103  US 10,915,021 B2  104  AcO  0  0  0  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.  In formula (IC),  W’cl,  Wc 2  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. 