US 2018/0335696 Al  2  Nov. 22, 2018  [0015]  In a preferred embodiment, the polymer further  comprises recurring units having to the formula (bl) or (b2).  Herein  RA  is hydrogen or methyl; X$^{1 }$is a single bond or ester  group; X 2  is a  C$_{1 }$-C$_{12 }$ straight, branched or cyclic alkylene  group or  CcC$_{10 }$ arylene group, any methylene moiety in the  alkylene group may be substituted by an ether moiety, ester  moiety or lactone ring-containing moiety, at least one hydro› gen in the group X 2  is substituted by iodine; X 3  is a single  bond, ether group, ester group or C$_{1 }$-C$_{12 }$straight, branched  or cyclic alkylene group, any methylene moiety in the  alkylene group may be substituted by an ether or ester  moiety; Rf$^{1 }$to R:t4 are each independently hydrogen, fluorine  or trifluoromethyl, at least one of Rf 1  to Rf4 is fluorine or  trifluoromethyl, Rf 1  and Rf 2  may bond together to form a  carbonyl group; R 1  to Rf4 are each independently a C$_{1}$-C$_{12 }$ straight, branched or cyclic alkyl group, C$_{2}$ -C$_{12 }$ straight,  branched or cyclic alkenyl group, C$_{2}$-C$_{12 }$straight, branched  or cyclic alkynyl group, C$_{6}$-C$_{20 }$ aryl group, C$_{1 }$-C$_{2 }$ aralkyl  group, or C$_{7}$-C$_{12 }$ aryloxyalkyl group, in which at least one  hydrogen may be substituted by hydroxyl, carboxyl, halo› gen, oxo, cyano, amide, nitro, sultone, sulfone or sulfonium  salt-containing moiety, and in which any methylene moiety  may be substituted by an ether, ester, carbonyl, carbonate or  sulfonate moiety, and R$^{1 }$and R 2  may bond together to form  a ring with the sulfur atom to which they are attached.  [0013]  Preferably the recurring units having formulae (al)  and (a2) are represented by the formulae (al-1) and (a2-1),  respectively.  Herein  RA,  R$^{1 }$to R 5 , Rf4 to Rf4, andX $^{1 }$are as defined above;  R  6  is a C$_{1 }$-C$_{4 }$ straight, branched or cyclic alkyl group,  halogen atom exclusive of iodine, hydroxyl group. C$_{1 }$-C$_{4 }$ straight, branched or cyclic alkoxy group, or C$_{2}$-C$_{5 }$ straight,  branched or cyclic alkoxycarbonyl group, mis an integer of  1 to 4, and n is an integer of Oto 3.  [0014]  The resist composition may further comprise an  organic solvent.  [0021]  A resist material containing a polymer comprising  recurring units derived from a sulfonium or iodonium salt  having a polymerizable unsaturated bond and containing  iodine in the linker between the polymerizable unsaturated  bond and a fluorosulfonic acid has the advantage of reduced  acid diffusion because of the high atomic weight of iodine.  This prevents resolution from declining due to blur by acid  diffusion and enables to reduce LWR and improve CDU.  [0020]  In a preferred embodiment, the high-energy radia› tion is ArF excimer laser radiation of wavelength 193 nm,  KrF excimer laser radiation of wavelength 248 nm, EB or  EUV of wavelength 3 to 15 nm.  [0019]  In another aspect, the invention provides a process  for forming a pattern comprising the steps of applying the  resist composition defined above onto a substrate, baking to  form a resist film, exposing the resist film to high-energy  radiation, and developing the exposed film in a developer.  [0018]  The resist composition may further comprise a  surfactant.  [0017]  In one embodiment, the polymer is free of an acid  labile group. The resist composition may further comprise a  crosslinker, the resist composition being a chemically ampli› fied negative tone resist composition.  [0016]  The resist composition may further comprise a  dissolution inhibitor, the resist composition being a chemi› cally amplified positive tone resist composition.  Herein  RA  is independently hydrogen or methyl; Y 1  is a  single bond, phenylene group, naphthylene group, or a  C$_{1 }$-C$_{12 }$ linking group containing an ester moiety and/or  lactone ring; Y 2  is a single bond or ester group; R$^{11 }$and R 12  are each independently an acid labile group; R$^{13 }$is halogen,  trifluoromethyl, cyano, C$_{1 }$-C$_{6 }$ straight, branched or cyclic  alkyl or alkoxy group, or C$_{2}$-C$_{7 }$ straight, branched or cyclic  acyl, acyloxy or alkoxycarbonyl group; R$^{14 }$is a single bond  or C$_{1 }$-C$_{6 }$ straight or branched alkylene group in which at  least one carbon atom may be substituted by an ether or ester  moiety, p is 1 or 2, and q is an integer of O to 4.  Advantageous Effects of Invention  ~  A  R\-~~  lm~Rf1  RF  A  S03- 0  0  Rf3  R–4  (al-1)  ~  A  R\-~~  lm~Rfl  Rf$_{2 }$ A  S03- 0  0  Rf3  R–4  (a2-1)  R4  I  r+  I  Rs  (bl)  (b2) 