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In formula (18), W1’ 1 and W1’ 2 are each independently fluorine or a C$_{1 }$-C$_{40 }$monovalent hydrocarbon group which may contain a heteroatom. The monovalent hydrocarbon groups may be straight, branched or cyclic, and examples thereof are as exemplified above for R 105 . Preferably WZ, 1 and W1’ 2 each are fluorine or a straight C$_{1 }$-C$_{4 }$ fluorinated alkyl group. A pair of W1’ 1 and W1’ 2 may bond together to form a ring with the linkage (-CF$_{2}$-S0$_{2}$-N--So$_{2}$ - CF $_{2}$ -) to which they are attached, and preferably the pair is a fluorinated ethylene or fluorinated propylene group. 2 

In formula (IC), W’cl, Wc and Wc3 are each indepen› dently fluorine or a C$_{1 }$-C$_{40 }$monovalent hydrocarbon group which may contain a heteroatom. The monovalent hydro- carbon groups may be straight, branched or cyclic, and examples thereof are as exemplified above for R 105 . Pref› erably wc1, wc 2 and Wc3 each are fluorine or a straight cl -C4 fluorinated alkyl group. A pair of wc1 and wc 2 may bond together to form a ring with the linkage (----CF$_{2}$ - S0$_{2}$-c--S0$_{2}$----CF $_{2}$-) to which they are attached, and preferably the pair is a fluorinated ethylene or fluorinated propylene group. 

In formula (ID), Wd is a C$_{1}$-C$_{40 }$monovalent hydrocarbon group which may contain a heteroatom. The monovalent 60 hydrocarbon groups may be straight, branched or cyclic, and examples thereof are as exemplified above for R 105 . 

With respect to the synthesis of the sulfonium salt having an anion of formula (ID), reference is made to JP-A 2010-215608 and JP-A 2014-133723. 

Examples of the anion having formula (ID) are shown below, but not limited thereto. 

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