Nov. 17,  2016  19  US 2016/0334706 Al  mo! %, more preferably at least 5 mo! %. The upper limit is  the same as above. When constituent units having formula  ( 6a) or ( 6b) are incorporated, the molar fraction of units (Al)  and/or (A2), especially (A2) may be accordingly reduced.  acid ester bond, carbonate bond, lactone ring, sultone ring,  carboxylic acid anhydride, or haloalkyl radical may form or  intervene. Those structures shown below are preferable  because of availability, but the cation is not limited thereto.  [0077]  Also essentially, the resist composition comprises  an ammonium salt having the general formula (3).  Herein R 1  to R 4  are each independently a straight C$_{1}$-C$_{20}$,  branched or cyclic C$_{3}$ -C$_{20 }$ monovalent hydrocarbon group  which may be substituted with or separated by a heteroatom,  any two or more of R 1  to R 4  may bond together to form a  ring with the nitrogen atom to which they are attached.  x› is a structure of the general formula (3a), (3b) or (3c):  (3a)  (3b)  (3c)  (3)  wherein  wa,  Rfi’ 1 ,  Rfi’ 2 ,  wc1,  wc 2  and R’c3 are each inde› pendently fluorine or a straight C$_{1 }$-C$_{40}$, branched or cyclic  C$_{3}$ -C$_{40 }$monovalent hydrocarbon group which may be sub› stituted with or separated by a heteroatom, or a pair of Rfi’ 1  and  Rfi’ 2 ,  or R’c1 and R’c $^{2 }$may bond together to form a ring  with the carbon atom to which they are attached and any  intervening atoms.  [0078]  In the cation moiety in formula (3), examples of the  hydrocarbon group represented by R$^{1 }$to R 4  include methyl,  ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, tert› pentyl, n-pentyl, n-hexyl, n-octyl, n-nonyl, n-decyl, cyclo› pentyl, cyclohexyl, 2-ethylhexyl, cyclopentylmethyl, cyclo› pentylethyl,  cyclopentylbutyl,  cyclohexylmethyl,  cyclohexy lethy I, cyclohexy lbuty I, norborny I, oxanorborny I,  tricyclo[5.2.l .0 2 • $^{6}$]decanyl, adamantyl, phenyl, naphthyl and  anthracenyl. Also included are the foregoing groups in  which at least one hydrogen atom is replaced by a heteroa› tom such as oxygen, sulfur, nitrogen or halogen, or in which  a heteroatom such as oxygen, sulfur or nitrogen intervenes  between carbon atoms, so that a hydroxyl radical, cyano  radical, carbonyl radical, ether bond, ester bond, sulfonic  (B) Ammonium Salt  Rfi’ 1  -CF2-S02  ’N› Rfi’2  -cF 2 -so( 