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[0104] In formulae (1-1) and (1-2), x- is an anion of the following formula (IA), (18), (IC) or (ID). 

[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. 

[0107] In formula (IA’), R$^{106 }$is hydrogen or trifluorom› ethyl, preferably trifluoromethyl. 107 

[0108] R 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 

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(lA) 

(lD) 

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. 

(lB) 

(lC) 

[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. 

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