US 10,180,626 B2  84  83  -continued  (c3)  (c5)  (c6)  (c4)  In formulae ( c 1) to ( c4 ), R  dl  is each independently hydro› gen, fluorine, methyl or trifluoromethyl.  Rd $^{2 }$is a single bond,  phenylene group, -O-Rd 11 -,  or -C(=O)-Ydl_  Rd 11 -,  wherein Yd 1  is -0- or -NH-, and Rd 11  is a  C 1  -C$_{20 }$ straight, branched or cyclic alkylene group, C 2 -C 20  straight, branched or cyclic alkenylene group, or phenylene  group, which may contain a heteroatom.  Rd 3 ,  Rd 4 ,  Rd 5 ,  Rd 6  and Rd 7  are each independently a C 1 -C 20  straight, branched  or cyclic monovalent hydrocarbon group which may contain  a heteroatom. Any two of R  d 2 ,  R  d 3  and R  d 4  may bond  together to form a ring with the sulfur atom to which they are  attached, and any two ofR  ds,  R  d $^{6 }$and R d $^{7 }$may bond together  to form a ring with the sulfur atom to which they are  attached. Xd- is a non-nucleophilic counter ion. Ad 1  is  hydrogen or trifluoromethyl. L  dl  is a single bond or a C 1  -C$_{20 }$ straight, branched or cyclic divalent hydrocarbon group  which may contain a heteroatom. The subscript nd is  O  or 1,  and nd is  O  when L  dl  is a single bond. zd 1  is a single bond,  methylene, ethylene, phenylene, fluorinated phenylene,  -O-Rd 11 ,  or----C(=0)-Yd 1 -Rd 12 -whereinRd 12  is an  optionally substituted phenylene group.  In formulae (cl) to (c4), preferably  Rd 2  to Rd 7  are each  independently a structure containing a phenyl group which  bonds withs+ in the formula.  Examples of the non-nucleophilic counter ion represented  by Xd- in formula (cl) include halide ions such as chloride  and bromide ions; fluoroalkylsulfonate ions such as triflate,  1, 1, 1-trifluoroethanesulfonate,  and  nonafluorobutanesul› fonate; arylsulfonate ions such as tosylate, benzenesul› fonate, 4-fluorobenzenesulfonate, and 1,2,3,4,5-pentafluo› robenzenesulfonate; alkylsulfonate ions such as mesylate  and butanesulfonate; imides such as bis(trifluoromethylsul› fonyl)imide, bis(perfluoroethylsulfonyl)imide, and bis(per› fluorobutylsulfonyl)imide; and methides such as tris(trifluo› romethylsulfonyl)methide and tris(perfluoroethylsulfonyl)  methide.  Other non-nucleophilic counter ions include anions hav› ing the formulae ( c5) and ( c6).  In formulae ( c5) and ( c6), A  dl  is as defined above, and  $_{Rd}$13 is a C 1  -C 40  straight, branched or cyclic monovalent  hydrocarbon group which may contain a heteroatom.  The anion moiety of formula ( c5) is exemplified by the  aforementioned structures of the anion of formula (3 ), ( 4) or  (5) and those structures illustrated in JP-A 2014-177407,  paragraphs [0100]-[0101]. The anion moiety of formula (c6)  is exemplified by the aforementioned structures of the anion  of formula (3 ), ( 4) or ( 5) and those structures illustrated in  JP-A 2010-215608, paragraphs [0080]-[0081].  Illustrative structures of the anion moiety in formula (c2)  include those described in JP-A 2014-177407, paragraphs  [0021 ]-[0026]. Illustrative structures of the anion moiety in  formula ( c2) wherein A  dl  is hydrogen include those  described in JP-A 2010-116550, paragraphs [0021]-[0028].  Illustrative structures of the anion moiety in formula (c2)  wherein Ad is trifluoromethyl include those described in  JP-A 2010-077404, paragraphs [0021]-[0027]. Illustrative  structures of the cation moiety in formula (c2) include those  described in JP-A 2008-158339, paragraph [0223].  Illustrative structures of the anion moiety in formula (c3)  include the structures illustrated for formula ( c2) wherein  ----CH(Ad 1 )CF2So3- is replaced by----C(CF3)2CH2So3-› Illustrative structures of the sulfonium cation in formulae  (c2) to (c4) include those cations described in JP-A 2008- 158339, paragraph [0223] and those cations in the onium  salt having formula (6) which will be exemplified later.  The polymer as the base resin may have further copoly› merized therein recurring units of the structure having a  hydroxyl group protected with an acid labile group. The  recurring unit of the structure having a hydroxyl group  protected with an acid labile group is not particularly limited  as long as it has one or more protected hydroxyl-bearing  structure such that the protective group may be decomposed  to generate a hydroxyl group under the action of acid.  Examples of these recurring units include those described in  JP-A 2014-225005, paragraphs [0055]-[0065] and JP-A  2015-214634, paragraphs [0110]-[0115].  In addition to the foregoing units, the polymer may further  comprise other recurring units, for example, recurring units  having an oxirane ring or oxetane ring. The inclusion of  recurring units having an oxirane or oxetane ring ensures  that the exposed region of resist film is improved in film  retention and etch resistance because the exposed region is  crosslinked.  Also included in the other recurring units are units derived  from substituted acrylates such as methyl methacrylate,  methyl crotonate, dimethyl maleate, and dimethyl itaconate;  unsaturated carboxylic acids such as maleic acid, fumaric  acid, and itaconic acid; cyclic olefins such as norbomene,  norbornene derivatives, and tetracyclo[ 6.2.  1.  1  3 • $^{6 }$.O 2 .7]dode- cane derivatives; unsaturated acid anhydrides such as  itaconic anhydride; vinyl aromatics such as styrene, vinyl› naphthalene,  hydroxystyrene,  hydroxyvinylnaphthalene,  l  1 1  .so- Rdl3  o,.......  A  3  F  F 