Patent Publication Number: US-8124310-B2

Title: Positive resist composition and pattern forming method using the same

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a positive resist composition suitably usable in the production of a resist for implantation, a semiconductor integrated circuit device, a mask for integrated circuit production, a printed wiring board, a liquid crystal panel, and the like. 
     2. Description of the Related Art 
     An early chemical amplification-type positive resist composition comprising a photoacid generator and a resin protected by an acid-decomposable group is disclosed, for example, in U.S. Pat. No. 4,491,628. This chemical amplification-type positive resist composition is a pattern forming material of forming a pattern on a substrate by producing an acid in the exposed area upon irradiation with radiation such as far ultraviolet light and through a reaction using the acid as the catalyst, causing the area irradiated with actinic radiation and the area not irradiated therewith to change the solubility in a developer. 
     Various positive resist compositions containing a resin protected by an acid-decomposable group have been heretofore known, and for example, JP-A-5-249682 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) discloses a resist composition using a polyhydroxystyrene resin protected by an alkoxy (acetal) group, JP-A-9-211866 discloses a resist composition using a polyhydroxystyrene resin protected by two different acid-decomposable groups, JP-A-2000-352822 discloses a resist composition using a resin protected by an acetal group having a heterocyclic group at the terminal through a linking group, JP-A-2002-49156 discloses a resist composition using a polyhydroxystyrene resin protected by two different acetal groups, and JP-A-2004-246326 discloses a resist composition using a polyhydroxystyrene resin protected by an acid-decomposable group containing a group (hetero ring) having absorption at least at 248 nm. 
     However, in the case of using a high-reflection substrate as it is without applying an antireflection film, like the case of forming a pattern for implantation such as ion injection, the positive resist composition in general produces a strong standing wave and is demanded to be improved in this respect. Improvements are demanded also in the sensitivity and resolution. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a chemical amplification-type positive resist composition with high sensitivity and high resolution, ensuring that even when a high-reflection substrate is used as it is without applying an antireflection film, generation of a standing wave is suppressed and a rectangular profile is obtained. 
     The present inventors have made intensive studies, as a result, the object of the present invention has been achieved by the following constructions. 
     (1) A positive resist composition, comprising: 
     (A) a resin containing a repeating unit represented by formula (I) or (I′), of which solubility in an alkali developer increases under an action of an acid; and 
     (B) a compound capable of generating an acid upon irradiation with actinic rays or radiation: 
     
       
         
         
             
             
         
       
     
     wherein Ra and Rb each independently represents a hydrogen atom, an alkyl group, a hydroxyl group, an alkoxy group, a halogen atom, a cyano group, a nitro group, an acyl group, an acyloxy group, a cycloalkyl group, an aryl group, a carboxyl group, an alkyloxycarbonyl group, an alkylcarbonyloxy group or an aralkyl group; 
     Z represents an alkyl group, an alkoxy group, a halogen atom, a cyano group, a nitro group, an acyl group, an acyloxy group, a cycloalkyl group, a carboxyl group, an alkyloxycarbonyl group, an alkylcarbonyloxy group or an aralkyl group; 
     Z 1  represents a non-acid-decomposable group; 
     Y represents a single bond or a divalent linking group; and 
     k represents an integer of 0 to 4, n represents an integer of 1 to 5, provided that 1≦k+n≦5, 
     when a plurality of Z&#39;s, Y&#39;s or Z 1 &#39;s are present, the plurality of Z&#39;s, Y&#39;s or Z 1 &#39;s may be the same or different, and 
     when a plurality of Z 1 &#39;s are present, the plurality of Z 1 &#39;s may combine with each other to form a ring. 
     (2) The positive resist composition as described in (1) above, 
     wherein in the repeating unit represented by formula (I) or (I′) of (A), Z 1  is a non-acid-decomposable group having absorption at least at 248 nm. 
     (3) The positive resist composition as described in (1) or (2) above, 
     wherein in the repeating unit represented by formula (I) of (A), Ra and Rb are a hydrogen atom and Y is a single bond, —O—, —S—, —C(═O)—, —C(═O)O— or —NH—, provided that when n is an integer of 2 to 5, the plurality of Y&#39;s or Z 1 &#39;s may be the same or different. 
     (4) The positive resist composition as described in (1) above, 
     wherein the repeating unit represented by formula (I) or (I′) is a repeating unit represented by formula (Ib), (Ib′), (Ic) or (Ic′): 
     
       
         
         
             
             
         
       
     
     wherein Z 1′  represents a non-acid-decomposable group having absorption at least at 248 nm, when a plurality of Z 1′ &#39;s are present, the plurality of Z 1′ &#39;s may be the same or different, and when a plurality of Z 1′ &#39;s are present, the plurality of Z 1′ &#39;s may combine with each other to form a ring; and 
     Y represents —O— or —S—. 
     (5) The positive resist composition as described in any of (2) to (4) above, 
     wherein in the repeating unit represented by formula (I) or (I′), Z 1  is a group having absorption at least at 248 nm and having one or more benzene ring. 
     (6) The positive resist composition as described in (5) above, 
     wherein in the repeating unit represented by formula (I) or (I′), Z 1  is a group having absorption at least at 248 nm and having two or more benzene rings. 
     (7) The positive resist composition as described in (5) or (6) above, 
     wherein in the repeating unit represented by formula (I) or (I′), Z 1  is a group having absorption at least at 248 nm and having three or more benzene rings. 
     (8) The positive resist composition as described in any of (1) to (7) above, 
     wherein the resin containing a repeating unit represented by formula (I) or (I′) further contains a repeating unit represented by formula (A1) or (A2): 
     
       
         
         
             
             
         
       
     
     wherein in formula (A1), n represents an integer of 0 to 5, m represents an integer of 0 to 5, provided that m+n≦5; 
     A 1  represents a hydrogen atom or a group containing a group that decomposes under an action of an acid, and when a plurality of A 1 &#39;s are present, the plurality of A 1 &#39;s may be the same or different; and 
     S 1  represents an arbitrary substituent, and when a plurality of S 1 &#39;s are present, the plurality of S 1 &#39;s may be the same or different, and 
     in formula (A2), X represents a hydrogen atom, an alkyl group, a hydroxyl group, an alkoxy group, a halogen atom, a cyano group, a nitro group, an acyl group, an acyloxy group, a cycloalkyl group, an aryl group, a carboxyl group, an alkyloxycarbonyl group, an alkyl-carbonyloxy group or an aralkyl group; and 
     A 2  represents a group containing a group that decomposes under an action of an acid. 
     (9) The positive resist composition as described in any of (1) to (8) above, 
     wherein the (B) compound capable of generating an acid upon irradiation with actinic rays or radiation is oxime sulfonate or diazodisulfone. 
     (10) The positive resist composition as described in any of (1) to (9) above, farther comprising: 
     a compound having a proton acceptor functional group and undergoing decomposition upon irradiation with actinic rays or radiation to generate a compound reduced in or deprived of the proton acceptor property or changed to be acidic from being proton acceptor-functioning. 
     (11) The positive resist composition as described in any of (1) to (10) above, 
     wherein the weight average molecular weight (Mw) of the resin (A) is from 1,000 to 200,000. 
     (12) The positive resist composition as described in any of (1) to (11) above, 
     wherein the weight average molecular weight (Mw) of the resin (A) is from 1,000 to 100,000. 
     (13) The positive resist composition as described in any of (1) to (12) above, 
     wherein the weight average molecular weight (Mw) of the resin (A) is from 1,000 to 50,000. 
     (14) The positive resist composition as described in any of (1) to (13) above, 
     wherein the weight average molecular weight (Mw) of the resin (A) is from 1,000 to 25,000. 
     (15) The positive resist composition as described in any of (1) to (14) above, further comprising: 
     (C) an organic basic compound. 
     (16) The positive resist composition as described in any of (1) to (15) above, further comprising: 
     (D) a surfactant. 
     (17) The positive resist composition as described in any of (1) to (16) above, further comprising: 
     a solvent. 
     (18) The positive resist composition as described in (17) above, 
     wherein the solvent contains propylene glycol monomethyl ether acetate. 
     (19) The positive resist composition as described in (18) above, further comprising: 
     propylene glycol monomethyl ether. 
     (20) The positive resist composition as described in any of (1) to (19) above, which is exposed by the irradiation with KrF, electron beam, X-ray or EUV. 
     (21) A pattern forming method, comprising: 
     forming a resist film from the positive resist composition as described in any of (1) to (19) above; and 
     exposing and developing the resist film. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is described in detail below. 
     Incidentally, in the context of the present invention, when a group (atomic group) is denoted without specifying whether substituted or unsubstituted, the group includes both a group having no substituent and a group having a substituent. For example, an “alkyl group” includes not only an alkyl group having no substituent (unsubstituted alkyl group) but also an alkyl group having a substituent (substituted alkyl group). 
     The positive resist composition of the present invention comprises (A) a resin containing a repeating unit represented by formula (I) or (I′), of which solubility in an alkali developer increases under the action of an acid, and (B) a compound capable of generating an acid upon irradiation with actinic rays or radiation. 
     The components blended in the positive resist composition of the present invention are described below. 
     [1] Resin Containing a Repeating Unit Represented by Formula (I) or (I′): 
     The positive resist composition of the present invention comprises (A) a resin containing a repeating unit represented by formula (I) or (I′), of which solubility in an alkali developer increases under the action of an acid. The resin (A) is insoluble or sparingly soluble in an alkali developer. 
     The repeating unit represented by formula (I) or (I′) preferably has absorption at least at 248 nm. 
     The repeating unit represented by formula (I) or (I′) is also preferably a repeating unit that reduces the solubility in an alkali developer after the irradiation of radiation. 
     
       
         
         
             
             
         
       
     
     In formulae (I) and (I′), Ra and Rb each independently represents a hydrogen atom, an alkyl group, a hydroxyl group, an alkoxy group, a halogen atom, a cyano group, a nitro group, an acyl group, an acyloxy group, a cycloalkyl group, an aryl group, a carboxyl group, an alkyloxycarbonyl group, an alkylcarbonyloxy group or an aralkyl group and is preferably a hydrogen atom or an alkyl group and most preferably a hydrogen atom. 
     Z represents an alkyl group, an alkoxy group, a halogen atom, a cyano group, a nitro group, an acyl group, an acyloxy group, a cycloalkyl group, a carboxyl group, an alkyloxycarbonyl group, an alkylcarbonyloxy group or an aralkyl group and is preferably an alkyl group, an alkoxy group or a carboxyl group. 
     Z 1  represents a non-acid-decomposable group. 
     Y represents a single bond or a divalent linking group. 
     k represents an integer of 0 to 4, and n represents an integer of 1 to 5, provided that 1≦k+n≦5. k is preferably 0 or 1, more preferably 0. 
     In the case where a plurality of Z&#39;s, Y&#39;s or Z 1 &#39;s are present, these may be the same or different, and in the case where a plurality of Z 1 &#39;s are present, these may combine with each other to form a ring. 
     The alkyl group of Ra and Rb may have a substituent and may be either linear or branched. The linear alkyl group is preferably an alkyl group having a carbon number of 1 to 30, more preferably from 1 to 20, and examples thereof include a methyl group, an ethyl group, an n-propyl group, an n-butyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group and an n-decanyl group. The branched alkyl group is preferably an alkyl group having a carbon number of 3 to 30, more preferably from 3 to 20, and examples thereof include an i-propyl group, an i-butyl group, a tert-butyl group, an i-pentyl group, a tert-pentyl group, an i-hexyl group, a tert-hexyl group, an i-heptyl group, a tert-heptyl group, an i-octyl group, a tert-octyl group, an i-nonyl group and a tert-decenoyl group. 
     The alkoxy group of Ra and Rb may have a substituent and is, for example, the above-described alkoxy group having a carbon number of 1 to 8, and examples thereof include a methoxy group, an ethoxy group, a propoxy group, a butoxy group, a pentyloxy group, a hexyloxy group and a cyclohexyloxy group. 
     The halogen atom of Ra and Rb includes a fluorine atom, a chlorine atom, a bromine atom and an iodine atom and is preferably a fluorine atom. 
     The acyl group of Ra and Rb may have a substituent and is, for example, an acyl group having a carbon number of 2 to 8, and specific preferred examples thereof include a formyl group, an acetyl group, a propanoyl group, a butanoyl group, a pivaloyl group and a benzoyl group. 
     The acyloxy group of Ra and Rb may have a substituent and is preferably an acyloxy group having a carbon number of 2 to 8, and examples thereof include an acetoxy group, a propionyloxy group, a butyloxy group, a valeryloxy group, a pivaloyloxy group, a hexanoyloxy group, an octanoyloxy group and a benzoyloxy group. 
     The cycloalkyl group of Ra and Rb may have a substituent, may be monocyclic or polycyclic, or may be crosslinked. For example, the cycloalkyl group may have a crosslinked structure. The monocyclic cycloalkyl group is preferably a cycloalkyl group having a carbon number of 3 to 8, and examples thereof include a cyclopropyl group, a cyclopentyl group, a cyclohexyl group, a cyclobutyl group and a cyclooctyl group. Examples of the polycyclic cycloalkyl group include a group having a bicyclo, tricyclo or tetracyclo structure and having a carbon number of 5 or more. A cycloalkyl group having a carbon number of 6 to 20 is preferred, and examples thereof include an adamantyl group, a norbornyl group, an isoboronyl group, a camphanyl group, a dicyclopentyl group, an α-pinel group, a tricyclodecanyl group, a tetracyclododecyl group, an androstanyl group, and the following structures. Incidentally, a part of the carbon atom in the cycloalkyl group may be substituted by a heteroatom such as oxygen atom. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     The preferred alicyclic moiety includes an adamantyl group, a noradamantyl group, a decalin group, a tricyclodecanyl group, a tetracyclododecanyl group, a norbornyl group, a cedrol group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a cyclodecanyl group and a cyclododecanyl group. An adamantyl group, a decalin group, a norbornyl group, a cedrol group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a cyclodecanyl group, a cyclododecanyl group and a tricyclodecanyl group are more preferred. 
     The substituent of the alicyclic structure includes an alkyl group, a halogen atom, a hydroxyl group, an alkoxy group, a carboxyl group and an alkoxycarbonyl group. The alkyl group is preferably a lower alkyl group such as methyl group, ethyl group, propyl group, isopropyl group and butyl group, more preferably a methyl group, an ethyl group, a propyl group or an isopropyl group. The alkoxy group is preferably an alkoxy group having a carbon number of 1 to 4, such as methoxy group, ethoxy group, propoxy group and butoxy group. Examples of the substituent which the alkyl group and alkoxy group may have include a hydroxyl group, a halogen atom and an alkoxy group (preferably having a carbon number of 1 to 4). 
     The substituent which these groups each may further have includes a hydroxyl group, a halogen atom (e.g., fluorine, chlorine, bromine, iodine), a nitro group, a cyano group, the above-described alkyl group, an alkoxy group such as methoxy group, ethoxy group, hydroxyethoxy group, propoxy group, hydroxypropoxy group, n-butoxy group, isobutoxy group, sec-butoxy group and tert-butoxy group, an alkoxycarbonyl group such as methoxycarbonyl group and ethoxycarbonyl group, an aralkyl group such as benzyl group, phenethyl group and cumyl group, an acyl group such as aralkyloxy group, formyl group, acetyl group, butyryl group, benzoyl group, cinnamyl group and valeryl group, an acyloxy group such as butyryloxy group, the above-described alkenyl group, an alkenyloxy group such as vinyloxy group, propenyloxy group, allyloxy group and butenyloxy group, the above-described aryl group, an aryloxy group such as phenoxy group, and an aryloxycarbonyl group such as benzoyloxy group. 
     The substituent which the alicyclic structure in the cycloalkyl group of Ra and Rb may have is preferably an alkyl group having a carbon number of 1 to 20, an aryl group having a carbon number of 6 to 20, or an alkyl group having a carbon number of 7 to 20. These substituents each may further have a substituent. 
     The aryl group of Ra and Rb may have a substituent and is preferably an aryl group having a carbon number of 6 to 14, and examples thereof include a phenyl group, a xylyl group, a toluyl group, a cumenyl group, a naphthyl group and an anthracenyl group. 
     The alkyloxycarbonyl group of Ra and Rb may have a substituent and is preferably an alkyloxycarbonyl group having a carbon number of 2 to 8, and examples thereof include a methoxycarbonyl group, an ethoxycarbonyl group and a propoxycarbonyl group. 
     The alkylcarbonyloxy group of Ra and Rb may have a substituent and is preferably an alkylcarbonyloxy group having a carbon number of 2 to 8, and examples thereof include a methylcarbonyloxy group and an ethylcarbonyloxy group. 
     The aralkyl group of Ra and Rb may have a substituent and is preferably an aralkyl group having a carbon number of 7 to 16, and examples thereof include a benzyl group. 
     Z represents an alkyl group, an alkoxy group, a halogen atom, a cyano group, a nitro group, an acyl group, an acyloxy group, a cycloalkyl group, a carboxyl group, an alkyloxycarbonyl group, an alkylcarbonyloxy group or an aralkyl group. The alkyl group, alkoxy group, halogen atom, cyano group, nitro group, acyl group, acyloxy group, cycloalkyl group, carboxyl group, alkyloxycarbonyl group, alkylcarbonyloxy group and aralkyl group of Z are the same as respective groups described for Ra and Rb. 
     Z 1  represents a non-acid-decomposable group. The non-acid-decomposable group means a group which is not an acid-decomposable group (a group that decomposes under the action of an acid to generate an alkali-soluble group), that is, a group which does not produce an alkali-soluble group such as hydroxyl group and carboxyl group by decomposing under the action of an acid generated from a photoacid generator or the like upon exposure. 
     Specific examples of the non-acid-decomposable group of Z 1  include a halogen atom, an alkyl group, a cycloalkyl group, an aryl group, an alkoxy group, an acyl group, —OC(═O)R 01 , —OC(═O)OR 01 , —C(═O)OR 01 , —C(═O)N(R 02 )R 01 , —N(R 02 )C(═O)R 01 , —N(R 02 )C(═O)OR 01 , —N(R 02 )SO 2 R 01 , —SR 01 , —SO 2 R 01 , —SO 3 R 01  and —SO 2 N(R 02 )R 01 . 
     R 01  and R 02  are the groups defined in the same manner as those of Ra and Rb in formula (I) or (I′). 
     The alkyl group of Z 1  may have a substituent as long as it is a non-acid-decomposable group, and may be linear or branched. The linear alkyl group is preferably an alkyl group having a carbon number of 1 to 30, more preferably from 1 to 20, and examples thereof include a methyl group, an ethyl group, an n-propyl group, an n-butyl group, a sec-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group and an n-decanyl group. The branched alkyl group is preferably an alkyl group having a carbon number of 3 to 30, more preferably from 3 to 20, and examples thereof include an i-propyl group, an i-butyl group, an i-pentyl group, an i-hexyl group, an i-heptyl group, an i-octyl group and an i-nonyl group. 
     The halogen atom, cycloalkyl group, aryl group, alkoxy group and acyl group of Z 1  are the same as respective groups described for Ra and Rb. 
     Z 1  is preferably a non-acid-decomposable group having absorption at least at 248 nm. 
     The non-acid-decomposable group having absorption at least at 248 nm of Z 1  may be any group as long as it has some absorption at 248 nm, but the absorption is preferably higher. 
     The group having absorption at least at 248 nm preferably has at least one or more benzene ring, more preferably further has a conjugate substituent. A group having two or more benzene rings is preferred, and a group having three or more benzene rings is more preferred. 
     The benzene ring as used herein means a ring structure consisting of 6 carbon atoms and containing a largest number of non-cumulative double bonds (a largest number of conjugated double bonds) in the ring. 
     The group having two benzene rings includes a group having a naphthalene structure, a group having a biphenyl structure and a group having a benzophenone structure. Also, the group having three benzene rings includes a group having an anthracene structure and a group having a terphenyl structure. 
     Examples of the conjugate substituent include —C═C—, —C≡C—, —C(═O)—, —CN and —NO 2 . Among these, preferred are —C═C—, —C≡C— and —C(═O)—, still more preferred is —C(═O)—. 
     The group as Z 1  may have an arbitrary group together with the group having absorption at 248 nm, and the arbitrary group is, for example, an alkylene group, a carbonyl group, —O—, —S—, —C(═S)—, an ester group, a thioester group, an alkenyl group, an alkynyl group, —NHC(═O)—, —C(=O)NH— or —NH—, preferably an alkylene group, a carbonyl group, —O—, an ester group or an alkenyl group. 
     Incidentally, the group of Z 1  containing a group having at least one benzene ring and having absorption at 248 nm may be a group itself having at least one benzene ring and having absorption at 248 nm. 
     The number of atoms constituting the group containing a group having absorption at 248 nm is preferably 100 or less, more preferably 50 or less. 
     Examples of the group as Z 1  include an arylcarbonyl group, a condensed aryl group, a condensed arylcarbonyl group, a heteroarylcarbonyl group, a condensed heteroaryl group, a condensed heteroarylcarbonyl group, an arylcarbonyl group-containing alkyl group, a condensed aryl group-containing alkyl group, a condensed arylcarbonyl group-containing alkyl group, a heteroarylcarbonyl group-containing alkyl group, a condensed heteroaryl group-containing alkyl group, and a condensed heteroarylcarbonyl group-containing alkyl group. 
     The group need not be limited to an aromatic ring such as phenyl group, and a hetero ring or the like may also be used as long as it is a group having absorption at 248 nm. Also in this case, it is more preferred to further has a conjugated double bond (including a carbonyl group). 
     The molar extinction coefficient ε at 248 nm of the monomer corresponding to the repeating unit represented by formula (I) or (I′) is preferably 200 or more, more preferably from 200 to 500,000, still more preferably from 300 to 300,000, yet still more preferably from 500 to 200,000, and most preferably from 1,000 to 100,000. The molar extinction coefficient ε as used herein indicates the value in a tetrahydrofuran solution (23° C.). 
     In the present invention, the resin has a group having absorption at 248 nm, whereby the transmittance of the film coated on a substrate for light at 248 nm can be controlled to a desired value. Therefore, the film thickness at coating may be varied. In other words, the transmittance can be controlled independently of the film thickness. 
     For example, the transmittance at 248 nm with a film thickness of 4,000 Å is 90% or less, preferably form 30 to 85%, more preferably from 35 to 80%, still more preferably from 38 to 78%, and most preferably from 40 to 75%. 
     Also, for example, in the case of a film thickness of 1,900 Å, the transmittance at 248 nm is 90% or less, preferably from 30 to 88%, more preferably from 40 to 85%, still more preferably from 50 to 83%, and most preferably from 60 to 80%. 
     The transmittance is preferably larger in view of resolution and sensitivity and preferably smaller from the standpoint of suppressing the standing wave. The film thickness is not limited to those described above. 
     Y represents a single bond or a divalent linking group and is, for example, a direct bond, an alkylene group, an arylene group, a carbonyl group, a sulfide group, a sulfone group, —COO—, —CONH—, —SO 2 NH—, —CF 2 —, —CF 2 CF 2 —, —OCF 2 O—, —CF 2 OCF 2 —, —SS—, —CH 2 SO 2 CH 2 —, —CH 2 COCH 2 —, —COCF 2 CO—, —COCO—, —OCOO—, —OSO 2 O—, —NH—, an ether group (oxygen atom), a thioether group (sulfur atom), an acyl group, an alkylsulfonyl group, —CH═CH—, —C≡C—, an aminocarbonylamino group, or an aminosulfonylamino group, which groups each may have a substituent. 
     The liking group of Y is preferably a linking group having a carbon number of 15 or less, more preferably 10 or less. 
     Y is preferably a direct bond, an ether group (oxygen atom), a thioether group (sulfur atom), —NH—, a carbonyl group or —COO—. Y is more preferably a direct bond, an ether group (oxygen atom), a thioether group (sulfur atom), —NH— or a carbonyl group, still more preferably an ether group (oxygen atom), a thioether group (sulfur atom) or —NH—, yet still more preferably an ether group (oxygen atom) or —NH—. 
     n is an integer of 1 to 5, preferably an integer of 1 to 3, more preferably 1 or 2, still more preferably 1. 
     k is an integer of 0 to 4, preferably an integer of 0 to 3, more preferably an integer of 0 to 2, still more preferably 0 or 1. 
     The resin (A) for use in the present invention is preferably a resin where in the repeating unit represented by formula (I), Ra and Rb are a hydrogen atom and Y is a single bond, —O—, —S—, —C(═O)—, —C(═O)O— or —NH—. 
     The repeating unit represented by formula (I) or (I′) is more preferably a repeating unit represented by formula (Ib), (Ib′), (Ic) or (Ic′): 
                         
wherein Z 1′  represents a non-acid-decomposable group having absorption at least at 248 nm, when a plurality of Z 1′ &#39;s are present, these may be the same or different, and when a plurality of Z 1′ &#39;s are present, these may combine with each other to form a ring; and
 
     Y′ represents —O— or —S—. 
     Specific examples of the repeating unit represented by formula (I) or (I′) are set forth below, but the present invention is not limited thereto. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     The (A) resin containing a repeating unit represented by formula (I) or (I′) preferably further contains a repeating unit represented by formula (A1) or (A2): 
     
       
         
         
             
             
         
       
     
     In formula (A1), n represents an integer of 0 to 5, m represents an integer of 0 to 5, provided that m+n+n≦5. 
     A 1  represents a hydrogen atom or a group containing a group that decomposes under the action of an acid, and when a plurality of A 1 &#39;s are present, these may be the same or different. 
     S 1  represents an arbitrary substituent, and when a plurality of S 1 &#39;s are present, these may be the same or different. 
     The group containing a group that decomposes under the action of an acid may be a group where as a result of leaving of A 1 , a hydroxyl group is produced in the repeating unit represented by formula (A1), that is, an acid-decomposable group itself, or may be a group containing an acid-decomposable group, that is, a group which decomposes under the action of an acid to produce an alkali-soluble group such as hydroxyl group or carboxyl group in the residue bonded to the repeating unit. 
     Examples of the group containing a group that decomposes under the action of an acid include a tertiary alkyl group such as tert-butyl group and tert-amyl group, a tert-butoxycarbonyl group, a tert-butoxycarbonylmethyl group, and an acetal group as represented by —C(L 1 )(L 2 )-O-Z 2 . 
     L 1  and L 2 , which may be the same or different, each represents an atom or group selected from a hydrogen atom, an alkyl group, a cycloalkyl group and an aralkyl group. 
     Z 2  represents an alkyl group, a cycloalkyl group or an aralkyl group. 
     Z 2  and L 1  may combine with each other to form a 5- or 6-membered ring. 
     The aralkyl group of L 1 , L 2  and Z 2  includes an aralkyl group having a carbon number of 7 to 15, such as benzyl group and phenethyl group. These groups each may have a substituent. 
     Preferred examples of the substituent of the aralkyl group include an alkoxy group, a hydroxyl group, a halogen atom, a nitro group, an acyl group, an acylamino group, a sulfonylamino group, an alkylthio group, an arylthio group and an aralkylthio group. Examples of the aralkyl group having a substituent include an alkoxybenzyl group, a hydroxybenzyl group and a phenylthiophenethyl group. 
     The carbon number of the substituent which the aralkyl group of L 1 , L 2  and Z 2  may have is preferably 12 or less. 
     Examples of the 5- or 6-membered ring formed by combining Z 2  and L 1  with each other include a tetrahydropyran ring and a tetrahydrofuran ring. 
     In the present invention, Z 2  is preferably a linear or branched alkyl group. By virtue of this construction, the effect of the present invention is brought out more prominently. 
     S 1  represents, when a plurality of S 1 &#39;s are present, each independently represents an arbitrary substituent, and examples thereof include an alkyl group, an alkoxy group, an acyl group, an acyloxy group, an aryl group, an aryloxy group, an aralkyl group, an aralkyloxy group, a hydroxy group, a halogen atom, a cyano group, a nitro group, a sulfonylamino group, an alkylthio group, an arylthio group and an aralkylthio group. 
     For example, the alkyl group and cycloalkyl group are preferably a linear or branched alkyl group and a cycloalkyl group each having a carbon number of 1 to 20, such as methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, isobutyl group, tert-butyl group, pentyl group, cyclopentyl group, hexyl group, cyclohexyl group, octyl group and dodecyl group. These groups each may further have a substituent. 
     Preferred examples of the substituent which these groups each may further have include an alkyl group, an alkoxy group, a hydroxyl group, a halogen atom, a nitro group, an acyl group, an acyloxy group, an acylamino group, a sulfonylamino group, an alkylthio group, an arylthio group, an aralkylthio group, a thiophenecarbonyloxy group, a thiophenemethylcarbonyloxy group, and a heterocyclic residue such as pyrrolidone residue. The substituent is preferably a substituent having a carbon number of 12 or less. 
     Examples of the alkyl group having a substituent include a cyclohexylethyl group, an alkylcarbonyloxymethyl group, an alkylcarbonyloxyethyl group, a cycloalkyl-carbonyloxymethyl group, a cycloalkylcarbonyloxyethyl group, an arylcarbonyloxyethyl group, an aralkylcarbonyloxyethyl group, an alkyloxymethyl group, a cycloalkyloxymethyl group, an aryloxymethyl group, an aralkyloxymethyl group, an alkyloxyethyl group, a cycloalkyloxyethyl group, an aryloxyethyl group, an aralkyloxyethyl group, an alkylthiomethyl group, a cycloalkylthiomethyl group, an arylthiomethyl group, an aralkylthiomethyl group, an alkylthioethyl group, a cycloalkylthioethyl group, an arylthioethyl group and an aralkylthioethyl group. 
     The alkyl group and cycloalkyl group in these groups are not particularly limited and each may further have the above-described substituent such as alkyl group, cycloalkyl group and alkoxy group. 
     Examples of the alkylcarbonyloxyethyl group and cycloalkylcarbonyloxyethyl group include a cyclohexylcarbonyloxyethyl group, a tert-butylcyclohexylcarbonyloxyethyl group and an n-butylcyclohexylcarbonyloxyethyl group. 
     The aryl group is also not particularly limited but generally includes an aryl group having a carbon number of 6 to 14, such as phenyl group, xylyl group, toluyl group, cumenyl group, naphthyl group and anthracenyl group, and may further have the above-described substituent such as alkyl group, cycloalkyl group and alkoxy group. 
     Examples of the aryloxyethyl group include a phenyloxyethyl group and a cyclohexylphenyloxyethyl group. These groups each may further have a substituent. 
     The aralkyl group is also not particularly limited but examples thereof include a benzyl group. 
     Examples of the aralkylcarbonyloxyethyl group include a benzylcarbonyloxyethyl group. These groups each may further have a substituent. 
     The repeating unit represented by formula (A2) is described below. 
     In formula (A2), X represents a hydrogen atom, an acyl group, a hydroxyl group, an alkoxy group, a halogen atom, a cyano group, a nitro group, an acyl group, an acyloxy group, a cycloalkyl group, an aryl group, a carboxyl group, an alkyloxycarbonyl group, an alkylcarbonyloxy group or an aralkyl group. Details of each group are the same as those in Ra and Rb of formula (I) or (I′). X is preferably a hydrogen atom or an alkyl group, more preferably an alkyl group, still more preferably a methyl group. 
     A 2  represents a group containing a group that decomposes under the action of an acid. 
     The group containing a group that decomposes under the action of an acid may be a group where as a result of leaving of A 2 , a carboxyl group is produced in the repeating unit represented by formula (A2), that is, an acid-decomposable group itself, or may be a group containing an acid-decomposable group, that is, a group which decomposes under the action of an acid to produce an alkali-soluble group such as hydroxyl group or carboxyl group in the residue bonded to the repeating unit. 
     A 2  is preferably a hydrocarbon group (preferably having a carbon number of 20 or less, more preferably from 4 to 12), more preferably a tert-butyl group, a tert-amyl group or an alicyclic structure-containing hydrocarbon group (for example, an alicyclic group itself, or a group with the alkyl group being substituted by an alicyclic group). 
     The alicyclic structure may be monocyclic or polycyclic. Specific examples thereof include a monocyclo, bicyclo, tricyclo or tetracyclo structure having a carbon number of 5 or more. The carbon number of the alicyclic structure is preferably from 6 to 30, more preferably from 7 to 25. These alicyclic structure-containing hydrocarbon groups each may have a substituent. 
     Examples of the alicyclic structure are set forth below. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In the present invention, the preferred alicyclic structure includes, as denoted in terms of the monovalent alicyclic group, an adamantyl group, a noradamantyl group, a decalin residue, a tricyclodecanyl group, a tetracyclododecanyl group, a norbornyl group, a cedrol group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a cyclodecanyl group and a cyclododecanyl group. Among these, an adamantyl group, a decalin residue, a norbornyl group, a cedrol group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a cyclodecanyl group and a cyclododecanyl group are more preferred. 
     The substituent which the alicyclic ring in these groups may have includes an alkyl group, a halogen atom, a hydroxyl group, an alkoxy group, a carboxyl group, and an alkoxycarbonyl group. The alkyl group is preferably a lower alkyl group such as methyl group, ethyl group, propyl group, isopropyl group and butyl group, more preferably a methyl group, an ethyl group, a propyl group or an isopropyl group. The alkoxy group includes an alkoxy group having a carbon number of 1 to 4, such as methoxy group, ethoxy group, propoxy group and butoxy group. The alkyl group and alkoxy group each may further have a substituent. The substituent which the alkyl group and alkoxy group each may further have includes a hydroxyl group, a halogen atom and an alkoxy group. 
     The alicylcic structure-containing acid-decomposable group is preferably a group represented by any one of the following formulae (pI) to (pV): 
     
       
         
         
             
             
         
       
     
     In formulae (pI) to (pV), R 11  represents a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group or a sec-butyl group. Z represents an atomic group necessary for forming an alicyclic hydrocarbon group together with the carbon atom. 
     R 12  to R 16  each independently represents a linear or branched alkyl group having a carbon number of 1 to 4, or an alicyclic hydrocarbon group, provided that at least one of R 12  to R 14 , or either R 15  or R 16 , represents an alicyclic hydrocarbon group. 
     R 17  to R 21  each independently represents a hydrogen atom, a linear or branched alkyl group having a carbon number of 1 to 4, or an alicyclic hydrocarbon group, provided that at least one of R 17  to R 21  represents an alicylcic hydrocarbon group. Also, either R 19  or R 21  represents a linear or branched alkyl group having a carbon number of 1 to 4, or an alicyclic hydrocarbon group. 
     R 22  to R 25  each independently represents a hydrogen atom, a linear or branched alkyl group having a carbon number of 1 to 4, or an alicyclic hydrocarbon group, provided that at least one of R 22  to R 25  represents an alicyclic hydrocarbon group. R 23  and R 24  may combine with each other to form a ring. 
     In formulae (pI) to (pV), the alkyl group of R 12  to R 25  is a linear or branched alkyl group having a carbon number of 1 to 4, which may be substituted or unsubstituted. Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group and a tert-butyl group. 
     Examples of the substituent which the alkyl group may further have include an alkoxy group having a carbon number of 1 to 4, a halogen atom (fluorine, chlorine, bromine, iodine), an acyl group, an acyloxy group, a cyano group, a hydroxyl group, a carboxy group, an alkoxycarbonyl group and a nitro group. 
     The alicyclic hydrocarbon group of R 11  to R 25  and the alicyclic hydrocarbon group formed by Z together with the carbon atom include those described above as the alicyclic structure. 
     Specific examples of the alicyclic structure-containing group that decomposes under the action of an acid or the group (acid-decomposable group) containing a group that decomposes under the action of an acid, as A 2 , are set forth below. 
     
       
         
         
             
             
         
       
     
     The monomer corresponding to the repeating unit represented by formula (A2) may be synthesized by esterifying a (meth)acrylic acid chloride and an alcohol compound in a solvent such as THF, acetone and methylene chloride in the presence of a basic catalyst such as triethylamine, pyridine and DBU. A commercially available product may also be used. 
     The monomer corresponding to the repeating unit represented by formula (A1) may be synthesized by acetalizing a hydroxy-substituted styrene monomer and a vinyl ether compound in a solvent such as THF and methylene chloride in the presence of an acidic catalyst such as p-toluenesulfonic acid and pyridine p-toluenesulfonate, or by effecting tert-Boc protection using tert-butyl dicarbonate in the presence of a basic catalyst such as triethylamine, pyridine and DBU. A commercially available product may also be used. 
     Specific examples of the repeating unit represented by formula (A1) are set forth below, but the present invention is not limited thereto. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Specific examples of the repeating unit represented by formula (A2) or monomers corresponding thereto are set forth below, but the present invention is not limited thereto. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     The repeating unit represented by formula (A2) is more preferably a repeating unit represented by formula (A2′): 
     
       
         
         
             
             
         
       
     
     In formula (A2′), AR represents a benzene ring, a naphthalene ring or an anthracene ring, which rings each may have one or more substituents. Examples of the substituent include a linear or branched alkyl group preferably having a carbon number of 1 to 20, such as methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, isobutyl group, tert-butyl group, pentyl group, cyclopentyl group, hexyl group, cyclohexyl group, octyl group and dodecyl group, an alkoxy group, a hydroxy group, a halogen atom, an aryl group, a cyano group, a nitro group, an acyl group, an acyloxy group, an acylamino group, a sulfonylamino group, an alkylthio group, an arylthio group, an aralkylthio group, a thiophenecarbonyloxy group, a thiophenemethylcarbonyloxy group, and a heterocyclic residue such as pyrrolidone residue. The substituent is preferably a linear or branched alkyl group having a carbon number of 1 to 5 or an alkoxy group in view of resolving power, more preferably benzene, p-methylbenzene or p-methoxybenzene. 
     Rn represents an alkyl group or an aryl group. 
     AR and Rn may combine with each other to form a ring. 
     A represents a hydrogen atom, an alkyl group, a halogen atom, a cyano group or an alkyloxycarbonyl group. 
     The alkyl group of Rn includes a linear or branched alkyl group preferably having a carbon number of 1 to 20, such as methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, isobutyl group, tert-butyl group, pentyl group, cyclopentyl group, hexyl group, cyclohexyl group, octyl group and dodecyl group. 
     The aryl group of Rn is preferably an aryl group having a carbon number of 6 to 14, such as phenyl group, xylyl group, toluyl group, cumenyl group, naphthyl group and anthracenyl group. 
     Preferred examples of the substituent which the groups of Rn each may have include an alkoxy group, a hydroxyl group, a halogen atom, a nitro group, an acyl group, an acyloxy group, an acylamino group, a sulfonylamino group, an alkylthio group, an arylthio group, an aralkylthio group, a thiophenecarbonyloxy group, a thiophenemethylcarbonyloxy group, and a heterocyclic residue such as pyrrolidone residue. Among these, more preferred are an alkoxy group, a hydroxyl group, a halogen atom, a nitro group, an acyl group, an acyloxy group, an acylamino group and a sulfonylamino group. 
     The alkyl group of A includes a linear or branched alkyl group preferably having a carbon number of 1 to 20, such as methyl group, ethyl group, propyl group, isopropyl group, n-butyl group, isobutyl group, tertbutyl group, pentyl group, cyclopentyl group, hexyl group, cyclohexyl group, octyl group and dodecyl group. These groups each may have a substituent, and preferred examples of the substituent which these groups each may have include an alkoxy group, a hydroxyl group, a halogen atom, a nitro group, an acyl group, an acyloxy group, an acylamino group, a sulfonylamino group, an alkylthio group, an arylthio group, an aralkylthio group, a thiophenecarbonyloxy group, a thiophenemethylcarbonyloxy group, and a heterocyclic residue such as pyrrolidone residue. Among these, preferred are a CF 3  group, an alkyloxycarbonylmethyl group, an alkylcarbonyloxymethyl group, a hydroxymethyl group and an alkoxymethyl group. 
     The halogen atom in A includes a fluorine atom, a chlorine atom, a bromine atom and an iodine atom and is preferably a fluorine atom. 
     Examples of the alkyl contained in the alkyloxycarbonyl group of A are the same as those of the alkyl group of A above. 
     Specific examples of the repeating unit represented by formula (A2′) are set forth below, but the present invention is not limited thereto. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     The resin (A) may preferably further contain a repeating unit represented by formula (A4): 
     
       
         
         
             
             
         
       
     
     In formula (A4), R 2  represents a hydrogen atom, a methyl group, a cyano group, a halogen atom or a perfluoro group having a carbon number of 1 to 4. 
     R 3  represents a hydrogen atom, an alkyl group, a halogen atom, an aryl group, an alkoxy group or an acyl group. 
     q represents an integer of 0 to 4. 
     W represents a group that does not decompose under the action of an acid. 
     W represents a group that does not decompose under the action of an acid (sometimes referred to as an “acid-stable group”), and specific examples thereof include a hydrogen atom, a halogen atom, an alkyl group, a cycloalkyl group, an alkenyl group, an aryl group, an acyl group, an alkylamido group, an arylamidomethyl group and an arylamido group. The acid-stable group is preferably an acyl group or an alkylamido group, more preferably an acyl group, an alkylcarbonyloxy group, an alkyloxy group, a cycloalkyloxy group or an aryloxy group. 
     In the acid-stable group represented by W, the alkyl group is preferably an alkyl group having a carbon number of 1 to 4, such as methyl group, ethyl group, propyl group, n-butyl group, sec-butyl group and tert-butyl group; the cycloalkyl group is preferably a cycloalkyl group having a carbon number of 3 to 10, such as cyclopropyl group, cyclobutyl group, cyclohexyl group and adamantyl group; the alkenyl group is preferably an alkenyl group having a carbon number of 2 to 4, such as vinyl group, propenyl group, allyl group and butenyl group; the alkenyl group is preferably an alkenyl group having a carbon number of 2 to 4, such as vinyl group, propenyl group, allyl group and butenyl group; and the aryl group is preferably an aryl group having a carbon number of 6 to 14, such as phenyl group, xylyl group, toluyl group, cumenyl group, naphthyl group and anthracenyl group. W may be present at any position on the benzene ring but is preferably present at the meta-position or para-position, more preferably at the para-position, of the styrene skeleton. 
     Specific examples of the repeating unit represented by formula (A4) are set forth below, but the present invention is not limited thereto. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     The resin (A) may preferably further contain a repeating unit comprising a (meth)acrylic acid derivative that does not decompose under the action of an acid. Specific examples thereof are set forth below, but the present invention is not limited thereto. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     The resin (A) is a resin of which solubility in an alkali developer increases under the action of an acid (acid-decomposable resin), and contains a group that decomposes under the action of an acid to produce an alkali-soluble group (acid-decomposable group), in an arbitrary repeating unit. 
     As described above, an acid-decomposable group may be contained in the repeating unit represented by formula (I), (I′), (A1) or (A2) or in other repeating units. 
     Examples of the acid-decomposable group include, in addition to those described above, a group represented by —C(═O)—X 1 —R 0 . 
     In the formula above, R 0  represents, for example, a tertiary alkyl group such as tert-butyl group and tert-amyl group, a 1-alkoxyethyl group such as isobornyl group, 1-ethoxyethyl group, 1-butoxyethyl group, 1-isobutoxyethyl group and 1-cyclohexyloxyethyl group, an alkoxymethyl group such as 1-methoxymethyl group and 1-ethoxymethyl group, a 3-oxoalkyl group, a tetrahydropyranyl group, a tetrahydrofuranyl group, a trialkylsilyl ester group, a 3-oxocyclohexyl ester group, a 2-methyl-2-adamantyl group, or a mevalonic lactone group. X 1  represents an oxygen atom, a sulfur atom, —NH—, —NHSO 2 — or —NHSO 2 NH—. 
     The content of the repeating unit having an acid-decomposable group in the resin (A) is preferably from 5 to 95 mol %, more preferably from 10 to 60 mol %, still more preferably from 15 to 50 mol %, based on all repeating units. 
     The content of the repeating unit represented by formula (I) or (I′) in the resin (A) is preferably from 0.5 to 70 mol %, more preferably from 1 to 50 mol %, still more preferably from 1 to 30 mol %, based on all repeating units. 
     The content of the repeating unit represented by formula (A1) in the resin (A) is preferably from 10 to 90 mol %, more preferably from 20 to 80 mol %, still more preferably from 30 to 70 mol %, based on all repeating units. 
     The content of the repeating unit represented by formula (A2) in the resin (A) is preferably from 5 to 85 mol %, more preferably from 10 to 75 mol %, still more preferably from 15 to 65 mol %, based on all repeating units. 
     As regards each of these repeating units, a plurality of species may be contained in the resin, and the contents above each is a total amount. 
     The resin (A) may further contain a repeating unit represented by formula (A4) and this is preferred from the standpoint oft for example, enhancing the film quality and reducing the film loss in the unexposed area. The content of the repeating unit represented by formula (A4) is preferably from 0 to 50 mol %, more preferably from 0 to 40 mol %, still more preferably from 0 to 30 mol %, based on all repeating units. 
     In the resin (A), for maintaining good developability in an alkali developer, another appropriate polymerizable monomer may be copolymerized so that an alkali-soluble group such as phenolic hydroxyl group and carboxyl group can be introduced, or for enhancing the film property, another hydrophobic polymerizable monomer such as alkyl acrylate and alkyl methacrylate may be copolymerized. 
     The weight average molecular weight (Mw) of the resin (A) is preferably from 1,000 to 200,000. The weight average molecular weight is preferably 200,000 or less in view of dissolution rate of the resin itself in an alkali and sensitivity. The dispersity (Mw/Mn) is preferably from 1.0 to 3.0, more preferably from 1.0 to 2.5, still more preferably from 1.0 to 2.0, Above all, the weight average molecular weight (Mw) of the resin is preferably from 1,000 to 200,000, more preferably from 1,000 to 100,000, still more preferably from 1,000 to 50,000, and most preferably from 1,000 to 25,000. 
     Here, the weight average molecular weight is defined as a polystyrene-reduced value determined by gel permeation chromatography. 
     The resin (A) having a dispersity of 1.5 to 2.0 can be synthesized by radical polymerization using an azo-based polymerization initiator. Also, the resin (A) having a still more preferred dispersity of 1.0 to 1.5 can be synthesized by living radical polymerization. 
     As for the resin (A), two or more kinds may be used in combination. 
     The amount of the resin (A) added is, in terms of the total amount, usually from 10 to 99 mass %, preferably from 20 to 99 mass %, more preferably from 30 to 99 mass %, based on the entire solid content of the positive resist composition. (In this specification, mass ratio is equal to weight ratio.) 
     Specific examples of the (A) resin containing a repeating unit represented by formula (I) or (I′) are set forth below, but the present invention is not limited thereto. 
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
[2] (B) Compound Capable of Generating an Acid Upon Irradiation with Actinic Rays or Radiation
 
     The resist composition of the present invention comprises a compound capable of generating an acid upon irradiation with actinic rays or radiation (hereinafter sometimes referred to as an “acid generator”). 
     The acid generator which can be used may be appropriately selected from a photoinitiator for photocationic polymerization, a photoinitiator for photoradical polymerization, a photo-decoloring agent for coloring matters, a photo-discoloring agent, a compound known to generate an acid upon irradiation with actinic rays or radiation such as KrF excimer laser light, electron beam and EUV and used for microresist or the like, and a mixture thereof. 
     Examples of such an acid generator include a diazonium salt, a phosphonium salt, a sulfonium salt, an iodonium salt, imidosulfonate, oxime sulfonate, diazodisulfone, disulfone and o-nitrobenzyl sulfonate. The acid generator is preferably oxime sulfonate or diazodisulfone. 
     Also, a compound where a group or compound capable of generating an acid upon irradiation with actinic rays or radiation is introduced into the main or side chain of a polymer, for example, compounds described in U.S. Pat. No. 3,849,137, German Patent 3,914,407, JP-A-63-26653, JP-A-55-164824, JP-A-62-69263, JP-A-63-146038, JP-A-63-163452, JP-A-62-153853 and JP-A-63-146029, may be used. 
     Furthermore, compounds capable of generating an acid by the effect of light described, for example, in U.S. Pat. No. 3,779,778 and European Patent 126,712 may also be used. 
     Out of the acid generators, the compounds represented by the following formulae (ZI), (ZII) and (ZIII) are preferred. 
     
       
         
         
             
             
         
       
     
     In formula (ZI), R 201 , R 202  and R 203  each independently represents an organic group. 
     The number of carbons in the organic group as R 201 , R 202  and R 203  is generally from 1 to 30, preferably from 1 to 20. 
     Two members out of R 201  to R 203  may combine with each other to form a ring structure, and the ring may contain an oxygen atom, a sulfur atom, an ester bond, an amide bond or a carbonyl group. Examples of the group formed by combining two members out of R 201  to R 203  include an alkylene group (e.g., butylene, pentylene). 
     Z −  represents a non-nucleophilic anion. 
     Examples of the non-nucleophilic anion as Z −  include sulfonate anion, carboxylate anion, sulfonylimide anion, bis(alkylsulfonyl)imide anion and tris(alkylsulfonyl)methyl anion. 
     The non-nucleophilic anion is an anion having an extremely low ability of causing a nucleophilic reaction and this anion can suppress the decomposition with aging due to intramolecular nucleophilic reaction. By this anion, the aging stability of the resist is enhanced. 
     Examples of the sulfonate anion include aliphatic sulfonate anion, aromatic sulfonate anion and camphorsulfonate anion. 
     Examples of the carboxylate anion include aliphatic carboxylate anion, aromatic carboxylate anion and aralkylcarboxylate anion. 
     The aliphatic moiety in the aliphatic sulfonate anion may be an alkyl group or a cycloalkyl group but is preferably an alkyl group having a carbon number of 1 to 30 or a cycloalkyl group having a carbon number of 3 to 30, and examples thereof include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a pentyl group, a neopentyl 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, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, a nonadecyl group, an eicosyl group, a cyclopropyl group, a cyclopentyl group, a cyclohexyl group, an adamantyl group, a norbornyl group and a boronyl group. 
     The aromatic group in the aromatic sulfonate anion is preferably an aryl group having a carbon number of 6 to 14, and examples thereof include a phenyl group, a tolyl group and a naphthyl group. 
     The alkyl group, cycloalkyl group and aryl group in the aliphatic sulfonate anion and aromatic sulfonate anion each may have a substituent. Examples of the substituent of the alkyl group, cycloalkyl group and aryl group in the aliphatic sulfonate anion and aromatic sulfonate anion include a nitro group, a halogen atom (e.g., fluorine, chlorine, bromine, iodine), a carboxyl group, a hydroxyl group, an amino group, a cyano group, an alkoxy group (preferably having a carbon number of 1 to 15), a cycloalkyl group (preferably having a carbon number of 3 to 15), an aryl group (preferably having a carbon number of 6 to 14), an alkoxycarbonyl group (preferably having a carbon number of 2 to 7), an acyl group (preferably having a carbon number of 2 to 12), an alkoxycarbonyloxy group (preferably having a carbon number of 2 to 7), an alkylthio group (preferably having a carbon number of 1 to 15), an alkylsulfonyl group (preferably having a carbon number of 1 to 15), an alkyliminosulfonyl group (preferably having a carbon number of 2 to 15), an aryloxysulfonyl group (preferably having a carbon number of 6 to 20), an alkylaryloxysulfonyl group (preferably having a carbon number of 7 to 20), a cycloalkylaryloxysulfonyl group (preferably having a carbon number of 10 to 20), an alkyloxyalkyloxy group (preferably having a carbon number of 5 to 20), and a cycloalkylalkyloxyalkyloxy group (preferably having a carbon number of 8 to 20). As for the aryl group or ring structure in each group, examples of the substituent further include an alkyl group (preferably having a carbon number of 1 to 15). 
     Examples of the aliphatic moiety in the aliphatic carboxylate anion include the same alkyl group and cycloalkyl group as in the aliphatic sulfonate anion. 
     Examples of the aromatic group in the aromatic carboxylate anion include the same aryl group as in the aromatic sulfonate anion. 
     The aralkyl group in the aralkylcarboxylate anion is preferably an aralkyl group having a carbon number of 6 to 12, and examples thereof include a benzyl group, a phenethyl group, a naphthylmethyl group, a naphthylethyl group and a naphthylmethyl group. 
     The alkyl group, cycloalkyl group, aryl group and aralkyl group in the aliphatic carboxylate anion, aromatic carboxylate anion and aralkylcarboxylate anion each may have a substituent. Examples of the substituent of the alkyl group, cycloalkyl group, aryl group and aralkyl group in the aliphatic carboxylate anion, aromatic carboxylate anion and aralkylcarboxylate anion include the same halogen atom, alkyl group, cycloalkyl group, alkoxy group and alkylthio group as in the aromatic sulfonate anion. 
     Examples of the sulfonylimide anion include saccharin anion. 
     The alkyl group in the bis(alkylsulfonyl)imide anion and tris(alkylsulfonyl)methyl anion is preferably an alkyl group having a carbon number of 1 to 5, and examples thereof include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a pentyl group and a neopentyl group. Examples of the substituent of such an alkyl group include a halogen atom, a halogen atom-substituted alkyl group, an alkoxy group, an alkylthio group, an alkyloxysulfonyl group, an aryloxysulfonyl group, and a cycloalkylaryloxysulfonyl group, with a fluorine atom-substituted alkyl group being preferred. 
     Other examples of the non-nucleophilic anion include fluorinated phosphorus, fluorinated boron and fluorinated antimony. 
     The non-nucleophilic anion of Z −  is preferably an aliphatic sulfonate anion substituted by a fluorine atom at the α-position of the sulfonic acid, an aromatic sulfonate anion substituted by a fluorine atom or a group having a fluorine atom, a bis(alkylsulfonyl)imide anion with the alkyl group being substituted by a fluorine atom, or a tris(alkylsulfonyl)methide anion with the alkyl group being substituted by a fluorine atom. The non-nucleophilic anion is more preferably a perfluoroaliphatic sulfonate anion having a carbon number of 4 to 8 or a benzenesulfonate anion having a fluorine atom, still more preferably nonafluorobutanesulfonate anion, perfluorooctanesulfonate anion, pentafluorobenzenesulfonate anion or 3,5-bis(trifluoromethyl)benzenesulfonate anion. 
     Examples of the organic group as R 201 , R 202  and R 203  include the corresponding groups in the compounds (ZI-1), (ZI-2) and (ZI-3) described later. 
     The compound may be a compound having a plurality of structures represented by formula (ZI), for example, may be a compound having a structure where at least one of R 201  to R 203  in the compound represented by formula (ZI) is bonded to at least one of R 201  to R 203  in another compound represented by formula (ZI). 
     The component (ZI) is more preferably a compound (ZI-1), (ZI-2) or (ZI-3) described below. 
     The compound (ZI-1) is an arylsulfonium compound where at least one of R 201  to R 203  in formula (ZI) is an aryl group, that is, a compound having arylsulfonium as the cation. 
     In the arylsulfonium compound, R 201  to R 203  all may be an aryl group or a part of R 201  to R 203  may be an aryl group with the remaining being an alkyl group or a cycloalkyl group. 
     Examples of the arylsulfonium compound include a triarylsulfonium compound, a diarylalkylsulfonium compound, an aryldialkylsulfonium compound, a diarylcycloalkylsulfonium compound and an aryldicycloalkylsulfonium compound. 
     The aryl group in the arylsulfonium compound is preferably a phenyl group or a naphthyl group, more preferably a phenyl group. The aryl group may be an aryl group having a heterocyclic structure containing an oxygen atom, a nitrogen atom, a sulfur atom or the like. Examples of the aryl group having a heterocyclic structure include a pyrrole residue (a group formed by removing one hydrogen atom from a pyrrole), a furan residue (a group formed by removing one hydrogen atom from a furan), a thiophene residue (a group formed by removing one hydrogen atom from a thiophene), an indole residue (a group formed by removing one hydrogen atom from an indole), a benzofuran residue (a group formed by removing one hydrogen atom from a benzofuran) and a benzothiophene residue (a group formed by removing one hydrogen atom from a benzothiophene). In the case where the arylsulfonium compound has two or more aryl groups, these two or more aryl groups may be the same or different. 
     The alkyl or cycloalkyl group which is present, if desired, in the arylsulfonium compound is preferably a linear or branched alkyl group having a carbon number of 1 to 15 or a cycloalkyl group having a carbon number of 3 to 15, and examples thereof include a methyl group, an ethyl group, a propyl group, an n-butyl group, a sec-butyl group, a tert-butyl group, a cyclopropyl group, a cyclobutyl group and a cyclohexyl group. 
     The aryl group, alkyl group and cycloalkyl group of R 201  to R 203  each may have, as the substituent, an alkyl group (for example, an alkyl group having a carbon number of 1 to 15), a cycloalkyl group (for example, a cycloalkyl group having a carbon number of 3 to 15), an aryl group (for example, an aryl group having a carbon number of 6 to 14), an alkoxy group (for example, an alkoxy group having a carbon number of 1 to 15), a halogen atom, a hydroxyl group or a phenylthio group. The substituent is preferably a linear or branched alkyl group having a carbon number of 1 to 12, a cycloalkyl group having a carbon number of 3 to 12, or a linear, branched or cyclic alkoxy group having a carbon number of 1 to 12, more preferably an alkyl group having a carbon number of 1 to 4, or an alkoxy group having a carbon number of 1 to 4. The substituent may be substituted to any one of three members R 201  to R 203  or may be substituted to all of these three members. In the case where R 201  to R 203  are an aryl group, the substituent is preferably substituted at the p-position of the aryl group. 
     The compound (ZI-2) is described below. 
     The compound (ZI-2) is a compound where R 201  to R 203  in formula (ZI) each independently represents an aromatic ring-free organic group. The aromatic ring as used herein includes an aromatic ring containing a heteroatom. 
     The aromatic ring-free organic group as R 201  to R 203  has a carbon number of generally from 1 to 30, preferably from 1 to 20. 
     R 201  to R 203  each independently represents preferably an alkyl group, a cycloalkyl group, an allyl group or a vinyl group, more preferably a linear or branched 2-oxoalkyl group, a 2-oxocycloalkyl group or an alkoxycarbonylmethyl group, still more preferably a linear or branched 2-oxoalkyl group. 
     The alkyl group or cycloalkyl group of R 201  to R 203  is preferably a linear or branched alkyl group having a carbon number of 1 to 10 (e.g., methyl, ethyl, propyl, butyl, pentyl) or a cycloalkyl group having a carbon number of 3 to 10 (e.g., cyclopentyl, cyclohexyl, norbornyl). The alkyl group is more preferably a 2-oxoalkyl group or an alkoxycarbonylmethyl group. The cycloalkyl group is more preferably a 2-oxocycloalkyl group. 
     The 2-oxoalkyl group may be either linear or branched and is preferably a group having &gt;C═O at the 2-position of the above-described alkyl group. 
     The 2-oxocycloalkyl group is preferably a group having &gt;C═O at the 2-position of the above-described cycloalkyl group. 
     The alkoxy group in the alkoxycarbonylmethyl group is preferably an alkoxy group having a carbon number of 1 to 5 (e.g., methoxy, ethoxy, propoxy, butoxy, pentoxy). 
     R 201  to R 203  each may be further substituted by a halogen atom, an alkoxy group (for example, an alkoxy group having a carbon number of 1 to 5), a hydroxyl group, a cyano group or a nitro group. 
     The compound (ZI-3) is a compound represented by the following formula (ZI-3), and this is a compound having a phenacylsulfonium salt structure. 
     
       
         
         
             
             
         
       
     
     In formula (ZI-3), R 1c  to R 5c  each independently represents a hydrogen atom, an alkyl group, a cycloalkyl group, an alkoxy group or a halogen atom. 
     R 6c  and R 7c  each independently represents a hydrogen atom, an alkyl group or a cycloalkyl group. 
     R x  and R y  each independently represents an alkyl group, a cycloalkyl group, an allyl group or a vinyl group. 
     Any two or more members out of R 1c  to R 5c , a pair of R 6c  and R 7c , or a pair of R x  and R y  may combine with each other to form a ring structure. This ring structure may contain an oxygen atom, a sulfur atom, an ester bond or an amido bond. Examples of the group formed by combining any two or more members out of R 1c  to R 5c , a pair of R 6c  and R 7c , or a pair of R x  and R y  include a butylene group and a pentylene group. 
     Zc −  represents a non-nucleophilic anion, and examples thereof are the same as those of the non-nucleophilic anion of Z −  in formula (ZI). 
     The alkyl group as R 1c  to R 7c  may be either linear or branched and is, for example, an alkyl group having a carbon number of 1 to 20, preferably a linear or branched alkyl group having a carbon number of 1 to 12 (e.g., methyl, ethyl, linear or branched propyl, linear or branched butyl, linear or branched pentyl). The cycloalkyl group is, for example, a cycloalkyl group having a carbon number of 3 to 8 (e.g., cyclopentyl, cyclohexyl). 
     The alkoxy group as R 1c  to R 5c  may be linear, branched or cyclic and is, for example, an alkoxy group having a carbon number of 1 to 10, preferably a linear or branched alkoxy group having a carbon number of 1 to 5 (e.g., methoxy, ethoxy, linear or branched propoxy, linear or branched butoxy, linear or branched pentoxy) or a cyclic alkoxy group having a carbon number of 3 to 8 (e.g., cyclopentyloxy, cyclohexyloxy). 
     A compound where any one of R 1c  to R 5c  is a linear or branched alkyl group, a cycloalkyl group or a linear, branched or cyclic alkoxy group is preferred, and a compound where the sum of carbon numbers of R 1c  to R 5c  is from 2 to 15 is more preferred. By virtue of such a compound, the solvent solubility is more enhanced and production of particles during storage can be suppressed. 
     Examples of the alkyl group and cycloalkyl group as R x  and R y  are the same as those of the alkyl group and cycloalkyl group in R 1c  to R 7c . Among these, a 2-oxoalkyl group, a 2-oxocycloalkyl group and an alkoxycarbonylmethyl group are preferred. 
     Examples of the 2-oxoalkyl group and 2-oxocycloalkyl group include a group having &gt;C═O at the 2-position of the alkyl group or cycloalkyl group as R 1c  to R 7c . 
     Examples of the alkoxy group in the alkoxycarbonylmethyl group are the same as those of the alkoxy group in R 1c  to R 5c . 
     R x  and R y  each is preferably an alkyl or cycloalkyl group having a carbon number of 4 or more, more preferably 6 or more, still more preferably 8 or more. 
     In formulae (ZII) and (ZIII), R 204  to R 207  each independently represents an aryl group, an alkyl group or a cycloalkyl group. 
     The aryl group of R 204  to R 207  is preferably a phenyl group or a naphthyl group, more preferably a phenyl group. The aryl group of R 204  to R 207  may be an aryl group having a heterocyclic structure containing an oxygen atom, a nitrogen atom, a sulfur atom or the like. Examples of the aryl group having a heterocyclic structure include a pyrrole residue (a group formed by removing one hydrogen atom from a pyrrole), a furan residue (a group formed by removing one hydrogen atom from a furan), a thiophene residue (a group formed by removing one hydrogen atom from a thiophene), an indole residue (a group formed by removing one hydrogen atom from an indole), a benzofuran residue (a group formed by removing one hydrogen atom from a benzofuran) and a benzothiophene residue (a group formed by removing one hydrogen atom from a benzothiophene). 
     The alkyl group and cycloalkyl group in R 204  to R 207  are preferably a linear or branched alkyl group having a carbon number of 1 to 10 (e.g., methyl, ethyl, propyl, butyl, pentyl) and a cycloalkyl group having a carbon number of 3 to 10 (e.g., cyclopentyl, cyclohexyl, norbornyl). 
     The aryl group, alkyl group and cycloalkyl group of R 204  to R 207  each may have a substituent. Examples of the substituent which the aryl group, alkyl group and cycloalkyl group of R 204  to R 207  each may have include an alkyl group (for example, an alkyl group having a carbon number of 1 to 15), a cycloalkyl group (for example, a cycloalkyl group having a carbon number of 3 to 15), an aryl group (for example, an aryl group having a carbon number of 6 to 15), an alkoxy group (for example, an alkoxy group having a carbon number of 1 to 15), a halogen atom, a hydroxyl group and a phenylthio group. 
     Z −  represents a non-nucleophilic anion, and examples thereof are the same as those of the non-nucleophilic anion of Z −  in formula (ZI). 
     Other examples of the acid generator include the compounds represented by the following formulae (ZIV), (ZV) and (ZVI), and a compound having a molecular weight of 3,000 or less is preferred. 
     
       
         
         
             
             
         
       
     
     In formulae (ZIV) to (ZVI), Ar 3  and Ar 4  each independently represents an aryl group. 
     R 206 , R 207  and R 208  each independently represents an alkyl group, a cycloalkyl group or an aryl group. 
     A represents an alkylene group, an alkenylene group or an arylene group. 
     The acid generator is preferably a compound capable of generating an acid having one sulfonic acid group or imide group, more preferably a compound capable of generating a monovalent perfluoroalkanesulfonic acid, a compound capable of generating a monovalent aromatic sulfonic acid substituted by a fluorine atom or a fluorine atom-containing group, or a compound capable of generating a monovalent imide acid substituted by a fluorine atom or a fluorine atom-containing group, still more preferably a sulfonium salt of fluoro-substituted alkanesulfonic acid, fluorine-substituted benzenesulfonic acid, fluorine-substituted imide acid or fluorine-substituted methide acid. In particular, the acid generated from the acid generator which can be used is preferably a fluoro-substituted alkanesulfonic acid, fluoro-substituted benzenesulfonic acid or fluoro-substituted imide acid having a pKa of −1 or less and in this case, the sensitivity can be enhanced. 
     &lt;Sulfonic Acid Generator&gt; 
     The compound capable of generating a sulfonic acid upon irradiation with actinic rays or radiation (hereinafter, sometimes referred to as a “sulfonic acid generator”), which is preferred as the acid generator, is a compound capable of generating a sulfonic acid upon irradiation with actinic rays or radiation such as KrF excimer laser light, electron beam and EUV, and examples thereof include a diazonium salt, a phosphonium salt, a sulfonium salt, an iodonium salt, imidosulfonate, oxime sulfonate, diazodisulfone, disulfone and o-nitrobenzyl sulfonate. 
     From the standpoint of enhancing the image performance such as resolving power and pattern profile, a sulfonium salt, an iodonium salt, imidosulfonate, oxime sulfonate, diazodisulfone and disulfone are preferred. 
     In consideration of remaining of a standing wave, imidosulfonate, oxime sulfonate, diazodisulfone and disulfone are more preferred, and oxime sulfonate and diazodisulfone are still more preferred. 
     The sulfonic acid generator can be synthesized by a known method such as synthesis method described in JP-A-2002-27806. 
     Particularly preferred examples of the sulfonic acid generator are set forth below. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     The content of the acid generator used is from 0.5 to 20 mass %, preferably from 1 to 15 mass %, more preferably from 1 to 10 mass %, based on the entire solid content of the resist composition. That is, the content is preferably 1 mass % or more in view of sensitivity or line edge roughness and preferably 10 mass % or less in view of resolving power, pattern profile and film quality. 
     One kind of the acid generator may be used, or two or more kinds thereof may be mixed and used. For example, a compound capable of generating an arylsulfonic acid upon irradiation with actinic rays or radiation and a compound capable of generating an alkylsulfonic acid upon irradiation with actinic rays or radiation may be used in combination as the acid generator. 
     &lt;Carboxylic Acid Generator&gt; 
     A compound capable of generating a carboxylic acid upon irradiation with actinic rays or radiation (hereinafter, sometimes referred to as a “carboxylic acid generator”) may also be used as the acid generator. 
     The carboxylic acid generator is preferably a compound represented by the following formula (C): 
     
       
         
         
             
             
         
       
     
     In formula (C), R 21  to R 23  each independently represents an alkyl group, a cycloalkyl group, an alkenyl group or an aryl group, R 24  represents a hydrogen atom, an alkyl group, a cycloalkyl group, an alkenyl group or an aryl group, and Z represents a sulfur atom or an iodine atom. When Z is a sulfur atom, p is 1, and when an iodine atom, p is 0. 
     In formula (C), R 21  to R 23  each independently represents an alkyl group, a cycloalkyl group, an alkenyl group or an aryl group, and these groups each may have a substituent. 
     Examples of the substituent which the alkyl group, cycloalkyl group and alkenyl group each may have include a halogen atom (e.g., chlorine, bromine, fluorine), an aryl group (e.g., phenyl, naphthyl), a hydroxy group and an alkoxy group (e.g., methoxy, ethoxy, butoxy). 
     Examples of the substituent which the aryl group may have include a halogen atom (e.g., chlorine, bromine, fluorine), a nitro group, a cyano group, an alkyl group (e.g., methyl, ethyl, tert-butyl, tert-amyl, octyl), a hydroxy group and an alkoxy group (e.g., methoxy, ethoxy, butoxy). 
     R 21  to R 23  each is, independently, preferably an alkyl group having a carbon number of 1 to 12, a cycloalkyl group having a carbon number of 3 to 12, an alkenyl group having a carbon number of 2 to 12, or an aryl group having a carbon number of 6 to 24, more preferably an alkyl group having a carbon number of 1 to 6, a cycloalkyl group having a carbon number of 3 to 6, or an aryl group having a carbon number of 6 to 18, still more preferably an aryl group having a carbon number of 6 to 15, and these groups each may have a substituent. 
     R 24  represents a hydrogen atom, an alkyl group, a cycloalkyl group, an alkenyl group or an aryl group. 
     Examples of the substituent which the alkyl group, cycloalkyl group and alkenyl group each may have are the same as those of the substituent described above when R 21  is an alkyl group. Examples of the substituent of the aryl group are the same as those of the substituent described above when R 21  is an aryl group. 
     R 24  is preferably a hydrogen atom, an alkyl group having a carbon number of 1 to 30, a cycloalkyl group having a carbon number of 3 to 30, an alkenyl group having a carbon number of 2 to 30, or an aryl group having a carbon number of 6 to 24, more preferably an alkyl group having a carbon number of 1 to 18, a cycloalkyl group having a carbon number of 3 to 18, or an aryl group having a carbon number of 6 to 18, still more preferably an alkyl group having a carbon number of 1 to 12, a cycloalkyl group having a carbon number of 3 to 12, or an aryl group having a carbon number of 6 to 15. These groups each may have a substituent. 
     Z represents a sulfur atom or an iodine atom. p is 1 when Z is a sulfur atom, and 0 when Z is an iodine atom. 
     Incidentally, two or more cation moieties of formula (C) may combine through a single bond or a linking group (e.g., —S—, —O—) to form a cation structure having a plurality of cation moieties of formula (C). 
     Specific preferred examples of the carboxylic acid generator are set forth below, but the present invention is of course not limited thereto. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In the case of using a carboxylic acid generator, the content of the carboxylic acid generator in the positive resist composition of the present invention is preferably from 0.01 to 10 mass %, more preferably from 0.03 to 5 mass %, still more preferably from 0.05 to 3 mass %, based on the entire solid content of the composition. One kind of these carboxylic acid generators may be used, or two or more kinds thereof may be mixed and used. 
     The carboxylic acid generator can be synthesized by a known method such as synthesis method described in JP-A-2002-27806. 
     In the case of using a sulfonic acid generator (B) and a carboxylic acid generator (C) in combination, C/B (ratio by mass) is usually from 99.9/0.1 to 50/50, preferably from 99/1 to 60/40, more preferably from 98/2 to 70/30. 
     [3] Compound Having a Proton Acceptor Functional Group and Undergoing Decomposition Upon Irradiation with Actinic Rays or Radiation to Generate a Compound Reduced in or Deprived of the Proton Acceptor Property or Changed to be Acidic from Being Proton Acceptor-Functioning 
     In view of sensitivity, resolution and line edge roughness, the positive resist composition of the present invention preferably contains a compound having a proton acceptor functional group and undergoing decomposition upon irradiation with actinic rays or radiation to generate a compound reduced in or deprived of the proton acceptor property or changed to be acidic from being proton acceptor-functioning (Hereinafter sometimes referred to as a “compound (PA)”). 
     The compound reduced in or deprived of the proton acceptor property or changed to be acidic from being proton acceptor-functioning, which is generated resulting from decomposition of the compound (PA) upon irradiation with actinic rays or radiation, includes a compound represented by the following formula (PA-I): 
     The compound reduced in or deprived of the proton acceptor property or changed to be acidic from being proton acceptor-functioning, which is generated resulting from decomposition of the compound (PA) upon irradiation with actinic rays or radiation, includes a compound represented by the following formula (PA-I):
 
Q-A-(X) n —B—R   (PA-I)
 
     In formula (PA-I), Q represents a sulfo group (—SO 3 H) or a carboxyl group (—CO 2 H). 
     A represents a divalent linking group. 
     X represents —SO 2 — or —CO—. 
     n represents 0 or 1. 
     B represents a single bond, an oxygen atom or —N(Rx)-. Rx represents a hydrogen atom or a monovalent organic group. 
     R represents a monovalent organic group containing a proton acceptor functional group, or a monovalent organic group containing an ammonium group. 
     The divalent linking group of A is preferably a divalent linking group having a carbon number of 2 to 12, such as alkylene group and phenylene group, more preferably an alkylene group having at least one fluorine atom, and the carbon number thereof is preferably from 2 to 6, more preferably from 2 to 4. The alkylene chain may contain a linking group such as oxygen atom and sulfur atom. The alkylene group is preferably an alkylene group where from 30 to 100% by number of the hydrogen atom is replaced by a fluorine atom, more preferably an alkylene group where the carbon atom bonded to the Q site has a fluorine atom, still more preferably a perfluoroalkylene group, yet still more preferably a perfluoroethylene group, a perfluoropropylene group, or a perfluorobutylene group. 
     The monovalent organic group of Rx is preferably a monovalent organic group having a carbon number of 4 to 30, and examples thereof include an alkyl group, a cycloalkyl group, an aryl group, an aralkyl group and an alkenyl group. 
     The alkyl group of Rx, which may have a substituent, is preferably a linear or branched alkyl group having a carbon number of 1 to 20 and may contain an oxygen atom, a sulfur atom or a nitrogen atom in the alkyl chain. Specific examples thereof include a linear alkyl group such as methyl group, ethyl group, n-propyl group, n-butyl group, n-pentyl group, n-hexyl group, n-octyl group, n-dodecyl group, n-tetradecyl group and n-octadecyl group; and a branched alkyl group such as isopropyl group, isobutyl group, tert-butyl group, neopentyl group and 2-ethylhexyl group. 
     The alkyl group having a substituent includes, particularly, a group where a cycloalkyl group is substituted to a linear or branched alkyl group, such as adamantylmethyl group, adamantylethyl group, cyclohexylethyl group and camphor residue. 
     The cycloalkyl group of Rx, which may have a substituent, is preferably a cycloalkyl group having a carbon number of 3 to 20 and may contain an oxygen atom in the ring. Specific examples thereof include a cyclopropyl group, a cyclopentyl group, a cyclohexyl group, a norbornyl group and an adamantyl group. 
     The aryl group of Rx, which may have a substituent, is preferably an aryl group having a carbon number of 6 to 14, and examples thereof include a phenyl group and a naphthyl group. 
     The aralkyl group of Rx, which may have a substituent, is preferably an aralkyl group having a carbon number of 7 to 20, and examples thereof include a benzyl group, a phenethyl group, a naphthylmethyl group and a naphthylethyl group. 
     The alkenyl group of Rx, which may have a substituent, includes, for example, a group having a double bond at an arbitrary position of the alkyl group described as Rx. 
     The proton acceptor functional group of R is a functional group having a group or electron capable of electrostatically interacting with a proton and indicates, for example, a functional group having a macrocyclic structure such as cyclic polyether, or a functional group containing a nitrogen atom having a lone electron pair not contributing to π-conjugation. The nitrogen atom having a lone electron pair not contributing to π-conjugation is, for example, a nitrogen atom having a partial structure represented by either one of the following formulae: 
                         
unshared electron pair
 
     Preferred examples of the partial structure of the proton acceptor functional group include a crown ether structure, an aza-crown ether structure, a tertiary amine structure, a secondary amine structure, a primary amine structure, a pyridine structure, an imidazole structure and a pyrazine structure. 
     Preferred examples of the partial structure of the ammonium group include a tertiary ammonium structure, a secondary ammonium structure, a primary ammonium structure, a pyridinium structure, an imidazolinium structure and a pyrazinium structure. 
     The group containing such a structure preferably has a carbon number of 4 to 30, and examples thereof include an alkyl group, a cycloalkyl group, an aryl group, an aralkyl group and an alkenyl group. 
     The alkyl group, cycloalkyl group, aryl group, aralkyl group and alkenyl group in the alkyl group, cycloalkyl group, aryl group, aralkyl group or alkenyl group as R containing a proton acceptor functional group or an ammonium group are the same as the alkyl group, cycloalkyl group, aryl group, aralkyl group and alkenyl group described for Rx. 
     Examples of the substituent which the above-described groups each may have include a halogen atom, a hydroxyl group, a nitro group, a cyano group, a carboxy group, a carbonyl group, a cycloalkyl group (preferably having a carbon number of 3 to 10), an aryl group (preferably having a carbon number of 6 to 14), an alkoxy group (preferably having a carbon number of 1 to 10), an acyl group (preferably having a carbon number of 2 to 20), an acyloxy group (preferably having a carbon number of 2 to 10), an alkoxycarbonyl group (preferably having a carbon number of 2 to 20), and an aminoacyl group (preferably having a carbon number of 2 to 20). As for the cyclic structure in the aryl group, cycloalkyl group and the like, examples of the substituent further include an alkyl group (preferably having a carbon number of 1 to 20). As for the aminoacyl group, examples of the substituent further include one or two alkyl groups (preferably having a carbon number of 1 to 20). 
     When B is —N(Rx)-, R and Rx preferably combine with each other to form a ring. By forming a ring structure, the stability is enhanced and the composition using this compound is also increased in the storage stability. The number of carbons constituting the ring is preferably from 4 to 20, and the ring may be monocyclic or polycyclic and may contain an oxygen atom, a sulfur atom or a nitrogen atom. 
     Examples of the monocyclic structure include a 4-membered ring, a 5-membered ring, a 6-membered ring, a 7-membered ring and a 8-membered ring each containing a nitrogen atom. Examples of the polycyclic structure include a structure comprising a combination of two monocyclic structures or three or more monocyclic structures. The monocyclic structure and polycyclic structure each may have a substituent, and preferred examples of the substituent include a halogen atom, a hydroxyl group, a cyano group, a carboxy group, a carbonyl group, a cycloalkyl group (preferably having a carbon number of 3 to 10), an aryl group (preferably having a carbon number of 6 to 14), an alkoxy group (preferably having a carbon number of 1 to 10), an acyl group (preferably having a carbon number of 2 to 15), an acyloxy group (preferably having a carbon number of 2 to 15), an alkoxycarbonyl group (preferably having a carbon number of 2 to 15), and an aminoacyl group (preferably having a carbon number of 2 to 20). As for the cyclic structure in the aryl group, cycloalkyl group and the like, examples of the substituent further include an alkyl group (preferably having a carbon number of 1 to 15). As for the aminoacyl group, examples of the substituent further include one or two alkyl groups (preferably having a carbon number of 1 to 15). 
     Out of the compounds represented by formula (PA-I), a compound where the Q site is a sulfonic acid can be synthesized using a general sulfonamidation reaction. For example, this compound can be obtained by a method of selectively reacting one sulfonyl halide moiety of a bis-sulfonyl halide compound with an amine compound to form a sulfonamide bond, and then hydrolyzing the other sulfonyl halide moiety, or a method of ring-opening a cyclic sulfonic anhydride through reaction with an amine compound. 
     Specific examples of the compound represented by formula (PA-I) are set forth below, but the present invention is not limited thereto. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     The compound reduced in or deprived of the proton acceptor property or changed to be acidic from being proton acceptor-functioning, which is generated resulting from decomposition of the compound (PA) upon irradiation with actinic rays or radiation, also includes a compound represented by the following formula (PA-II):
 
Q 1 -X 1 —NH—X 2 -Q 2    (PA-II)
 
     In formula (PA-II), Q 1  and Q 2  each independently represents a monovalent organic group, provided that either one of Q 1  and Q 2  has a proton acceptor functional group. Q 1  and Q 2  may combine with each other to form a ring and the ring formed may have a proton acceptor functional group. 
     X 1  and X 2  each independently represents —CO— or —SO 2 —. 
     The monovalent organic group of Q 1  and Q 2  in formula (PA-II) is preferably a monovalent organic group having a carbon number of 1 to 40, and examples thereof include an alkyl group, a cycloalkyl group, an aryl group, an aralkyl group, and an alkenyl group. 
     The alkyl group of Q 1  and Q 2 , which may have a substituent, is preferably a linear or branched alkyl group having a carbon number of 1 to 30 and may contain an oxygen atom, a sulfur atom or a nitrogen atom in the alkyl chain. Specific examples thereof include a linear alkyl group such as methyl group, ethyl group, n-propyl group, n-butyl group, n-pentyl group, n-hexyl group, n-octyl group, n-dodecyl group, n-tetradecyl group and n-octadecyl group; and a branched alkyl group such as isopropyl group, isobutyl group, tert-butyl group, neopentyl group and 2-ethylhexyl group. 
     The cycloalkyl group of Q 1  and Q 2 , which may have a substituent, is preferably a cycloalkyl group having a carbon number of 3 to 20 and may contain an oxygen atom or a nitrogen atom in the ring. Specific examples thereof include a cyclopropyl group, a cyclopentyl group, a cyclohexyl group, a norbornyl group and an adamantyl group. 
     The aryl group of Q 1  and Q 2 , which may have a substituent is preferably an aryl group having a carbon number of 6 to 14, and examples thereof include a phenyl group and a naphthyl group. 
     The aralkyl group of Q 1  and Q 2 , which may have a substituent, is preferably an aralkyl group having a carbon number of 7 to 20, and examples thereof include a benzyl group, a phenethyl group, a naphthylmethyl group and a naphthylethyl group. 
     The alkenyl group of Q 1  and Q 2 , which may have a substituent, includes a group having a double bond at an arbitrary position of the alkyl group above. 
     Examples of the substituent which these groups each may have include a halogen atom, a hydroxyl group, a nitro group, a cyano group, a carboxy group, a carbonyl group, a cycloalkyl group preferably having a carbon number of 3 to 10), an aryl group (preferably having a carbon number of 6 to 14), an alkoxy group (preferably having a carbon number of 1 to 10), an acyl group (preferably having a carbon number of 2 to 20), an acyloxy group (preferably having a carbon number of 2 to 10), an alkoxycarbonyl group (preferably having a carbon number of 2 to 20), and an aminoacyl group (preferably having a carbon number of 2 to 10). As for the cyclic structure in the aryl group, cycloalkyl group and the like, examples of the substituent further include an alkyl group (preferably having a carbon number of 1 to 10). As for the aminoacyl group, examples of the substituent further include an alkyl group (preferably having a carbon number of 1 to 10). Examples of the alkyl group having a substituent include a perfluoroalkyl group such as perfluoromethyl group, perfluoroethyl group, perfluoropropyl group and perfluorobutyl group. 
     Either one monovalent organic group Q 1  or Q 2  has a proton acceptor functional group. 
     The proton acceptor functional group may be substituted by an organic group having a bond which is breakable by an acid. Examples of the organic group having a bond breakable by an acid include an amido group, an ester group (preferably a tertiary alkyloxycarbonyl group), an acetal group (preferably a 1-alkyloxy-alkyloxy group), a carbamoyl group and a carbonate group. 
     When Q 1  and Q 2  combine with each other to form a ring and the ring formed has a proton acceptor functional group, examples of the structure thereof include a structure where the organic group of Q 1  or Q 2  is further bonded by an alkylene group, an oxy group, an imino group or the like. 
     In formula (PA-II), at least either one of X 1  and X 2  is preferably —SO 2 —. 
     The compound represented by formula (PA-II) is preferably a compound represented by the following formula (PA-III):
 
Q 1 -X 1 —NH—X 2 -A-(X 3 ) n —B-Q 3    (PA-III)
 
     In formula (PA-III), Q 1  and Q 3  each independently represents a monovalent organic group, provided that either one of Q 1  and Q 3  has a proton acceptor functional group. Q 1  and Q 3  may combine with each other to form a ring and the ring formed may have a proton acceptor functional group. 
     X 1 , X 2  and X 3  each independently represents —CO— or —SO 2 —. 
     A represents a divalent linking group. 
     B represents a single bond, an oxygen atom or —N(Qx)-. 
     Qx represents a hydrogen atom or a monovalent organic group. 
     When B is —N(Qx)-, Q 3  and Qx may combine with each other to form a ring. 
     n represents 0 or 1. 
     Q 1  has the same meaning as Q 1  in formula (PA-II). 
     Examples of the organic group of Q 3  are the same as those of the organic group of Q 1  and Q 2  in formula (PA-II). 
     The divalent linking group of A is preferably a divalent linking group having a carbon number of 1 to 8 and containing a fluorine atom, and examples thereof include a fluorine atom-containing alkylene group having a carbon number of 1 to 8, and a fluorine atom-containing phenylene group. A fluorine atom-containing alkylene group is preferred, and the carbon number thereof is preferably from 2 to 6, more preferably from 2 to 4. The alkylene chain may contain a linking group such as oxygen atom and sulfur atom. The alkylene group is preferably an alkylene group where from 30 to 100% by number of the hydrogen atom is replaced by a fluorine atom, more preferably a perfluoroalkylene group, still more preferably a perfluoroethylene group, a perfluoropropylene group, or a perfluorobutylene group. 
     The monovalent organic group of Qx is preferably an organic group having a carbon number of 4 to 30, and examples thereof include an alkyl group, a cycloalkyl group, an aryl group, an aralkyl group and an alkenyl group. Examples of the alkyl group, cycloalkyl group, aryl group, aralkyl group and alkenyl group are the same as those described above. 
     In formula (PA-III), X 1 , X 2  and X 3  each is preferably —SO 2 —. 
     Specific examples of the compound represented by formula (PA-II) are set forth below, but the present invention is not limited thereto. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     The compound (PA) is preferably a sulfonium salt compound of the compound represented by formula (PA-I), (PA-II) or (PA-III), or an iodonium salt compound of the compound represented by formula (PA-I), (PA-II) or (PA-III), more preferably a compound represented by the following formula (PA1) or (PA2): 
     
       
         
         
             
             
         
       
     
     In formula (PA1), R 201 , R 202  and R 203  each independently represents an organic group. 
     X −  represents a sulfonate or carboxylate anion resulting from removal of a hydrogen atom in the —SO 3 H moiety or —COOH moiety of the compound represented by formula (PA-I), or an anion of the compound represented by formula (PA-II) or (PA-III). 
     The carbon number of the organic group of R 201 , R 202  and R 203  is generally from 1 to 30, preferably from 1 to 20. 
     Two members out of R 201  to R 203  may combine with each other to form a ring structure, and the ring may contain an oxygen atom, a sulfur atom, an ester bond, an amido bond or a carbonyl group. Examples of the group formed by combining two members out of R 201  to R 203  include an alkylene group (e.g., butylene, pentylene). 
     Specific examples of the organic group of R 201 , R 202  and R 203  include the corresponding groups in the compounds (A1a), (A1b) and (A1c) described later. 
     The compound may be a compound having a plurality of structures represented by formula (PA1). For example, the compound may be a compound having a structure where at least one of R 201  to R 203  in the compound represented by formula (PA1) is bonded to at least one of R 201  to R 203  in another compound represented by formula (PA1). 
     The component (PA1) is more preferably a compound (A1a), (A1b) or (A1c) described below. 
     The compound (A1a) is an arylsulfonium compound where at least one of R 201  to R 203  in formula (PA1) is an aryl group, that is, a compound having arylsulfonium as the cation. 
     In the arylsulfonium compound, R 201  to R 203  all may be an aryl group or a part of R 201  to R 203  may be an aryl group with the remaining being an alkyl group or a cycloalkyl group. 
     Examples of the arylsulfonium compound include a triarylsulfonium compound, a diarylalkylsulfonium compound, a diarylcycloalkylsulfonium compound, an aryldialkyl-sulfonium compound, an aryldicycloalkylsulfonium compound and an arylalkylcycloalkylsulfonium compound. 
     The aryl group in the arylsulfonium compound is preferably a phenyl group or a naphthyl group, more preferably a phenyl group. In the case where the arylsulfonium compound has two or more aryl groups, these two or more aryl groups may be the same of different. 
     The alkyl group which is present, if desired, in the arylsulfonium compound is preferably a linear or branched alkyl group having a carbon number of 1 to 15, and examples thereof include a methyl group, an ethyl group, a propyl group, an n-butyl group, a sec-butyl group and a tert-butyl group. 
     The cycloalkyl group which is present, if desired, in the arylsulfonium compound is preferably a cycloalkyl group having a carbon number of 3 to 15, and examples thereof include a cyclopropyl group, a cyclobutyl group and a cyclohexyl group. 
     The aryl group, alkyl group and cycloalkyl group of R 201  to R 203  each may have, as the substituent, an alkyl group (for example, an alkyl group having a carbon number of 1 to 15), a cycloalkyl group (for example, a cycloalkyl group having a carbon number of 3 to 15), an aryl group (for example, an aryl group having a carbon number of 6 to 14), an alkoxy group (for example, an alkoxy group having a carbon number of 1 to 15), a halogen atom, a hydroxyl group or a phenylthio group. The substituent is preferably a linear or branched alkyl group having a carbon number of 1 to 12, a cycloalkyl group having a carbon number of 3 to 12, or a linear, branched or cyclic alkoxy group having a carbon number of 1 to 12, and most preferably an alkyl group having a carbon number of 1 to 4, or an alkoxy group having a carbon number of 1 to 4. The substituent may be substituted to any one of three members R 201  to R 203  or may be substituted to all of these three members. In the case where R 201  to R 203  are an aryl group, the substituent is preferably substituted at the p-position of the aryl group. 
     The compound (A1b) is described below. 
     The compound (A1b) is a compound when R 201  to R 203  in formula (PA1) each independently represents an aromatic ring-free organic group. The aromatic ring as used herein includes an aromatic ring having a heteroatom. 
     The aromatic ring-free organic group of R 201  to R 203  is an organic group having a carbon number of generally from 1 to 30, preferably from 1 to 20. 
     R 201  to R 203  each independently, preferably represents an alkyl group, a cycloalkyl group, an allyl group or a vinyl group, more preferably a linear or branched 2-oxoalkyl group, a 2-oxocycloalkyl group or an alkoxycarbonylmethyl group, still more preferably a linear or branched 2-oxoalkyl group. 
     The alkyl group of R 201  to R 203  may be either linear or branched and is preferably a linear or branched alkyl group having a carbon number of 1 to 20 (e.g., methyl, ethyl, propyl, butyl, pentyl). The alkyl group as R 201  to R 203  is more preferably a linear or branched 2-oxoalkyl group or an alkoxycarbonylmethyl group. 
     The cycloalkyl group of R 201  to R 203  is preferably a cycloalkyl group having a carbon number of 3 to 10 (e.g., cyclopentyl, cyclohexyl, norbornyl). The cycloalkyl group as R 201  to R 203  is more preferably a 2-oxocycloalkyl group. 
     The linear or branched 2-oxoalkyl group of R 201  to R 203  may have a double bond in the chain and is preferably a group having &gt;C═O at the 2-position of the alkyl group above. 
     The 2-oxocycloalkyl group of R 201  to R 203  may have a double bond in the chain and is preferably a group having &gt;C═O at the 2-position of the cycloalkyl group above. 
     The alkoxy group in the alkoxycarbonylmethyl group of R 201  to R 203  is preferably an alkoxy group having a carbon number of 1 to 5 (e.g., methoxy, ethoxy, propoxy, butoxy, pentoxy). 
     R 201  to R 203  each may be further substituted by a halogen atom, an alkoxy group (for example, an alkoxy group having a carbon number of 1 to 5), an alkoxycarbonyl group (for example, an alkoxycarbonyl group having a carbon number of 2 to 5), a hydroxyl group, a cyano group or a nitro group. 
     The compound (A1c) is a compound represented by the following formula (A1c), and this is a compound having an arylacylsulfonium salt structure. 
     
       
         
         
             
             
         
       
     
     In formula (A1c), R 213  represents an aryl group which may have a substituent, and is preferably a phenyl group or a naphthyl group. Preferred examples of the substituent in R 213  include an alkyl group, an alkoxy group, an acyl group, a nitro group, a hydroxyl group, an alkoxycarbonyl group and a carboxy group. 
     R 214  and R 215  each independently represents a hydrogen atom, an alkyl group or a cycloalkyl group. 
     Y 201  and Y 202  each independently represents an alkyl group, a cycloalkyl group, an aryl group or a vinyl group. 
     X −  represents a sulfonate or carboxylate anion resulting from removal of a hydrogen atom in the —SO 3 H moiety or —COOR moiety of the compound represented by formula (PA-I), or an anion of the compound represented by formula (PA-II) or (PA-III). 
     R 213  and R 214  may combine with each other to form a ring structure, R 214  and R 215  may combine with each other to form a ring structure, and Y 201  and Y 202  may combine with each other to form a ring structure. The ring structure formed may contain an oxygen atom, a sulfur atom, an ester bond or an amide bond. Examples of the group formed by combining each pair of R 213  and R 214 , R 214  and R 215 , and Y 201  and Y 202  include a butylene group and a pentylene group. 
     The alkyl group of R 214 , R 215 , Y 201  and Y 202  is preferably a linear or branched alkyl group having a carbon number of 1 to 20. The alkyl group of Y 201  and Y 202  is more preferably a 2-oxoalkyl group having &gt;C═O at the 2-position of the alkyl group, an alkoxycarbonylalkyl group (preferably with the alkoxy group having a carbon number of 2 to 20), or a carboxyalkyl group. 
     The cycloalkyl group of R 214 , R 215 , Y 201  and Y 202  is preferably a cycloalkyl group having a carbon number of 3 to 20. 
     Y 201  and Y 202  each is preferably an alkyl group having a carbon number of 4 or more, more preferably from 4 to 6, still more preferably from 4 to 12. 
     At least either one of R 214  and R 215  is preferably an alkyl group, and more preferably, R 214  and R 215  both are an alkyl group. 
     In formula (PA2), R 204  and R 205  each independently represents an aryl group, an alkyl group or a cycloalkyl group. 
     X −  represents a sulfonate or carboxylate anion resulting from removal of a hydrogen atom in the —SO 3 H moiety or —COOH moiety of the compound represented by formula (PA-I), or an anion of the compound represented by formula (PA-II) or (PA-III). 
     The aryl group of R 204  and R 205  is preferably a phenyl group or a naphthyl group, more preferably a phenyl group. 
     The alkyl group of R 204  and R 205  may be either linear or branched and is preferably a linear or branched alkyl group having a carbon number of 1 to 10 (e.g., methyl, ethyl, propyl, butyl, pentyl). 
     The cycloalkyl group of R 204  and R 205  is preferably a cycloalkyl group having a carbon number of 3 to 10 (e.g., cyclopentyl, cyclohexyl, norbornyl). 
     R 204  and R 205  each may have a substituent, and examples of the substituent which R 204  and R 205  each may have include an alkyl group (for example, an alkyl group having a carbon number of 1 to 15), a cycloalkyl group (for example, a cycloalkyl group having a carbon number of 3 to 15), an aryl group (for example, an aryl group having a carbon number of 6 to 15), an alkoxy group (for example, an alkoxy group having a carbon number of 1 to 15), a halogen atom, a hydroxyl group and a phenylthio group. 
     The compound which generates a compound represented by formula (PA-I), (PA-II) or (PA-III) upon irradiation with actinic rays or radiation is preferably a compound represented by formula (PA1), more preferably a compound represented by any one of formulae (A1a) to (A1c). 
     The compound (PA) decomposes upon irradiation with actinic rays or radiation to generate, for example, a compound represented by formula (PA-1) or (PA-2). 
     The compound represented by formula (PA-1) is a compound having a sulfo group or carboxyl group together with a proton acceptor functional group and thereby being reduced in or deprived of the proton acceptor property or changed to be acidic from being proton acceptor-functioning as compared with the compound (PA). 
     The compound represented by formula (PA-2) is a compound having an organic sulfonylimino group or organic carbonylimino group together with a proton acceptor functional group and thereby being reduced in or deprived of the proton acceptor property or changed to be acidic from being proton acceptor-functioning as compared with the compound (PA). 
     In the present invention, reduction in the acceptor property means that when a noncovalent bond complex as a proton adduct is produced from a proton acceptor functional group-containing compound and a proton, the equilibrium constant at the chemical equilibrium decreases. 
     The proton acceptor property can be confirmed by measuring the pH. 
     Specific examples of the compound (PA) capable of generating a compound represented by formula (PA-I) upon irradiation with actinic rays or radiation are set forth below, but the present invention is not limited thereto. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     These compounds can be easily synthesized from a compound represented by formula (PA-I) or a lithium, sodium or potassium salt thereof and a hydroxide, bromide, chloride or the like of iodonium or sulfonium, by utilizing the salt-exchange method described in JP-T-11-501909 (the term “JP-T” as used herein means a “published Japanese translation of a PCT patent application”) or JP-A-2003-246786. 
     Specific examples of the compound (PA) capable of generating a compound represented by formula (PA-II) upon irradiation with actinic rays or radiation are set forth below, but the present invention is not limited thereto. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     These compounds can be easily synthesized by using a general sulfonic acid esterification reaction or sulfonamidation reaction. For example, the compound may be obtained by a method of selectively reacting one sulfonyl halide moiety of a bis-sulfonyl halide compound with an amine, alcohol or the like containing a partial structure represented by formula (PA-II) to form a sulfonamide bond or a sulfonic acid ester bond, and then hydrolyzing the other sulfonyl halide moiety, or a method of ring-opening a cyclic sulfonic anhydride by an amine or alcohol containing a partial structure represented by formula (PA-II). The amine or alcohol containing a partial structure represented by formula (PA-II) can be synthesized by reacting an amine or alcohol with an anhydride (e.g., (R′O 2 C) 2 O, R′O 2 CCl) or an acid chloride compound under basic conditions. 
     The content of the compound (PA) in the positive resist composition of the present invention is preferably from 0.1 to 20 mass %, more preferably from 0.1 to 10 mass %, based on the solid content of the composition. 
     [4] (C) Organic Basic Compound 
     The resist composition of the present invention preferably contains an organic basic compound. The organic basic compound is a compound having basicity stronger than that of phenol. The molecular weight of the organic basic compound is usually from 100 to 900, preferably from 150 to 800, more preferably from 200 to 700. In particular, a nitrogen-containing basic compound is preferred. 
     The nitrogen-containing basic compound preferred as the organic basic compound is preferably, in terms of the chemical environment, a compound having a structure of any one of the following formulae (CI) to (CV). Formulae (CII) to (CV) each may be a part of a ring structure. 
     
       
         
         
             
             
         
       
     
     In these formulae, R 250 , R 251  and R 252 , which may be the same or different, each represents a hydrogen atom, an alkyl group (preferably having a carbon number of 1 to 20), a cycloalkyl group (preferably having a carbon number of 3 to 20), or an aryl group (preferably having a carbon number of 6 to 20), and R 251  and R 252  may combine with each other to form a ring. 
     The alkyl group may be unsubstituted or may have a substituent, and the alkyl group having a substituent is preferably an aminoalkyl group having a carbon number of 1 to 6, or a hydroxyalkyl group having a carbon number of 1 to 6. 
     R 253 , R 254 , R 255  and R 256 , which may be the same or different, each represents an alkyl group having a carbon number of 1 to 6. 
     The compound is more preferably a nitrogen-containing basic compound having two or more nitrogen atoms differing in the chemical environment within one molecule, still more preferably a compound containing both a substituted or unsubstituted amino group and a nitrogen-containing ring structure, or a compound having an alkylamino group. 
     The organic basic compound may also be at least one kind of a nitrogen-containing compound selected from an amine compound having a phenoxy group, an ammonium salt compound having a phenoxy group, an amine compound having a sulfonic acid ester group, and an ammonium salt compound having a sulfonic acid ester group. 
     As for the amine compound, a primary, secondary or tertiary amine compound can be used, and an amine compound where at least one alkyl group is bonded to the nitrogen atom is preferred. The amine compound is more preferably a tertiary amine compound. In the amine compound, as long as at least one alkyl group (preferably having a carbon number of 1 to 20) is bonded to the nitrogen atom, a cycloalkyl group (preferably having a carbon number of 3 to 20) or an aryl group (preferably having a carbon number of 6 to 12) may be bonded to the nitrogen atom in addition to the alkyl group. The amine compound preferably has an oxygen atom in the alkyl chain to form an oxyalkylene group. The number of oxyalkylene groups within the molecule is 1 or more, preferably from 3 to 9, more preferably from 4 to 6. Among oxyalkylene groups, an oxyethylene group (—CH 2 CH 2 O—) and an oxypropylene group (—CH(CH 3 )CH 2 O— or —CH 2 CH 2 CH 2 O—) are preferred, and an oxyethylene group is more preferred. 
     As for the ammonium salt compound, a primary, secondary, tertiary or quaternary ammonium salt compound can be used, and an ammonium salt compound where at least one alkyl group is bonded to the nitrogen atom is preferred. In the ammonium salt compound, as long as at least one alkyl group (preferably having a carbon number of 1 to 20) is bonded to the nitrogen atom, a cycloalkyl group (preferably having a carbon number of 3 to 20) or an aryl group (preferably having a carbon number of 6 to 12) may be bonded to the nitrogen atom in addition to the alkyl group. The ammonium salt compound preferably has an oxygen atom in the alkyl chain to form an oxyalkylene group. The number of oxyalkylene groups within the molecule is 1 or more, preferably from 3 to 9, more preferably from 4 to 6. Among oxyalkylene groups, an oxyethylene group (—CH 2 CH 2 O—) and an oxypropylene group (—CH(CH 3 )CH 2 O— or —CH 2 CH 2 CH 2 O—) are preferred, and an oxyethylene group is more preferred. Examples of the anion of the ammonium salt compound include a halogen atom, a sulfonate, a borate and a phosphate, with a halogen atom and a sulfonate being preferred. The halogen atom is preferably chloride, bromide or iodide, and the sulfonate is preferably an organic sulfonate having a carbon number of 1 to 20. Examples of the organic sulfonate include an alkylsulfonate having a carbon number of 1 to 20 and an arylsulfonate. The alkyl group of the alkylsulfonate may have a substituent, and examples of the substituent include fluorine, chlorine, bromine, an alkoxy group, an acyl group and an aryl group. Specific examples of the alkylsulfonate include methanesulfonate, ethanesulfonate, butanesulfonate, hexanesulfonate, octanesulfonate, benzylsulfonate, trifluoromethanesulfonate, pentafluoroethanesulfonate and nonafluorobutanesulfonate. The aryl group of the arylsulfonate includes a benzene ring, a naphthalene ring and an anthracene ring. The benzene ring, naphthalene ring and anthracene ring may have a substituent, and the substituent is preferably a linear or branched alkyl group having a carbon number of 1 to 6, or a cycloalkyl group having a carbon number of 3 to 6. Specific examples of the linear or branched alkyl group and cycloalkyl group include methyl, ethyl, n-propyl, isopropyl, n-butyl, i-butyl, tert-butyl, n-hexyl and cyclohexyl. Other examples of the substituent include an alkoxy group having a carbon number of 1 to 6, a halogen atom, cyano, nitro, an acyl group and an acyloxy group. 
     The amine compound having a phenoxy group and the ammonium salt compound having a phenoxy group are an amine compound or ammonium salt compound having a phenoxy group at the terminal opposite the nitrogen atom of the alkyl group. The phenoxy group may have a substituent. Examples of the substituent of the phenoxy group include an alkyl group, an alkoxy group, a halogen atom, a cyano group, a nitro group, a carboxyl group, a carboxylic acid ester group, a sulfonic acid ester group, an aryl group, an aralkyl group, an acyloxy group and an aryloxy group. The substitution site of the substituent may be any of 2- to 6-positions, and the number of substituents may be any in the range from 1 to 5. 
     The compound preferably has at least one oxyalkylene group between the phenoxy group and the nitrogen atom. The number of oxyalkylene groups within the molecule is 1 or more, preferably from 3 to 9, more preferably from 4 to 6. Among oxyalkylene groups, an oxyethylene group (—CH 2 CH 2 O—) and an oxypropylene group (—CH(CH 3 )CH 2 O— or —CH 2 CH 2 CH 2 O—) are preferred, and an oxyethylene group is more preferred. 
     The amine compound having a phenoxy group may be obtained by reacting a primary or secondary amine having a phenoxy group with a haloalkyl ether under heating, adding an aqueous solution of a strong base such as sodium hydroxide, potassium hydroxide and tetraalkylammonium, and performing extraction with an organic solvent such as ethyl acetate and chloroform, or by reacting a primary or secondary amine with a haloalkyl ether having a phenoxy group at the terminal under heating, adding an aqueous solution of a strong base such as sodium hydroxide, potassium hydroxide and tetraalkylammonium, and performing extraction with an organic solvent such as ethyl acetate and chloroform. 
     The sulfonic acid ester group in the amine compound having a sulfonic acid ester group and the ammonium salt compound having a sulfonic acid ester group may be any of an alkylsulfonic acid ester, a cycloalkylsulfonic acid ester and an arylsulfonic acid ester. In the case of an alkylsulfonic acid ester, the alkyl group preferably has a carbon number of 1 to 20; in the case of a cycloalkylsulfonic acid ester, the cycloalkyl group preferably has a carbon number of 3 to 20; and in the case of an arylsulfonic acid ester, the aryl group preferably has a carbon number of 6 to 12. The alkylsulfonic acid ester, cycloalkylsulfonic acid ester and arylsulfonic acid ester may have a substituent, and the substituent is preferably a halogen atom, a cyano group, a nitro group, a carboxyl group, a carboxylic acid ester group or a sulfonic acid ester group. 
     The compound preferably has at least one oxyalkylene group between the sulfonic acid ester group and the nitrogen atom. The number of oxyalkylene groups within the molecule is 1 or more, preferably from 3 to 9, more preferably from 4 to 6. Among oxyalkylene groups, an oxyethylene group (—CH 2 CH 2 O—) and an oxypropylene group (—CH(CH 3 )CH 2 O— or —CH 2 CH 2 CH 2 O—) are preferred, and an oxyethylene group is more preferred. 
     Preferred examples of the organic basic compound include guanidine, aminopyridine, aminoalkylpyridine, aminopyrrolidine, indazole, imidazole, pyrazole, pyrazine, pyrimidine, purine, imidazoline, pyrazoline, piperazine, aminomorpholine and aminoalkylmorpholine. These compounds each may have a substituent, and preferred examples of the substituent include an amino group, an aminoalkyl group, an alkylamino group, an aminoaryl group, an arylamino group, an alkyl group, an alkoxy group, an acyl group, an acyloxy group, an aryl group, an aryloxy group, a nitro group, a hydroxyl group and a cyano group. 
     Particularly preferred examples of the organic basic compound include, but are not limited to, guanidine, 1,1-dimethylguanidine, 1,1,3,3-tetramethylguanidine, imidazole, 2-methylimidazole, 4-methylimidazole, N-methylimidazole, 2-phenylimidazole, 4,5-diphenylimidazole, 2,4,5-triphenylimidazole, 2-aminopyridine, 3-aminopyridine, 4-aminopyridine, 2-dimethylaminopyridine, 4-dimethylaminopyridine, 2-diethylaminopyridine, 2-(aminomethyl)pyridine, 2-amino-3-methylpyridine, 2-amino-4-methylpyridine, 2-amino-5-methylpyridine, 2-amino-6-methylpyridine, 3-aminoethylpyridine, 4-aminoethylpyridine, 3-aminopyrrolidine, piperazine, N-(2-aminoethyl)piperazine, N-(2-aminoethyl)piperidine, 4-amino-2,2,6,6-tetramethylpiperidine, 4-piperidinopiperidine, 2-iminopiperidine, 1-(2-aminoethyl)pyrrolidine, pyrazole, 3-amino-5-methylpyrazole, 5-amino-3-methyl-1-p-tolylpyrazole, pyrazine, 2-(aminomethyl)-5-methylpyrazine, pyrimidine, 2,4-diaminopyrimidine, 4,6-dihydroxypyrimidine, 2-pyrazoline, 3-pyrazoline, N-aminomorpholine and N-(2-aminoethyl)morpholine. 
     A tetraalkylammonium salt-type nitrogen-containing basic compound can also be used. Among these compounds, a tetraalkylammonium hydroxide having a carbon number of 1 to 8 (e.g., tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetra-(n-butyl)ammonium hydroxide) is preferred. One of these nitrogen-containing basic compounds is used alone, or two or more thereof are used in combination. 
     As for the ratio between the acid generator and the organic basic compound used in the composition, the ratio of organic basic compound/acid generator (by mol) is preferably from 0.01 to 10. That is, the molar ratio is preferably 10 or less in view of sensitivity and resolution and is preferably 0.01 or more from the standpoint of suppressing reduction in the resolution due to thickening of the resist pattern with aging after exposure until heat treatment. The ratio of organic basic compound/acid generator (by mol) is more preferably from 0.05 to 5, still more preferably from 0.1 to 3. 
     [5] Surfactants 
     In the present invention, surfactants can be used and use thereof is preferred in view of film-forming property, adhesion of pattern, reduction in development defects, and the like. 
     Specific examples of the surfactant include a nonionic surfactant such as polyoxyethylene alkyl ethers (e.g., polyoxyethylene lauryl ether, polyoxyethylene stearyl ether, polyoxyethylene cetyl ether, polyoxyethylene oleyl ether), polyoxyethylene alkylallyl ethers (e.g., polyoxyethylene octylphenol ether, polyoxyethylene nonylphenol ether), polyoxyethylene•polyoxypropylene block copolymers, sorbitan fatty acid esters (e.g., sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan monooleate, sorbitan trioleate, sorbitan tristearate) and polyoxyethylene sorbitan fatty acid esters (e.g., polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan trioleate, polyoxyethylene sorbitan tristearate); a fluorine-containing or silicon-containing surfactant such as EFtop EF301, EF303, EF352 (produced by Shin Akita Chemical Co., Ltd.), MEGAFACE F171, F173 (produced by Dainippon Ink &amp; Chemicals, Inc.), Florad FC430, FC431 (produced by Sumitomo 3M Inc.), Asahiguard AG710, Surflon S-382, SC101, SC102, SC103, SC104, SC105 and SC106 (produced by Asahi Glass Co., Ltd.) and Troysol S-366 (produced by Troy Chemical Industries, Inc.); organosiloxane polymer KP-341 (produced by Shin-Etsu Chemical Co., Ltd.); and acrylic acid-based or methacrylic acid-based (co)polymer Polyflow No. 75 and No. 95 (produced by Kyoeisha Chemical Co., Ltd.). The amount of the surfactant blended is usually 2 parts by mass or less, preferably 1 part by mass or less, per 100 parts by mass of the solid content in the composition of the present invention. 
     One of these surfactants may be used alone, or some species thereof may be added in combination. 
     As for the surfactant, the composition preferably contains any one of fluorine- and/or silicon-containing surfactants (a fluorine-containing surfactant, a silicon-containing surfactant or a surfactant containing both a fluorine atom and a silicon atom), or two or more thereof. 
     Examples of such surfactants include the surfactants described in JP-A-62-36663, JP-A-61-226746, JP-A-61-226745, JP-A-62-170950, JP-A-63-34540, JP-A-7-230165, JP-A-8-62834, JP-A-9-54432, JP-A-9-5988, JP-A-2002-277862 and U.S. Pat. Nos. 5,405,720, 5,360,692, 5,529,881, 5,296,330, 5,436,098, 5,576,143, 5,294,511 and 5,824,451. The following commercially available surfactants each may also be used as it is. 
     Examples of the commercially available surfactant which can be used include a fluorine-containing or silicon-containing surfactant such as EFtop EF301 and EF303 (produced by Shin-Akita Chemical Co., Ltd.), Florad FC430 and 431 (produced by Sumitomo 3M Inc.), MEGAFACE F171, F173, F176, F189 and R08 (produced by Dainippon Ink &amp; Chemicals, Inc.), Surflon S-382, SC101, 102, 103, 104, 105 and 106 (produced by Asahi Glass Co., Ltd.), Troysol S-366 (produced by Troy Chemical Industries, Inc.), and PF6320 (produced by OMNOVA). In addition, polysiloxane polymer KP-341 (produced by Shin-Etsu Chemical Co., Ltd.) may also be used as a silicon-containing surfactant. 
     Other than those known surfactants, a surfactant using a polymer having a fluoro-aliphatic group which is derived from a fluoro-aliphatic compound produced by a telomerization process (also called a telomer process) or an oligomerization process (also called an oligomer process) may be used. The fluoro-aliphatic compound can be synthesized by the method described in JP-A-2002-90991. 
     The polymer having a fluoro-aliphatic group is preferably a copolymer of a fluoro-aliphatic group-containing monomer with a (poly(oxyalkylene))acrylate and/or a (poly(oxyalkylene))methacrylate, and the polymer may have an irregular distribution or may be block-copolymerized. Examples of the poly(oxyalkylene) group include a poly(oxyethylene) group, a poly(oxypropylene) group and a poly(oxybutylene) group. This group may also be a unit having alkylenes differing in the chain length within the same chain, such as block-linked poly(oxyethylene, oxypropylene and oxyethylene) and block-linked poly(oxyethylene and oxypropylene). Furthermore, the copolymer of a fluoro-aliphatic group-containing monomer and a (poly(oxyalkylene))acrylate (or methacrylate) is not limited only to a binary copolymer but may also be a ternary or higher copolymer obtained by simultaneously copolymerizing two or more different fluoro-aliphatic group-containing monomers or two or more different (poly(oxyalkylene))acrylates (or methacrylates). 
     Examples thereof include, as the commercially available surfactant, MEGAFACE F178, F-470, F-473, F-475, F476 and F-472 (produced by Dainippon Ink &amp; Chemicals, Inc.) and further include a copolymer of a C 6 F 13  group-containing acrylate (or methacrylate) with a (poly(oxyalkylene))acrylate (or methacrylate), a copolymer of a C 6 F 13  group-containing acrylate (or methacrylate) with a (poly(oxyethylene))acrylate (or methacrylate) and a (poly(oxypropylene))acrylate (or methacrylate), a copolymer of a C 8 F 17  group-containing acrylate (or methacrylate) with a (poly(oxyalkylene))acrylate (or methacrylate), a copolymer of a C 8 F 17  group-containing acrylate (or methacrylate) with a (poly(oxyethylene))acrylate (or methacrylate) and a (poly(oxypropylene))acrylate (or methacrylate). 
     The amount of the surfactant used is preferably from 0.0001 to 2 mass %, more preferably from 0.001 to 1 mass %, based on the entire amount of the positive resist composition (excluding solvent). 
     [6] Other Components 
     The positive resist composition of the present invention may further contain, if desired, a dye, a photo-base generator and the like. 
     1. Dye 
     In the present invention, a dye can be used. 
     The suitable dye includes an oily dye and a basic dye. Specific examples thereof include Oil Yellow #101, Oil Yellow #103, Oil Pink #312, Oil Green BG, Oil Blue BOS, Oil Blue #603, Oil Black BY, Oil Black BS, Oil Black T-505 (all produced by Orient Chemical Industries Co., Ltd.), Crystal Violet (CI42555), Methyl Violet (CI42535), Rhodamine B (CI45170B), Malachite Green (CI42000) and Methylene Blue (CI52015). 
     2. Photo-Base Generator 
     Examples of the photo-base generator which can be added to the composition of the present invention include the compounds described in JP-A-4-151156, JP-A-4-162040, JP-A-5-197148, JP-A-5-5995, JP-A-6-194834, JP-A-8-146603, JP-A-10-83079 and European Patent 622,682. Specific examples of the photo-base generator which can be suitably used include 2-nitrobenzyl carbamate, 2,5-dinitrobenzylcyclohexyl carbonate, N-cyclohexyl-4-methylphenylsulfonamide and 1,1-dimethyl-2-phenylethyl-N-isopropyl carbamate. The photo-base generator is added for the purpose of improving the resist profile or the like. 
     3. Antioxidant 
     An antioxidant may be used as the additive. 
     The antioxidant is added for preventing the organic material from being oxidized in the presence of oxygen. The antioxidant is not particularly limited as long as it has an effect of preventing oxidation of a plastic and the like used in general, and examples thereof include a phenol-based antioxidant, an antioxidant composed of an organic acid derivatives a sulfur-containing antioxidant, a phosphorus-based antioxidant, an amine-based antioxidant, an antioxidant composed of an amine-aldehyde condensate, and an antioxidant composed of an amine-ketone condensate. Out of these antioxidants, in order to bring out the effects of the present invention without reducing the functions of the resist, the antioxidant is preferably a phenol-based antioxidant or an antioxidant composed of an organic acid derivative. 
     Examples of the phenol-based antioxidant include substituted phenols such as 1-oxy-3-methyl-4-isopropylbenzene, 2,6-di-tert-butylphenol, 2,6-di-tert-butyl-4-ethylphenol, 2,6-di-tert-butyl-4-methylphenol, 4-hydroxymethyl-2,6-di-tert-butylphenol, butyl•hydroxyanisole, 2-(1-methylcyclohexyl)-4,6-dimethylphenol, 2,4-dimethyl-6-tert-butylphenol, 2-methyl-4,6-dinonylphenol, 2,6-di-tert-butyl-α-dimethylamino-p-cresol, 6-(4-hydroxy-3,5-di-tert-butyl•anilino)2,4-bis•octyl-thio-1,3,5-triazine, n-octadecyl-3-(4′-hydroxy-3′,5′-di-tert-butyl•phenyl)propionate, octylated phenol, aralkyl-substituted phenols, alkylated p-cresol and hindered phenol; bis- and trisphenols such as 4,4′-dihydroxyediphenyl, methylene•bis-(dimethyl-4,6-phenol), 2,2′-methylene-bis-(4-methyl-6-tert-butylphenol), 2,2′-methylene-bis-(4-methyl-6-cyclohexyl•phenol), 2,2′-methylene-bis-(4-ethyl-6-tert-butylphenol), 4,4′-methylene-bis-(2,6-di-tert-butylphenol), 2,2′-methylene-bis-(6-α-methyl-benzyl-p-cresol), methylene crosslinked polyvalent alkylphenol, 4,4′-butylidenebis-(3-methyl-6-tert-butylphenol), 1,1-bis-(4hydroxyphenyl)-cyclohexane, 2,2′-dihydroxy-3,3′-di-(α-methylcyclohexyl)-5,5′-dimethyldiphenylmethane, alkylated bisphenol, hindered bisphenol, 1,3,5-trimethyl-2,4,6-tris(3,5-di-tertbutyl-4-hydroxybenzyl)benzene, tris-(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, and tetrakis-[methylene-3-(3′,5′-di-tert-butyl-4′-hydroxyphenyl)propionate]methane. 
     Specific preferred examples of the antioxidant for use in the present invention include 2,6-di-tert-butyl-4-methylphenol, 4-hydroxymethyl-2,6-di-tert-butylphenol, 2,2′-methylenebis(4-methyl-6-tert-butylphenol), butylhydroxyanisole, tert-butyl hydroquinone, 2,4,5-trihydroxybutyrophenone, nordihydroguajaretic acid, propyl gallate, octyl gallate, lauryl gallate and isopropyl citrate. Among these, 2,6-di-tert-butyl-4-methylphenol, 4-hydroxymethyl-2,6-di-tert-butylphenol, butylhydroxyanisole and tert-butyl hydroquinone are preferred, and 2,6-di-tert-butyl-4-methylphenol and 4-hydroxymethyl-2,6-di-tert-butylphenol are more preferred. 
     In the case of using an antioxidant, the content of the antioxidant in the positive resist composition of the present invention is preferably 1 ppm or more, more preferably 5 ppm or more, still more preferably 10 ppm or more, yet still more preferably 50 ppm or more, even yet still more preferably 100 ppm or more, and most preferably from 100 to 1,000 ppm. One kind of an antioxidant may be used, or two or more kinds may be mixed. 
     4. Solvents 
     The resist composition of the present invention is dissolved in a solvent capable of dissolving respective components described above and then coated on a support. Usually, the concentration is, in terms of the solid content concentration of all resist components, preferably from 2 to 30 mass %, more preferably from 3 to 25 mass %. 
     Preferred examples of the solvent used here include ethylene dichloride, cyclohexanone, cyclopentanone, 2-heptanone, γ-butyrolactone, methyl ethyl ketone, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, 2-methoxyethyl acetate, ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, toluene, ethyl acetate, methyl lactate, ethyl lactate, methyl methoxypropionate, ethyl ethoxypropionate, methyl pyruvate, ethyl pyruvate, propyl pyruvate, N,N-dimethylformamide, dimethylsulfoxide, N-methylpyrrolidone and tetrahydrofuran. These solvents are used individually or as a mixture of two or more thereof. 
     In particular, a solvent containing propylene glycol monomethyl ether acetate is preferred, and a mixed solvent containing propylene glycol monomethyl ether is more preferred. 
     The positive resist composition of the present invention is coated on a substrate to form a thin film. The thickness of this coating film is preferably from 0.05 to 4.0 μm. 
     The composition of the present invention has an excellent effect that even when the composition is coated directly on a substrate having a high-reflection surface without applying an antireflection film, generation of a standing wave is remarkably suppressed and a good pattern is obtained, but a good pattern can be formed also when an antireflection film is used. 
     The antireflection film used as an underlying layer of the resist may be either an inorganic film such as titanium, titanium dioxide, titanium nitride, chromium oxide, carbon and amorphous silicon, or an organic film comprising a light absorbent and a polymer material. The former requires equipment for the film formation, such as vacuum deposition apparatus, CVD apparatus and sputtering apparatus. Examples of the organic antireflection film include a film comprising a diphenylamine derivative and formaldehyde-modified melamine resin condensate, an alkali-soluble resin and a light absorbent described in JP-B-7-69611 (the term “JP-B” as used herein means an “examined Japanese patent publication”), a reaction product of a maleic anhydride copolymer and a diamine-type light absorbent described in U.S. Pat. No. 5,294,680, a film comprising a resin binder and a methylolmelamine-based heat crosslinking agent described in JP-A-6-118631, an acrylic resin-type antireflection film containing a carboxylic acid group, an epoxy group and a light absorbing group within the same molecule described in JP-A-6-118656, a film comprising methylolmelamine and a benzophenone-based light absorbent described in JP-A-8-87115, and a film obtained by adding a low molecular light absorbent to a polyvinyl alcohol resin described in JP-A-8-179509. 
     Also, the organic antireflection film may be a commercially available organic antireflection film such as DUV-30 Series, DUV-40 Series (produced by Brewer Science, Inc.), AR-2, AR-3 and AR-5 (produced by Shipley Co., Ltd.). 
     Also, an antireflection film may be used as an upper layer of the resist, if desired. 
     Examples of the antireflection film include AQUATAR-II, AQUATAR-III and AQUATAR-VII produced by AZ Electronic Materials K.K. 
     In the production or the like of a precision integrated circuit device, the step of forming a pattern on a resist film is performed by coating the positive resist composition of the present invention on a substrate (for example, a silicon/silicon dioxide-coated substrate, a glass substrate, an ITO substrate or a quartz/chromium oxide-coated substrate) to form a resist film, irradiating actinic rays or radiation such as KrF, excimer laser light, electron beam and EUV light, and then subjecting the resist film to heating, development, rinsing and drying, whereby a good pattern can be formed. 
     The alkali developer which can be used in the development is an aqueous solution of an alkali (usually, from 0.1 to 20 mass %) such as inorganic alkalis (e.g., sodium hydroxide, potassium hydroxide, sodium carbonate, sodium silicate, sodium metasilicate, aqueous ammonia), primary amines (e.g., ethylamine, n-propylamine), secondary amines (e.g., diethylamine, di-n-butylamine), tertiary amines (e.g., triethylamine, methyldiethylamine), alcohol amines (e.g., dimethylethanolamine, triethanolamine), quaternary ammonium salts (e.g., tetramethylammonium hydroxide, tetraethylammonium hydroxide, choline) and cyclic amines (e.g., pyrrole, piperidine). In this aqueous solution of an alkali, alcohols such as isopropyl alcohol and a surfactant such as nonionic surfactant may be added each in an appropriate amount. 
     Among these developers, a quaternary ammonium salt is preferred, and tetramethylammonium hydroxide and choline are more preferred. 
     The pH of the alkali developer is usually from 10 to 15. 
     Examples of the actinic rays or radiation as the light source for exposure include infrared light, visible light, ultraviolet light, far ultraviolet light, X-ray and electron beam, but the radiation is preferably far ultraviolet light at a wavelength of 250 nm or less, more preferably 220 nm or less, still more preferably from 1 to 200 nm. Specific examples thereof include KrF excimer laser light (248 nm), ArF excimer laser light (193 nm), F 2  excimer laser light (157 nm), X-ray, electron beam and EUV. The resist film is preferably exposed by the irradiation with KrF, electron beam, X-ray or EUV. 
     The present invention is described in greater detail below by referring to Examples, but the present invention should not be construed as being limited thereto. 
     SYNTHESIS EXAMPLE 1 
     Synthesis of Polymer (A-1): 
     4-Acetoxystyrene (32.11 g, 0.198 mol), 13.65 g (0.096 mol) of tert-butyl methacrylate, 1.70 g (0.006 mol) of 4-((N-carbazole)methyl)styrene and 3.45 g (0.015 mol) of polymerization initiator V-601 (produced by Wako Pure Chemical Industries, Ltd.) were dissolved in 151.89 g of cyclohexanone. Subsequently, 37.97 g of cyclohexanone was charged into a reaction vessel, and the solution above was added dropwise to the system at 80° C. in a nitrogen gas atmosphere over 6 hours. After the completion of dropwise addition, the reaction solution was heated with stirring for 2 hours, then allowed to cool to room temperature and added dropwise in 2.5 L of hexane to precipitate a polymer, followed by filtration. The solid collected by filtration was washed by splashing with 500 mL of hexane and then dried under reduced pressure to obtain 42.25 g of a 4-acetoxystyrene/tert-butyl methacrylate/4-((N-carbazole)methyl)styrene copolymer. 
     In a reaction vessel, 40.00 g of the polymer obtained above was dissolved in 92 mL of ethyl acetate and 92 mL of methanol, 39.02 g of a sodium methoxide 28% methanol solution was added thereto and after stirring for 3 hours, hydrochloric acid to make the solution acidic. Furthermore, 500 mL of ethyl acetate was added and washing with 200 mL of distilled water was performed 5 times. The organic layer was extracted, concentrated, dissolved in 150 mL of methanol and added dropwise in 1.5 L of distilled water/methanol=7/3 to precipitate a polymer, followed by filtration. The solid after filtration was washed by splashing with 500 mL of distilled water/methanol=7/3 and then dried under reduced pressure to obtain 30.34 g of a 4-hydroxystyrene/tert-butyl methacrylate/4-((N-carbazole)-methyl)styrene copolymer. The weight average molecular weight by GPC was 8,000, and the molecular weight dispersity (Mw/Mn) was 1.45. 
     In the case of requiring acetalization like Polymers (A-84), (A-85) and (A-86), the following process is performed. 
     SYNTHESIS EXAMPLE 2 
     Synthesis of Polymer (A-84): 
     In a reaction vessel, 20.00 g of Polymer (A-1) was dissolved in 300 g of PGMEA. The resulting solution was depressurized to 20 mmHg at 60° C. to remove by distillation about 150 g of the solvent together with water remaining in the system. After cooling to 20° C., 1.94 g of cyclohexyl vinyl ether and 5.6 mg of p-toluenesulfonic acid were added thereto, and the resulting mixture was stirred at room temperature for 2 hours. Thereafter, 0.06 g of triethylamine was added to effect neutralization and then, a washing operation was performed three times by adding 300 g of ethyl acetate and 100 g of water. Subsequently, the amount of the solvent was adjusted to obtain a polymer solution at a concentration of 30 mass %. The weight average molecular weight by GPC was 8,100, the molecular weight dispersity was 1.45, and from the 1H- and 13C-NMR analyses, the acetal protection rate of phenolic OH was 10%. 
     Resins shown in Table 1, each having a structure exemplified above, were synthesized in the same manner as in Synthesis Examples 1 and 2 except for changing the monomers and vinyl ether used. The compositional ratio (by mol) is a ratio of repeating units starting from the left in the structure shown above of the resin with the same denotation as in Table 1. 
                                     TABLE 1                       Weight Average                   Molecular Weight   Compositional Ratio   Dispersity                                                            A-1   8000   66/32/2   1.45           A-2   6000   65/32/3   1.46           A-4   15000   66/30/4   1.50           A-5   9000   63/33/4   1.60           A-6   16000   67/31/2   1.55           A-7   10000   61/35/4   1.48           A-10   4000   60/36/4   1.40           A-11   18000   64/32/4   1.52           A-12   19000   67/31/2   1.55           A-13   8000   63/32/5   1.46           A-17   6000   64/33/3   1.48           A-18   10000   63/32/5   1.42           A-19   8000   62/32/6   1.44           A-20   15000   57/33/10   1.50           A-25   14000   51/34/15   1.53           A-27   13000   59/33/8   1.55           A-30   10000   58/32/10   1.56           A-31   10000   61/35/4   1.54           A-32   14000   63/33/4   1.56           A-33   12000   61/35/4   1.56           A-34   6000   67/31/2   1.52           A-41   17000   70/28/2   1.44           A-47   15000   71/27/2   1.48           A-48   14000   70/28/2   1.58           A-56   10000   58/38/2/2   1.53           A-57   15000   63/33/3/1   1.58           A-58   20000   65/31/2/2   1.50           A-59   24000   66/30/3/1   1.50           A-60   2000   60/38/1/1   1.59           A-61   15000   61/33/3/3   1.57           A-62   9000   64/34/1/1   1.56           A-63   16000   65/33/1/1   1.54           A-64   8000   59/35/3/3   1.45           A-67   8000   60/35/4/1   1.45           A-69   13000   64/33/1/2   1.41           A-70   18000   62/32/3/3   1.41           A-75   8000   59/35/6   1.58           A-81   5000   66/25/4/5   1.60           A-84   8100   56/32/2/10   1.45           A-89   10000   60/30/5/5   1.50           A-94   10000   71/25/4   1.45           A-95   10000   71/25/2/2   1.48                        
[Preparation of Resist Composition]
 
     The resin, acid generator, proton acceptor-containing compound, surfactant and basic compound shown in Table 2 each in the added amount shown below were dissolved in propylene glycol monomethyl ether acetate/propylene glycol monomethyl ether (8/2 by mass) to prepare a solution having a solid content concentration of 5.0 mass %, and the obtained solution was microfiltered through a membrane filter having a pore size of 0.1 μm to obtain a resist solution. 
     &lt;Formulation of Resist Composition&gt; 
                                                Resin   17.1653 g           Acid Generator    0.1479 g           Basic compound or proton acceptor group-containing    0.0393 g           compound (when a proton acceptor group-containing           compound and a basic compound were used in           combination, the proton acceptor group-containing           compound and basic compound both in an amount of           0.0196 g)           Surfactant    0.4020 g                        
[Production and Evaluation of Pattern (KrF)]
 
     The positive resist solution prepared above was uniformly coated on a hexamethyldisilazane-treated silicon wafer by using a spin coater and dried under heating at 120° C. for 90 seconds to form a positive resist film having a thickness of 0.4 μm. This resist film was then pattern-exposed using a KrF excimer laser stepper (FPA3000EX-5, manufactured by Canon Inc., wavelength: 248 nm). After the irradiation, the resist film was baked at 110° C. for 90 seconds, dipped in an aqueous 2.38 mass % tetramethylammonium hydroxide (TMAH) solution for 60 seconds, rinsed with water for 30 seconds and dried. The obtained pattern was evaluated by the following methods. 
     The resist performances were evaluated as follows. The results are shown in Table 2. 
     [Remaining of Standing Wave] 
     The side wall of the resist pattern obtained using a 0.30-μm line-and-space mask pattern was observed through a scanning electron microscope and evaluated on the following 5-step scale. 
     A: Standing wave was not observed at all and the side wall of the pattern was very clear. 
     B: Standing wave was slightly observed or the side wall of the pattern was uneven. 
     C: Standing wave was confirmed at a glance (not applicable in this Example). 
     D: Slightly strong standing wave was confirmed. 
     E: Very strong standing wave was confirmed. 
     [Profile] 
     The profile of the pattern obtained above was observed through a cross-sectional SEM and evaluated on the following 3-step scale. 
     1: The profile was rectangular. 
     2: The profile was nearly rectangular with almost no taper. 
     3: The profile was distinctly tapered. 
     [Sensitivity] 
     The cross-sectional profile of the pattern obtained was observed using a scanning electron microscope (S-4300, manufactured by Hitachi, Ltd.). The minimum irradiation energy when resolving a 180-nm line (line:space=1:1) was taken as the sensitivity. 
     [Resolving Power] 
     The limiting resolving power (the minimum line width at which the line and the space were separated and resolved) at the irradiation dose giving the sensitivity above was taken as the resolving power. 
     The component (c) and other components used in Examples and the resins used in Comparative Examples are as follows. 
     [Organic Basic Compound] 
     
         
         D-1: Dicyclohexylmethylamine 
         D-2: 2,4,6-Triphenylimidazole 
         D-3: Tetra-(n-butyl)ammonium hydroxide 
       
    
                         
[Other Components (Surfactant)]
     W-1: Fluorine-containing surfactant, PF6320 produced by OMNOVA)   W-2: Fluorine/silicon-containing surfactant, MEGAFACE R08 (produced by Dainippon Ink &amp; Chemicals, Inc.)   W-3: Silicon-containing surfactant, Polysiloxane Polymer KP-341 (produced by Shin-Etsu Chemical Co., Ltd.)   

     
       
         
         
             
             
         
       
     
     Compositional molar ratio: 65/35, weight average molecular weight: 12,000, and dispersity: 1.55. 
     
       
         
         
             
             
         
       
     
     Compositional molar ratio: 60/30, weight average molecular weight: 8,000, and dispersity: 1.20. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 2 
               
             
            
               
                   
                   
               
               
                   
                 Composition 
                 Evaluation 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                 Acid 
                 Proton Acceptor Group- 
                 Basic 
                   
                 Sensitivity 
                 Resolution 
                 Remaining of 
                 Pattern 
               
               
                   
                 Resin 
                 Generator 
                 Containing Compound 
                 Compound 
                 Surfactant 
                 (mJ/cm 2 ) 
                 (nm) 
                 Standing Wave 
                 Profile 
               
               
                   
                   
               
            
           
           
               
            
               
                 Example 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                  1 
                 A-1 
                 B-84 
                 PA-74 
                 none 
                 W-1 
                 18 
                 120 
                 A 
                 1 
               
               
                  2 
                 A-2 
                 B-57 
                 PA-74 
                 none 
                 W-1 
                 19 
                 120 
                 A 
                 1 
               
               
                  3 
                 A-4 
                 B-91 
                 PA-74 
                 none 
                 W-1 
                 20 
                 130 
                 A 
                 1 
               
               
                  4 
                 A-5 
                 B-41 
                 PA-74 
                 none 
                 W-1 
                 20 
                 120 
                 A 
                 1 
               
               
                  5 
                 A-6 
                 B-84 
                 PA-74 
                 none 
                 W-2 
                 18 
                 100 
                 A 
                 1 
               
               
                  6 
                 A-7 
                 B-1 
                 PA-74 
                 D-1 
                 W-3 
                 18 
                 130 
                 A 
                 1 
               
               
                  7 
                 A-10 
                 B-42 
                 PA-74 
                 D-1 
                 W-1 
                 20 
                 120 
                 A 
                 1 
               
               
                  8 
                 A-11 
                 B-58 
                 PA-74 
                 D-2 
                 W-1 
                 18 
                 100 
                 A 
                 1 
               
               
                  9 
                 A-12 
                 B-82 
                 PA-74 
                 D-3 
                 W-1 
                 18 
                 100 
                 A 
                 1 
               
               
                 10 
                 A-13 
                 B-40 
                 PA-74 
                 D-4 
                 W-1 
                 20 
                 130 
                 A 
                 1 
               
               
                 11 
                 A-17 
                 B-34 
                 none 
                 D-4 
                 W-2 
                 16 
                 120 
                 A 
                 1 
               
               
                 12 
                 A-18 
                 B-16 
                 none 
                 D-1 
                 W-3 
                 18 
                 140 
                 A 
                 1 
               
               
                 13 
                 A-19 
                 B-59 
                 none 
                 D-1 
                 W-1 
                 16 
                 120 
                 A 
                 1 
               
               
                 14 
                 A-20 
                 B-87 
                 none 
                 D-2 
                 W-1 
                 20 
                 130 
                 A 
                 1 
               
               
                 15 
                 A-25 
                 B-19 
                 none 
                 D-3 
                 W-1 
                 21 
                 130 
                 A 
                 1 
               
               
                 16 
                 A-27 
                 B-86 
                 none 
                 D-4 
                 W-1 
                 18 
                 140 
                 A 
                 1 
               
               
                 17 
                 A-30 
                 B-84 
                 none 
                 D-4 
                 W-2 
                 18 
                 120 
                 A 
                 1 
               
               
                 18 
                 A-31 
                 B-12 
                 none 
                 D-1 
                 W-3 
                 19 
                 120 
                 A 
                 1 
               
               
                 19 
                 A-32 
                 B-78 
                 none 
                 D-1 
                 W-1 
                 21 
                 130 
                 A 
                 1 
               
               
                 20 
                 A-33 
                 B-85 
                 none 
                 D-2 
                 W-1 
                 19 
                 140 
                 A 
                 1 
               
               
                 21 
                 A-34 
                 B-88 
                 none 
                 D-3 
                 W-1 
                 18 
                 120 
                 A 
                 1 
               
               
                 22 
                 A-41 
                 B-79 
                 none 
                 D-4 
                 W-1 
                 21 
                 120 
                 A 
                 1 
               
               
                 23 
                 A-47 
                 B-80 
                 none 
                 D-4 
                 W-2 
                 18 
                 100 
                 A 
                 1 
               
               
                 24 
                 A-48 
                 B-90 
                 none 
                 D-1 
                 W-3 
                 18 
                 130 
                 A 
                 1 
               
               
                 25 
                 A-56 
                 B-2 
                 none 
                 D-1 
                 W-1 
                 19 
                 120 
                 A 
                 1 
               
               
                 26 
                 A-57 
                 B-83 
                 PA-73 
                 D-2 
                 W-1 
                 20 
                 100 
                 A 
                 1 
               
               
                 27 
                 A-58 
                 B-17 
                 PA-50 
                 D-3 
                 W-1 
                 19 
                 120 
                 A 
                 1 
               
               
                 28 
                 A-59 
                 B-81 
                 PA-56 
                 D-4 
                 W-1 
                 18 
                 100 
                 A 
                 1 
               
               
                 29 
                 A-60 
                 B-84 
                 PA-64 
                 D-4 
                 W-2 
                 19 
                 110 
                 A 
                 1 
               
               
                 30 
                 A-61 
                 B-73 
                 PA-5 
                 D-1 
                 W-3 
                 20 
                 110 
                 A 
                 1 
               
               
                 31 
                 A-62 
                 B-64 
                 PA-74 
                 D-1 
                 W-1 
                 19 
                 120 
                 A 
                 1 
               
               
                 32 
                 A-63 
                 B-9 
                 PA-13 
                 D-2 
                 W-1 
                 18 
                 130 
                 A 
                 1 
               
               
                 33 
                 A-64 
                 B-84 
                 PA-31 
                 D-3 
                 W-1 
                 18 
                 110 
                 A 
                 1 
               
               
                 34 
                 A-67 
                 B-3 
                 PA-33 
                 D-4 
                 W-1 
                 20 
                 110 
                 A 
                 1 
               
               
                 35 
                 A-69 
                 B-40 
                 PA-74 
                 D-4 
                 W-2 
                 19 
                 120 
                 A 
                 1 
               
               
                 36 
                 A-70 
                 B-56 
                 PA-66 
                 D-1 
                 W-3 
                 18 
                 110 
                 A 
                 1 
               
               
                 37 
                 A-75 
                 B-48 
                 PA-68 
                 D-1 
                 W-1 
                 20 
                 130 
                 A 
                 1 
               
               
                 38 
                 A-81 
                 B-14 
                 PA-72 
                 D-2 
                 W-1 
                 20 
                 110 
                 A 
                 1 
               
               
                 39 
                 A-84 
                 B-84 
                 PA-32 
                 D-3 
                 W-2 
                 18 
                 130 
                 A 
                 1 
               
               
                 40 
                 A-89 
                 B-18 
                 PA-8 
                 D-4 
                 W-3 
                 20 
                 100 
                 A 
                 1 
               
               
                 41 
                 A-7 
                 B-84 
                 none 
                 D-1 
                 W-1 
                 21 
                 130 
                 A 
                 1 
               
               
                 42 
                 A-4 
                 B-84 
                 none 
                 D-1 
                 W-1 
                 19 
                 110 
                 A 
                 1 
               
               
                 43 
                 A-56 
                 B-84 
                 none 
                 D-1 
                 W-1 
                 18 
                 110 
                 A 
                 1 
               
               
                 44 
                 A-6 
                 B-84 
                 none 
                 D-1 
                 W-1 
                 17 
                 100 
                 A 
                 1 
               
               
                 45 
                 A-56 
                 B-92 
                 none 
                 D-1 
                 W-1 
                 19 
                 110 
                 A 
                 1 
               
               
                 46 
                 A-56 
                 B-57 
                 none 
                 D-1 
                 W-1 
                 17 
                 120 
                 A 
                 1 
               
               
                 47 
                 A-94 
                 B-84 
                 none 
                 D-1 
                 W-1 
                 19 
                 110 
                 A 
                 1 
               
               
                 48 
                 A-95 
                 B-84 
                 none 
                 D-1 
                 W-1 
                 17 
                 100 
                 A 
                 1 
               
            
           
           
               
            
               
                 Comparative 
               
               
                 Example 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                  1 
                 C-1 
                 B-84 
                 PA-74 
                 D-1 
                 W-1 
                 40 
                 230 
                 E 
                 3 
               
               
                  2 
                 C-1 
                 B-84 
                 none 
                 D-1 
                 W-1 
                 42 
                 250 
                 E 
                 3 
               
               
                  3 
                 C-1 
                 B-84 
                 PA-74 
                 none 
                 W-1 
                 41 
                 240 
                 E 
                 3 
               
               
                  4 
                 C-2 
                 B-84 
                 PA-74 
                 D-1 
                 W-1 
                 39 
                 230 
                 E 
                 3 
               
               
                  5 
                 C-2 
                 B-84 
                 none 
                 D-1 
                 W-1 
                 39 
                 250 
                 E 
                 3 
               
               
                  6 
                 C-2 
                 B-84 
                 PA-74 
                 none 
                 W-1 
                 40 
                 240 
                 E 
                 3 
               
               
                   
               
            
           
         
       
     
     It is seen from the results in Table 2 that even when an antireflection film is not used as the underlying layer, the resist composition of the present invention is excellent in terms of standing wave, profile, sensitivity and resolving power as compared with the case using the compound of Comparative Example and is suitable for implantation. 
     The positive resist composition of the present invention comprises a specific acid-decomposable resin and thereby produces an excellent effect that even when the composition is coated on a substrate having a high-reflection surface without applying an antireflection film, substantially no standing wave is generated and good profile, high sensitivity and high resolution are ensured. 
     The entire disclosure of each and every foreign patent application from which the benefit of foreign priority has been claimed in the present application is incorporated herein by reference, as if fully set forth.