Patent Publication Number: US-8986919-B2

Title: Resist composition, method of forming resist pattern and polymeric compound

Description:
TECHNICAL FIELD 
     The present invention relates to a polymeric compound which generates acid upon exposure and exhibits increased polarity by the action of acid, a resist composition containing the polymeric compound, and a method of forming a resist pattern using the resist composition. 
     Priority is claimed on Japanese Patent Application No. 2011-028987, filed Feb. 14, 2011, the content of which is incorporated herein by reference. 
     DESCRIPTION OF RELATED ART 
     In lithography techniques, for example, a resist film composed of a resist material is formed on a substrate, and the resist film is subjected to selective exposure of radial rays such as light or electron beam through a mask having a predetermined pattern, followed by development, thereby forming a resist pattern having a predetermined shape on the resist film. 
     A resist material in which the exposed portions become soluble in a developing solution is called a positive-type, and a resist material in which the exposed portions become insoluble in a developing solution is called a negative-type. 
     In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of pattern miniaturization. 
     Typically, these miniaturization techniques involve shortening the wavelength of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers and ArF excimer lasers are starting to be introduced in mass production. Furthermore, research is also being conducted into lithography techniques that use an exposure light source having a wavelength shorter than these excimer lasers, such as F 2  excimer lasers, electron beam, extreme ultraviolet radiation (EUV), and X-ray. 
     Resist materials for use with these types of exposure light sources require lithography properties such as a high resolution capable of reproducing patterns of minute dimensions, and a high level of sensitivity to these types of exposure light sources. 
     As a resist material that satisfies these conditions, a chemically amplified composition is used which includes an acid generator that generates acid upon exposure. 
     A chemically amplified composition generally used includes an acid generator and a base component for forming a film. 
     As acid generators usable in a chemically amplified resist composition, various types have been proposed including, for example, onium salt acid generators; oxime sulfonate acid generators; diazomethane acid generators; nitrobenzylsulfonate acid generators; iminosulfonate acid generators; and disulfone acid generators. 
     Further, in general, a base component which exhibits changed solubility in a developing solution under action of acid generated from the acid generator is used. For example, in the case of an alkali developing process using an alkali developing solution, a base component which exhibits changed solubility in an alkali developing solution under action of acid is used. When the resist film formed using the chemically amplified resist composition is selectively exposed, acid is generated from the acid-generator component within the exposed portions, and the action of this acid causes an increase in the solubility of the resin component in an alkali developing solution, making the exposed portions soluble in the alkali developing solution. Thus, by conducting developing by an alkali developing solution, the exposed portions are dissolved and removed, whereas the unexposed portions remain as patterns, thereby forming a positive resist pattern. 
     In the formation of a positive pattern by an alkali developing process, a base component having an acid decomposable group which exhibits increased polarity by the action of acid is used. By the increase in the polarity by the action of acid, the base component exhibits increased solubility in an alkali developing solution. On the other hand, since the solubility of the organic solvent decreases, by utilizing this property, a process in which a developing solution containing an organic solvent (organic developing solution) is used instead of an alkali developing solution has been proposed (hereafter, this process is frequently referred to as “solvent developing process” or “negative-tone developing process”). When a resist film formed using a chemically amplified resist composition containing a base component having the aforementioned acid decomposable group is subjected to selective exposure, the solubility of the resist film in an organic solvent is relatively decreased at exposed portions. Thus, by conducting developing by an organic developing process, the unexposed portions are dissolved and removed, whereas the exposed portions remain as patterns, thereby forming a negative resist pattern. The negative tone-developing process is proposed, for example, in Patent Document 1. 
     Currently, resins that contain structural units derived from (meth)acrylate esters within the main chain (acrylic resins) are now widely used as base resins for resists that use ArF excimer laser lithography, as they exhibit excellent transparency in the vicinity of 193 nm (for example, see Patent Document 2). 
     As the miniaturization of resist pattern progresses, for example, lithography using electron beam or EUV is aiming the formation of a fine pattern having a size of several tens of nanometers. As the size of the resist pattern becomes smaller, further improvement in the resolution of resist materials has been demanded while maintaining excellent lithography properties and capability of forming a resist pattern with excellent shape. Further, as the pattern size becomes smaller, it becomes extremely important that the resist composition exhibits a high sensitivity to the exposure light source. Particularly in EUV lithography, since the reaction mechanism is different from that of lithography processes using other exposure light source, development of resist materials for EUV has been demanded. 
     In order to meet such demands, in recent years, there have been proposed chemically amplified resist compositions containing a resin component which has in the structure thereof an acid-generator group which generates acid upon exposure and an acid decomposable group which exhibits increased polarity by the action of acid (for example, Patent Documents 3 to 5). 
     Such a resin component has both the function as an acid generator and the function as a base component, and hence, can compose a chemically amplified resist composition by just one component. That is, when such a resin component is subjected to exposure, acid is generated from the acid-generator group in the structure thereof, and the acid decomposable group is decomposed by the generated acid, thereby forming a polar group such as a carboxy group so as to exhibit increased polarity. When a resin film (resist film) formed using such a resin component is subjected to selective exposure, the polarity of the exposed portions is increased. Thus, by conducting developing by using an alkali developing solution, the exposed portions are dissolved and removed, thereby forming a positive resist pattern. 
     DOCUMENTS OF RELATED ART 
     Patent Document 
     
         
         [Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2008-292975 
         [Patent Document 2] Japanese Unexamined Patent Application, First Publication No. 2003-241385 
         [Patent Document 3] Japanese Unexamined Patent Application, First Publication No. Hei 10-221852 
         [Patent Document 4] Japanese Unexamined Patent Application, First Publication No. 2006-045311 
         [Patent Document 5] Japanese Unexamined Patent Application, First Publication No. 2006-215526 
       
    
     SUMMARY OF THE INVENTION 
     The resist composition disclosed in Patent Document 3 is advantageous in that, by using a resin containing a group which generates acid upon exposure, an alicyclic group and an acid decomposable group in the same molecule, it exhibits an excellent compatibility as compared to a resist composition in which an acid generator is separately added. By improving the compatibility, the resolution and the like are improved. 
     The resist composition disclosed in Patent Document 4 is advantageous in that, by virtue of the resin itself having an acid-generator group, localization of the acid generator can be prevented, and the uniformity of the diffusion of the acid generator is improved. 
     By virtue of the improvement in the uniformity of the diffusion of the acid generator, it is presumed that dissociation of the acid dissociable group within the resin uniformly occurs, thereby improving the line edge roughness and the resolution. 
     The resist composition disclosed in Patent Document 5 is advantageous in that, by using a resin containing a structural unit having a sulfonium salt, the problem of the anion of the acid generator dissolving in water during immersion exposure can be solved. 
     However, these resist compositions were unsatisfactory in terms of the sensitivity and the pattern shape required in lithography using electron beam or EUV. 
     The present invention takes the above circumstances into consideration, with an object of providing a novel polymeric compound useful as a base component for a resist composition, a resist composition containing the polymeric compound, and a method of forming a resist pattern using the resist composition. 
     For solving the above-mentioned problems, the present invention employs the following aspects. 
     Specifically, a first aspect of the present invention is a resist composition including a base component (A) which generates acid upon exposure and exhibits changed solubility in a developing solution under action of acid, the base component (A) including a resin component (A1) containing a structural unit (a0-1) having a group represented by general formula (a0-1) shown below and a structural unit (a1) derived from an acrylate ester which may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent and contains an acid decomposable group which exhibits increased polarity by the action of acid. 
                         
In the formula, Q 1  represents a group containing —O—, —CH 2 —O— or —C(═O)—O—; R q1  represents a fluorine atom or a fluorinated alkyl group; Y 3  represents a linear or branched alkylene group of 1 to 4 carbon atoms; m3 represents an integer of 1 to 4; and X +  represents an organic cation.
 
     A second aspect of the present invention is a method of forming a resist pattern, including using a resist composition according to the first aspect to form a resist film on a substrate, subjecting the resist film to exposure, and subjecting the resist film to developing to form a resist pattern. 
     A third aspect of the present invention is a polymeric compound including a structural unit (a0-1) having a group represented by general formula (a0-1) shown below and a structural unit (a1) derived from an acrylate ester which may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent and contains an acid decomposable group which exhibits increased polarity by the action of acid. 
                         
In the formula, Q 1  represents a group containing —O—, —CH 2 —O— or —C(═O)—O—; R q1  represents a fluorine atom or a fluorinated alkyl group; Y 3  represents a linear or branched alkylene group of 1 to 4 carbon atoms; m3 represents an integer of 1 to 4; and X +  represents an organic cation.
 
     In the present description and claims, an “alkyl group” includes linear, branched or cyclic, monovalent saturated hydrocarbon, unless otherwise specified. 
     The term “alkylene group” includes linear, branched or cyclic divalent saturated hydrocarbon, unless otherwise specified. 
     A “lower alkyl group” is an alkyl group of 1 to 5 carbon atoms. 
     A “halogenated alkyl group” is a group in which part or all of the hydrogen atoms of an alkyl group is substituted with a halogen atom. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom. 
     The term “aliphatic” is a relative concept used in relation to the term “aromatic”, and defines a group or compound that has no aromaticity. 
     The term “structural unit” refers to a monomer unit that contributes to the formation of a polymeric compound (polymer, copolymer). 
     The term “exposure” is used as a general concept that includes irradiation with any form of radiation. 
     The term “(meth)acrylic acid” is a generic term that includes either or both of acrylic acid having a hydrogen atom bonded to the α-position and methacrylic acid having a methyl group bonded to the α-position. 
     The term “(meth)acrylate ester” is a generic term that includes either or both of the acrylate ester having a hydrogen atom bonded to the α-position and the methacrylate ester having a methyl group bonded to the α-position. 
     The term “(meth)acrylate” is a generic term that includes either or both of the acrylate having a hydrogen atom bonded to the α-position and the methacrylate having a methyl group bonded to the α-position. 
     According to the present invention, there are provided a novel polymeric compound useful as a base component for a resist composition, a resist composition containing the polymeric compound, and a method of forming a resist pattern using the resist composition. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     &lt;&lt;Resist Composition&gt;&gt; 
     The resist composition according to a first aspect of the present invention includes a base component (A) which generates acid upon exposure and exhibits changed solubility in a developing solution under action of acid (hereafter, referred to as “component (A)”). 
     When a resist film formed using the resist composition is subjected to a selective exposure, acid is generated from the component (A) at exposed portions, and the generated acid acts on the component (A) to change the solubility of the component (A) in a developing solution. On the other hand, at unexposed portions, the solubility of the component (A) in a developing solution remains unchanged, so that there is a difference between the exposed portions and the unexposed portions in terms of solubility in a developing solution. Therefore, by developing the resist film using an alkali developing solution described later, the exposed portions are dissolved and removed in the case of a positive resist pattern, whereas the unexposed portions are dissolved and removed in the case of a negative resist pattern, thereby forming a resist pattern. 
     In the present specification, a resist composition which forms a positive pattern is called a positive resist composition, and a resist composition which forms a negative pattern is called a negative resist composition. 
     In the formation of a resist pattern, the resist composition of the present invention can be applied to an alkali developing process using an alkali developing solution in the developing treatment, or a solvent developing process (negative-tone developing process) using a developing solution containing an organic solvent (organic developing solution) in the developing treatment. 
     &lt;Component (A)&gt; 
     The component (A) is a base component which generates acid upon exposure and exhibits changed solubility in a developing solution under action of acid. 
     In the present description and claims, the term “base component” refers to an organic compound capable of forming a film, and is preferably an organic compound having a molecular weight of 500 or more. When the organic compound has a molecular weight of 500 or more, the organic compound exhibits a satisfactory film-forming ability, and a resist pattern of nano level can be easily formed. 
     The “organic compound having a molecular weight of 500 or more” is broadly classified into non-polymers and polymers. 
     In general, as a non-polymer, any of those which have a molecular weight in the range of 500 to less than 4,000 is used. Hereafter, a “low molecular weight compound” refers to a non-polymer having a molecular weight in the range of 500 to less than 4,000. 
     As a polymer, any of those which have a molecular weight of 1,000 or more is generally used. In the present description and claims, the term “polymeric compound” or the term “resin” refers to a polymer having a molecular weight of 1,000 or more. 
     With respect to a polymeric compound, the “molecular weight” is the weight average molecular weight in terms of the polystyrene equivalent value determined by gel permeation chromatography (GPC). 
     [Component (A1)] 
     In the present invention, the component (A) includes a resin component (A1) (hereafter, referred to as “component (A1)”) containing a structural unit (a0-1) having a group represented by the aforementioned general formula (a0-1) and a structural unit (a1) derived from an acrylate ester which may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent and contains an acid decomposable group which exhibits increased polarity by the action of acid. 
     In the resist composition of the present invention, the component (A) includes a component (A1) which has a structural unit (a1) containing an acid decomposable group that exhibits increased polarity by the action of acid. 
     Therefore, according to the resist composition of the present invention, since the polarity of the base component changes prior to and after exposure, an excellent development contrast can be obtained not only in an alkali developing process, but also in a solvent developing process. 
     More specifically, in the case of applying an alkali developing process, the component (A) is substantially insoluble in an alkali developing solution prior to exposure, but when acid is generated from the component (A1) upon exposure, the action of this acid causes an increase in the polarity of the base component, thereby increasing the solubility of the component (A) in an alkali developing solution. Therefore, in the formation of a resist pattern, by conducting selective exposure of a resist film formed by applying the resist composition to a substrate, the exposed portions change from an insoluble state to a soluble state in an alkali developing solution, whereas the unexposed portions remain insoluble in an alkali developing solution, and hence, a positive resist pattern can be formed by alkali developing. 
     On the other hand, in the case of a solvent developing process, the component (A) exhibits high solubility in an organic developing solution prior to exposure, and when acid is generated from the component (A1) upon exposure, the polarity of the component (A) is increased by the action of the generated acid, thereby decreasing the solubility of the component (A) in an organic developing solution. Therefore, in the formation of a resist pattern, by conducting selective exposure of a resist film formed by applying the resist composition to a substrate, the exposed portions changes from an soluble state to an insoluble state in an organic developing solution, whereas the unexposed portions remain soluble in an organic developing solution. As a result, by conducting development using an organic developing solution, a contrast can be made between the exposed portions and unexposed portions, thereby enabling the formation of a negative resist pattern. 
     In the present descriptions and the claims, the expression “structural unit derived from an acrylate ester” refers to a structural unit that is formed by the cleavage of the ethylenic double bond of an acrylate ester. 
     An “acrylate ester” refers to a compound in which the terminal hydrogen atom of the carboxy group of acrylic acid (CH 2 ═CH—COOH) has been substituted with an organic group. 
     Examples of the substituent bonded to the carbon atom on the α-position in the “acrylate ester which may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent” include a halogen atom, an alkyl group of 1 to 5 carbon atoms, a halogenated alkyl group of 1 to 5 carbon atoms and a hydroxyalkyl group. 
     A carbon atom on the α-position of an acrylate ester refers to the carbon atom bonded to the carbonyl group, unless specified otherwise. 
     In the present specification, an acrylate ester in which the hydrogen atom bonded to the carbon atom on the α position has been substituted with a substituent is referred to as an “α-substituted acrylate ester”. Further, acrylate esters and α-substituted acrylate esters are collectively referred to as “(α-substituted) acrylate ester”. 
     In the α-substituted acrylate ester, examples of the halogen atom which substitutes the hydrogen atom bonded to the carbon atom on the α-position include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is particularly desirable. 
     The alkyl group which substitutes the hydrogen atom bonded to the carbon atom on the α-position is preferably a linear or branched alkyl group of 1 to 5 carbon atoms, and specific examples include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a pentyl group, an isopentyl group, and a neopentyl group. 
     Specific examples of the halogenated alkyl group which substitutes the hydrogen atom bonded to the carbon atom on the α-position include groups in which part or all of the hydrogen atoms of the aforementioned “alkyl group which substitutes the hydrogen atom bonded to the carbon atom on the α-position” are substituted with halogen atoms. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is particularly desirable. 
     Specific examples of the hydroxy alkyl group which substitutes the hydrogen atom bonded to the carbon atom on the α-position include groups in which part or all of the hydrogen atoms of the aforementioned “alkyl group which substitutes the hydrogen atom bonded to the carbon atom on the α-position” are substituted with hydroxy groups. 
     In the present invention, it is preferable that a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms is bonded to the α-position of the acrylate ester, a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a fluorinated alkyl group of 1 to 5 carbon atoms is more preferable, and in terms of industrial availability, a hydrogen atom or a methyl group is the most desirable. 
     In the resist composition of the present invention, the component (A1) has a structural unit (a0-1) and a structural unit (a1) derived from an acrylate ester which may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent and contains an acid decomposable group which exhibits increased polarity by the action of acid. 
     The component (A1) preferably includes, in addition to the structural unit (a1), at least one structural unit (a2) selected from the group consisting of a structural unit (a2 L ) derived from an acrylate ester containing a lactone-containing cyclic group and a structural unit (a2 S ) derived from an acrylate ester containing an —SO 2 — containing cyclic group, wherein the structural unit (a2) may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent. 
     In addition to the structural unit (a0-1) and the structural unit (a1) or in addition to the structural unit (a0-1), the structural unit (a1) and the structural unit (a2), it is preferable that the component (A1) further include a structural unit (a3) derived from an acrylate ester containing a polar group-containing aliphatic hydrocarbon group and may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent. 
     Further, in the present invention, the component (A1) may also include a structural unit other than the aforementioned structural units (a1) to (a3). 
     (Structural unit (a0-1)) 
     The structural unit (a0-1) is a structural unit which generates acid upon exposure. 
     The structural unit (a0-1) is not particularly limited as long as it has a group represented by general formula (a0-1) shown below, and preferable examples thereof include structural units which contain a polymerizable group capable of being copolymerized with other structural units. 
                         
In the formula, Q 1  represents a group containing —O—, —CH 2 —O— or —C(═O)—O—; R q1  represents a fluorine atom or a fluorinated alkyl group; Y 3  represents a linear or branched alkylene group of 1 to 4 carbon atoms; m3 represents an integer of 1 to 4; and X +  represents an organic cation.
 
     The group represented by the aforementioned formula (a0-1) contains a base dissociable group “—O—Y 3 —(CF 2 ) m3 —SO 3   − X + . The term “base dissociable group” refers to an organic group which can be dissociated from the structural unit (a0-1) by the action of a base. Examples of the base include alkali developing solutions generally used in the fields of lithography. That is, the “base dissociable group” refers to a group which is dissociated by the action of an alkali developing solution (for example, a 2.38% by weight aqueous solution of tetramethylammonium hydroxide (TMAH) at 23° C.). 
     A base dissociable group dissociates due to hydrolysis caused by the action of an alkali developing solution. 
     Therefore, a hydrophilic group is formed when the base dissociable group dissociates and the hydrophilicity of the component (A1) is enhanced, and hence, the compatibility of the component (A1) with the alkali developing solution is improved. 
     In the aforementioned general formula (a0-1), Q 1  represents a group containing —O—, —CH 2 —O— or —C(═O)—O—. 
     Specific examples of Q 1  include a group consisting of —O—, —CH 2 —O— or —C(═O)—O—; and a group composed of —O—, —CH 2 —O— or —C(═O)—O— and a divalent hydrocarbon group which may have a substituent. 
     A hydrocarbon “may have a substituent” means that part or all of the hydrogen atoms within the hydrocarbon group may be substituted with groups or atoms other than hydrogen. 
     The hydrocarbon group may be either an aliphatic hydrocarbon group or an aromatic hydrocarbon group. An “aliphatic hydrocarbon group” refers to a hydrocarbon group that has no aromaticity. 
     The aliphatic hydrocarbon group may be saturated or unsaturated. In general, the aliphatic hydrocarbon group is preferably saturated. 
     As specific examples of the aliphatic hydrocarbon group, a linear or branched aliphatic hydrocarbon group, and an aliphatic hydrocarbon group containing a ring in the structure thereof can be given. 
     The linear or branched aliphatic hydrocarbon group preferably has 1 to 10 carbon atoms, more preferably 1 to 8, still more preferably 1 to 5, and most preferably 1 or 2. 
     As the linear aliphatic hydrocarbon group, a linear alkylene group is preferable. Specific examples thereof include a methylene group [—CH 2 —], an ethylene group [—(CH 2 ) 2 —], a trimethylene group [—(CH 2 ) 3 —], a tetramethylene group [—(CH 2 ) 4 —] and a pentamethylene group [—(CH 2 ) 5 —]. 
     As the branched aliphatic hydrocarbon group, branched alkylene groups are preferred, and specific examples include various alkylalkylene groups, including alkylmethylene groups such as —CH(CH 3 )—, —CH(CH 2 CH 3 )—, —C(CH 3 ) 2 —, —C(CH 3 )(CH 2 CH 3 )—, —C(CH 3 )(CH 2 CH 2 CH 3 )—, and —C(CH 2 CH 3 ) 2 —; alkylethylene groups such as —CH(CH 3 )CH 2 —, —CH(CH 3 )CH(CH 3 )—, —C(CH 3 ) 2 CH 2 —, —CH(CH 2 CH 3 )CH 2 —, and —C(CH 2 CH 3 ) 2 —CH 2 —; alkyltrimethylene groups such as —CH(CH 3 )CH 2 CH 2 —, and —CH 2 CH(CH 3 )CH 2 —; and alkyltetramethylene groups such as —CH(CH 3 )CH 2 CH 2 CH 2 —, and —CH 2 CH(CH 3 )CH 2 CH 2 —. As the alkyl group within the alkylalkylene group, a linear alkyl group of 1 to 5 carbon atoms is preferable. 
     The linear or branched aliphatic hydrocarbon group (chain-like aliphatic hydrocarbon group) may or may not have a substituent. Examples of the substituent include a fluorine atom, a fluorinated alkyl group of 1 to 5 carbon atoms, and an oxygen atom (═O). 
     As examples of the hydrocarbon group containing a ring in the structure thereof, a cyclic aliphatic hydrocarbon group (a group in which two hydrogen atoms have been removed from an aliphatic hydrocarbon ring), and a group in which the cyclic aliphatic hydrocarbon group is bonded to the terminal of the aforementioned chain-like aliphatic hydrocarbon group or interposed within the aforementioned chain-like aliphatic hydrocarbon group, can be given. 
     The cyclic aliphatic hydrocarbon group preferably has 3 to 20 carbon atoms, and more preferably 3 to 12 carbon atoms. 
     The cyclic aliphatic hydrocarbon group may be either a polycyclic group or a monocyclic group. 
     As the monocyclic group, a group in which two hydrogen atoms have been removed from a monocycloalkane of 3 to 6 carbon atoms is preferable. Examples of the monocycloalkane include cyclopentane and cyclohexane. 
     As the polycyclic group, a group in which two hydrogen atoms have been removed from a polycycloalkane of 7 to 12 carbon atoms is preferable. Examples of the polycycloalkane include adamantane, norbornane, isobornane, tricyclodecane and tetracyclododecane. 
     The cyclic aliphatic hydrocarbon group may or may not have a substituent. 
     Examples of the substituent include an alkyl group of 1 to 5 carbon atoms, a fluorine atom, a fluorinated alkyl group of 1 to 5 carbon atoms, and an oxygen atom (═O). 
     Examples of aromatic hydrocarbon groups include a divalent aromatic hydrocarbon group in which one hydrogen atom has been removed from a benzene ring of a monovalent aromatic hydrocarbon group such as a phenyl group, a biphenyl group, a fluorenyl group, a naphthyl group, an anthryl group or a phenanthryl group; 
     an aromatic hydrocarbon group in which part of the carbon atoms constituting the ring of the aforementioned divalent aromatic hydrocarbon group has been substituted with a hetero atom such as an oxygen atom, a sulfur atom or a nitrogen atom; and 
     and an aromatic hydrocarbon group in which one hydrogen atom has been removed from a benzene ring of an arylalkyl group such as a benzyl group, a phenethyl group, a 1-naphthylmethyl group, a 2-naphthylmethyl group, a 1-naphthylethyl group or a 2-naphthylethyl group. 
     The aromatic hydrocarbon group may or may not have a substituent. Examples of the substituent include an alkyl group of 1 to 5 carbon atoms, a fluorine atom, a fluorinated alkyl group of 1 to 5 carbon atoms, and an oxygen atom (═O). 
     Among these examples, as the “divalent hydrocarbon group” for the “divalent hydrocarbon group which may have a substituent”, an aliphatic hydrocarbon group is preferable, and a linear or branched alkylene group is more preferable. 
     In terms of the stability in the synthesis thereof and the stability in the resist composition, Q 1  is preferably a group consisting of —C(═O)—O— and a divalent hydrocarbon group which may have a substituent, more preferably a group consisting of —C(═O)—O— and an aliphatic hydrocarbon group, and most preferably a group consisting of —C(═O)—O— and a linear or branched alkylene group. 
     As a specific example of a preferable group for Q 1 , a group represented by general formula (Q 1 -1) can be given. 
                         
In general formula (Q 1 -1), each of R q2  and R q3  independently represents a hydrogen atom, an alkyl group or a fluorinated alkyl group, wherein R q2  and R q3  may be mutually bonded to form a ring.
 
     In general formula (Q 1 -1), each of R q2  and R q3  independently represents a hydrogen atom, an alkyl group or a fluorinated alkyl group, wherein R q2  and R q3  may be mutually bonded to form a ring. 
     The alkyl group for R q2  and R q3  may be linear, branched or cyclic, and is preferably linear or branched. 
     The linear or branched alkyl group is preferably a linear or branched alkyl group of 1 to 5 carbon atoms, more preferably a methyl group or an ethyl group, and most preferably an ethyl group. 
     The cyclic alkyl group preferably has 4 to 15 carbon atoms, more preferably 4 to 12, and most preferably 5 to 10. Specific examples include groups in which one or more hydrogen atoms have been removed from a monocycloalkane or a polycycloalkane such as a bicycloalkane, tricycloalkane or tetracycloalkane. Specific examples include groups in which one or more hydrogen atoms have been removed from a monocycloalkane such as cyclopentane and cyclohexane; and groups in which one or more hydrogen atoms have been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane. Among these examples, a group in which one or more hydrogen atoms have been removed from adamantane is preferable. 
     The fluorinated alkyl group for R q2  and R q3  is an alkyl group in which part or all of the hydrogen atoms have been substituted with a fluorine atom. 
     In the fluorinated alkyl group, the alkyl group prior to being substituted with a fluorine atom may be linear, branched or cyclic, and examples thereof include the same groups as those described above for the alkyl group represented by R q2  and R q3 . 
     R q2  and R q3  may be mutually bonded to form a ring. As examples of such a ring constituted of R q2 , R q3  and the carbon atom having R q2  and R q3  bonded thereto, there can be mentioned a group in which two hydrogen atoms have been removed from a monocycloalkane or a polycycloalkane described above for the aforementioned cyclic alkyl group, preferably a 4- to 10-membered ring, and more preferably a 5- to 7-membered ring. 
     Among these examples, R q2  and R q3  preferably represent a hydrogen atom or an alkyl group. 
     In the aforementioned general formula (a0-1), R q1  represents a fluorine atom or a fluorinated alkyl group. 
     With respect to the fluorinated alkyl group for R q1 , the alkyl group prior to being fluorinated may be linear, branched or cyclic. 
     The linear or branched alkyl group preferably has 1 to 5 carbon atoms, more preferably 1 to 3 carbon atoms, and most preferably 1 or 2 carbon atoms. 
     In the fluorinated alkyl group, the percentage of the number of fluorine atoms based on the total number of hydrogen atoms and fluorine atoms (fluorination ratio (%)) is preferably 30 to 100%, and more preferably 50 to 100%. The higher the fluorination ratio, the higher the hydrophobicity of the resist film. 
     Among these, as R q1 , a fluorine atom is preferable. 
     In the aforementioned formula (a0-1), Y 3  represents a linear or branched alkylene group of 1 to 4 carbon atoms. 
     Specific examples of the linear alkylene group include a methylene group [—CH 2 —], an ethylene group [—(CH 2 ) 2 —], a trimethylene group [—(CH 2 ) 3 —] and a tetramethylene group [—(CH 2 ) 4 ]. 
     Specific examples of the branched alkylene group of 1 to 4 carbon atoms include alkylalkylene groups, e.g., an alkylmethylene group, such as —CH(CH 3 )—, —CH(CH 2 CH 3 )—, —C(CH 3 ) 2 — or —C(CH 3 )(CH 2 CH 3 )—; an alkylethylene group such as —CH(CH 3 )CH 2 —, —CH(CH 3 )CH(CH 3 )—, —C(CH 3 ) 2 CH 2 — or —CH(CH 2 CH 3 )CH 2 —; and an alkyltrimethylene group such as —CH(CH 3 )CH 2 CH 2 — or —CH 2 CH(CH 3 )CH 2 —. 
     In terms of the stability in the synthesis thereof and the stability in the resist composition, Y 3  is preferably a linear alkylene group, more preferably a methylene group [—CH 2 —] or an ethylene group [—(CH 2 ) 2 —], and a methylene group [—CH 2 —] is most preferable. 
     In the aforementioned general formula (a0-1), m3 represents an integer of 1 to 4, preferably 1 or 2, and more preferably 1. 
     In the aforementioned general formula (a0-1), X +  represents an organic cation. 
     In the aforementioned general formula (a0-1), as the organic cation for X + , there is no particular limitation, and any of those conventionally known as cation moiety for an onium salt-based acid generator can be appropriately selected for use. 
     Examples of such a cation moiety include a sulfonium cation, an iodonium cation, a phosphonium cation, a diazonium cation, an ammonium cation and a pyridinium cation. Among these, a cation moiety which is the same as those of an onium salt represented by general formula (b-1) or (b-2) described later in the explanation of the component (B) is preferable. 
     Specific examples of the group represented by the aforementioned general formula (a0-1) are shown below. 
                                                                                                 
In the formulas, m3 represents an integer of 1 to 4; and m1 represents an integer of 1 to 4.
 
     The structural unit (a0-1) is preferably a structural unit having a polymerizable group which is copolymerizable with other structural units, and more preferably a structural unit represented by general formula (a0-1-1) shown below. 
                         
In the formula, R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; Q 1  represents a group containing —O—, —CH 2 —O— or —C(═O)—O—; R q1  represents a fluorine atom or a fluorinated alkyl group; Y 3  represents a linear or branched alkylene group of 1 to 4 carbon atoms; m3 represents an integer of 1 to 4; and X +  represents an organic cation.
 
     In general formula (a0-1-1) above, the alkyl group of 1 to 5 carbon atoms or halogenated alkyl group of 1 to 5 carbon atoms for R are the same as the alkyl group of 1 to 5 carbon atoms or halogenated alkyl group of 1 to 5 carbon atoms which can be used as the substituent for the hydrogen atom bonded to the carbon atom on the α-position of the aforementioned acrylate ester. As R, a hydrogen atom or a methyl group is preferable. 
     In general formula (a0-1-1), Q 1 , R″, Y 3 , m3 and X +  are respectfully the same as defined for Q 1 , R q1 , Y 3 , m3 and X +  in the aforementioned general formula (a0-1). 
     Specific examples of structural units represented by general formula (a0-1-1) are shown below. 
                                                                                                 
In the formulas, m3 represents an integer of 1 to 4; and m1 represents an integer of 1 to 4.
 
     By virtue of the structural unit (a0-1) having an acid-generator group, the compatibility and the dispersity in the resist composition are improved, as compared to a resist composition having an acid generator separately added. 
     Further, in the structural unit (a0-1), since a relatively long side chain i.e., from Q 1  to (CF 2 ) m3  is introduced between the polymerizable group (which is copolymerizable with other structural units) and the acid-generator group, the reactivity of the resin component and the acid-generator group is improved, thereby improving the sensitivity. 
     Furthermore, since the structural unit (a0-1) has a “base dissociable group”, the resin component and the acid-generator group are dissociated during alkali developing. As a result, it is presumed that defects can be reduced. 
     Moreover, by virtue of the structural unit (a0-1) containing fluorine atom, during EUV exposure, it is presumed that generation efficiency of a secondary electron can be enhanced, thereby improving the sensitivity. 
     In the component (A1), the amount of the structural unit (a0-1) based on the combined total of all structural units constituting the component (A1) is preferably 1 to 50 mol %, more preferably 1 to 30 mol %, and still more preferably 1 to 15 mol %. When the amount of the structural unit (a0-1) is at least as large as the lower limit of the above-mentioned range, the effect of including the structural unit (a0-1) in the resist composition can be satisfactorily obtained. On the other hand, when the amount of the structural unit (a0-1) is no more than the upper limit of the above-mentioned range, a good balance can be achieved with the other structural units. 
     (Structural Unit (a1)) 
     The structural unit (a1) is a structural unit derived from an acrylate ester which may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent and contains an acid decomposable group which exhibits increased polarity by the action of acid. 
     The acid decomposable group within the structural unit (a1) is decomposed by the action of acid and changes the solubility of the entire component (A) in a developing solution. 
     The term “acid decomposable group” refers to a group in which at least a part of the bond within the structure thereof is cleaved by the action of an acid. Examples of acid decomposable groups which exhibit increased polarity by the action of an acid include groups which are decomposed by the action of an acid to form a polar group. 
     Examples of the polar group include a carboxy group, a hydroxy group, an amino group and a sulfo group (—SO 3 H). Among these, a polar group containing —OH in the structure thereof (hereafter, referred to as “OH-containing polar group”) is preferable, and a carboxy group or a hydroxy group is more preferable. 
     More specifically, as an example of an acid decomposable group, a group in which the aforementioned polar group has been protected with an acid dissociable group (such as a group in which the hydrogen atom of the OH-containing polar group has been replaced by with an acid dissociable group) can be given. 
     An “acid dissociable group” is a group in which at least the bond between the acid dissociable group and the adjacent carbon atom is cleaved by the action of acid generated from the component (A1) upon exposure. The acid dissociable group that constitutes the acid decomposable group is a group which exhibits a lower polarity than the polar group generated by the dissociation of the acid dissociable group. Thus, when the acid dissociable group is dissociated by the action of acid, a polar group exhibiting a higher polarity than that of the acid dissociable group is generated, thereby increasing the polarity. 
     As a result, the polarity of the entire base component (A) is increased. By the increase in the polarity, in the case of applying an alkali developing process, the solubility in an alkali developing solution is relatively increased. On the other hand, in the case of applying a solvent developing process, the solubility in an organic developing solution containing an organic solvent is relatively decreased. 
     Generally, as the acid dissociable group, groups that form either a cyclic or chain-like tertiary alkyl ester with the carboxyl group of the (meth)acrylic acid, and acetal-type acid dissociable groups such as alkoxyalkyl groups are widely known. 
     Here, a tertiary alkyl ester describes a structure in which an ester is formed by substituting the hydrogen atom of a carboxyl group with a chain-like or cyclic tertiary alkyl group, and a tertiary carbon atom within the chain-like or cyclic tertiary alkyl group is bonded to the oxygen atom at the terminal of the carbonyloxy group (—C(═O)—O—). In this tertiary alkyl ester, the action of acid causes cleavage of the bond between the oxygen atom and the tertiary carbon atom. 
     The chain-like or cyclic alkyl group may have a substituent. 
     Hereafter, for the sake of simplicity, groups that exhibit acid dissociability as a result of the formation of a tertiary alkyl ester with a carboxyl group are referred to as “tertiary alkyl ester-type acid dissociable groups”. 
     Examples of tertiary alkyl ester-type acid dissociable groups include aliphatic branched, acid dissociable groups and aliphatic cyclic group-containing acid dissociable groups. 
     In the present description and claims, the term “aliphatic” is a relative concept used in relation to the term “aromatic”, and defines a group or compound that has no aromaticity. 
     The term “aliphatic branched” refers to a branched structure having no aromaticity. 
     The “aliphatic branched, acid dissociable group” is not limited to be constituted of only carbon atoms and hydrogen atoms (not limited to hydrocarbon groups), but is preferably a hydrocarbon group. 
     Further, the “hydrocarbon group” may be either saturated or unsaturated, but is preferably saturated. 
     Examples of aliphatic branched, acid dissociable groups include tertiary alkyl groups of 4 to 8 carbon atoms, and specific examples include a tert-butyl group, tert-pentyl group and tert-heptyl group. 
     The term “aliphatic cyclic group” refers to a monocyclic group or polycyclic group that has no aromaticity. 
     The “aliphatic cyclic group” within the structural unit (a1) may or may not have a substituent. Examples of the substituent include an alkyl group of 1 to 5 carbon atoms, a fluorine atom, a fluorinated alkyl group of 1 to 5 carbon atoms, and an oxygen atom (═O). 
     The basic ring of the “aliphatic cyclic group” exclusive of substituents is not limited to be constituted from only carbon and hydrogen (not limited to hydrocarbon groups), but is preferably a hydrocarbon group. 
     Further, the “hydrocarbon group” may be either saturated or unsaturated, but is preferably saturated. Furthermore, the “aliphatic cyclic group” is preferably a polycyclic group. 
     As such aliphatic cyclic groups, groups in which one or more hydrogen atoms have been removed from a monocycloalkane or a polycycloalkane such as a bicycloalkane, tricycloalkane or tetracycloalkane which may or may not be substituted with an alkyl group of 1 to 5 carbon atoms, a fluorine atom or a fluorinated alkyl group, may be used. Examples of such groups include groups in which one or more hydrogen atoms have been removed from a monocycloalkane such as cyclopentane or cyclohexane; and groups in which one or more hydrogen atoms have been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane. 
     As the aliphatic cyclic group-containing acid dissociable group, for example, a group which has a tertiary carbon atom on the ring structure of the cycloalkyl group can be used. Specific examples include 2-methyl-2-adamantyl group and a 2-ethyl-2-adamantyl group. Further, groups having an aliphatic cyclic group such as an adamantyl group, cyclohexyl group, cyclopentyl group, norbornyl group, tricyclodecyl group or tetracyclododecyl group, and a branched alkylene group having a tertiary carbon atom bonded thereto, as the groups bonded to the oxygen atom of the carbonyl group (—C(O)—O—) within the structural units represented by general formulas (a1″-1) to (a1″−6) shown below, can be used. 
                                           
In the formulas, R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; and R 15  and R 16  each independently represent an alkyl group (which may be linear or branched, and preferably has 1 to 5 carbon atoms).
 
     In general formulas (a1″-1) to (a1″-6) above, the alkyl group of 1 to 5 carbon atoms or halogenated alkyl group of 1 to 5 carbon atoms for R are the same as the alkyl group of 1 to 5 carbon atoms or halogenated alkyl group of 1 to 5 carbon atoms which can be used as the substituent for the hydrogen atom bonded to the carbon atom on the α-position of the aforementioned acrylate ester. 
     An “acetal-type acid dissociable group” generally substitutes a hydrogen atom at the terminal of an alkali-soluble group such as a carboxy group or hydroxyl group, so as to be bonded with an oxygen atom. When acid is generated upon exposure, the generated acid acts to break the bond between the acetal-type acid dissociable group and the oxygen atom to which the acetal-type, acid dissociable group is bonded. 
     Examples of acetal-type acid dissociable groups include groups represented by general formula (p1) shown below. 
                         
In the formula, R 1′  and R 2′  each independently represent a hydrogen atom or an alkyl group of 1 to 5 carbon atoms; n represents an integer of 0 to 3; and Y represents an alkyl group of 1 to 5 carbon atoms or an aliphatic cyclic group.
 
     In general formula (p1) above, n is preferably an integer of 0 to 2, more preferably 0 or 1, and most preferably 0. 
     As the alkyl group of 1 to 5 carbon atoms for R 1′  and R 2′ , the same alkyl groups of 1 to 5 carbon atoms as those described above for R can be used, although a methyl group or ethyl group is preferable, and a methyl group is particularly desirable. 
     In the present invention, it is preferable that at least one of R 1′  and R 2′  be a hydrogen atom. That is, it is preferable that the acid dissociable group (p1) is a group represented by general formula (p1-1) shown below. 
                         
In the formula, R 1′  n and Y are the same as defined above.
 
     As the alkyl group of 1 to 5 carbon atoms for Y, the same alkyl groups of 1 to 5 carbon atoms as those described above can be used. 
     As the aliphatic cyclic group for Y, any of the aliphatic monocyclic/polycyclic groups which have been proposed for conventional ArF resists and the like can be appropriately selected for use. For example, the same groups described above in connection with the “aliphatic cyclic group” can be used. 
     Further, as the acetal-type, acid dissociable group, groups represented by general formula (p2) shown below can also be used. 
                         
In the formula, R 17  and R 18  each independently represent a linear or branched alkyl group or a hydrogen atom; and R 19  represents a linear, branched or cyclic alkyl group; or R 17  and R 19  each independently represents a linear or branched alkylene group, and the terminal of R 17  is bonded to the terminal of R 19  to form a ring.
 
     The alkyl group for R 17  and R 18  preferably has 1 to 15 carbon atoms, and may be either linear or branched. As the alkyl group, an ethyl group or a methyl group is preferable, and a methyl group is most preferable. 
     It is particularly desirable that either one of R 17  and R 18  be a hydrogen atom, and the other be a methyl group. 
     R 19  represents a linear, branched or cyclic alkyl group which preferably has 1 to 15 carbon atoms, and may be any of linear, branched or cyclic. 
     When R 19  represents a linear or branched alkyl group, it is preferably an alkyl group of 1 to 5 carbon atoms, more preferably an ethyl group or methyl group, and most preferably an ethyl group. 
     When R 19  represents a cycloalkyl group, it preferably has 4 to 15 carbon atoms, more preferably 4 to 12 carbon atoms, and most preferably 5 to 10 carbon atoms. As examples of the cycloalkyl group, groups in which one or more hydrogen atoms have been removed from a monocycloalkane or a polycycloalkane such as a bicycloalkane, tricycloalkane or tetracycloalkane, which may or may not be substituted with a fluorine atom or a fluorinated alkyl group, may be used. Examples of such groups include groups in which one or more hydrogen atoms have been removed from a monocycloalkane such as cyclopentane or cyclohexane; and groups in which one or more hydrogen atoms have been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane. Among these, a group in which one or more hydrogen atoms have been removed from adamantane is preferable. 
     In general formula (p2) above, R 17  and R 19  may each independently represent a linear or branched alkylene group (preferably an alkylene group of 1 to 5 carbon atoms), and the terminal of R 19  may be bonded to the terminal of R 17 . 
     In such a case, a cyclic group is formed by R′ 7 , R 19 , the oxygen atom having R 19  bonded thereto, and the carbon atom having the oxygen atom and R 17  bonded thereto. Such a cyclic group is preferably a 4- to 7-membered ring, and more preferably a 4- to 6-membered ring. Specific examples of the cyclic group include tetrahydropyranyl group and tetrahydrofuranyl group. 
     As the structural unit (a1), it is preferable to use at least one member selected from the group consisting of structural units represented by formula (a1-0-1) shown below and structural units represented by formula (a1-0-2) shown below. 
                         
In the formula, R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; and X′ represents an acid dissociable group.
 
                         
In the formula, R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; X 2  represents an acid dissociable group; and Y 2  represents a divalent linking group.
 
     In general formula (a1-O-1) above, the alkyl group of 1 to 5 carbon atoms or halogenated alkyl group of 1 to 5 carbon atoms for R are the same as the alkyl group of 1 to 5 carbon atoms or halogenated alkyl group of 1 to 5 carbon atoms which can be bonded to the α-position of the aforementioned acrylate ester. 
     X 1  is not particularly limited as long as it is an acid dissociable group. Examples thereof include the aforementioned tertiary alkyl ester-type acid dissociable groups and acetal-type acid dissociable groups, and tertiary alkyl ester-type acid dissociable groups are preferable. 
     In general formula (a1-0-2), R is the same as defined above. 
     X 2  is the same as defined for X′ in general formula (a1-O-1). 
     As the divalent linking group for Y 2 , an alkylene group, a divalent aliphatic cyclic group or a divalent linking group containing a hetero atom can be mentioned. 
     As the aliphatic cyclic group, the same as those used above in connection with the explanation of “aliphatic cyclic group” can be used, except that two hydrogen atoms have been removed therefrom. 
     When Y 2  represents an alkylene group, it preferably has 1 to 10 carbon atoms, more preferably 1 to 6, still more preferably 1 to 4, and most preferably 1 to 3. 
     When Y 2  represents a divalent aliphatic cyclic group, it is particularly desirable that the divalent aliphatic cyclic group be a group in which two or more hydrogen atoms have been removed from cyclopentane, cyclohexane, norbornane, isobornane, adamantane, tricyclodecane or tetracyclododecane. 
     When Y 2  represents a divalent linking group containing a hetero atom, examples thereof include —O—, —C(═O)—O—, —C(═O)—, —C(═O)—NH—, —NH— (H may be substituted with a substituent such as an alkyl group or an acyl group), —S—, —S(═O) 2 —O—, and “-A-O—B— (wherein 0 is an oxygen atom, and each of A and B independently represents a divalent hydrocarbon group which may have a substituent)”. 
     When Y 2  represents a divalent linking group —NH— and the H in the formula is replaced with a substituent such as an alkyl group or an acyl group, the substituent preferably has 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms, and most preferably 1 to 5 carbon atoms. 
     When Y 2  is “A-O—B”, each of A and B independently represents a divalent hydrocarbon group which may have a substituent. 
     A hydrocarbon “has a substituent” means that part or all of the hydrogen atoms within the hydrocarbon group is substituted with groups or atoms other than hydrogen atom. 
     The hydrocarbon group for A may be either an aliphatic hydrocarbon group, or an aromatic hydrocarbon group. An “aliphatic hydrocarbon group” refers to a hydrocarbon group that has no aromaticity. 
     The aliphatic hydrocarbon group for A may be either saturated or unsaturated. In general, the aliphatic hydrocarbon group is preferably saturated. 
     As specific examples of the aliphatic hydrocarbon group for A, a linear or branched aliphatic hydrocarbon group, and an aliphatic hydrocarbon group having a ring in the structure thereof can be given. 
     The linear or branched aliphatic hydrocarbon group preferably has 1 to 10 carbon atoms, more preferably 1 to 8, still more preferably 2 to 5, and most preferably 2. 
     As a linear aliphatic hydrocarbon group, a linear alkylene group is preferable, and specific examples include a methylene group, an ethylene group [—(CH 2 ) 2 —], a trimethylene group [—(CH 2 ) 3 —], a tetramethylene group [—(CH 2 ) 4 —] and a pentamethylene group [—(CH 2 ) 5 —]. 
     As the branched aliphatic hydrocarbon group, a branched alkylene group is preferable, and specific examples include alkylalkylene groups, e.g., alkylmethylene groups such as —CH(CH 3 )—, —CH(CH 2 CH 3 )—, —C(CH 3 ) 2 —, —C(CH 3 )(CH 2 CH 3 )—, —C(CH 3 )(CH 2 CH 2 CH 3 )— and —C(CH 2 CH 3 ) 2 —; alkylethylene groups such as —CH(CH 3 )CH 2 —, —CH(CH 3 )CH(CH 3 )—, —C(CH 3 ) 2 CH 2 — and —CH(CH 2 CH 3 )CH 2 —; alkyltrimethylene groups such as —CH(CH 3 )CH 2 CH 2 — and —CH 2 CH(CH 3 )CH 2 —; and alkyltetramethylene groups such as —CH(CH 3 )CH 2 CH 2 CH 2 — and —CH 2 CH(CH 3 )CH 2 CH 2 —. As the alkyl group within the alkylalkylene group, a linear alkyl group of 1 to 5 carbon atoms is preferable. 
     The linear or branched aliphatic hydrocarbon group (chain-like aliphatic hydrocarbon group) may or may not have a substituent. Examples of the substituent include a fluorine atom, a fluorinated alkyl group of 1 to 5 carbon atoms, and an oxygen atom (═O). 
     As examples of the hydrocarbon group containing a ring, a cyclic aliphatic hydrocarbon group (a group in which two hydrogen atoms have been removed from an aliphatic hydrocarbon ring), and a group in which the cyclic aliphatic hydrocarbon group is bonded to the terminal of the aforementioned chain-like aliphatic hydrocarbon group or interposed within the aforementioned chain-like aliphatic hydrocarbon group, can be given. 
     The cyclic aliphatic hydrocarbon group preferably has 3 to 20 carbon atoms, and more preferably 3 to 12 carbon atoms. 
     The cyclic aliphatic hydrocarbon group may be either a polycyclic group or a monocyclic group. As the monocyclic group, a group in which two hydrogen atoms have been removed from a monocycloalkane of 3 to 6 carbon atoms is preferable. Examples of the monocycloalkane include cyclopentane and cyclohexane. 
     As the polycyclic group, a group in which two hydrogen atoms have been removed from a polycycloalkane of 7 to 12 carbon atoms is preferable. Examples of the polycycloalkane include adamantane, norbornane, isobornane, tricyclodecane and tetracyclododecane. 
     The cyclic aliphatic hydrocarbon group may or may not have a substituent. Examples of the substituent include an alkyl group of 1 to 5 carbon atoms, a fluorine atom, a fluorinated alkyl group of 1 to 5 carbon atoms, and an oxygen atom (═O). 
     As A, a linear aliphatic hydrocarbon group is preferable, more preferably a linear alkylene group, still more preferably a linear alkylene group of 2 to 5 carbon atoms, and most preferably an ethylene group. 
     Examples of the hydrocarbon group for A include a divalent aromatic hydrocarbon group in which one hydrogen atom has been removed from a benzene ring of a monovalent aromatic hydrocarbon group such as a phenyl group, a biphenyl group, a fluorenyl group, a naphthyl group, an anthryl group or a phenanthryl group; an aromatic hydrocarbon group in which part of the carbon atoms constituting the ring of the aforementioned divalent aromatic hydrocarbon group has been substituted with a hetero atom such as an oxygen atom, a sulfur atom or a nitrogen atom; and an aromatic hydrocarbon group in which one hydrogen atom has been removed from a benzene ring of an arylalkyl group such as a benzyl group, a phenethyl group, a 1-naphthylmethyl group, a 2-naphthylmethyl group, a 1-naphthylethyl group or a 2-naphthylethyl group. 
     The aromatic hydrocarbon group may or may not have a substituent. Examples of the substituent include an alkyl group of 1 to 5 carbon atoms, a fluorine atom, a fluorinated alkyl group of 1 to 5 carbon atoms, and an oxygen atom (═O). 
     As the hydrocarbon group for B, the same divalent hydrocarbon groups as those described above for A can be used. 
     As B, a linear or branched aliphatic hydrocarbon group is preferable, and a methylene group or an alkylmethylene group is particularly desirable. 
     The alkyl group within the alkyl methylene group is preferably a linear alkyl group of 1 to 5 carbon atoms, more preferably a linear alkyl group of 1 to 3 carbon atoms, and most preferably a methyl group. 
     Specific examples of the structural unit (a1) include structural units represented by general formulas (a1-1) to (a1-4) shown below. 
                         
In the formulas, X′ represents a tertiary alkyl ester-type acid dissociable group; Y represents an alkyl group of 1 to 5 carbon atoms or an aliphatic cyclic group; n represents an integer of 0 to 3; Y 2  represents a divalent linking group; R is the same as defined above; and each of R 1′  and R 2′  independently represents a hydrogen atom or an alkyl group of 1 to 5 carbon atoms.
 
     Examples of the tertiary alkyl ester-type acid dissociable group for X′ include the same tertiary alkyl ester-type acid dissociable groups as those described above for X 1 . 
     As R 1′ , R 2′ , n and Y are respectively the same as defined for R 1′ , R 2′ , n and Yin general formula (p1) described above in connection with the “acetal-type acid dissociable group”. 
     As examples of Y 2 , the same groups as those described above for Y 2  in general formula (a1-0-2) can be given. 
     Specific examples of structural units represented by general formula (a1-1) to (a1-4) are shown below. 
     In the formulas shown below, R α  represents a hydrogen atom, a methyl group or a trifluoromethyl group. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     As the structural unit (a1), one type of structural unit may be used, or two or more types may be used in combination. 
     Among these, structural units represented by general formula (a1-1) or (a1-3) are preferable. More specifically, at least one structural unit selected from the group consisting of structural units represented by formulas (a1-1-1) to (a-1-1-4), (a1-1-16), (a1-1-17), (a1-1-20) to (a1-1-23), (a1-1-26), (a1-1-32), (a1-1-33), (a1-1-34) and (a1-3-25) to (a1-3-28) is more preferable. 
     Further, as the structural unit (a1), structural units represented by general formula (a1-1-01) shown below which includes the structural units represented by formulas (a1-1-1) to (a1-1-3), (a1-1-26) and (a1-1-34), structural units represented by general formula (a1-1-02) shown below which includes the structural units represented by formulas (a1-1-16), (a1-1-17), (a1-1-20) to (a1-1-23), (a1-1-32) and (a1-1-33), structural units represented by general formula (a1-3-01) shown below which include the structural units represented by formulas (a1-3-25) and (a1-3-26), structural units represented by general formula (a1-3-02) shown below which include the structural units represented by formulas (a1-3-27) and (a1-3-28), structural units represented by general formula (a1-3-03-1) shown below which include the structural units represented by formulas (a1-3-29) and (a1-3-31), and structural units represented by general formula (a1-3-03-2) shown below which include the structural units represented by formulas (a1-3-30) and (a1-3-32) are also preferable. 
                         
In general formula (a1-1-01), R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; and R 21  represents an alkyl group of 1 to 5 carbon atoms. In general formula (a1-1-02), R is the same as defined above; R 22  represents an alkyl group of 1 to 5 carbon atoms; and h represents an integer of 1 to 6.
 
     In general formula (a1-1-01), R is the same as defined above. 
     The alkyl group of 1 to 5 carbon atoms for R 21  is the same as defined for the alkyl group of 1 to 5 carbon atoms for R, and a methyl group, an ethyl group or an isopropyl group is preferable. 
     In general formula (a1-1-02), R is the same as defined above. 
     The alkyl group of 1 to 5 carbon atoms for R 22  is the same as defined for the alkyl group of 1 to 5 carbon atoms for R, and a methyl group, an ethyl group or an isopropyl group is preferable. h is preferably 1 or 2, and more preferably 2. 
                         
In the formula, R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; R 14  represents an alkyl group of 1 to 5 carbon atoms; R 13  represents a hydrogen atom or a methyl group; and a represents an integer of 1 to 10.
 
     
       
         
         
             
             
         
       
     
     In the formula, R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; R 14  represents an alkyl group of 1 to 5 carbon atoms; R 13  represents a hydrogen atom or a methyl group; a represents an integer of 1 to 10; and n′ represents an integer of 1 to 6. 
     In general formulas (a1-3-01) and (a1-3-02), R is the same as defined above. 
     R 13  is preferably a hydrogen atom. 
     The alkyl group of 1 to 5 carbon atoms for R 14  is the same as defined for the alkyl group of 1 to 5 carbon atoms for R, and a methyl group or an ethyl group is preferable. 
     a is preferably an integer of 1 to 8, more preferably an integer of 2 to 5, and most preferably 2. 
                         
In the formulas, R and R 24  are the same as defined above; v represents an integer of 1 to 10; w represents an integer of 1 to 10; and t represents an integer of 0 to 3.
 
     v is preferably an integer of 1 to 5, and most preferably 1 or 2. 
     w is preferably an integer of 1 to 5, and most preferably 1 or 2. 
     t is preferably an integer of 1 to 3, and most preferably 1 or 2. 
     In the component (A1), the amount of the structural unit (a1) based on the combined total of all structural units constituting the component (A1) is preferably 10 to 80 mol %, more preferably 20 to 70 mol %, and still more preferably 25 to 50 mol %. When the amount of the structural unit (a1) is at least as large as the lower limit of the above-mentioned range, a pattern can be easily formed using a resist composition prepared from the component (A1). On the other hand, when the amount of the structural unit (a1) is no more than the upper limit of the above-mentioned range, a good balance can be achieved with the other structural units. 
     Structural Unit (a2) 
     The structural unit (a2) is at least one structural unit selected from the group consisting of a structural unit derived from an acrylate ester containing and —SO 2 — containing cyclic group (hereafter, referred to as “structural unit (a2 S )) and a structural unit derived from an acrylate ester containing a lactone-containing cyclic group (hereafter, referred to as “structural unit (a2 L )), wherein the structural unit (a2) may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent. 
     By virtue of the structural unit (a2) containing a —SO 2 — containing cyclic group or a lactone-containing cyclic group, a resist composition containing the component (A1) including the structural unit (a2) is capable of improving the adhesion of a resist film to a substrate and the compatibility with the developing solution containing water, thereby contributing to improvement of lithography properties. 
     Structural Unit (a2 S ): 
     The structural unit (a2 S ) is a structural unit derived from an acrylate ester which may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent and contains an —SO 2 — containing cyclic group. 
     Here, an “—SO 2 — containing cyclic group” refers to a cyclic group having a ring containing —SO 2 — within the ring structure thereof, i.e., a cyclic group in which the sulfur atom (S) within —SO 2 — forms part of the ring skeleton of the cyclic group. The ring containing —SO 2 — within the ring skeleton thereof is counted as the first ring. A cyclic group in which the only ring structure is the ring that contains —SO 2 — in the ring skeleton thereof is referred to as a monocyclic group, and a group containing other ring structures is described as a polycyclic group regardless of the structure of the other rings. The —SO 2 — containing cyclic group may be either a monocyclic group or a polycyclic group. 
     As the —SO 2 — containing cyclic group, a cyclic group containing —O—SO 2 — within the ring skeleton thereof, i.e., a cyclic group containing a sultone ring in which —O—S— within the —O—SO 2 — group forms part of the ring skeleton thereof is particularly desirable. 
     The —SO 2 — containing cyclic group preferably has 3 to 30 carbon atoms, more preferably 4 to 20, still more preferably 4 to 15, and most preferably 4 to 12. Herein, the number of carbon atoms refers to the number of carbon atoms constituting the ring skeleton, excluding the number of carbon atoms within a substituent. 
     The —SO 2 — containing cyclic group may be either a —SO 2 — containing aliphatic cyclic group or a —SO 2 — containing aromatic cyclic group. A —SO 2 — containing aliphatic cyclic group is preferable. 
     Examples of the —SO 2 — containing aliphatic cyclic group include aliphatic cyclic groups in which part of the carbon atoms constituting the ring skeleton has been substituted with a —SO 2 — group or a —O—SO 2 — group and has at least one hydrogen atom removed from the aliphatic hydrocarbon ring. Specific examples include an aliphatic hydrocarbon ring in which a —CH 2 — group constituting the ring skeleton thereof has been substituted with a —SO 2 — group and has at least one hydrogen atom removed therefrom; and an aliphatic hydrocarbon ring in which a —CH 2 —CH 2 — group constituting the ring skeleton has been substituted with a —O—SO 2 — group and has at least one hydrogen atom removed therefrom. 
     The alicyclic hydrocarbon group preferably has 3 to 20 carbon atoms, and more preferably 3 to 12 carbon atoms. 
     The alicyclic hydrocarbon group may be either a monocyclic group or a polycyclic group. As the monocyclic group, a group in which two hydrogen atoms have been removed from a monocycloalkane of 3 to 6 carbon atoms is preferable. Examples of the monocycloalkane include cyclopentane and cyclohexane. As the polycyclic group, a group in which two hydrogen atoms have been removed from a polycycloalkane of 7 to 12 carbon atoms is preferable. Examples of the polycycloalkane include adamantane, norbornane, isobornane, tricyclodecane and tetracyclododecane. 
     The —SO 2 — containing cyclic group may have a substituent. Examples of the substituent include an alkyl group, an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxy group, an oxygen atom (═O), —COOR″, —OC(═O)R″, a hydroxyalkyl group and a cyano group. 
     The alkyl group for the substituent is preferably an alkyl group of 1 to 6 carbon atoms. Further, the alkyl group is preferably a linear alkyl group or a branched alkyl group. Specific examples include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a pentyl group, an isopentyl group, a neopentyl group and a hexyl group. Among these, a methyl group or ethyl group is preferable, and a methyl group is particularly desirable. 
     As the alkoxy group for the substituent, an alkoxy group of 1 to 6 carbon atoms is preferable. Further, the alkoxy group is preferably a linear alkoxy group or a branched alkyl group. Specific examples of the alkoxy group include the aforementioned alkyl groups for the substituent having an oxygen atom (—O—) bonded thereto. 
     Examples of the halogen atom for the substituent include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is preferable. 
     Examples of the halogenated alkyl group for the substituent include groups in which part or all of the hydrogen atoms within the aforementioned alkyl groups has been substituted with the aforementioned halogen atoms. 
     As examples of the halogenated lower alkyl group for the substituent, groups in which part or all of the hydrogen atoms of the aforementioned alkyl groups for the substituent have been substituted with the aforementioned halogen atoms can be given. As the halogenated alkyl group, a fluorinated alkyl group is preferable, and a perfluoroalkyl group is particularly desirable. 
     In the —COOR″ group and the —OC(═O)R″ group, R″ represents a hydrogen atom or a linear, branched or cyclic alkyl group of 1 to 15 carbon atoms. 
     When R″ represents a linear or branched alkyl group, it is preferably an alkyl group of 1 to 10 carbon atoms, more preferably an alkyl group of 1 to 5 carbon atoms, and most preferably a methyl group or an ethyl group. 
     When R″ is a cyclic alkyl group (cycloalkyl group), it preferably has 3 to 15 carbon atoms, more preferably 4 to 12 carbon atoms, and most preferably 5 to 10 carbon atoms. As examples of the cycloalkyl group, groups in which one or more hydrogen atoms have been removed from a monocycloalkane or a polycycloalkane such as a bicycloalkane, tricycloalkane or tetracycloalkane, which may or may not be substituted with a fluorine atom or a fluorinated alkyl group, may be used. Specific examples include groups in which one or more hydrogen atoms have been removed from a monocycloalkane such as cyclopentane and cyclohexane; and groups in which one or more hydrogen atoms have been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane. 
     The hydroxyalkyl group for the substituent preferably has 1 to 6 carbon atoms, and specific examples thereof include the aforementioned alkyl groups for the substituent in which at least one hydrogen atom has been substituted with a hydroxy group. 
     More specific examples of the —SO 2 — containing cyclic group include groups represented by general formulas (3-1) to (3-4) shown below. 
                         
In the formulas, A′ represents an oxygen atom, a sulfur atom or an alkylene group of 1 to 5 carbon atoms which may contain an oxygen atom or a sulfur atom; z represents an integer of 0 to 2; and R 27  represents an alkyl group, an alkoxy group, a halogenated alkyl group, a hydroxyl group, —COOR″, —OC(═O)R″, a hydroxyalkyl group or a cyano group, wherein R″ represents a hydrogen atom or an alkyl group.
 
     In general formulas (3-1) to (3-4) above, A′ represents an oxygen atom (—O—), a sulfur atom (—S—) or an alkylene group of 1 to 5 carbon atoms which may contain an oxygen atom or a sulfur atom. 
     As the alkylene group of 1 to 5 carbon atoms represented by A′, a linear or branched alkylene group is preferable, and examples thereof include a methylene group, an ethylene group, an n-propylene group and an isopropylene group. 
     Examples of alkylene groups that contain an oxygen atom or a sulfur atom include the aforementioned alkylene groups in which —O— or —S— is bonded to the terminal of the alkylene group or present between the carbon atoms of the alkylene group. Specific examples of such alkylene groups include —O—CH 2 —, —CH 2 —O—CH 2 —, —S—CH 2 —, —CH 2 —S—CH 2 —. 
     As A′, an alkylene group of 1 to 5 carbon atoms or —O— is preferable, more preferably an alkylene group of 1 to 5 carbon atoms, and most preferably a methylene group. 
     z represents an integer of 0 to 2, and is most preferably 0. 
     When z is 2, the plurality of R 27  may be the same or different from each other. 
     As the alkyl group, alkoxy group, halogenated alkyl group, —COOR″, —OC(═O)R″ and hydroxyalkyl group for R 27 , the same alkyl groups, alkoxy groups, halogenated alkyl groups, —COOR″, —OC(═O)R″ and hydroxyalkyl groups as those described above as the substituent for the —SO 2 — containing cyclic group can be mentioned. 
     Specific examples of the cyclic groups represented by general formulas (3-1) to (3-4) are shown below. In the formulas shown below, “Ac” represents an acetyl group. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     As the —SO 2 — containing cyclic group, a group represented by any of the aforementioned general formulas (3-1), (3-3) and (3-4) is preferable, at least one member selected from the group consisting of groups represented by the aforementioned chemical formulas (3-1-1), (3-1-18), (3-3-1) and (3-4-1) is more preferable, and a group represented by chemical formula (3-1-1) is most preferable. 
     More specific examples of the structural unit (a2 S ) include structural units represented by general formula (a2-0) shown below. 
                         
In the formula, R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; R 28  represents a —SO 2 — containing cyclic group; and R 29  represents a single bond or a divalent linking group.
 
     In genera formula (a2-0), R is the same as defined above. 
     R 28  is the same as defined for the aforementioned —SO 2 — containing group. 
     R 29  may be either a single bond or a divalent linking group. In terms of the effects of the present invention, a divalent linking group is preferable. 
     The divalent linking group for R 29  is not particularly limited. For example, the same divalent linking groups as those described for Y 2  in general formula (a1-O-2) explained above in relation to the structural unit (a1) can be mentioned. Among these, an alkylene group or a divalent linking group containing an ester bond (—C(═O)—O—) is preferable. 
     As the alkylene group, a linear or branched alkylene group is preferable. Specific examples include the same linear alkylene groups and branched alkylene groups as those described above for the aliphatic hydrocarbon group represented by Y 2 . 
     As the divalent linking group containing an ester bond, a group represented by general formula: —R 30 —C(═O)—O— (in the formula, R 30  represents a divalent linking group) is particularly desirable. That is, the structural unit (a2 S ) is preferably a structural unit represented by general formula (a2-0-1) shown below. 
                         
In the formula, R and R 28  are the same as defined above; and R 30  represents a divalent linking group.
 
     R 30  is not particularly limited. For example, the same divalent linking groups as those described for Y 2  in general formula (a1-0-2) explained above in relation to the structural unit (a1) can be mentioned. 
     As the divalent linking group for R 30 , an alkylene group, a divalent alicyclic hydrocarbon group or a divalent linking group containing a hetero atom is preferable. 
     As the linear or branched alkylene group, the divalent alicyclic hydrocarbon group and the divalent linking group containing a hetero atom, the same linear or branched alkylene group, divalent alicyclic hydrocarbon group and divalent linking group containing a hetero atom as those described above as preferable examples of Y 2  can be mentioned. 
     Among these, a linear or branched alkylene group, or a divalent linking group containing an oxygen atom as a hetero atom is more preferable. 
     As the linear alkylene group, a methylene group or an ethylene group is preferable, and a methylene group is particularly desirable. 
     As the branched alkylene group, an alkylmethylene group or an alkylethylene group is preferable, and —CH(CH 3 )—, —C(CH 3 ) 2 — or —C(CH 3 ) 2 CH 2 — is particularly desirable. 
     As the divalent linking group containing a hetero atom, a divalent linking group containing an ether bond or an ester bond is preferable, and a group represented by the aforementioned formula -A-O—B—, -[A-C(═O)—O] m —B— or -A-O—C(═O)—B— is more preferable. 
     Among these, a group represented by the formula -A-O—C(═O)—B— is preferable, and a group represented by the formula: —(CH 2 ) c —C(═O)—O—(CH 2 ) d — is particularly desirable. c represents an integer of 1 to 5, and preferably 1 or 2. d represents an integer of 1 to 5, and preferably 1 or 2. 
     In particular, as the structural unit (a2 S ), a structural unit represented by general formula (a0-1-11) or (a0-1-12) shown below is preferable, and a structural unit represented by general formula (a0-1-12) shown below is more preferable. 
                         
In the formulas, R, A′, R 27 , z and R 30  are the same as defined above.
 
     In general formula (a0-1-11), A′ is preferably a methylene group, an oxygen atom (—O—) or a sulfur atom (—S—). 
     As R 30 , a linear or branched alkylene group or a divalent linking group containing an oxygen atom is preferable. As the linear or branched alkylene group and the divalent linking group containing an oxygen atom represented by R 30 , the same linear or branched alkylene groups and the divalent linking groups containing an oxygen atom as those described above can be mentioned. 
     As the structural unit represented by general formula (a0-1-12), a structural unit represented by general formula (a0-1-12a) or (a0-1-12b) shown below is particularly desirable. 
                         
In the formulas, R and A′ are the same as defined above; and each of c to e independently represents an integer of 1 to 3.
 
     Structural Unit (a2 L ): 
     The structural unit (a2 L ) is a structural unit derived from an acrylate ester which may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent and contains a lactone-containing cyclic group. 
     The term “lactone-containing cyclic group” refers to a cyclic group including a ring containing a —O—C(O)— structure (lactone ring). The term “lactone ring” refers to a single ring containing a —O—C(O)— structure, and this ring is counted as the first ring. A lactone-containing cyclic group in which the only ring structure is the lactone ring is referred to as a monocyclic group, and groups containing other ring structures are described as polycyclic groups regardless of the structure of the other rings. The lactone-containing cyclic group may be either a monocyclic group or a polycyclic group. 
     The lactone-containing cyclic group for the structural unit (a2 L ) is not particularly limited, and an arbitrary structural unit may be used. Specific examples of lactone-containing monocyclic groups include a group in which one hydrogen atom has been removed from a 4- to 6-membered lactone ring, such as a group in which one hydrogen atom has been removed from β-propionolatone, a group in which one hydrogen atom has been removed from γ-butyrolactone, and a group in which one hydrogen atom has been removed from δ-valerolactone. Further, specific examples of lactone-containing polycyclic groups include groups in which one hydrogen atom has been removed from a lactone ring-containing bicycloalkane, tricycloalkane or tetracycloalkane. 
     Examples of the structural unit (a2 L ) include structural units represented by the aforementioned general formula (a2-0) in which the R 28  group has been substituted with a lactone-containing cyclic group. Specific examples include structural units represented by general formulas (a2-1) to (a2-5) shown below. 
                         
In the formulas, R represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms or a halogenated alkyl group of 1 to 5 carbon atoms; each R′ independently represents a hydrogen atom, an alkyl group of 1 to 5 carbon atoms, an alkoxy group of 1 to 5 carbon atoms or —COOR″, wherein R″ represents a hydrogen atom or an alkyl group; R 29  represents a single bond or a divalent linking group; s″ represents an integer of 0 to 2; A″ represents an oxygen atom, a sulfur atom or an alkylene group of 1 to 5 carbon atoms which may contain an oxygen atom or a sulfur atom; and m represents 0 or 1.
 
     In general formulas (a2-1) to (a2-5), R is the same as defined for R in the structural unit (a1). 
     Examples of the alkyl group of 1 to 5 carbon atoms for R′ include a methyl group, an ethyl group, a propyl group, an n-butyl group and a tert-butyl group. 
     Examples of the alkoxy group of 1 to 5 carbon atoms for R′ include a methoxy group, an ethoxy group, an n-propoxy group, an iso-propoxy group, an n-butoxy group and a tert-butoxy group 
     In terms of industrial availability, R′ is preferably a hydrogen atom. 
     The alkyl group for R″ may be any of linear, branched or cyclic. 
     When R″ is a linear or branched alkyl group, it preferably has 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms. 
     When R″ is a cyclic alkyl group (cycloalkyl group), it preferably has 3 to 15 carbon atoms, more preferably 4 to 12 carbon atoms, and most preferably 5 to 10 carbon atoms. As examples of the cycloalkyl group, groups in which one or more hydrogen atoms have been removed from a monocycloalkane or a polycycloalkane such as a bicycloalkane, tricycloalkane or tetracycloalkane, which may or may not be substituted with a fluorine atom or a fluorinated alkyl group, may be used. Examples of such groups include groups in which one or more hydrogen atoms have been removed from a monocycloalkane such as cyclopentane or cyclohexane; and groups in which one or more hydrogen atoms have been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane. 
     As examples of A″, the same groups as those described above for A′ in general formula (3-1) can be given. A″ is preferably an alkylene group of 1 to 5 carbon atoms, an oxygen atom (—O—) or a sulfur atom (—S—), and more preferably an alkylene group of 1 to 5 carbon atoms or —O—. As the alkylene group of 1 to 5 carbon atoms, a methylene group or a dimethylethylene group is preferable, and a methylene group is particularly desirable. 
     R 29  is the same as defined for R 29  in the aforementioned general formula (a2-0). 
     In formula (a2-1), s″ is preferably 1 or 2. 
     Specific examples of structural units represented by general formulas (a2-1) to (a2-5) are shown below. In the formulas shown below, R α  represents a hydrogen atom, a methyl group or a trifluoromethyl group. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     As the structural unit (a2 L ), at least one structural unit selected from the group consisting of formulas (a2-1) to (a2-5) is preferable, and at least one structural unit selected from the group consisting of formulas (a2-1) to (a2-3) is more preferable. 
     Specifically, it is particularly desirable to use at least one structural unit selected from the group consisting of formulas (a2-1-1), (a2-1-2), (a2-2-1), (a2-2-7), (a2-2-12), (a2-2-14), (a2-3-1) and (a2-3-5). 
     In the component (A1), as the structural unit (a2), one type of structural unit may be used, or two or more types may be used in combination. For example, as the structural unit (a2), a structural unit (a2 S ) may be used alone, or a structural unit (a2 L ), or a combination of these structural units may be used. Further, as the structural unit (a2 S ) or the structural unit (a2 L ), either a single type of structural unit may be used, or two or more types may be used in combination. 
     In the component (A1), the amount of the structural unit (a2) based on the combined total of all structural units constituting the component (A1) is preferably 1 to 80 mol %, more preferably 10 to 70 mol %, still more preferably 10 to 65 mol %, and most preferably 10 to 60 mol %. When the amount of the structural unit (a2) is at least as large as the lower limit of the above-mentioned range, the effect of using the structural unit (a2) can be satisfactorily achieved. On the other hand, when the amount of the structural unit (a2) is no more than the upper limit of the above-mentioned range, a good balance can be achieved with the other structural units, and various lithography properties such as DOF and CDU and pattern shape can be improved. 
     Structural Unit (a3) 
     The structural unit (a3) is a structural unit derived from an acrylate ester which may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent and contains a polar group-containing aliphatic hydrocarbon group. 
     In the case of applying an alkali developing process, when the component (A1) includes the structural unit (a3), the hydrophilicity of the component (A) is improved, and hence, the compatibility of the component (A) with the developing solution is improved. As a result, the alkali solubility of the exposed portions improves, which contributes to favorable improvements in the resolution. 
     Examples of the polar group include a hydroxyl group, cyano group, carboxyl group, or hydroxyalkyl group in which part of the hydrogen atoms of the alkyl group have been substituted with fluorine atoms, although a hydroxyl group is particularly desirable. 
     Examples of the aliphatic hydrocarbon group include linear or branched hydrocarbon groups (preferably alkylene groups) of 1 to 10 carbon atoms, and polycyclic aliphatic hydrocarbon groups (polycyclic groups). These polycyclic groups can be selected appropriately from the multitude of groups that have been proposed for the resins of resist compositions designed for use with ArF excimer lasers. The polycyclic group preferably has 7 to 30 carbon atoms. 
     Of the various possibilities, structural units derived from an acrylate ester that include an aliphatic polycyclic group that contains a hydroxyl group, cyano group, carboxyl group or a hydroxyalkyl group in which part of the hydrogen atoms of the alkyl group have been substituted with fluorine atoms are particularly desirable. Examples of the polycyclic group include groups in which two or more hydrogen atoms have been removed from a bicycloalkane, tricycloalkane, tetracycloalkane or the like. Specific examples include groups in which two or more hydrogen atoms have been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane. Of these polycyclic groups, groups in which two or more hydrogen atoms have been removed from adamantane, norbornane or tetracyclododecane are preferred industrially. 
     When the aliphatic hydrocarbon group within the polar group-containing aliphatic hydrocarbon group is a linear or branched hydrocarbon group of 1 to 10 carbon atoms, the structural unit (a3) is preferably a structural unit derived from a hydroxyethyl ester of acrylic acid. On the other hand, when the hydrocarbon group is a polycyclic group, structural units represented by formulas (a3-1), (a3-2), (a3-3) and (a3-4) shown below are preferable. 
                         
In the formulas, R is the same as defined above; j represents an integer of 1 to 3; j″ represents an integer of 1 to 3; k represents an integer of 1 to 3; t′ represents an integer of 1 to 3; 1 represents an integer of 1 to 5; and s represents an integer of 1 to 3.
 
     In formula (a3-1), j is preferably 1 or 2, and more preferably 1. When j is 2, it is preferable that the hydroxyl groups be bonded to the 3rd and 5th positions of the adamantyl group. When j is 1, it is preferable that the hydroxyl group be bonded to the 3rd position of the adamantyl group. 
     In formula (a3-2), k is preferably 1. The cyano group is preferably bonded to the 5th or 6th position of the norbornyl group. 
     In formula (a3-3), t′ is preferably 1. l is preferably 1. s is preferably 1. Further, in formula (a3-3), it is preferable that a 2-norbornyl group or 3-norbornyl group be bonded to the terminal of the carboxy group of the acrylic acid. The fluorinated alkyl alcohol is preferably bonded to the 5th or 6th position of the norbornyl group. 
     In the component (A1), as the structural unit (a3), one type of structural unit may be used, or two or more types may be used in combination. 
     In the component (A1), the amount of the structural unit (a3) based on the combined total of all structural units constituting the component (A1) is preferably 5 to 50 mol %, more preferably 5 to 40 mol %, and still more preferably 5 to 25 mol %. When the amount of the structural unit (a3) is at least as large as the lower limit of the above-mentioned range, the effect of using the structural unit (a3) can be satisfactorily achieved. On the other hand, when the amount of the structural unit (a3) is no more than the upper limit of the above-mentioned range, a good balance can be achieved with the other structural units. 
     Structural Unit (a4) 
     The component (A1) may also have a structural unit (a4) which is other than the above-mentioned structural units (a1) to (a3), as long as the effects of the present invention are not impaired. 
     As the structural unit (a4), any other structural unit which cannot be classified as one of the above structural units (a1) to (a3) can be used without any particular limitation, and any of the multitude of conventional structural units used within resist resins for ArF excimer lasers or KrF excimer lasers (and particularly for ArF excimer lasers) can be used. 
     Preferable examples of the structural unit (a4) include a structural unit derived from an acrylate ester which may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent and contains an acid non-dissociable aliphatic polycyclic group. Examples of this polycyclic group include the same groups as those described above in relation to the aforementioned structural unit (a1), and any of the multitude of conventional polycyclic groups used within the resin component of resist compositions for ArF excimer lasers or KrF excimer lasers (and particularly for ArF excimer lasers) can be used. 
     In consideration of industrial availability and the like, at least one polycyclic group selected from amongst a tricyclodecyl group, adamantyl group, tetracyclododecyl group, isobornyl group, and norbornyl group is particularly desirable. These polycyclic groups may be substituted with a linear or branched alkyl group of 1 to 5 carbon atoms. 
     Specific examples of the structural unit (a4) include units with structures represented by general formulas (a-4-1) to (a-4-5) shown below. 
                         
In the formulas, R is the same as defined above.
 
     When the structural unit (a4) is included in the component (A1), the amount of the structural unit (a4) based on the combined total of all the structural units that constitute the component (A1) is preferably within the range from 1 to 30 mol %, and more preferably from 10 to 20 mol %. 
     In the resist composition of the present invention, the component (A1) is preferably a polymeric compound having a structural unit (a1). 
     Examples of the component (A1) include a copolymer consisting of the structural units (a0-1), (a1) and (a2); a copolymer consisting of the structural units (a0-1), (a1), (a2) and (a3); and a copolymer consisting of the structural units (a0-1) and (a1). 
     In the component (A1), each structural unit may be constituted of a plurality of different structural units. 
     In the component (A), as the component (A1), one type of resin may be used, or two or more types of resins may be used in combination. 
     In the present invention, as the component (A1), a polymeric compound that includes a combination of structural units such as that shown below is particularly desirable. 
                         
In the formula, R 13  represents a branched alkyl group of 3 or more carbon atoms; and R, R 2 , A′, Q 1 , R q1 , Y 3  and m3 are the same as defined above, and the plurality of R may be the same or different from each other.
 
     In formula (A1-11), the branched alkyl group of 3 or more carbon atoms for R 13  is preferably an isopropyl group or a sec-butyl group, and more preferably an isopropyl group. 
                         
In the formula, R, R 2 , A′, R 13 , R 22 , Q 1 , R q1 , Y 3  and m3 are the same as defined above, and the plurality of R may be the same or different from each other.
 
     
       
         
         
             
             
         
       
     
     In the formula, R, Q 1 , R q1 , Y 3  and m3 are the same as defined above, wherein the plurality of R may be the same or different from each other; and n is the same as defined for n in the aforementioned formula (p1). 
     The component (A1) can be obtained, for example, by a conventional radical polymerization or the like of the monomers corresponding with each of the structural units, using a radical polymerization initiator such as azobisisobutyronitrile (AIBN). 
     Furthermore, in the component (A1), by using a chain transfer agent such as HS—CH 2 —CH 2 —CH 2 —C(CF 3 ) 2 —OH, a —C(CF 3 ) 2 —OH group can be introduced at the terminals of the component (A1). Such a copolymer having introduced a hydroxyalkyl group in which some of the hydrogen atoms of the alkyl group are substituted with fluorine atoms is effective in reducing developing defects and LER (line edge roughness: unevenness of the side walls of a line pattern). 
     The weight average molecular weight (Mw) (the polystyrene equivalent value determined by gel permeation chromatography) of the component (A1) is not particularly limited, but is preferably 1,000 to 50,000, more preferably 1,500 to 30,000, and most preferably 2,500 to 20,000. When the weight average molecular weight is no more than the upper limit of the above-mentioned range, the resist composition exhibits a satisfactory solubility in a resist solvent. On the other hand, when the weight average molecular weight is at least as large as the lower limit of the above-mentioned range, dry etching resistance and the cross-sectional shape of the resist pattern becomes satisfactory. 
     Further, the dispersity (Mw/Mn) of the component (A1) is preferably 1.0 to 5.0, more preferably 1.0 to 3.0, and most preferably 1.0 to 2.5. Here, Mn is the number average molecular weight. 
     In the resist composition of the present invention, the component (A) may contain “a base component which exhibits changed solubility in an alkali developing solution under action of acid” other than the component (A1). 
     Such base component other than the component (A1) is not particularly limited, and any of the multitude of conventional base components used within chemically amplified resist compositions (e.g., a novolak resin, a polyhydroxystyrene-based resin (PHS), a low molecular weight component (component (A2))) can be appropriately selected for use. 
     Examples of the component (A2) include low molecular weight compounds that have a molecular weight of at least 500 and less than 2,000, contains a hydrophilic group, and also contains an acid dissociable group described above in connection with the component (A1). Specific examples of the low molecular weight compound include compounds containing a plurality of phenol skeletons in which a part of the hydrogen atoms within hydroxyl groups have been substituted with the aforementioned acid dissociable groups. 
     In the resist composition of the present invention, as the component (A), one type may be used, or two or more types of compounds may be used in combination. 
     In the component (A), the amount of the component (A1) based on the total weight of the component (A) is preferably 25% by weight or more, more preferably 50% by weight or more, still more preferably 75% by weight or more, and may be even 100% by weight. When the amount of the component (A1) is 25% by weight or more, a resist pattern exhibiting a high resolution and a high rectangularity can be formed. 
     In the resist composition of the present invention, the amount of the component (A) can be appropriately adjusted depending on the thickness of the resist film to be formed, and the like. 
     &lt;Optional Component—Component (B)&gt; 
     The resist composition of the present invention may further include an acid-generator component (B) (hereafter, referred to as “component (B)”) which generates acid upon irradiation of radial rays. 
     When the resist composition of the present invention includes the component (B), as the component (B), there is no particular limitation, and any of the known acid generators used in conventional chemically amplified resist compositions can be used. Examples of these acid generators are numerous, and include onium salt acid generators such as iodonium salts and sulfonium salts; oxime sulfonate acid generators; diazomethane acid generators such as bisalkyl or bisaryl sulfonyl diazomethanes and poly(bis-sulfonyl)diazomethanes; nitrobenzylsulfonate acid generators; iminosulfonate acid generators; and disulfone acid generators. 
     As an onium salt acid generator, a compound represented by general formula (b-1) or (b-2) shown below can be used. 
                         
In the formulas above, R 1″  to R 3″ , R 5″  and R 6″  each independently represent an aryl group or alkyl group, wherein two of R 1″  to R 3″  may be bonded to each other to form a ring with the sulfur atom; and R 4″  represents an alkyl group, a halogenated alkyl group, an aryl group or an alkenyl group which may have a substituent, provided that at least one of R 1″  to R 3″  represents an aryl group, and at least one of R 5″  and R 6″  represents an aryl group.
 
     In formula (b-1), R 1″  to R 3″  each independently represents an aryl group or an alkyl group. In formula (b-1), two of R 1″  to R 3″  may be bonded to each other to form a ring with the sulfur atom. 
     Further, among R 1″  to R 3″ , at least one group represents an aryl group. Among R 1″  to R 3″ , two or more groups are preferably aryl groups, and it is particularly desirable that all of R 1″  to R 3″  are aryl groups. 
     The aryl group for R 1″  to R 3″  is not particularly limited. For example, an aryl group having 6 to 20 carbon atoms may be used in which part or all of the hydrogen atoms of the aryl group may or may not be substituted with alkyl groups, alkoxy groups, halogen atoms or hydroxyl groups. 
     The aryl group is preferably an aryl group having 6 to 10 carbon atoms because it can be synthesized at a low cost. Specific examples thereof include a phenyl group and a naphthyl group. 
     The alkyl group, with which hydrogen atoms of the aryl group may be substituted, is preferably an alkyl group having 1 to 5 carbon atoms, and most preferably a methyl group, an ethyl group, a propyl group, an n-butyl group, or a tert-butyl group. 
     The alkoxy group, with which hydrogen atoms of the aryl group may be substituted, is preferably an alkoxy group having 1 to 5 carbon atoms, more preferably a methoxy group, an ethoxy group, an n-propoxy group, an iso-propoxy group, an n-butoxy group or a tert-butoxy group, and most preferably a methoxy group or an ethoxy group. 
     The halogen atom, with which hydrogen atoms of the aryl group may be substituted, is preferably a fluorine atom. 
     The alkyl group for R 1″  to R 3″  is not particularly limited and includes, for example, a linear, branched or cyclic alkyl group having 1 to 10 carbon atoms. In terms of achieving excellent resolution, the alkyl group preferably has 1 to 5 carbon atoms. Specific examples thereof include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, an n-pentyl group, a cyclopentyl group, a hexyl group, a cyclohexyl group, a nonyl group, and a decyl group, and a methyl group is most preferable because it is excellent in resolution and can be synthesized at a low cost. 
     When two of R 1″  to R 3″  in formula (b-1) are bonded to each other to form a ring with the sulfur atom, it is preferable that the two of R 1″  to R 3″  form a 3 to 10-membered ring including the sulfur atom, and it is particularly desirable that the two of R 1″  to R 3 ″ form a 5 to 7-membered ring including the sulfur atom. 
     When two of R 1″  to R 3″  in formula (b-1) are bonded to each other to form a ring with the sulfur atom, the remaining one of R 1″  to R 3″  is preferably an aryl group. As examples of the aryl group, the same as the above-mentioned aryl groups for R 1″  to R 3 ″ can be given. 
     As preferable examples of the cation moiety for the compound represented by general formula (b-1), those represented by formulas (I-1-1) to (1-1-10) shown below can be given. Among these, a cation moiety having a triphenylmethane skeleton, such as a cation moiety represented by any one of formulas (I-1-1) to (1-1-8) shown below is particularly desirable. 
     In formulas (I-1-9) and (1-1-10), each of R 9  and R 10  independently represents a phenyl group or naphthyl group which may have a substituent, an alkyl group of 1 to 5 carbon atoms, an alkoxy group or a hydroxy group. 
     u is an integer of 1 to 3, and most preferably 1 or 2. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     R 4″  represents an alkyl group, a halogenated alkyl group, an aryl group or an alkenyl group which may have a substituent. 
     The alkyl group for R 4″  may be any of linear, branched or cyclic. 
     The linear or branched alkyl group preferably has 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms, and most preferably 1 to 4 carbon atoms. 
     The cyclic alkyl group preferably has 4 to 15 carbon atoms, more preferably 4 to 10 carbon atoms, and most preferably 6 to 10 carbon atoms. 
     As an example of the halogenated alkyl group for R 4 ″, a group in which part of or all of the hydrogen atoms of the aforementioned linear, branched or cyclic alkyl group have been substituted with halogen atoms can be given. Examples of the aforementioned halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is preferable. 
     In the halogenated alkyl group, the percentage of the number of halogen atoms based on the total number of halogen atoms and hydrogen atoms (halogenation ratio (%)) is preferably 10 to 100%, more preferably 50 to 100%, and most preferably 100%. Higher halogenation ratio is preferable because the acid strength increases. 
     The aryl group for R 4″  is preferably an aryl group of 6 to 20 carbon atoms. 
     The alkenyl group for R 4″  is preferably an alkenyl group of 2 to 10 carbon atoms. 
     With respect to R 4 ″, the expression “may have a substituent” means that part of or all of the hydrogen atoms within the aforementioned linear, branched or cyclic alkyl group, halogenated alkyl group, aryl group or alkenyl group may be substituted with substituents (atoms other than hydrogen atoms, or groups). 
     R 4″  may have one substituent, or two or more substituents. 
     Examples of the substituent include a halogen atom, a hetero atom, an alkyl group, and a group represented by the formula X-Q 1 - (in the formula, Q 1  represents a divalent linking group containing an oxygen atom; and X represents a hydrocarbon group of 3 to 30 carbon atoms which may have a substituent). 
     Examples of halogen atoms and alkyl groups as substituents for R 4″  include the same halogen atoms and alkyl groups as those described above with respect to the halogenated alkyl group for R 4″ . 
     Examples of hetero atoms include an oxygen atom, a nitrogen atom, and a sulfur atom. 
     In the group represented by formula X-Q 1 -, Q 1  represents a divalent linking group containing an oxygen atom. 
     Q 1  may contain an atom other than oxygen. Examples of atoms other than oxygen include a carbon atom, a hydrogen atom, a sulfur atom and a nitrogen atom. 
     Examples of divalent linking groups containing an oxygen atom include non-hydrocarbon, oxygen atom-containing linking groups such as an oxygen atom (an ether bond; —O—), an ester bond (—C(═O)—O—), an amido bond (—C(═O)—NH—), a carbonyl group (—C(═O)—) and a carbonate bond (—O—C(═O)—O—); and combinations of the aforementioned non-hydrocarbon, hetero atom-containing linking groups with an alkylene group. 
     Specific examples of the combinations of the aforementioned non-hydrocarbon, hetero atom-containing linking groups and an alkylene group include —R 91 —O—, —R 92 —O—C(═O)—, —C(═O)—O—R 93 —O—C(═O)— (in the formulas, each of R 91  to R 93  independently represents an alkylene group). 
     The alkylene group for R 91  to R 93  is preferably a linear or branched alkylene group, and preferably has 1 to 12 carbon atoms, more preferably 1 to 5, and most preferably 1 to 3. 
     Specific examples of alkylene groups include a methylene group [—CH 2 —]; alkylmethylene groups such as —CH(CH 3 )—, —CH(CH 2 CH 3 )—, —C(CH 3 ) 2 —, —C(CH 3 )(CH 2 CH 3 )—, —C(CH 3 )(CH 2 CH 2 CH 3 )— and —C(CH 2 CH 3 ) 2 —; an ethylene group [—CH 2 CH 2 —]; alkylethylene groups such as —CH(CH 3 )CH 2 —, —CH(CH 3 )CH(CH 3 )—, —C(CH 3 ) 2 CH 2 — and —CH(CH 2 CH 3 )CH 2 —; a trimethylene group (n-propylene group) [—CH 2 CH 2 CH 2 —]; alkyltrimethylene groups such as —CH(CH 3 )CH 2 CH 2 — and —CH 2 CH(CH 3 )CH 2 —; a tetramethylene group [—CH 2 CH 2 CH 2 CH 2 —]; alkyltetramethylene groups such as —CH(CH 3 )CH 2 CH 2 CH 2 — and —CH 2 CH(CH 3 )CH 2 CH 2 —; and a pentamethylene group [—CH 2 CH 2 CH 2 CH 2 CH 2 —]. 
     Q 1  is preferably a divalent linking group containing an ester linkage or ether linkage, and more preferably a group of —R 91 —O—, —R 92 —O—C(═O)— or —C(═O)—O—R 93 —O—C(═O)—. 
     In the group represented by the formula X-Q 1 -, the hydrocarbon group for X may be either an aromatic hydrocarbon group or an aliphatic hydrocarbon group. 
     The aromatic hydrocarbon group is a hydrocarbon group having an aromatic ring. The aromatic hydrocarbon ring preferably has 3 to 30 carbon atoms, more preferably 5 to 30, still more preferably 5 to 20, still more preferably 6 to 15, and most preferably 6 to 12. Here, the number of carbon atoms within a substituent(s) is not included in the number of carbon atoms of the aromatic hydrocarbon group. 
     Specific examples of aromatic hydrocarbon groups include an aryl group which is an aromatic hydrocarbon ring having one hydrogen atom removed therefrom, such as a phenyl group, a biphenyl group, a fluorenyl group, a naphthyl group, an anthryl group or a phenanthryl group; and an alkylaryl group such as a benzyl group, a phenethyl group, a 1-naphthylmethyl group, a 2-naphthylmethyl group, a 1-naphthylethyl group, or a 2-naphthylethyl group. The alkyl chain within the arylalkyl group preferably has 1 to 4 carbon atom, more preferably 1 or 2, and most preferably 1. 
     The aromatic hydrocarbon group may have a substituent. For example, part of the carbon atoms constituting the aromatic ring within the aromatic hydrocarbon group may be substituted with a hetero atom, or a hydrogen atom bonded to the aromatic ring within the aromatic hydrocarbon group may be substituted with a substituent. 
     In the former example, a heteroaryl group in which part of the carbon atoms constituting the ring within the aforementioned aryl group has been substituted with a hetero atom such as an oxygen atom, a sulfur atom or a nitrogen atom, and a heteroarylalkyl group in which part of the carbon atoms constituting the aromatic hydrocarbon ring within the aforementioned arylalkyl group has been substituted with the aforementioned heteroatom can be used. 
     In the latter example, as the substituent for the aromatic hydrocarbon group, an alkyl group, an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxyl group, an oxygen atom (═O) or the like can be used. 
     The alkyl group as the substituent for the aromatic hydrocarbon group is preferably an alkyl group of 1 to 5 carbon atoms, and a methyl group, an ethyl group, a propyl group, an n-butyl group or a tert-butyl group is particularly desirable. 
     The alkoxy group as the substituent for the aromatic hydrocarbon group is preferably an alkoxy group having 1 to 5 carbon atoms, more preferably a methoxy group, ethoxy group, n-propoxy group, iso-propoxy group, n-butoxy group or tert-butoxy group, and most preferably a methoxy group or an ethoxy group. 
     Examples of the halogen atom as the substituent for the aromatic hydrocarbon group include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is preferable. 
     Example of the halogenated alkyl group as the substituent for the aromatic hydrocarbon group includes a group in which part or all of the hydrogen atoms within the aforementioned alkyl group have been substituted with the aforementioned halogen atoms. 
     The aliphatic hydrocarbon group for X may be either a saturated aliphatic hydrocarbon group, or an unsaturated aliphatic hydrocarbon group. Further, the aliphatic hydrocarbon group may be linear, branched or cyclic. 
     In the aliphatic hydrocarbon group for X, part of the carbon atoms constituting the aliphatic hydrocarbon group may be substituted with a substituent group containing a hetero atom, or part or all of the hydrogen atoms constituting the aliphatic hydrocarbon group may be substituted with a substituent group containing a hetero atom. 
     As the “hetero atom” for X, there is no particular limitation as long as it is an atom other than carbon and hydrogen. Examples of hetero atoms include a halogen atom, an oxygen atom, a sulfur atom and a nitrogen atom. Examples of the halogen atom include a fluorine atom, a chlorine atom, an iodine atom and a bromine atom. 
     The substituent group containing a hetero atom may consist of a hetero atom, or may be a group containing a group or atom other than a hetero atom. 
     Specific examples of the substituent group for substituting part of the carbon atoms include —O—, —C(═O)—O—, —C(═O)—, —O—C(═O)—O—, —C(═O)—NH—, —NH— (the H may be replaced with a substituent such as an alkyl group or an acyl group), —S—, —S(═O) 2 — and —S(═O) 2 —O—. When the aliphatic hydrocarbon group is cyclic, the aliphatic hydrocarbon group may contain any of these substituent groups in the ring structure. 
     Examples of the substituent group for substituting part or all of the hydrogen atoms include an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxyl group, an oxygen atom (═O) and a cyano group. 
     The aforementioned alkoxy group is preferably an alkoxy group having 1 to 5 carbon atoms, more preferably a methoxy group, ethoxy group, n-propoxy group, iso-propoxy group, n-butoxy group or tert-butoxy group, and most preferably a methoxy group or an ethoxy group. 
     Examples of the aforementioned halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and a fluorine atom is preferable. 
     Example of the aforementioned halogenated alkyl group includes a group in which part or all of the hydrogen atoms within an alkyl group of 1 to 5 carbon atoms (e.g., a methyl group, an ethyl group, a propyl group, an n-butyl group or a tert-butyl group) have been substituted with the aforementioned halogen atoms. 
     As the aliphatic hydrocarbon group, a linear or branched saturated hydrocarbon group, a linear or branched monovalent unsaturated hydrocarbon group, or a cyclic aliphatic hydrocarbon group (aliphatic cyclic group) is preferable. 
     The linear saturated hydrocarbon group (alkyl group) preferably has 1 to 20 carbon atoms, more preferably 1 to 15, and most preferably 1 to 10. Specific examples 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 nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, an isotridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, an isohexadecyl group, a heptadecyl group, an octadecyl group, a nonadecyl group, an icosyl group, a henicosyl group and a docosyl group. 
     The branched saturated hydrocarbon group (alkyl group) preferably has 3 to 20 carbon atoms, more preferably 3 to 15, and most preferably 3 to 10. Specific examples include a 1-methylethyl group, a 1-methylpropyl group, a 2-methylpropyl group, a 1-methylbutyl group, a 2-methylbutyl group, a 3-methylbutyl group, a 1-ethylbutyl group, a 2-ethylbutyl group, a 1-methylpentyl group, a 2-methylpentyl group, a 3-methylpentyl group and a 4-methylpentyl group. 
     The unsaturated hydrocarbon group preferably has 2 to 10 carbon atoms, more preferably 2 to 5, still more preferably 2 to 4, and most preferably 3. Examples of linear monovalent unsaturated hydrocarbon groups include a vinyl group, a propenyl group (an allyl group) and a butynyl group. Examples of branched monovalent unsaturated hydrocarbon groups include a 1-methylpropenyl group and a 2-methylpropenyl group. 
     Among the above-mentioned examples, as the unsaturated hydrocarbon group, a propenyl group is particularly desirable. 
     The aliphatic cyclic group may be either a monocyclic group or a polycyclic group. The aliphatic cyclic group preferably has 3 to 30 carbon atoms, more preferably 5 to 30, still more preferably 5 to 20, still more preferably 6 to 15, and most preferably 6 to 12. 
     As the aliphatic cyclic group, a group in which one or more hydrogen atoms have been removed from a monocycloalkane or a polycycloalkane such as a bicycloalkane, tricycloalkane or tetracycloalkane can be used. Specific examples include groups in which one or more hydrogen atoms have been removed from a monocycloalkane such as cyclopentane or cyclohexane; and groups in which one or more hydrogen atoms have been removed from a polycycloalkane such as adamantane, norbornane, isobornane, tricyclodecane or tetracyclododecane. 
     When the aliphatic cyclic group does not contain a hetero atom-containing substituent group in the ring structure thereof, the aliphatic cyclic group is preferably a polycyclic group, more preferably a group in which one or more hydrogen atoms have been removed from a polycycloalkane, and a group in which one or more hydrogen atoms have been removed from adamantane is particularly desirable. 
     When the aliphatic cyclic group contains a hetero atom-containing substituent group in the ring structure thereof, the hetero atom-containing substituent group is preferably —O—, —C(═O)—O—, —S—, —S(═O) 2 — or —S(═O) 2 —O—. Specific examples of such aliphatic cyclic groups include groups represented by formulas (L1) to (L6) and (S1) to (S4) shown below. 
                                           
In the formula, Q″ represents an alkylene group of 1 to 5 carbon atoms, —O—, —S—, —O—R 94 — or —S—R 95 — (wherein each of R 94  and R 95  independently represents an alkylene group of 1 to 5 carbon atoms); and m represents 0 or 1.
 
     As the alkylene group for Q″, R 94  and R 95 , the same alkylene groups as those described above for R 91  to R 93  can be used. 
     In these aliphatic cyclic groups, part of the hydrogen atoms bonded to the carbon atoms constituting the ring structure may be substituted with a substituent. Examples of substituents include an alkyl group, an alkoxy group, a halogen atom, a halogenated alkyl group, a hydroxyl group and an oxygen atom (═O). 
     As the alkyl group, an alkyl group of 1 to 5 carbon atoms is preferable, and a methyl group, an ethyl group, a propyl group, an n-butyl group or a tert-butyl group is particularly desirable. 
     As the alkoxy group and the halogen atom, the same groups as the substituent groups for substituting part or all of the hydrogen atoms can be used. 
     In the present invention, as X, a cyclic group which may have a substituent is preferable. The cyclic group may be either an aromatic hydrocarbon group which may have a substituent, or an aliphatic cyclic group which may have a substituent, and an aliphatic cyclic group which may have a substituent is preferable. 
     As the aromatic hydrocarbon group, a naphthyl group which may have a substituent, or a phenyl group which may have a substituent is preferable. 
     As the aliphatic cyclic group which may have a substituent, an aliphatic polycyclic group which may have a substituent is preferable. As the aliphatic polycyclic group, the aforementioned group in which one or more hydrogen atoms have been removed from a polycycloalkane, and groups represented by the aforementioned formulas (L2) to (L6), (S3) and (S4) are preferable. 
     In the present invention, R 4″  preferably has X-Q 1 - as a substituent. In such a case, R 4″  is preferably a group represented by the formula X-Q 1 -Y 1 — (in the formula, Q 1  and X are the same as defined above; and Y 1  represents an alkylene group of 1 to 4 carbon atoms which may have a substituent, or a fluorinated alkylene group of 1 to 4 carbon atoms which may have a substituent). 
     In the group represented by the formula X-Q 1 -Y 1 —, as the alkylene group for Y 1 , the same alkylene group as those described above for Q 1  in which the number of carbon atoms is 1 to 4 can be used. 
     As the fluorinated alkylene group, the aforementioned alkylene group in which part or all of the hydrogen atoms has been substituted with fluorine atoms can be used. 
     Specific examples of Y 1  include —CF 2 —, —CF 2 CF 2 —, —CF 2 CF 2 CF 2 —, —CF(CF 3 )CF 2 —, —CF(CF 2 CF 3 )—, —C(CF 3 ) 2 —, —CF 2 CF 2 CF 2 CF 2 —, —CF(CF 3 )CF 2 CF 2 —, —CF 2 CF(CF 3 )CF 2 —, —CF(CF 3 )CF(CF 3 )—, —C(CF 3 ) 2 CF 2 —, —CF(CF 2 CF 3 )CF 2 —, —CF(CF 2 CF 2 CF 3 )—, —C(CF 3 )(CF 2 CF 3 )—; —CHF—, —CH 2 CF 2 —, —CH 2 CH 2 CF 2 —, —CH 2 CF 2 CF 2 —, —CH(CF 3 )CH 2 —, —CH(CF 2 CF 3 )—, —C(CH 3 )(CF 3 )—, —CH 2 CH 2 CH 2 CF 2 —, —CH 2 CH 2 CF 2 CF 2 —, —CH(CF 3 )CH 2 CH 2 —, —CH 2 CH(CF 3 )CH 2 —, —CH(CF 3 )CH(CF 3 )—, —C(CF 3 ) 2 CH 2 —; —CH 2 —, —CH 2 CH 2 —, —CH 2 CH 2 CH 2 —, —CH(CH 3 )CH 2 —, —CH(CH 2 CH 3 )—, —C(CH 3 ) 2 —, —CH 2 CH 2 CH 2 CH 2 —, —CH(CH 3 )CH 2 CH 2 —, —CH 2 CH(CH 3 )CH 2 —, —CH(CH 3 )CH(CH 3 )—, —C(CH 3 ) 2 CH 2 —, —CH(CH 2 CH 3 )CH 2 —, —CH(CH 2 CH 2 CH 3 )—, and —C(CH 3 )(CH 2 CH 3 )—. 
     Y 1  is preferably a fluorinated alkylene group, and particularly preferably a fluorinated alkylene group in which the carbon atom bonded to the adjacent sulfur atom is fluorinated. Examples of such fluorinated alkylene groups include —CF 2 —, —CF 2 CF 2 —, —CF 2 CF 2 CF 2 —, —CF(CF 3 )CF 2 —, —CF 2 CF 2 CF 2 CF 2 —, —CF(CF 3 )CF 2 CF 2 —, —CF 2 CF(CF 3 )CF 2 —, —CF(CF 3 )CF(CF 3 )—, —C(CF 3 ) 2 CF 2 —, —CF(CF 2 CF 3 )CF 2 —; —CH 2 CF 2 —, —CH 2 CH 2 CF 2 —, —CH 2 CF 2 CF 2 —; —CH 2 CH 2 CH 2 CF 2 —, —CH 2 CH 2 CF 2 CF 2 —, and —CH 2 CF 2 CF 2 CF 2 —. 
     Of these, —CF 2 —, —CF 2 CF 2 —, —CF 2 CF 2 CF 2 — or CH 2 CF 2 CF 2 — is preferable, —CF 2 —, —CF 2 CF 2 — or —CF 2 CF 2 CF 2 — is more preferable, and —CF 2 — is particularly desirable. 
     The alkylene group or fluorinated alkylene group may have a substituent. The alkylene group or fluorinated alkylene group “has a substituent” means that part or all of the hydrogen atoms or fluorine atoms in the alkylene group or fluorinated alkylene group has been substituted with groups other than hydrogen atoms and fluorine atoms. 
     Examples of substituents which the alkylene group or fluorinated alkylene group may have include an alkyl group of 1 to 4 carbon atoms, an alkoxy group of 1 to 4 carbon atoms, and a hydroxyl group. 
     In formula (b-2), R 5″  and R 6″  each independently represent an aryl group or alkyl group. At least one of R 5″  and R 6″  represents an aryl group. It is preferable that both of R 5″  and R 6″  represent an aryl group. 
     As the aryl group for R 5″  and R 6 ″, the same aryl groups as those described above for R 1″  to R 3″  can be used. 
     As the alkyl group for R 5″  and R 6 ″, the same alkyl groups as those described above for R 1″  to R 3″  can be used. 
     It is particularly desirable that both of R 5″  and R 6″  represents a phenyl group. 
     As R 4″  in formula (b-2), the same groups as those mentioned above for R 4″  in formula (b-1) can be used. Specific examples of suitable onium salt acid generators represented by formula (b-1) or (b-2) include diphenyliodonium trifluoromethanesulfonate or nonafluorobutanesulfonate; bis(4-tert-butylphenyl)iodonium trifluoromethanesulfonate or nonafluorobutanesulfonate; triphenylsulfonium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; tri(4-methylphenyl)sulfonium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; dimethyl(4-hydroxynaphthyl)sulfonium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; monophenyldimethylsulfonium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; diphenylmonomethylsulfonium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; (4-methylphenyl)diphenylsulfonium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; (4-methoxyphenyl)diphenylsulfonium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; tri(4-tert-butyl)phenylsulfonium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; diphenyl(1-(4-methoxy)naphthyl)sulfonium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; di(1-naphthyl)phenylsulfonium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; 1-phenyltetrahydrothiophenium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; 1-(4-methylphenyl)tetrahydrothiophenium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; 1-(3,5-dimethyl-4-hydroxyphenyl)tetrahydrothiophenium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; 1-(4-methoxynaphthalene-1-yl)tetrahydrothiophenium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; 1-(4-ethoxynaphthalene-1-yl)tetrahydrothiophenium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; 1-(4-n-butoxynaphthalene-1-yl)tetrahydrothiophenium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; 1-phenyltetrahydrothiopyranium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; 1-(4-hydroxyphenyl)tetrahydrothiopyranium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; 1-(3,5-dimethyl-4-hydroxyphenyl)tetrahydrothiopyranium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate; and 1-(4-methylphenyl)tetrahydrothiopyranium trifluoromethanesulfonate, heptafluoropropanesulfonate or nonafluorobutanesulfonate. 
     It is also possible to use onium salts in which the anion moiety of these onium salts is replaced by an alkyl sulfonate, such as methanesulfonate, n-propanesulfonate, n-butanesulfonate, n-octanesulfonate, 1-adamantanesulfonate, 2-norbonanesulfonate or d-camphor-10-sulfonate; or replaced by an aromatic sulfonate, such as benzenesulfonate, perfluorobenzenesulfonate or p-toluenesulfonate. 
     Furthermore, onium salts in which the anion moiety of these onium salts are replaced by an anion moiety represented by any one of formulas (b1) to (b8) shown below can be used. 
                         
In the formulas, p represents an integer of 1 to 3; each of q1 and q2 independently represents an integer of 1 to 5; q3 represents an integer of 1 to 12; t3 represents an integer of 1 to 3; each of r1 and r2 independently represents an integer of 0 to 3; g represents an integer of 1 to 20; R 7  represents a substituent; each of n1 to n5 independently represents 0 or 1; each of v0 to v5 independently represents an integer of 0 to 3; each of w1 to w5 independently represents an integer of 0 to 3; and Q″ is the same as defined above.
 
     As the substituent for R 7 , the same groups as those which the aforementioned aliphatic hydrocarbon group or aromatic hydrocarbon group for X may have as a substituent can be used. 
     If there are two or more of the R 7  group, as indicated by the values r1, r2, and w1 to w5, then the two or more of the R 7  groups may be the same or different from each other. 
     Further, onium salt-based acid generators in which the anion moiety in general formula (b-1) or (b-2) is replaced by an anion moiety represented by general formula (b-3) or (b-4) shown below (the cation moiety is the same as (b-1) or (b-2)) may be used. 
                         
In the formulas, X″ represents an alkylene group of 2 to 6 carbon atoms in which at least one hydrogen atom has been substituted with a fluorine atom; and each of Y″ and Z″ independently represents an alkyl group of 1 to 10 carbon atoms in which at least one hydrogen atom has been substituted with a fluorine atom.
 
     X″ represents a linear or branched alkylene group in which at least one hydrogen atom has been substituted with a fluorine atom, and the alkylene group has 2 to 6 carbon atoms, preferably 3 to 5 carbon atoms, and most preferably 3 carbon atoms. 
     Each of Y″ and Z″ independently represents a linear or branched alkyl group in which at least one hydrogen atom has been substituted with a fluorine atom, and the alkyl group has 1 to 10 carbon atoms, preferably 1 to 7 carbon atoms, and most preferably 1 to 3 carbon atoms. 
     The smaller the number of carbon atoms of the alkylene group for X″ or those of the alkyl group for Y″ and Z″ within the above-mentioned range of the number of carbon atoms, the more the solubility in a resist solvent is improved. 
     Further, in the alkylene group for X″ or the alkyl group for Y″ and Z″, it is preferable that the number of hydrogen atoms substituted with fluorine atoms is as large as possible because the acid strength increases and the transparency to high energy radiation of 200 nm or less or electron beam is improved. The fluorination ratio of the alkylene group or alkyl group is preferably from 70 to 100%, more preferably from 90 to 100%, and it is particularly desirable that the alkylene group or alkyl group be a perfluoroalkylene group or perfluoroalkyl group in which all hydrogen atoms are substituted with fluorine atoms. 
     Furthermore, as an onium salt-based acid generator, a sulfonium salt having a cation moiety represented by general formula (b-5) or (b-6) shown below may be used. 
                         
In formulas (b-5) and (b-6) above, each of R 41  to R 46  independently represents an alkyl group, an acetyl group, an alkoxy group, a carboxy group, a hydroxyl group or a hydroxyalkyl group; each of n 1  to n 5  independently represents an integer of 0 to 3; and n 6  represents an integer of 0 to 2.
 
     With respect to R 41  to R 46 , the alkyl group is preferably an alkyl group of 1 to 5 carbon atoms, more preferably a linear or branched alkyl group, and most preferably a methyl group, ethyl group, propyl group, isopropyl group, n-butyl group or tert-butyl group. 
     The alkoxy group is preferably an alkoxy group of 1 to 5 carbon atoms, more preferably a linear or branched alkoxy group, and most preferably a methoxy group or an ethoxy group. 
     The hydroxyalkyl group is preferably the aforementioned alkyl group in which one or more hydrogen atoms have been substituted with hydroxy groups, and examples thereof include a hydroxymethyl group, a hydroxyethyl group and a hydroxypropyl group. 
     If there are two or more of an individual R 41  to R 46  group, as indicated by the corresponding value of n 1  to n 6 , then the two or more of the individual R 41  to R 46  group may be the same or different from each other. 
     n 1  is preferably 0 to 2, more preferably 0 or 1, and still more preferably 0. 
     It is preferable that n 2  and n 3  each independently represent 0 or 1, and more preferably 0. 
     n 4  is preferably 0 to 2, and more preferably 0 or 1. 
     n 5  is preferably 0 or 1, and more preferably 0. 
     n 6  is preferably 0 or 1, and more preferably 1. 
     The anion moiety of the sulfonium salt having a cation moiety represented by general formula (b-5) or (b-6) is not particularly limited, and the same anion moieties for onium salt-based acid generators which have been proposed may be used. Examples of such anion moieties include fluorinated alkylsulfonic acid ions such as anion moieties (R 4″ SO 3   − ) for onium salt-based acid generators represented by general formula (b-1) or (b-2) shown above; and anion moieties represented by general formula (b-3) or (b-4) shown above. 
     In the present description, an oximesulfonate-based acid generator is a compound having at least one group represented by general formula (B-1) shown below, and has a feature of generating acid by irradiation. Such oximesulfonate acid generators are widely used for a chemically amplified resist composition, and can be appropriately selected. 
                         
In formula (B-1), each of R 31  and R 32  independently represents an organic group.
 
     The organic group for R 31  and R 32  refers to a group containing a carbon atom, and may include atoms other than carbon atoms (e.g., a hydrogen atom, an oxygen atom, a nitrogen atom, a sulfur atom, a halogen atom (such as a fluorine atom and a chlorine atom) and the like). 
     As the organic group for R 31 , a linear, branched, or cyclic alkyl group or aryl group is preferable. The alkyl group or the aryl group may have a substituent. The substituent is not particularly limited, and examples thereof include a fluorine atom and a linear, branched, or cyclic alkyl group having 1 to 6 carbon atoms. The alkyl group or the aryl group “has a substituent” means that part or all of the hydrogen atoms of the alkyl group or the aryl group is substituted with a substituent. 
     The alkyl group preferably has 1 to 20 carbon atoms, more preferably 1 to 10 carbon atoms, still more preferably 1 to 8 carbon atoms, still more preferably 1 to 6 carbon atoms, and most preferably 1 to 4 carbon atoms. As the alkyl group, a partially or completely halogenated alkyl group (hereinafter, sometimes referred to as a “halogenated alkyl group”) is particularly desirable. The “partially halogenated alkyl group” refers to an alkyl group in which part of the hydrogen atoms are substituted with halogen atoms and the “completely halogenated alkyl group” refers to an alkyl group in which all of the hydrogen atoms are substituted with halogen atoms. Examples of halogen atoms include fluorine atoms, chlorine atoms, bromine atoms and iodine atoms, and fluorine atoms are particularly desirable. In other words, the halogenated alkyl group is preferably a fluorinated alkyl group. 
     The aryl group preferably has 4 to 20 carbon atoms, more preferably 4 to 10 carbon atoms, and most preferably 6 to 10 carbon atoms. As the aryl group, partially or completely halogenated aryl group is particularly desirable. The “partially halogenated aryl group” refers to an aryl group in which some of the hydrogen atoms are substituted with halogen atoms and the “completely halogenated aryl group” refers to an aryl group in which all of hydrogen atoms are substituted with halogen atoms. 
     As R 31 , an alkyl group of 1 to 4 carbon atoms which has no substituent or a fluorinated alkyl group of 1 to 4 carbon atoms is particularly desirable. 
     As the organic group for R 32 , a linear, branched, or cyclic alkyl group, aryl group, or cyano group is preferable. Examples of the alkyl group and the aryl group for R 32  include the same alkyl groups and aryl groups as those described above for R 31 . 
     As R 32 , a cyano group, an alkyl group of 1 to 8 carbon atoms having no substituent or a fluorinated alkyl group of 1 to 8 carbon atoms is particularly desirable. 
     Preferred examples of the oxime sulfonate acid generator include compounds represented by general formula (B-2) or (B-3) shown below. 
                         
In the formula, R 33  represents a cyano group, an alkyl group having no substituent or a halogenated alkyl group; R 34  represents an aryl group; and R 35  represents an alkyl group having no substituent or a halogenated alkyl group.
 
                         
In the formula, R 36  represents a cyano group, an alkyl group having no substituent or a halogenated alkyl group; R 37  represents a divalent or trivalent aromatic hydrocarbon group; R 38  represents an alkyl group having no substituent or a halogenated alkyl group; and p″ represents 2 or 3.
 
     In general formula (B-2), the alkyl group having no substituent or the halogenated alkyl group for R 33  preferably has 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms, and most preferably 1 to 6 carbon atoms. 
     As R 33 , a halogenated alkyl group is preferable, and a fluorinated alkyl group is more preferable. 
     The fluorinated alkyl group for R 33  preferably has 50% or more of the hydrogen atoms thereof fluorinated, more preferably 70% or more, and most preferably 90% or more. 
     Examples of the aryl group for R 34  include groups in which one hydrogen atom has been removed from an aromatic hydrocarbon ring, such as a phenyl group, a biphenyl group, a fluorenyl group, a naphthyl group, an anthryl group, and a phenanthryl group, and heteroaryl groups in which some of the carbon atoms constituting the ring(s) of these groups are substituted with hetero atoms such as an oxygen atom, a sulfur atom, and a nitrogen atom. Of these, a fluorenyl group is preferable. 
     The aryl group for R 34  may have a substituent such as an alkyl group of 1 to 10 carbon atoms, a halogenated alkyl group, or an alkoxy group. The alkyl group and halogenated alkyl group as the substituent preferably has 1 to 8 carbon atoms, and more preferably 1 to 4 carbon atoms. Further, the halogenated alkyl group is preferably a fluorinated alkyl group. 
     The alkyl group having no substituent or the halogenated alkyl group for R 35  preferably has 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms, and most preferably 1 to 6 carbon atoms. 
     As R 35 , a halogenated alkyl group is preferable, and a fluorinated alkyl group is more preferable. 
     In terms of enhancing the strength of the acid generated, the fluorinated alkyl group for R 35  preferably has 50% or more of the hydrogen atoms fluorinated, more preferably 70% or more, still more preferably 90% or more. A completely fluorinated alkyl group in which 100% of the hydrogen atoms are substituted with fluorine atoms is particularly desirable. 
     In general formula (B-3), as the alkyl group having no substituent and the halogenated alkyl group for R 36 , the same alkyl group having no substituent and the halogenated alkyl group described above for R 33  can be used. 
     Examples of the divalent or trivalent aromatic hydrocarbon group for R 37  include groups in which one or two hydrogen atoms have been removed from the aryl group for R 34 . 
     As the alkyl group having no substituent or the halogenated alkyl group for R 38 , the same one as the alkyl group having no substituent or the halogenated alkyl group for R 35  can be used. 
     p″ is preferably 2. 
     Specific examples of suitable oxime sulfonate acid generators include
     α-(p-toluenesulfonyloxyimino)-benzyl cyanide,   α-(p-chlorobenzenesulfonyloxyimino)-benzyl cyanide,   α-(4-nitrobenzenesulfonyloxyimino)-benzyl cyanide,   α-(4-nitro-2-trifluoromethylbenzenesulfonyloxyimino)-benzyl cyanide,   α-(benzenesulfonyloxyimino)-4-chlorobenzyl cyanide,   α-(benzenesulfonyloxyimino)-2,4-dichlorobenzyl cyanide,   α-(benzenesulfonyloxyimino)-2,6-dichlorobenzyl cyanide,   α-(benzenesulfonyloxyimino)-4-methoxybenzyl cyanide,   α-(2-chlorobenzenesulfonyloxyimino)-4-methoxybenzyl cyanide,   α-(benzenesulfonyloxyimino)-thien-2-yl acetonitrile,   α-(4-dodecylbenzenesulfonyloxyimino)benzyl cyanide,   α-[(p-toluenesulfonyloxyimino)-4-methoxyphenyl]acetonitrile,   α-[(dodecylbenzenesulfonyloxyimino)-4-methoxyphenyl]acetonitrile,   α-(tosyloxyimino)-4-thienyl cyanide, α-(methylsulfonyloxyimino)-1-cyclopentenyl   acetonitrile, α-(methylsulfonyloxyimino)-1-cyclohexenyl acetonitrile,   α-(methylsulfonyloxyimino)-1-cycloheptenyl acetonitrile,   α-(methylsulfonyloxyimino)-1-cyclooctenyl acetonitrile,   α-(trifluoromethylsulfonyloxyimino)-1-cyclopentenyl acetonitrile,   α-(trifluoromethylsulfonyloxyimino)-cyclohexyl acetonitrile,   α-(ethylsulfonyloxyimino)-ethyl acetonitrile, α-(propylsulfonyloxyimino)-propyl   acetonitrile, α-(cyclohexylsulfonyloxyimino)-cyclopentyl acetonitrile,   α-(cyclohexylsulfonyloxyimino)-cyclohexyl acetonitrile,   α-(cyclohexylsulfonyloxyimino)-1-cyclopentenylacetonitrile,   α-(ethylsulfonyloxyimino)-1-cyclopentenyl acetonitrile,   α-(isopropylsulfonyloxyimino)-1-cyclopentenyl acetonitrile,   α-(n-butylsulfonyloxyimino)-1-cyclopentenyl acetonitrile,   α-(ethylsulfonyloxyimino)-1-cyclohexenyl acetonitrile,   α-(isopropylsulfonyloxyimino)-1-cyclohexenyl acetonitrile,   α-(n-butylsulfonyloxyimino)-1-cyclohexenyl acetonitrile,   α-(methylsulfonyloxyimino)-phenyl acetonitrile,   α-(methylsulfonyloxyimino)-p-methoxyphenyl acetonitrile,   α-(trifluoromethylsulfonyloxyimino)-phenyl acetonitrile,   α-(trifluoromethylsulfonyloxyimino)-p-methoxyphenyl acetonitrile,   α-(ethylsulfonyloxyimino)-p-methoxyphenyl acetonitrile,   α-(propylsulfonyloxyimino)-p-methylphenyl acetonitrile, and   α-(methylsulfonyloxyimino)-p-bromophenyl acetonitrile.   

     Further, oxime sulfonate acid generators disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 9-208554 (Chemical Formulas 18 and 19 shown in paragraphs [0012] to [0014]) and oxime sulfonate acid generators disclosed in WO 2004/074242A2 (Examples 1 to 40 described at pages 65 to 86) may be preferably used. 
     Furthermore, as preferable examples, the following can be used. 
     
       
         
         
             
             
         
       
     
     Of the aforementioned diazomethane acid generators, specific examples of suitable bisalkyl or bisaryl sulfonyl diazomethanes include bis(isopropylsulfonyl)diazomethane, bis(p-toluenesulfonyl)diazomethane, bis(1,1-dimethylethylsulfonyl)diazomethane, bis(cyclohexylsulfonyl)diazomethane, and bis(2,4-dimethylphenylsulfonyl)diazomethane. 
     Further, diazomethane acid generators disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 11-035551, Japanese Unexamined Patent Application, First Publication No. Hei 11-035552 and Japanese Unexamined Patent Application, First Publication No. Hei 11-035573 may be preferably used. 
     Furthermore, as examples of poly(bis-sulfonyl)diazomethanes, those disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 11-322707, including 1,3-bis(phenylsulfonyldiazomethylsulfonyl)propane, 1,4-bis(phenylsulfonyldiazomethylsulfonyl)butane, 1,6-bis(phenylsulfonyldiazomethylsulfonyl)hexane, 1,10-bis(phenylsulfonyldiazomethylsulfonyl)decane, 1,2-bis(cyclohexylsulfonyldiazomethylsulfonyl)ethane, 1,3-bis(cyclohexylsulfonyldiazomethylsulfonyl)propane, 1,6-bis(cyclohexylsulfonyldiazomethylsulfonyl)hexane, and 1,10-bis(cyclohexylsulfonyldiazomethylsulfonyl)decane, may be given. 
     As the component (B), one type of acid generator may be used, or two or more types of acid generators may be used in combination. 
     In the present invention, as the component (B), an onium salt having a fluorinated alkylsulfonic acid ion as the anion moiety is preferable. 
     When the resist composition of the present invention contains the component (B), the amount of the component (B) relative to 100 parts by weight of the component (A) is preferably 0.5 to 50 parts by weight, and more preferably 1 to 40 parts by weight. When the amount of the component (B) is within the above-mentioned range, formation of a resist pattern can be satisfactorily performed. Further, by virtue of the above-mentioned range, a uniform solution can be obtained and the storage stability becomes satisfactory. 
     &lt;Optional Component—Component (D)&gt; 
     The resist composition of the present invention may further contain a nitrogen-containing organic compound (D) (hereafter referred to as the component (D)) as an optional component. 
     As the component (D), there is no particular limitation as long as it functions as an acid diffusion control agent, i.e., a quencher which traps the acid generated from the component (A1) and the component (B) upon exposure. A multitude of these components (D) have already been proposed, and any of these known compounds may be used, although an aliphatic amine, and particularly a secondary aliphatic amine or tertiary aliphatic amine is preferable. The term “aliphatic cyclic group” refers to a monocyclic group or polycyclic group that has no aromaticity. An aliphatic amine is an amine having one or more aliphatic groups, and the aliphatic groups preferably have 1 to 20 carbon atoms. 
     Examples of these aliphatic amines include amines in which at least one hydrogen atom of ammonia (NH 3 ) has been substituted with an alkyl group or hydroxyalkyl group of no more than 20 carbon atoms (i.e., alkylamines or alkylalcoholamines), and cyclic amines. 
     Specific examples of alkylamines and alkylalcoholamines include monoalkylamines such as n-hexylamine, n-heptylamine, n-octylamine, n-nonylamine, and n-decylamine; dialkylamines such as diethylamine, di-n-propylamine, di-n-heptylamine, di-n-octylamine, and dicyclohexylamine; trialkylamines such as trimethylamine, triethylamine, tri-n-propylamine, tri-n-butylamine, tri-n-hexylamine, tri-n-pentylamine, tri-n-heptylamine, tri-n-octylamine, tri-n-nonylamine, tri-n-decylamine, and tri-n-dodecylamine; and alkyl alcohol amines such as diethanolamine, triethanolamine, diisopropanolamine, triisopropanolamine, di-n-octanolamine, tri-n-octanolamine, stearyldiethanolamine and laurildiethanolamine. Among these, trialkylamines and/or alkylalcoholamines are preferable. 
     Examples of the cyclic amine include heterocyclic compounds containing a nitrogen atom as a hetero atom. The heterocyclic compound may be a monocyclic compound (aliphatic monocyclic amine), or a polycyclic compound (aliphatic polycyclic amine). 
     Specific examples of the aliphatic monocyclic amine include piperidine, and piperazine. 
     The aliphatic polycyclic amine preferably has 6 to 10 carbon atoms, and specific examples thereof include 1,5-diazabicyclo[4.3.0]-5-nonene, 1,8-diazabicyclo[5.4.0]-7-undecene, hexamethylenetetramine, and 1,4-diazabicyclo[2.2.2]octane. 
     Examples of aromatic amines include aniline, pyridine, 4-dimethylaminopyridine, pyrrole, indole, pyrazole, imidazole and derivatives thereof, as well as diphenylamine, triphenylamine and tribenzylamine. 
     Examples of other aliphatic amines include tris(2-methoxymethoxyethyl)amine, tris{2-(2-methoxyethoxy)ethyl}amine, tris{2-(2-methoxyethoxymethoxy)ethyl}amine, tris {2-(1-methoxyethoxy)ethyl}amine, tris{2-(1-ethoxyethoxy)ethyl}amine, tris{2-(1-ethoxypropoxy)ethyl}amine and tris[2-{2-(2-hydroxyethoxy)ethoxy}ethyl]amine. 
     These compounds can be used either alone, or in combinations of two or more different compounds. 
     The component (D) is typically used in an amount within a range from 0.01 to 5.0 parts by weight, relative to 100 parts by weight of the component (A). When the amount of the component (D) is within the above-mentioned range, the shape of the resist pattern and the post exposure stability of the latent image formed by the pattern-wise exposure of the resist layer are improved. 
     &lt;Optional Component—Component (E)&gt; 
     Furthermore, in the resist composition of the present invention, for preventing any deterioration in sensitivity, and improving the resist pattern shape and the post exposure stability of the latent image formed by the pattern-wise exposure of the resist layer, at least one compound (E) (hereafter referred to as the component (E)) selected from the group consisting of an organic carboxylic acid, or a phosphorus oxo acid or derivative thereof can be added. 
     Examples of suitable organic carboxylic acids include acetic acid, malonic acid, citric acid, malic acid, succinic acid, benzoic acid, and salicylic acid. 
     Examples of phosphorus oxo acids or derivatives thereof include phosphoric acid, phosphonic acid and phosphinic acid. Among these, phosphonic acid is particularly desirable. 
     Examples of oxo acid derivatives include esters in which a hydrogen atom within the above-mentioned oxo acids is substituted with a hydrocarbon group. Examples of the hydrocarbon group include an alkyl group of 1 to 5 carbon atoms and an aryl group of 6 to 15 carbon atoms. 
     Examples of phosphoric acid derivatives include phosphoric acid esters such as di-n-butyl phosphate and diphenyl phosphate. 
     Examples of phosphonic acid derivatives include phosphonic acid esters such as dimethyl phosphonate, di-n-butyl phosphonate, phenylphosphonic acid, diphenyl phosphonate and dibenzyl phosphonate. 
     Examples of phosphinic acid derivatives include phosphinic acid esters such as phenylphosphinic acid. 
     As the component (E), one type may be used alone, or two or more types may be used in combination. 
     As the component (E), an organic carboxylic acid is preferable. 
     The component (E) is typically used in an amount within a range from 0.01 to 5.0 parts by weight, relative to 100 parts by weight of the component (A). 
     If desired, other miscible additives can also be added to the resist composition of the present invention. Examples of such miscible additives include additive resins for improving the performance of the resist film, surfactants for improving the applicability, dissolution inhibitors, plasticizers, stabilizers, colorants, halation prevention agents, and dyes. 
     &lt;Optional Component—Component (S)&gt; 
     The resist composition for immersion exposure according to the present invention can be prepared by dissolving the materials for the resist composition in an organic solvent (hereafter, frequently referred to as “component (S)”). 
     The component (S) may be any organic solvent which can dissolve the respective components to give a uniform solution, and one or more kinds of any organic solvent can be appropriately selected from those which have been conventionally known as solvents for a chemically amplified resist. 
     Examples thereof include lactones such as γ-butyrolactone; 
     ketones such as acetone, methyl ethyl ketone, cyclohexanone, methyl-n-pentyl ketone, methyl isopentyl ketone, and 2-heptanone; 
     polyhydric alcohols, such as ethylene glycol, diethylene glycol, propylene glycol and dipropylene glycol; 
     compounds having an ester bond, such as ethylene glycol monoacetate, diethylene glycol monoacetate, propylene glycol monoacetate, and dipropylene glycol monoacetate; polyhydric alcohol derivatives including compounds having an ether bond, such as a monoalkylether (e.g., monomethylether, monoethylether, monopropylether or monobutylether) or monophenylether of any of these polyhydric alcohols or compounds having an ester bond (among these, propylene glycol monomethyl ether acetate (PGMEA) and propylene glycol monomethyl ether (PGME) are preferable); 
     cyclic ethers such as dioxane; esters such as methyl lactate, ethyl lactate (EL), methyl acetate, ethyl acetate, butyl acetate, methyl pyruvate, ethyl pyruvate, methyl methoxypropionate, and ethyl ethoxypropionate; 
     and aromatic organic solvents such as anisole, ethylbenzylether, cresylmethylether, diphenylether, dibenzylether, phenetole, butylphenylether, ethylbenzene, diethylbenzene, pentylbenzene, isopropylbenzene, toluene, xylene, cymene and mesitylene. 
     These solvents can be used individually, or in combination as a mixed solvent. 
     Among these, propylene glycol monomethyl ether acetate (PGMEA), propylene glycol monomethyl ether (PGME), ethyl lactate (EL) and cyclohexanone are preferable. 
     Further, among the mixed solvents, a mixed solvent obtained by mixing PGMEA with a polar solvent is preferable. The mixing ratio (weight ratio) of the mixed solvent can be appropriately determined, taking into consideration the compatibility of the PGMEA with the polar solvent, but is preferably in the range of 1:9 to 9:1, more preferably from 2:8 to 8:2. 
     Specifically, when EL is mixed as the polar solvent, the PGMEA:EL weight ratio is preferably from 1:9 to 9:1, and more preferably from 2:8 to 8:2. Alternatively, when PGME is mixed as the polar solvent, the PGMEA:PGME weight ratio is preferably from 1:9 to 9:1, more preferably from 2:8 to 8:2, and still more preferably 3:7 to 7:3. 
     Alternatively, when cyclohexanone is mixed as the polar solvent, the PGMEA:cyclohexanone weight ratio is preferably from 1:9 to 9:1, more preferably from 2:8 to 8:2, and still more preferably 3:7 to 7:3. Further, the PGMEA:PGME:cyclohexanone weight ratio is preferably (2 to 9):(0 to 5):(0 to 4.5), and more preferably (3 to 9):(0 to 4):(0 to 3.5). 
     Further, as the component (S), a mixed solvent of at least one of PGMEA,EL and any of the aforementioned mixed solvents with γ-butyrolactone is also preferable. The mixing ratio (former:latter) of such a mixed solvent is preferably from 70:30 to 95:5. 
     The amount of the organic solvent is not particularly limited, and is appropriately adjusted to a concentration which enables coating of a coating solution to a substrate, depending on the thickness of the coating film. In general, the organic solvent is used in an amount such that the solid content of the resist composition becomes within the range from 1 to 20% by weight, and preferably from 1 to 15% by weight. 
     Dissolving of the components for a resist composition in the component (S) can be conducted by simply mixing and stirring each of the above components together using conventional methods, and where required, the composition may also be mixed and dispersed using a dispersion device such as a dissolver, a homogenizer, or a triple roll mill. Furthermore, following mixing, the composition may also be filtered using a mesh, or a membrane filter or the like. 
     According to the resist composition of the present invention, a resist film can be formed which is capable of forming a resist pattern with improved pattern shape. Furthermore, according to the resist composition of the present invention, lithography properties such as sensitivity and the like are excellent. 
     The reason why these effects can be achieved has not been elucidated yet, but is presumed as follows. Firstly, in the present invention, the component (A1) has a structural unit (a0-1) which generates acid upon exposure. As a result, the structural unit (a0-1) is uniformly distributed within the resist film together with the component (A1). It is presumed that acid is uniformly generated from the structural unit (a0-1) at exposed portions, so that the acid decomposable groups within the component (A1) are uniformly dissociated at exposed portions, thereby improving the pattern shape. Further, in the structural unit (a0-1), by virtue of a relatively long side chain being introduced between the polymerizable group (which is copolymerizable with other structural units) and the acid-generator group, the reactivity of the resin component and the acid-generator group is improved, thereby improving the lithography properties such as sensitivity. 
     Furthermore, by virtue of the structural unit (a0-1) containing fluorine atom, during EUV exposure, it is presumed that generation efficiency of a secondary electron can be enhanced, thereby improving the sensitivity. 
     Secondly, since the structural unit (a1) containing an acid dissociable group and a structural unit (a0-2) which generates acid upon exposure are copolymerized, diffusion of acid generated upon exposure can be suppressed. Further, the structural unit (a0-1) contains a base dissociable group —O—Y—(CF 2 ) m3 —SO 3   − X + . The “base dissociable group” is hydrolyzed by the action of an alkali developing solution to form a hydrophilic group. Therefore, it is presumed that the affinity of the component (A1) for the alkali developing solution is enhanced, thereby reducing defects. 
     &lt;&lt;Method of Forming a Resist Pattern&gt;&gt; 
     Next, a method of forming a resist pattern according to a second aspect of the present invention will be described. 
     The method of forming a resist pattern according to the present invention includes forming a resist film using a resist composition according to the first aspect, subjecting the resist film to exposure, and subjecting the resist film to developing to form a resist pattern. 
     The method for forming a resist pattern according to the present invention can be performed, for example, as follows. 
     Firstly, a resist composition of the present invention is applied to a substrate using a spinner or the like, and a bake treatment (post applied bake (PAB)) is conducted at a temperature of 80 to 150° C. for 40 to 120 seconds, preferably 60 to 90 seconds, to form a resist film. 
     Following selective exposure of the thus formed resist film, either by exposure through a mask having a predetermined pattern formed thereon (mask pattern) using an exposure apparatus such as an ArF exposure apparatus, an electron beam lithography apparatus or an EUV exposure apparatus, or by patterning via direct irradiation with an electron beam without using a mask pattern, baking treatment (post exposure baking (PEB)) is conducted under temperature conditions of 80 to 150° C. for 40 to 120 seconds, and preferably 60 to 90 seconds. 
     Next, the resist film is subjected to a developing treatment. 
     The developing treatment is conducted using an alkali developing solution in the case of an alkali developing process, and a developing solution containing an organic solvent (organic developing solution) in the case of a solvent developing process. 
     After the developing treatment, it is preferable to conduct a rinse treatment. 
     The rinse treatment is preferably conducted using pure water in the case of an alkali developing process, and a rinse solution containing an organic solvent in the case of a solvent developing process. 
     In the case of a solvent developing process, after the developing treatment or the rinsing, the developing solution or the rinse liquid remaining on the pattern can be removed by a treatment using a supercritical fluid. 
     After the developing treatment or the rinse treatment, drying is conducted. If desired, bake treatment (post bake) can be conducted following the developing. In this manner, a resist pattern can be obtained. 
     The substrate is not specifically limited and a conventionally known substrate can be used. For example, substrates for electronic components, and such substrates having wiring patterns formed thereon can be used. Specific examples of the material of the substrate include metals such as silicon wafer, copper, chromium, iron and aluminum; and glass. Suitable materials for the wiring pattern include copper, aluminum, nickel, and gold. 
     Further, as the substrate, any one of the above-mentioned substrates provided with an inorganic and/or organic film on the surface thereof may be used. As the inorganic film, an inorganic antireflection film (inorganic BARC) can be used. As the organic film, an organic antireflection film (organic BARC) and an organic film such as a lower-layer organic film used in a multilayer resist method can be used. 
     Here, a “multilayer resist method” is method in which at least one layer of an organic film (lower-layer organic film) and at least one layer of a resist film (upper resist film) are provided on a substrate, and a resist pattern formed on the upper resist film is used as a mask to conduct patterning of the lower-layer organic film. This method is considered as being capable of forming a pattern with a high aspect ratio. More specifically, in the multilayer resist method, a desired thickness can be ensured by the lower-layer organic film, and as a result, the thickness of the resist film can be reduced, and an extremely fine pattern with a high aspect ratio can be formed. 
     The multilayer resist method is broadly classified into a method in which a double-layer structure consisting of an upper-layer resist film and a lower-layer organic film is formed (double-layer resist method), and a method in which a multilayer structure having at least three layers consisting of an upper-layer resist film, a lower-layer organic film and at least one intermediate layer (thin metal film or the like) provided between the upper-layer resist film and the lower-layer organic film (triple-layer resist method). 
     The wavelength to be used for exposure is not particularly limited and the exposure can be conducted using radiation such as ArF excimer laser, KrF excimer laser, F 2  excimer laser, extreme ultraviolet rays (EUV), vacuum ultraviolet rays (VUV), electron beam (EB), X-rays, and soft X-rays. The resist composition of the present invention is effective to KrF excimer laser, ArF excimer laser, EB and EUV. 
     The exposure of the resist film can be either a general exposure (dry exposure) conducted in air or an inert gas such as nitrogen, or immersion exposure (immersion lithography). 
     In immersion lithography, the region between the resist film and the lens at the lowermost point of the exposure apparatus is pre-filled with a solvent (immersion medium) that has a larger refractive index than the refractive index of air, and the exposure (immersion exposure) is conducted in this state. 
     The immersion medium preferably exhibits a refractive index larger than the refractive index of air but smaller than the refractive index of the resist film to be exposed. The refractive index of the immersion medium is not particularly limited as long at it satisfies the above-mentioned requirements. 
     Examples of this immersion medium which exhibits a refractive index that is larger than the refractive index of air but smaller than the refractive index of the resist film include water, fluorine-based inert liquids, silicon-based solvents and hydrocarbon-based solvents. 
     Specific examples of the fluorine-based inert liquids include liquids containing a fluorine-based compound such as C 3 HCl 2 F 5 , C 4 F 9 OCH 3 , C 4 F 9 OC 2 H 5  or C 5 H 3 F 7  as the main component, which have a boiling point within a range from 70 to 180° C. and preferably from 80 to 160° C. A fluorine-based inert liquid having a boiling point within the above-mentioned range is advantageous in that the removal of the immersion medium after the exposure can be conducted by a simple method. 
     As a fluorine-based inert liquid, a perfluoroalkyl compound in which all of the hydrogen atoms of the alkyl group are substituted with fluorine atoms is particularly desirable. Examples of these perfluoroalkyl compounds include perfluoroalkylether compounds and perfluoroalkylamine compounds. 
     Specifically, one example of a suitable perfluoroalkylether compound is perfluoro(2-butyl-tetrahydrofuran) (boiling point 102° C.), and an example of a suitable perfluoroalkylamine compound is perfluorotributylamine (boiling point 174° C.). 
     As the immersion medium, water is preferable in terms of cost, safety, environment and versatility. 
     As an example of the alkali developing solution used in an alkali developing process, a 0.1 to 10% by weight aqueous solution of tetramethylammonium hydroxide (TMAH) can be given. 
     As the organic solvent contained in the organic developing solution used in a solvent developing process, any of the conventional organic solvents can be used which are capable of dissolving the component (A) (prior to exposure). Specific examples of the organic solvent include polar solvents such as ketone solvents, ester solvents, alcohol solvents, amide solvents and ether solvents, and hydrocarbon solvents. 
     If desired, the developing solution may have a conventional additive blended. Examples of the additive include surfactants. The surfactant is not particularly limited, and for example, an ionic or non-ionic fluorine and/or silicon surfactant can be used. 
     When a surfactant is added, the amount thereof based on the total amount of the developing solution is generally 0.001 to 5% by weight, preferably 0.005 to 2% by weight, and more preferably 0.01 to 0.5% by weight. 
     The developing treatment can be performed by a conventional developing method. Examples thereof include a method in which the substrate is immersed in the developing solution for a predetermined time (a dip method), a method in which the developing solution is cast up on the surface of the substrate by surface tension and maintained for a predetermined period (a puddle method), a method in which the developing solution is sprayed onto the surface of the substrate (spray method), and a method in which the developing solution is continuously ejected from a developing solution ejecting nozzle while scanning at a constant rate to apply the developing solution to the substrate while rotating the substrate at a constant rate (dynamic dispense method). 
     As the organic solvent contained in the rinse liquid used in the rinse treatment after the developing treatment in the case of a solvent developing process, any of the aforementioned organic solvents contained in the developing solution can be used which hardly dissolves the resist pattern. In general, at least one solvent selected from the group consisting of hydrocarbon solvents, ketone solvents, ester solvents, alcohol solvents, amide solvents and ether solvents is used. Among these, at least one solvent selected from the group consisting of hydrocarbon solvents, ketone solvents, ester solvents, alcohol solvents and amide solvents is preferable, more preferably at least one solvent selected from the group consisting of alcohol solvents and ester solvents, and an alcohol solvent is particularly desirable. 
     The rinse treatment (washing treatment) using the rinse liquid can be performed by a conventional rinse method. Examples thereof include a method in which the rinse liquid is continuously applied to the substrate while rotating it at a constant rate (rotational coating method), a method in which the substrate is immersed in the rinse liquid for a predetermined time (dip method), and a method in which the rinse liquid is sprayed onto the surface of the substrate (spray method). 
     &lt;&lt;Polymeric Compound&gt;&gt; 
     The polymeric compound according to a third aspect of the present invention includes a structural unit (a0-1) having a group represented by general formula (a0-1) shown below and a structural unit (a1) derived from an acrylate ester which may have the hydrogen atom bonded to the carbon atom on the α-position substituted with a substituent and contains an acid decomposable group which exhibits increased polarity by the action of acid. The explanation of the polymeric compound of the present invention is the same as the explanation of the component (A1) of the resist composition described above. 
                         
In the formula, Q 1  represents a group containing —O—, —CH 2 —O— or —C(═O)—O—; R q1  represents a fluorine atom or a fluorinated alkyl group; Y 3  represents a linear or branched alkylene group of 1 to 4 carbon atoms; m3 represents an integer of 1 to 4; and X +  represents an organic cation.
 
     The polymeric compound of the present invention (hereafter, referred to as “polymeric compound (A1)”) may be used as the component (A1) of the aforementioned resist composition. Alternatively, the polymeric compound (A1) may be used as an additive separately from the polymeric compound contained in the base component of a resist composition. 
     When the polymeric compound (A1) is used as an additive, the resist composition (hereafter, referred to as the “second resist composition”) preferably includes the polymeric compound (A1) and a base component (A′) which exhibits changed solubility in a developing solution by the action of acid (provided that the polymeric compound (A1) is excluded, hereafter referred to as “component (A′)”). 
     In the second resist composition, when radial rays are irradiated (when exposure is conducted), acid is generated from the polymeric compound (A1), and the solubility of the component (A′) in a developing solution is changed by the action of the generated acid. Therefore, in the case of an alkali developing process, in the formation of a resist pattern, by conducting selective exposure of a resist film formed by using the resist composition of the present invention, the solubility of the exposed portions in an alkali developing solution is increased, whereas the solubility of the unexposed portions in an alkali developing solution is unchanged, and hence, a resist pattern can be formed by alkali developing. 
     In the present invention, it is preferable to use the polymeric compound (A1) including a structural unit (a0-1) having a fluorine atom as an additive of a resist composition for immersion exposure. By virtue of the structural unit (a0-1) having a fluorine atom, when the resist composition is applied to a substrate, surface segregation of the resist composition containing the polymeric compound (A1) occurs, and the resist film exhibits an excellent hydrophobicity during immersion exposure. Therefore, the resist composition exhibits an excellent water tracking ability which is required when immersion exposure is conducted using a scanning-type immersion exposure apparatus. 
     When a polymeric compound (A1) containing a structural unit (a0-1) having a fluorine atom is used as an additive, the polymeric compound (A1) is mixed and dissolved in other components such as the component (A′) to form a resist film on a substrate, and the additive is distributed on the surface layer of the resist film by the action of the fluorine atom. The polymeric compound (A1) distributed on the surface layer of the resist film generates acid from the structural unit (a0-1) upon exposure, and the acid concentration on the resist film surface becomes high. As a result, the deprotection ratio on the resist film surface is improved, so that deterioration of the resist pattern shape caused by insufficient deprotection on the film surface can be reduced. Specifically, it is presumed that bridge defects (connection of patterns) can be reduced in the case of a line and space pattern, and non-open defects can be reduced in the case of a hole pattern. 
     By virtue of the second resist composition including the polymeric compound (A1) having the structural unit (a0-1) and the structural unit (a1), lithography properties such as sensitivity and the like becomes excellent. 
     The reason for this is the same as the reason that a resist composition including the component (A′) containing the polymeric compound (A1) exhibits excellent lithography properties. 
     Further, the second resist composition is advantageous in that, by including the polymeric compound (A1) having the structural unit (a0-1) and the structural unit (a1) as well as the base component (A), the aforementioned effects can be achieved even when the amount of the structural unit (a0-1) is small. 
     In the second resist composition, the component (A) may be a resin component (A0) which exhibits changed solubility in a developing solution under the action of acid (hereafter, frequently referred to as “component (A0)”), a low molecular weight compound (A3) which exhibits changed solubility in a developing solution under the action of acid (hereafter, frequently referred to as “component (A3)”), or a mixture of the component (A0) and the component (A3). 
     The component (A0) is not particularly limited as long as it does not fall under the category of the component (A1), and preferably has at least one member selected from the group consisting of the aforementioned structural units (a0-1), (a1), (a2), (a3) and (a4). 
     As the component (A3), the same examples as those described above for the component (A2) can be mentioned. 
     The second resist composition may include the component (B), the component (D), the component (E) and the component (S) as optional components other than the component (A′), and the same examples as those described above can be mentioned. 
     EXAMPLES 
     As follows is a description of examples of the present invention, although the scope of the present invention is in no way limited by these examples. In the NMR analysis, the internal standard for  1 H-NMR and  13 C-NMR was tetramethylsilane (TMS). The internal standard for  19 F-NMR was hexafluorobenzene (provided that the peak of hexafluorobenzene was regarded as −160 ppm). 
     The compound (1) used in the polymer synthesis examples described later can be synthesized by a method described in WO2010/001913. Further, the compound (3) can be synthesized in accordance with the method described in WO2010/140483, Japanese Unexamined Patent Application, First Publication No. 2009-91350 and Japanese Unexamined Patent Application, First Publication No. 2009-7327. 
     Polymer Synthesis Example 1 
     Synthesis of Polymeric Compound 1 
     In a separable flask equipped with a thermometer, a reflux tube and a nitrogen feeding pipe, 11.25 g (42.89 mmol) of a compound (3) was dissolved in 7.86 g of methyl ethyl ketone (MEK) and 7.86 g of cyclohexanone, and heated to 80° C. To the resulting solution was added a solution obtained by dissolving 7.00 g (22.13 mmol) of a compound (2) and 4.29 g (6.83 mmol) of a compound (6) and 5.03 mmol of dimethyl 2,2′-azobis(isobutyrate) (V-601) as a polymerization initiator in 14.21 g of MEK and 14.21 g of cyclohexanone in a dropwise manner over 4 hours in a nitrogen atmosphere. 
     Thereafter, the reaction solution was heated for 1 hour while stirring, and then cooled to room temperature. The obtained reaction polymer solution was dropwise added to an excess amount of n-heptane to deposit a polymer. Thereafter, the precipitated white powder was separated by filtration, followed by washing with methanol, and then drying, thereby obtaining 7.16 g of a polymeric compound 1 as an objective compound. 
     With respect to the polymeric compound 1, the weight average molecular weight (Mw) and the dispersity (Mw/Mn) were determined by the polystyrene equivalent value as measured by gel permeation chromatography (GPC). As a result, it was found that the weight average molecular weight was 10,000, and the dispersity was 1.82. Further, as a result of an analysis by carbon 13 nuclear magnetic resonance spectroscopy (600 MHz,  13 C-NMR), it was found that the composition of the copolymer (ratio (molar ratio) of the respective structural units within the structural formula) was l/m/n=45.9/41.4/12.7. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Polymer Synthesis Example 2 
     Synthesis of Polymeric Compound 2 
     A polymeric compound 2 was synthesized in the same manner as in Polymer Synthesis Example 1, except that a compound (8) shown below was used instead of the compound (6). 
     With respect to the polymeric compound 2, the weight average molecular weight (Mw) and the dispersity (Mw/Mn) were determined by the polystyrene equivalent value as measured by gel permeation chromatography (GPC). As a result, it was found that the weight average molecular weight was 11,300, and the dispersity was 1.70. Further, as a result of an analysis by carbon 13 nuclear magnetic resonance spectroscopy (600 MHz,  13 C-NMR), it was found that the composition of the copolymer (ratio (molar ratio) of the respective structural units within the structural formula) was l/m/n=44.8/41.0/14.2. 
     
       
         
         
             
             
         
       
     
     Polymer Synthesis Examples 3 and 4 
     Synthesis of Polymeric Compounds 3 and 4 
     Polymeric compounds 3 and 4 were synthesized in the same manner as in Polymer Synthesis Example 1, except that the following monomers (1) to (8) which derived the structural units constituting each polymeric compound were used in predetermined molar ratio. 
     With respect to each polymeric compound, the weight average molecular weight and the dispersity (Mw/Mn) determined by the polystyrene equivalent value as measured by gel permeation chromatography (GPC) are shown in Table 1. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     
       
         
           
               
               
               
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 (1) 
                 (2) 
                 (3) 
                 (4) 
                 (5) 
                 (6) 
                 (7) 
                 (8) 
                 Mw 
                 Mw/Mn 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Polymeric 
                 — 
                 45.9 
                 41.4 
                 — 
                 — 
                 12.7 
                 — 
                 — 
                 10000 
                 1.82 
               
               
                 compound 1 
               
               
                 Polymeric 
                 — 
                 44.8 
                 41.0 
                 — 
                 — 
                 — 
                 — 
                 14.2 
                 11300 
                 1.7 
               
               
                 compound 2 
               
               
                 Polymeric 
                 31.3 
                 18.0 
                 15.2 
                 12.1 
                 11.9 
                 11.5 
                 — 
                 — 
                 10800 
                 1.79 
               
               
                 compound 3 
               
               
                 Polymeric 
                 35.9 
                 — 
                 — 
                 — 
                 19.7 
                 12.0 
                 32.4 
                 — 
                 11500 
                 1.85 
               
               
                 compound 4 
               
               
                   
               
            
           
         
       
     
     &lt;Production of Positive Resist Composition&gt; 
     The components shown in Table 2 were mixed together and dissolved to obtain positive resist compositions. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Component 
                 Component 
                 Component 
                 Component 
               
               
                   
                 (A) 
                 (D) 
                 (E) 
                 (S) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Ex. 1 
                 (A)-1 
                 (D)-1 
                 (E)-1 
                 (S)-1 
               
               
                   
                 [100] 
                 [1.6] 
                 [0.64] 
                 [4300] 
               
               
                 Comp. Ex. 
                 (A)-2 
                 (D)-1 
                 (E)-1 
                 (S)-2 
               
               
                 1 
                 [100] 
                 [1.6] 
                 [0.64] 
                 [4300] 
               
               
                   
               
            
           
         
       
     
     In Table 2, the reference characters indicate the following. Further, the values in brackets [ ] indicate the amount (in terms of parts by weight) of the component added. 
     (A)-1: the aforementioned polymeric compound 1 
     (A)-2: the aforementioned polymeric compound 2 
     (D)-1: tri-n-octylamine 
     (E)-1: salicylic acid 
     (S)-1: a mixed solvent of PGMEA/cyclohexanone=30/70 (weight ratio) 
     (S)-2: a mixed solvent of PGMEA/PGME/cyclohexanone=30/20/50 (weight ratio) 
     &lt;Evaluation of Lithography Properties&gt; 
     Using the obtained positive resist compositions, resist patterns were formed in the following manner, and the following evaluations were conducted. 
     [Formation of Resist Pattern] 
     Using a spinner, each resist composition was applied to an 8-inch silicon wafer that had been treated with hexamethyldisilazane (HMDS) at 90° C. for 36 seconds, and the solution was then subjected to a bake treatment (PAB) at a temperature indicated in Table 3 for 60 seconds, thereby forming a resist film (film thickness: 60 nm). 
     Subsequently, the resist film was subjected to drawing (exposure) using an electron beam lithography apparatus HL-800D (VSB) (manufactured by Hitachi, Ltd.), followed by a bake treatment (PEB) at a temperature indicated in Table 3 for 60 seconds. Then, development was conducted with a 2.38 wt % aqueous TMAH solution (product name: NMD-3; manufactured by Tokyo Ohka Kogyo Co., Ltd.) at 23° C. for 60 seconds, followed by rinsing for 15 seconds with pure water, thereby forming a line and space pattern (hereafter, referred to as “L/pattern”). 
     [Evaluation of Sensitivity] 
     The optimum exposure dose Eop (μC/cm 2 ) with which an L/S pattern having a line width of 100 nm and a pitch of 200 nm was determined. The results are shown in Table 3. 
     [Evaluation of Resist Pattern Shape] 
     Each of the L/S patterns having a line width of 100 nm and a pitch of 200 nm and formed with the above Eop was observed using a scanning electron microscope (SEM), and the cross-sectional shape of the L/S pattern and the shape of the L/S pattern as observed from the upper side thereof were evaluated. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 PAB 
                 PEB 
                   
               
               
                   
                 temperature 
                 temperature 
                 Eop 
               
               
                   
                 (° C.) 
                 (° C.) 
                 (μC/cm 2 ) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Ex. 1 
                 120 
                 95 
                 51.3 
               
               
                   
                 Comp. Ex. 1 
                 130 
                 110 
                 53.8 
               
               
                   
                   
               
            
           
         
       
     
     [Measurement of E 0 ] 
     To an 8-inch silicon wafer that had been treated with hexamethyldisilazane (HMDS) at 90° C. for 36 seconds, a resist composition obtained by using only 100 parts by weight of the component (A) and 4,300 parts by weight of the component (S) for each of Example 1 and Comparative Example 1 as indicated in Table 2 was applied using a spinner, followed by a bake treatment (PAB) at 100° C. for 60 seconds, thereby forming a resist film having a film thickness of 60 nm. 
     Subsequently, the resist film was subjected to drawing (exposure) using an electron beam lithography apparatus HL-800D (VSB) (manufactured by Hitachi, Ltd.) at an acceleration voltage of 70 keV. Then, a post exposure bake (PEB) treatment was conducted at 90° C. for 60 seconds, followed by development for 60 seconds at 23° C. using a 2.38% by weight aqueous solution of tetramethylammonium hydroxide (TMAH). Thereafter, water rinsing was conducted for 30 seconds using pure water, followed by drying by shaking. The exposure dose at which the resist film first dissipated was determined as the E 0  sensitivity. 
     The results are shown in Table 4. 
     
       
         
           
               
               
             
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                 E 0   
               
               
                   
                 (μC/cm 2 ) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 Ex. 1 
                 15 
               
               
                   
                 Comp. Ex. 1 
                 30 
               
               
                   
                   
               
            
           
         
       
     
     As seen from the results shown in Tables 3 and 4, in Example 1, the Eop and the E 0  were smaller than those of Comparative Example 1, meaning that the sensitivity was superior to that in Comparative Example 1. Further, although both of the resist patterns formed using the resist compositions of Example 1 and Comparative Example 1 were rectangular, the resist pattern formed using the resist composition of Example 1 exhibited a high perpendicularity as compared to the resist pattern formed using the resist composition of Comparative Example 1. Thus, it was confirmed that the resist pattern formed using the resist composition of Example 1 had an excellent shape. 
     From these results, it was confirmed that, according to the resist composition of the present invention, a resist pattern having an excellent shape can be formed with high sensitivity. 
     While preferred embodiments of the invention have been described and illustrated above, it should be understood that these are exemplary of the invention and are not to be considered as limiting. Additions, omissions, substitutions, and other modifications can be made without departing from the spirit or scope of the present invention. Accordingly, the invention is not to be considered as being limited by the foregoing description, and is only limited by the scope of the appended claims.