content_image/916351.jpg content_image/916352.jpg content_image/916353.jpg content_image/916354.jpg content_image/916355.jpg content_image/916350.jpg content_image/916356.jpg
As the PAG used herein, sulfonium salts having the formula (1-1) and iodonium salts having the formula (1-2) are also preferred. 

<img src='content_image/916351.jpg'>

<img src='content_image/916352.jpg'>

In formulae (1-1) and (1-2), R 101 , R 102 , R 103 , R $^{104 }$and R $^{105 }$are each independently a C $_{1 }$-C$_{20 }$ straight, branched or cyclic monovalent hydrocarbon group which may contain a heteroatom. Any two of R 101 , R 102 and R 103 may bond together to form a ring with the sulfur atom to which they are attached. 

Suitable examples of the cation moiety in the sulfonium salt having formula (1-1) are as exemplified above as the cation moiety in the recurring unit (al). Suitable examples of the cation moiety in the iodonium salt having formula (1-2) are as exemplified above as the cation moiety in the recurring unit (a2). 

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

<img src='content_image/916353.jpg'>

<img src='content_image/916354.jpg'>

<img src='content_image/916355.jpg'>

In formula (IA), wa is fluorine or a cl -C40 straight, branched or cyclic monovalent hydrocarbon group which may contain a heteroatom. 

Of the anions of formula (IA), an anion having the formula (IA’) is preferred. 

<img src='content_image/916350.jpg'>

In formula (IA’), R 106 is hydrogen or trifluoromethyl, preferably trifluoromethyl. R 107 is a C$_{1 }$-C$_{38 }$ straight, branched or cyclic monovalent hydrocarbon group which may contain a heteroatom. As the heteroatom, oxygen, nitrogen, sulfur and halogen atoms are preferred, with oxygen being most preferred. Of the monovalent hydrocar› bon groups represented by R 107 , those groups of 6 to 30 carbon atoms are preferred from the aspect of achieving a high resolution in forming patterns of fine feature size. Suitable monovalent hydrocarbon groups include, but are not limited to, methyl, ethyl, propyl, isopropyl, butyl, isobu› tyl, s-butyl, t-butyl, pentyl, neopentyl, cyclopentyl, hexyl, cyclohexyl, 3-cyclohexenyl, heptyl, 2-ethylhexyl, nonyl, undecyl, tridecyl, pentadecyl, heptadecyl, 1-adamantyl, 2-adamantyl, 1-adamantylmethyl, norbornyl, norbornylm› ethyl, tricyclodecanyl, tetracyclododecanyl, tetracyclodode› canylmethyl, dicyclohexylmethyl, eicosanyl, ally!, benzyl, diphenylmethyl, 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. In these groups, one or more hydrogen atoms may be substituted by a moiety containing a heteroatom such as oxygen, sulfur, nitrogen or halogen, or one or more carbon atoms may be substituted by a moiety containing a heteroa› tom such as oxygen, sulfur or nitrogen, so that the group may contain a hydroxyl, cyano, carbonyl, ether, ester, sul- fonic acid ester, carbonate, lactone ring, sultone ring, car› boxylic anhydride or haloalkyl moiety. 

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-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. 

Examples of the anion of formula (IA) are shown below, but not limited thereto. 

<img src='content_image/916356.jpg'>

