Feb. 18,2021  53  US 2021/0048748 Al  [0104]  In formulae (1-1) and (1-2), x- is an anion of the  following formula (IA), (18), (IC) or (ID).  of achieving a high resolution in forming patterns of small  feature size. The hydrocarbyl groups may be saturated or  unsaturated and straight, branched or cyclic. Examples  thereof include, but are not limited to, alkyl groups such as  methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl,  tert-butyl, pentyl, neopentyl, hexyl, heptyl, 2-ethylhexyl,  nonyl, undecyl, tridecyl, pentadecyl, heptadecyl, and eicosa› nyl; cyclic saturated hydrocarbyl groups such as cyclopen› tyl, cyclohexyl, 1-adamantyl, 2-adamantyl, 1-adamantylm› ethyl,  norbornyl,  norbornylmethyl,  tricyclodecanyl,  tetracyclododecanyl, tetracyclododecanylmethyl, and dicy› clohexylmethyl; unsaturated aliphatic hydrocarbyl groups  such as ally! and 3-cyclohexenyl; aryl groups such as  phenyl, 1-naphthyl and 2-naphthyl: and aralkyl groups such  as benzyl and diphenylmethyl. In these groups, some or all  hydrogen may be substituted by a moiety containing a  heteroatom such as oxygen, sulfur, nitrogen or halogen, or  some carbon may be replaced by a moiety containing a  heteroatom such as oxygen, sulfur or nitrogen, so that the  group may contain a hydroxyl, cyano, carbonyl, ether bond,  ester bond, sulfonic acid ester bond, carbonate moiety,  lactone ring, sultone ring, carboxylic anhydride or haloalkyl  moiety. Examples of the heteroatom-containing hydrocarbyl  group include tetrahydrofuryl, methoxymethyl, ethoxym› ethyl, methylthiomethyl, acetamidomethyl, trifluoroethyl,  (2-methoxyethoxy)methyl, acetoxymethyl, 2-carboxy-1-cy› clohexyl, 2-oxopropyl, 4-oxo-1-adamantyl, and 3-oxocyclo› hexyl.  [0109]  With respect to the synthesis of the sulfonium salt  having an anion of formula (IA’), reference may be made to  JP-A 2007-145797, JP-A 2008-106045, JP-A 2009-007327,  and JP-A2009-258695. Also useful are the sulfonium salts  described in JP-A 2010-215608, JP-A 2012-041320, JP-A  2012-106986, and JP-A 2012-153644.  [0110]  Examples of the anion having formula (IA) are  shown below, bat not limited thereto.  [0105]  In formula (IA),  wa  is fluorine or a C$_{1}$-C$_{40 }$hydro› carbyl group which may contain a heteroatom. The hydro› carbyl group may be saturated or unsaturated and straight,  branched or cyclic. Examples thereof include those exem› plified later for R$^{107 }$in formula (IA’).  [0106]  Of the anions of formula (IA), an anion having the  formula (IA’) is preferred.  (lA)  (lB)  (lC)  (lD)  [0107]  In formula (IA’), R$^{106 }$is hydrogen or trifluorom› ethyl, preferably trifluoromethyl.  [0108]  R 107  is a C$_{1}$-C$_{38 }$ hydrocarbyl group which may  contain a heteroatom. As the heteroatom, oxygen, nitrogen,  sulfur and halogen atoms are preferred, with oxygen being  most preferred. Of the hydrocarbyl groups R 107 , those  groups of 6 to 30 carbon atoms are preferred from the aspect 