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[0188] Of the cationic structures represented by formulae (ZI-1) to (ZI-3), preferred are (ZI-1) and (ZI-2), and more preferred is (ZI-1 ). 

[0189] In the next place, (ZA-1-2) is described. 

[0190] (ZA-1-2) represents an organic group in which each ofR$_{201 }$to R$_{203 }$in (ZI-1) independently represents an organic group not having an aromatic ring. The aromatic ring here means to include an aromatic ring containing a heteroatom. 

[0191] The organic group not containing an aromatic ring as R$_{201 }$to R$_{203 }$is generally an organic group having 1 to 30 carbon atoms, and preferably 1 to 20 carbon atoms. 

[0192] Each ofR$_{201 }$to R$_{203 }$independently preferably rep› resents an alkyl group, a monovalent aliphatic hydrocarbon cyclic group, an ally! group, or a vinyl group, more preferably a linear or branched 2-oxoalkyl group, 2-oxo aliphatic hydro› carbon cyclic group, or alkoxycarbonylmethyl group, and especially preferably a linear or branched 2-oxo aliphatic hydrocarbon cyclic group. 

[0193] As the alkyl group and aliphatic hydrocarbon cyclic group ofR$_{201 }$to R$_{203}$, a linear or branched alkyl group having 1 to 10 carbon atoms (e.g., a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group), and an aliphatic hydrocarbon cyclic group having 3 to 10 carbon atoms ( e.g., a cyclopentyl group, a cyclohexyl group, a norbonyl group) can be preferably exemplified. The alkyl group is more pref› erably a 2-oxoalkyl group and an alkoxycarbonylmethyl group. The aliphatic hydrocarbon cyclic group is more pref› erably a 2-oxo aliphatic hydrocarbon cyclic group. The ali› phatic hydrocarbon cyclic group is preferably a cycloalkyl group. 

[0194] The 2-oxoalkyl group may be either linear or branched, and is preferably a group having >C=O at the 2-position of the above alkyl group. 

[0195] The 2-oxo aliphatic hydrocarbon cyclic group is preferably a group having >C=O at the 2-position of the above aliphatic hydrocarbon cyclic group. The 2-oxo ali› phatic hydrocarbon cyclic group is preferably a 2-oxocy› cloalkyl group. 

[0196] The alkoxy group in the alkoxycarbonylmethyl group is preferably an alkoxy group having 1 to 5 carbon atoms (e.g., a methoxy group, an ethoxy group, a propoxy group, a butoxy group, a pentoxy group). 

[0197] R$_{201 }$to R$_{203 }$may further be substituted with a halo› gen atom, an alkoxy group ( e.g., having 1 to 5 carbon atoms), a hydroxyl group, a cyano group, or a nitro group. 

[0198] (ZA-1-3) is described in the next place. 

[0199] (ZA-1-3) is a group represented by the following formula, and is a group having a phenacylsulfonium salt structure. 

<img src='content_image/893803.jpg'>

[0200] In formula (ZA-1-3), each ofR$_{1}$c to R$_{5}$c indepen› dently represents a hydrogen atom, an alkyl group, a monova› lent aliphatic hydrocarbon cyclic group, an alkoxy group, a phenylthio group, or a halogen atom. 

[0201] Each of R$_{6}$c and R$_{7}$c independently represents a hydrogen atom, an alkyl group, or a monovalent aliphatic hydrocarbon cyclic group. 

[0202] Each of Rx and Ry independently represents an alkyl group, a monovalent aliphatic hydrocarbon cyclic group, an ally! group, or a vinyl group. 

[0203] Any two or more ofR$_{1 }$c to R$_{5}$c, R$_{6}$c and R$_{7}$c, and Rx and Ry may be bonded to each other to form a ring, and the ring may contain an oxygen atom, a sulfur atom, an ester bond, or an amido bond. As the group formed by bonding any two or more of R$_{1 }$c to R$_{5}$c, R$_{6}$c and R$_{7}$c, and Rx and Ry, a butylene group and a pentylene group can be exemplified. 

[0204] The alkyl group as R$_{1 }$c to R$_{7}$c may be either linear or branched, and the examples thereof include an alkyl group having 1 to 20 carbon atoms, and preferably a linear or branched alkyl group having 1 to 12 carbon atoms (e.g., a methyl group, an ethyl group, a linear or branched propyl group, a linear or branched butyl group, and a linear or branched pentyl group). 

[0205] The monovalent aliphatic hydrocarbon cyclic group as R$_{1 }$c to R$_{7}$c may be either monocyclic or polycyclic, and the examples thereof include a monovalent aliphatic hydrocar› bon cyclic group having 3 to 8 carbon atoms ( e.g., a cyclo› pentyl group and a cyclohexyl group). The monovalent ali› phatic hydrocarbon cyclic group is preferably a cycloalkyl group. 

[0206] The alkoxy group as R$_{1 }$c to R$_{5}$c may be linear, branched or cyclic, and the examples thereof include an alkoxy group having 1 to 10 carbon atoms, and preferably a linear or branched alkoxy group having 1 to 5 carbon atoms ( e.g., a methoxy group, an ethoxy group, a linear or branched propoxy group, a linear or branched butoxy group, and a linear or branched pentoxy group), a cyclic alkoxy group having 3 to 8 carbon atoms ( e.g., a cyclopentyloxy group and a cyclohexyloxy group). 

[0207] Preferably any ofR$_{1}$c to R$_{5}$c is a linear or branched alkyl group, a monovalent aliphatic hydrocarbon cyclic group, or a linear, branched or cyclic alkoxy group, and more preferably the sum total of the carbon atoms ofR$_{1}$c to R$_{5}$c is 2 to 15, by which the solubility of solvent is improved and the generation of particles during preservation is controlled. 

[0208] As the alkyl group and monovalent aliphatic hydro› carbon cyclic group as Rx and Ry, the same alkyl group and monovalent aliphatic hydrocarbon cyclic group as in R$_{1 }$c to R$_{7}$c can be exemplified, and more preferably a 2-oxoalkyl group, a 2-oxo aliphatic hydrocarbon cyclic group, and an alkoxycarbonylmethyl group. 

[0209] As the 2-oxoalkyl group and 2-oxo aliphatic hydro› carbon cyclic group, the alkyl group and the group having >C=O at the 2-position of the aliphatic hydrocarbon cyclic group as R$_{1 }$c to R$_{7}$c can be exemplified. 

[0210] As for the alkoxy group in the alkoxycarbonylm› ethyl group, the alkoxy group same as those in R$_{1 }$c to R$_{5}$c can be exemplified. 

[0211] Each of Rx and Ry preferably represents an alkyl group having 4 or more carbon atoms or a monovalent ali› phatic hydrocarbon cyclic group, more preferably an alkyl group having 6 or more carbon atoms, and still more prefer› ably an alkyl group having 8 or more carbon atoms or a monovalent aliphatic hydrocarbon cyclic group. 

[0212] As the cyclic structure which may be formed by bonding Rx and Ry to each other, a 5- or 6-membered ring formed by divalent groups Rx and Ry (e.g., a methylene group, an ethylene group, a propylene group, and the like) 

