic acid were mixed, followed by stirring at 23° C. for 30 minutes and further cooling to 5° C. To the mixture thus obtained, 9.28 parts of trifluoroacetic anhydride was added dropwise over 15 minutes, followed by stirring at 23° C. for 12 hours. To the mixture thus obtained, 50 parts of an aqueous 10% sodium hydroxide solution was added and, after stirring at 23° C. for 2 hours, an organic layer was isolated through separation. This washing operation was performed three times. To the organic layer thus obtained, 50 parts of an aqueous 5% oxalic acid solution was added and, after stirring at 23° C. for 30 minutes, an organic layer was isolated through separation. To the organic layer thus obtained, 50 parts of ion-exchanged water was added and, after stirring at 23° C. for 30 minutes, an organic layer was isolated through separation. This water washing operation was performed five times. After the organic layer thus obtained was concentrated, 30 parts of t-butyl methyl ether was added to the residue thus obtained, followed by stirring at 23° C. for 30 minutes and further filtration to obtain 5.66 parts of a salt represented by formula (I-14). 
     MASS (ESI (+) Spectrum): 431.1 [M+H] +   
     Synthesis of Resin 
     Compounds (monomers) used in the synthesis of the resin (A) are shown below. Hereinafter, these compounds are referred to as “monomer (a1-1-3)” according to the number of formula. 
     
       
         
         
             
             
         
       
     
     Synthesis Example 1 [Synthesis of Resin A1] 
     Using a monomer (a1-4-2), a monomer (a1-1-3) and a monomer (a1-2-6) as monomers, these monomers were mixed in a molar ratio of 38:24:38 [monomer (a1-4-2):monomer (a1-1-3):monomer (a1-2-6)], and methyl isobutyl ketone was added to this monomer mixture in the amount of 1.5 mass times the total mass of all monomers. To the mixture thus obtained, azobisisobutyronitrile as an initiator was added in the amount of 7 mol % based on the total molar number of all monomers, and then the mixture was polymerized by heating at 83° C. for about 5 hours. To the polymerization reaction mixture thus obtained, an aqueous p-toluenesulfonic acid solution was added. After stirring for 6 hours, an organic layer was isolated through separation. The organic layer thus obtained was poured into a large amount of n-heptane to precipitate a resin, followed by filtration and collection to obtain a resin A1 (copolymer) having a weight-average molecular weight of about 5.3×10 3  in a yield of 78%. This resin A1 has the following structural units. 
                         
&lt;Preparation of Resist Compositions&gt;
 
     As shown in Table 1, the following respective components were mixed, and the mixtures thus obtained were filtered through a fluorine resin filter having a pore diameter of 0.2 μm to prepare resist compositions. 
                                         TABLE 1               Resist       Acid                   composition   Resin   generator   Salt (I)   Quencher (C)   PB/PEB                  Composition 1   Al =   B1-43 =   I-3 =   —   110° C./           10 parts   3.4 parts   0.7 parts       120° C.       Composition 2   Al =   B1-43 =   I-3 =   C1 =    110° C./           10 parts   3.4 parts   0.5 parts   0.2 parts   120° C.       Composition 3   Al =   B1-43 =   I-12 =   —   110° C./           10 parts   parts   0.7 parts       120° C.       Composition 4   Al =   B1-43 =   I-13 =   —   110° C./           10 parts   3.4 parts   0.7 parts       120° C.       Composition 5   Al =   B1-43 =   I-14 =   —   110° C./           10 parts   3.4 parts   0.7 parts       120° C.       Comparative   Al =   B1-43 =   —   IX-1 =   110° C./       Composition 1   10 parts   3.4 parts       0.7 parts   120° C.       Comparative   Al =   B1-43 =   —   IX-2 =   110° C./       Composition 2   10 parts   3.4 parts       0.7 parts   120° C.                    
&lt;Resin&gt;
 
     A1: Resin A1 
     &lt;Acid Generator (B)&gt; 
     B1-43: Salt Represented by Formula (B1-43) (synthesized in accordance with Examples JP 2016-47815 A) 
                         
&lt;Salt (I)&gt;
 
     I-3: Salt represented by formula (I-3) 
     I-12: Salt represented by formula (I-12) 
     I-13: Salt represented by formula (I-13) 
     I-14: Salt represented by formula (I-14) 
     &lt;Quencher (C)&gt; 
     IX-1: synthesized with reference to JP 2017-202993 A 
     
       
         
         
             
             
         
       
     
     IX-2: synthesized in accordance with Examples of JP 2018-066985 A 
     
       
         
         
             
             
         
       
     
     C1: synthesized in accordance with the method mentioned in JP 2011-39502 A 
                         
&lt;Solvent&gt;
 
                                                Propylene glycol monomethyl ether acetate   400 parts           Propylene glycol monomethyl ether   150 parts           γ-Butyrolactone    5 parts                        
(Evaluation of Exposure of Resist Composition with Electron Beam)
 
     Each 6 inch-diameter silicon wafer was treated with hexamethyldisilazane and then baked on a direct hot plate at 90° C. for 60 seconds. A resist composition was spin-coated on the silicon wafer so that the thickness of the composition later became 0.04 μm. The coated silicon wafer was prebaked on the direct hot plate at the temperature shown in the column “PB” of Table 1 for 60 second to form a composition layer. Using an electron-beam direct-write system (“ELS-F125 125 keV”, manufactured by ELIONIX INC.), contact hole patterns (hole pitch of 40 nm/hole diameter of 17 nm) were directly written on the composition layer formed on the wafer while changing the exposure dose stepwise. 
     After the exposure, post-exposure baking was performed on the hot plate at the temperature shown in the column “PEB” of Table 1 for 60 seconds, followed by paddle development with an aqueous 2.38% by mass tetramethylammonium hydroxide solution for 60 seconds to obtain a resist pattern. 
     In the resist pattern formed after the development, the effective sensitivity was expressed as the exposure dose that the hole diameter formed became 17 nm. 
     &lt;Evaluation of CD Uniformity (CDU)&gt; 
     In the effective sensitivity, the hole diameter of the pattern formed at a hole diameter of 17 nm was determined by measuring 24 times per one hole and the average of the measured values was regarded as the average hole diameter. The standard deviation was determined under the conditions that the average diameter of 400 holes about the patterns formed at a hole diameter of 17 nm in the same wafer was regarded as a population. 
     The results are shown in Table 2. The numerical value in the table indicates the standard deviation (nm). 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
                 Resist 
                   
               
               
                   
                   
                 composition 
                 CDU 
               
               
                   
                   
               
             
            
               
                   
                 Example 5 
                 Composition 1 
                 2.76 
               
               
                   
                 Example 6 
                 Composition 2 
                 2.75 
               
               
                   
                 Example 7 
                 Composition 3 
                 2.68 
               
               
                   
                 Example 8 
                 Composition 4 
                 2.70 
               
               
                   
                 Example 9 
                 Composition 5 
                 2.62 
               
               
                   
                 Comparative 
                 Comparative 
                 2.89 
               
               
                   
                 Example 1 
                 Composition 1 
                   
               
               
                   
                 Comparative 
                 Comparative 
                 2.85 
               
               
                   
                 Example 2 
                 Composition 2 
               
               
                   
                   
               
            
           
         
       
     
     As compared with comparative compositions 1 and 2, compositions 1 to 5 exhibited small standard deviation and satisfactory evaluation of CD uniformity (CDU). 
     INDUSTRIAL APPLICABILITY 
     Since resist patterns with satisfactory CD uniformity (CDU) can be obtained, a resist composition including a slat (1) of the present invention is useful for fine processing of semiconductors and is industrially very useful.