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In formula (Al), each ofR 1 a to R 13 a independently repre› sents a hydrogen atom, a halogen atom, a nitro group or an organic group. 1 13 

From one to three members out ofR a to R a are prefer› ably not a hydrogen atom, and it is more preferred that at least any one of R 9 a to R 13$_{a }$ is not a hydrogen atom. 

Za represents a single bond or a divalent linking group. 

x- has the same meaning as z- in formula (ZI). 1 13 

Specific examples of R a to R a when these are not a hydrogen atom include a halogen atom, a nitro group, a linear, branched or cyclic alkyl group, an alkenyl group, an alkynyl group, an aryl group, a heterocyclic group, a cyano group, a carboxyl group, an alkoxy group, an aryloxy group, a silyloxy group, a heterocyclic oxy group, an acyloxy group, a carbam› oyloxy group, an alkoxycarbonyloxy group, an aryloxycar- bonyloxy group, an amino group (including an anilino group), an acylamino group, an aminocarbonylamino group, an alkoxycarbonylamino group, an aryloxycarbonylamino group, a sulfamoylamino group, an alkylsulfonylamino group, an arylsulfonylamino group, an alkylthio group, an arylthio group, a heterocyclic thio group, an alkylsulfinyl group, an arylsulfinyl group, an alkylsulfonyl group, an aryl› sulfonyl group, an acyl group, an aryloxycarbonyl group, an alkoxycarbonyl group, a carbamoyl group, an arylazo group, a heterocyclic azo group, a phosphinylamino group, a silyl grouR, a ureido group, and other known organic groups. 13$_{a }$ 

R a to R are, when these are not a hydrogen atom, preferably a linear, branched or cyclic alkyl group substituted by a hydroxyl group. 

Examples of the divalent linking group of Za include an alkylene group, anarylene group, a carbonyl group, a sulfonyl group, a carbonyloxy group, a carbonylamino group, a sulfo› nylamide group, -0-, -S-, an amino group, a disulfide group, -(CH$_{2}$)n-CO-, -(CH$_{2}$)n-SO$_{2}$-, -CH=CH-, an aminocarbonylamino group and an ami- nosulfonylamino group (n is an integer of 1 to 3). 

Incidentally, preferred examples of the structure where at least one ofR$_{20}$ i, R$_{202 }$and R$_{203 }$is not an aryl group include a cation structure such as compounds described in paragraphs 0046 and 0047 ofJP-A-2004-233661 and paragraphs 0040 to 0046 of JP-A-2003-35948, compounds illustrated as formu- lae (I-1) to (1-70) in U.S. Patent Application Publication No. 2003/0224288Al, and compounds illustrated as formulae (IA-1) to (IA-54) and formulae (IB-1) to (IB-24) in U.S. Patent Application Publication No. 2003/0077540A 1. 

In formulae (ZII) and (ZIII), each ofR$_{204 }$to R$_{207 }$indepen- dently represents an aryl group, an alkyl group or a cycloalkyl group. 

The aryl group, alkyl group and cycloalkyl group ofR$_{204 }$to R$_{207 }$ are the same as the aryl group, alkyl group and cycloalkyl group ofR$_{201 }$to R$_{203 }$in the compound (ZI). 

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The aryl group, alkyl group and cycloalkyl group ofR$_{204 }$to R$_{207 }$ may have a substituent. Examples of the substituent include those of the substituent which the aryl group, alkyl group and cycloalkyl group ofR$_{201 }$to R$_{203 }$in the compound (ZI) may have. 

z- represents a non-nucleophilic anion, and examples thereof are the same as those of the non-nucleophilic anion of z- in formula (ZI). 

The acid generator further includes compounds repre› sented by the following formulae (ZIV), (ZV) and (ZVI): 

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In formulae (ZIV) to (ZVI), each ofAr$_{3 }$ andAr$_{4 }$ indepen› dently represents an aryl group. 

Each of R$_{208}$ , R $_{209 }$and R$_{210 }$independently represents an alkyl group, a cycloalkyl group or an aryl group. 

A represents an alkylene group, an alkenylene group or an arylene group. 

Specific examples of the aryl group of Ar$_{3}$ , Ar$_{4}$ , R$_{208}$, R 209 and R$_{210 }$are the same as specific examples of the aryl group ofR$_{20}$ i, R$_{202 }$and R$_{203 }$in formula (ZI). 

Specific examples of the alkyl group and cycloalkyl group ofR$_{208}$, R$_{209 }$and R$_{210 }$are the same as specific examples of the alkyl group and cycloalkyl group ofR$_{201}$ , R $_{202 }$and R$_{203 }$ in formula (ZI). 

The alkylene group of A includes an alkylene group having a carbon number of 1 to 12 (e.g., methylene, ethylene, pro› pylene, isopropylene, butylene, isobutylene ), the alkenylene group of A includes an alkenylene group having a carbon number of 2 to 12 (e.g., ethynylene, propenylene, bute› nylene ), and the arylene group of A includes an arylene group having a carbon number of 6 to 10 ( e.g., phenylene, tolylene, naphthylene ). 

Out of the acid generators, particularly preferred examples are set forth below. 

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