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[0071] In formula (3A’), R$^{104 }$is hydrogen or trifluorom› ethyl, preferably trifluoromethyl. 105 

[0072] R is a C$_{1 }$-C$_{38 }$ hydrocarbyl group which may contain a heteroatom. Suitable heteroatoms include oxygen, nitrogen, sulfur and halogen, with oxygen being preferred. Of the hydrocarbyl groups, those of 6 to 30 carbon atoms are preferred because a high resolution is available in fine pattern formation. Suitable hydrocarbyl groups include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, neopentyl, hexyl, hep› tyl, 2-ethylhexyl, nonyl, undecyl, tridecyl, pentadecyl, hep› tadecyl, icosanyl; cyclic saturated hydrocarbyl groups such as cyclopentyl, cyclohexyl, 1-adamantyl, 2-adamantyl, 1-adamantylmethyl, norbomyl, norbornylmethyl, tricyclo› decanyl, tetracyclododecanyl, tetracyclododecanyhnethyl, dicyclohexylmethyl; unsaturated aliphatic hydrocarbyl groups such as ally! and 3-cyclohexenyl; aryl groups such as phenyl, 1-naphthyl, 2-naphthyl; and aralkyl groups such as benzyl and diphenylmethyl. In these groups, some or all of the hydrogen atoms may be substituted by a moiety con› taining 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, ester, sulfonic acid ester, carbonate, lactone ring, sultone ring, carboxylic anhydride or haloalkyl moiety. Examples of the heteroatom-containing hydrocarbyl group include tetrahydrofuryl, methoxymethyl, ethoxymethyl, methylthiomethyl, acetamidomethyl, trifluoroethyl, (2-methoxyethoxy )methy I, acetoxymethy I, 2-carboxy-1-cy› clohexy l, 2-oxopropyl, 4-oxo-1-adamantyl, and 3-oxocyclo› hexyl. 

[0073] With respect to the synthesis of the sulfonium salt having an anion of formula (3A’), reference is made to JP-A 2007-145797, JP-A 2008-106045, JP-A 2009-007327, and JP-A 2009-258695. 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. 

[0074] Examples of the anion having formula (3A) are shown below, but not limited thereto. 

<img src='content_image/897229.jpg'>

<img src='content_image/897224.jpg'>

<img src='content_image/897230.jpg'>

