US 10,754,248 B2  97  98  to  40  carbon atoms optionally containing a heteroatom,  preferably a fluorine atom or a linear fluorinated alkyl group  having  1  to  4  carbon atoms. R’c1 and R’c $^{2 }$may be bonded to  form a ring together with a carbon atom bonded thereto and  an atom (-CF  $_{2}$-S0$_{2}$ ----e--S0$_{2}$----CF $_{2}$-), and preferably  forms a ring structure by a fluorinated ethylene group or a  fluorinated propylene group.  R’d  in the general formula (SD) represents a linear, a  branched, or a cyclic monovalent hydrocarbon group having  1  to 40  carbon atoms optionally containing a heteroatom.  These anions are described in detail in JP-A-2010-21560S  and  JP-A-2014-133723.  Illustrative  example  thereof  includes the anions in these patent documents and an anion  represented by the formula ( 4b ). The photo acid generator  having an anion represented by the general formula (SD) has  no fluorine atom at  a  position of a sulfa group, but has two  trifluoromethyl groups at  ~  position. Consequently, it has an  acidity strong enough to cut an acid labile group in a resist  polymer, which can thus be used as a photo acid generator.  Illustrative example of the anion represented by any of the  general formula (SA), (SB), (SC), or (SD) includes the  following anions, but the present invention is not restricted  thereto. A$^{1 }$represents a hydrogen atom or a trifluoromethyl  group,  -continued  O  0 5x,SO;  F  F  HO  0  0 5x,s~  F  F  H  c¢ o  0 5x,so;  o  F  F  o’-11  ~ 0 5x,so;  ~OFF  OID 