[0057] Z represents a phosphorus atom, a boron atom, or an antimony atom. A represents a halogen atom (preferably a fluorine atom). 

[0058] P represents a phosphorus atom, F represents a fluorine atom, B represents a boron atom, and Ga represents a gallium atom. 

[0059] S represents a sulfur atom, 0 represents an oxygen atom, C represents a carbon atom, and N represents a nitrogen atom. 

[0060] Rf is preferably an alkyl group having 80 mo!% or more of its hydrogen atom substituted with fluorine atom, and the alkyl group having 1 to 8 carbon atoms is preferable. The alkyl group made into Rf by fluorine substitution can include a linear alkyl group (methyl, ethyl, propyl, butyl, pentyl, octyl and the like), a branched alkyl group (isopro› pyl, isobutyl, s-butyl, t-butyl and the like), a cycloalkyl group (cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl and the like) and the like. In Rf, the ratio of the hydrogen atom of the alkyl group being substituted with fluorine atom is preferably 80 mo! % or more, more preferably 90% or more, and especially preferably 100%, based on the molar number of the hydrogen atom contained in the original alkyl group. 

[0061] When the ratio of substitution by fluorine atom is in such preferable range, the light responsiveness of the sulfonium salt becomes further favorable. The especially preferable Rf can include CF3-, CF$_{3}$CF 2 -, (CF$_{3}$ $^{)}$2 CF-, CF$_{3}$CF 2 CF 2 -, CF$_{3}$CF 2 CF 2 CF 2 -, (CF$_{3}$ $^{)}$2 CFCF 2 -, CF$_{3}$CF 2 (CF$_{3}$)CF- and (CF$_{3}$ ) $_{3}$C-. Rf contained by the number of"b" are independent from each other, and thus they can be the same or different from each other. 4 

[0062] R represents a phenyl group having a part of hydrogen atoms being substituted with at least one halogen atom or electron withdrawing group. The halogen atom can include a fluorine atom, a chlorine atom, a bromine atom and the like. The electron withdrawing group can include a trifluoromethyl group, a nitro group, a cyano group and the like. Among these, a phenyl group having one hydrogen atom substituted with a fluorine atom or a trifluoromethyl group is preferable. R 4 contained by the number of "c" are independent from each other, and thus they can be the same or different from each other. 

[0063] R $^{5 }$represents an alkyl group having 1 to 20 carbon atoms, a perfluoroalkyl group having 1 to 20 carbon atoms, or an aryl group having 6 to 20 carbon atoms. The alkyl group and the perfluoroalkyl group can be either linear, branched, or cyclic group, and the aryl group can be a non-substituted group or can have a substituent group. 

[0064] "a" represents an integer of 4 to 6. "b" represents an integer of 1 to 5, preferably 2 to 4, and especially preferably 2 or 3. "c" represents an integer of 1 to 4, preferably 4. 

[0065] The anion represented by ZAa - can include anions represented by SbF6-, PF$_{6}$ -, and BF 4 -. 

[0066] The anion represented by (Rf)$_{6}$PF c$_{6}$ _ 6 )- can include anions represented by (CF$_{3}$CF 2 ) 2 PF $_{4}$-, (CF$_{3}$CF 2 )$_{3}$PF$_{3 }$-, ((CF$_{3}$ ) 2 CF) 2 PF $_{4}$-, ((CF 3 ) 2 CF)$_{3}$PF$_{3 }$-, (CF$_{3}$CF 2 CF 2 ) 2 PF 4 -, (CF$_{3}$CF 2 CF 2 )$_{3}$PF$_{3 }$-, ((CF 3 ) 2 CFCF 2 ) 2 PF $_{4}$ -, ((CF 3 ) 2 CFCF 2 ) $_{3}$PF$_{3}$ -, (CF $_{3}$CF 2 CF 2 CF 2 ) 2 PF$_{4}$ - and (CF$_{3}$CF 2 CF 2 CF 2 )$_{3}$PF$_{3}$-. Among these, anions represented by ((CF$_{3}$ ) 2 CF 2 )$_{3}$PF$_{3 }$-, (CF$_{3}$CF 2 CF 2 )$_{3}$PF$_{3 }$-, (CF$_{3}$ $^{)}$2 CF)$_{3}$PF$_{3 }$ -, (CF$_{3}$ $^{)}$2 CF) 2 PF 4 -, (CF$_{3}$ ) 2 CFCF 2 )$_{3}$PF$_{3}$ - and ((CF$_{3}$ ) 2 CFCF 2 ) 2 PF $_{4}$ - are prefer› able. 

[0067] amon The anion represented by R $^{4}$cBAc$_{4}$ -c)- can include represented by (C$_{6}$F $_{5}$ ) $_{4}$B-, (CF$_{3}$ ) 2 C$_{6}$H$_{3}$ ) $_{4}$B-, 

(CF$_{3}$C$_{6}$H$_{4}$ ) $_{4}$B-, (C$_{6}$F $_{5}$ $^{)}$2 BF 2 -, C$_{6}$F $_{5}$BF$_{3 }$ - and (C$_{6}$H$_{3}$F 2 )$_{4}$ B-. Among these, anion represented by (C$_{6}$F$_{5}$ ) $_{4}$B- and ((CF$_{3}$ ) 2 C$_{6}$H$_{3}$ ) $_{4}$B- are preferable. [0068] 

The anion represented by R $^{4}$cGaAc$_{4}$ -c)- can include anion represented by (C$_{6}$F$_{5}$ ) $_{4}$Ga, (CF$_{3}$ ) 2 C$_{6}$H$_{3}$ ) $_{4}$Ga, (CF $_{3}$C$_{6}$H$_{4}$ ) $_{4}$Ga, (C$_{6}$F $_{5}$ $^{)}$2 GaF 2 , C$_{6}$F $_{5}$GaF $_{3 }$ and (C$_{6}$H$_{3}$F 2 )$_{4}$Ga-. Among these, anion represented by (C$_{6}$F$_{5}$)$_{4}$Ga- and ((CF$_{3}$) 2 C$_{6}$H$_{3}$ ) $_{4}$Ga- are preferable. [0069] The anion represented by R$^{5}$SO$_{3 }$ - can include 

those described in WO 2011/093139. As a radiation-sensi› tive acid generator, a sulfonic acid derivative having an anion structure represented by the following formula (al) is preferable, however, the present invention is not limited to these. 

[0070] In formula (al), R 5 a represents a monovalent organic group having 1 to 20 carbon atoms, which can have a substituent group. As the organic group, a group repre› sented by the following formula having 1 to 20 carbon atoms can be preferably mentioned. Rsb_(L-Rsc)n- (a2) 

[0071] In formula (a2), R$^{56 }$is either one of a monovalent group selected from a linear, branched, or cyclic monovalent aliphatic hydrocarbon group; a monovalent aromatic hydro› carbon group; and a monovalent aliphatic heterocyclic group or a monovalent aromatic heterocyclic group having in its skeleton at least one structure selected from the group consisting of -0-, -CO-, -COO-, ---OCO-, ---O-CO---0-, -NHCO-, ----CONH-, -NH-CO› O-, ---0-CO-NH-, -NH-, -N=, -S-, -SO-, and-SO 2 -. [0072] 

Here, L is either one of a group selected indepen› dently from each other, from a direct bond; or from the group consisting of -0-, -CO-, -COO-, ---OCO-, ---O-CO---0-, -NHCO-, ----CONH-, -NH-CO› O-, -O----CO-NH-, -NH-, -S-, and ----CO-O› CH2-CO---O-. 

[0073] R $^{5}$c is either one of a divalent group selected independently from each other, from a linear, branched, or cyclic divalent aliphatic hydrocarbon group; a divalent aro› matic hydrocarbon group; and a divalent aliphatic hetero› cyclic group or a divalent aromatic heterocyclic group having at least one structure in its skeleton, the structure being selected from a group consisting of ---0-, -CO-, -COO-, ---OCO-, ---O-CO---0-, -NHCO-, ----CONH-, -NH-CO---0-, ---0-CO-NH-, -NH-, -N=, -S-, and -SO 2 -. [0074] Here, in the afore-mentioned formula (a2), "m" is 

0 or an integer of 1 to 10. When "m" is 0, R 5 a includes the hydroxyl group, and when "m" is 1 or higher, at least either one of R 56 and R$^{5}$c includes the hydroxyl group. "m" is preferably O to 5, more preferably O to 3. 5 

[0075] Here, when R a has a substituent group, the number of carbon atom including the number of carbon atom of such substituent group is preferably 1 to 200, more preferably 1 to 100, further preferably 1 to 30, and especially preferably 3 to 30. Further, it is preferable that R 5 a has a substituent group. That is, at least one of the hydrogen atoms ofR$^{56 }$and R $^{5}$c is preferably substituted by the substituent group. [0076] The substituent group which can be included in R 5 a can include a hydroxy group, a carboxy group, an alkoxy group, an acyl group, an alkoxycarbonyl group, an aryl group, an aryloxy group, a phosphino group, an alkylthio 

(al) 

