US 10,620,533 B2  5  6  otherwise. "Optional" or "optionally" means that the sub› sequently described event or circumstances may or may not  occur, and that description includes instances where the  event or circumstance occurs and instances where it does  not. The notation  (Cn-Cm)  means a group containing from n  to m carbon atoms per group. Me stands for methyl, Ac for  acetyl, and Ph for phenyl.  The abbreviations and acronyms have the following  meaning.  EB: electron beam  EUV: extreme ultraviolet  Mw: weight average molecular weight  Mn: number average molecular weight  Mw/Mn: molecular weight distribution or dispersity  GPC: gel permeation chromatography  PEB: post-exposure bake  PPD: post PEB delay  PAG: photoacid generator  LWR: line width roughness  Herein R 51 , R 55  and R 59  each are hydrogen or methyl; R 52  is a sin§le bond, phenylene, ---O-R 63 -, or ----C(=O)› Y1-R6 -, Y 1  is ---0- or -NH-, R 63  is a straight,  branched or cyclic C 1  -C 6  alkylene or alkenylene group  which may contain a carbonyl, ester, ether or hydroxyl  moiety or phenylene group• R 53  R 54  R 56  R 57  R 58  R 60  R 61 , a~d R 62  are each indep;nde~tly a’strai~ht, b~ancl~ed o;  cyclic C 1  -C$_{12 }$ alkyl group which may contain a carbonyl,  ester or ether moiety, or a C 6 -C 12  aryl group, C 7 -C 20  aralkyl  group or mercaptophenyl group; A 1  is a single bond, -A 0 - C(=O)-O-, -A 0 -O- or -A 0 -O----C(=O)-, A 0  is a  straight, branched or cyclic C 1  -C$_{12 }$ alkylene group which  may contain a carbonyl, ester or ether moiety; A 2  is hydro› gen or trifluoromethyl; Z 1  is a single bond, methylene,  ethylene, phenylene, fluorinated phenylene, -O-R 64 -,  or  -C(=O)-Z 2 -R 64 -, Z 2  is -0- or-NH-, R 64  is a  straight, branched or cyclic C 1  -C 6  alkylene or alkenylene  group which may contain a carbonyl, ester, ether or hydroxyl  moiety, or phenylene, fluorinated phenylene or trifluorom› ethyl-substituted phenylene group; M- is a non-nucleophilic  counter ion, and fl, f2 and f3 are numbers in the range:  Osfls0.5, Osf2s0.5, Osf3s0.5, and O<fl+f2+f3s0.5.  The resist composition may further comprise a surfactant.  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 radia› tion, and developing the exposed film in a developer.  Typically, the high-energy radiation 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.  Since a resist film containing a sulfonium or iodonium salt  of formula (A) exhibits a high dissolution contrast, it offers  improved resolution, a wide focus margin, a reduced LWR,  and no dimensional changes on PPD as a positive or  negative tone resist film subject to alkaline development and  as a negative tone resist film subject to organic solvent  development.  As used herein, the singular forms "a," "an" and "the"  include plural referents unless the context clearly dictates  The resist composition of the invention is defined as  comprising a base polymer and a sulfonium or iodonium salt  of sulfonic acid containing a morpholino group. Although  the sulfonium or iodonium salt is an acid generator capable  of generating sulfonic acid containing a morpholino group  upon light exposure, it functions as a quencher because of  inclusion of nitrogen atom. Since the sulfonic acid does not  possess a sufficient acidity to induce deprotection reaction of  an acid labile group, it is recommended to separately add an  acid generator capable of generating a strong acid such as  a-fluorinated sulfonic acid, imide acid or methide acid, as  will be described later, in order to induce deprotection  reaction of an acid labile group. The acid generator capable  of generating a-fluorinated sulfonic acid, imide acid or  methide acid may be either of separate type which is added  to the base polymer or of bound type which is bound in the  base polymer.  When a resist composition containing the sulfonium or  iodonium salt of sulfonic acid containing a morpholino  group in admixture with an acid generator capable of  generating a perfluoroalkylsulfonic acid or superstrong acid  is exposed to radiation, sulfonic acid containing a mor› pholino group and perfluoroalkylsulfonic acid generate.  Since the acid generator is not entirely decomposed, the  undecomposed acid generator is present nearby. When the  sulfonium or iodonium salt capable of generating sulfonic  acid containing a morpholino group co-exists with the  perfluoroalkylsulfonic acid,  ion exchange takes place  whereby a sulfonium salt of perfluoroalkylsulfonic acid is  created and sulfonic acid containing a morpholino group is  released. This is because the salt of perfluoroalkylsulfonic  acid having a high acid strength is more stable. In contrast,  when a sulfonium salt of perfluoroalkylsulfonic acid co› exists with a sulfonic acid containing a morpholino group,  no ion exchange takes place.  The ion exchange reaction according to the acid strength  series occurs not only with sulfonium salts, but also simi› larly with iodonium salts. Likewise, ion exchange takes  place not only with the perfluoroalkylsulfonic acid, but also  similarly with arylsulfonic acid, alkylsulfonic acid, imide  acid and methide acid having a higher acid strength than the  sulfonic acid containing a morpholino group.  While the resist composition of the invention should  essentially contain the sulfonium or iodonium salt of sulfo- nic acid containing a morpholino group, another sulfonium  or iodonium salt may be separately added as the quencher.  Examples of the sulfonium or iodonium salt to be added as  Advantageous Effects of Invention  DESCRIPTION OF EMBODIMENTS  Resist Composition  (f2)  R56  I  +s-Rs7  I  Rss  (fJ)  -continued 