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the pattern or the pattern profile is degraded. The influences of Mw and Mw/Mn become stronger as the pattern rule becomes finer. Therefore, the base polymer should prefer› ably have a narrow dispersity (Mw/Mn) of 1.0 to 2.0, especially 1.0 to 1.5, in order to provide a resist composition suitable for micropatterning to a small feature size. 

[0093] It is understood that a blend of two or more polymers which differ in compositional ratio, Mw or Mw/Mn is acceptable. 

[0094] Acid Generator 

[0095] The resist composition may comprise an acid gen› erator capable of generating a strong acid (referred to as acid generator of addition type, hereinafter). As used herein, the term "strong acid" refers to a compound having a sufficient acidity to induce deprotection reaction of an acid labile group on the base polymer in the case of a chemically amplified positive resist composition, or a compound having a sufficient acidity to induce acid-catalyzed polarity switch reaction or crosslinking reaction in the case of a chemically amplified negative resist composition. The inclusion of such an acid generator ensures that the amine compound func› tions as a quencher and the inventive resist composition functions as a chemically amplified positive or negative resist composition. 

[0096] The acid generator is typically a compound (PAG) capable of generating an acid upon exposure to actinic ray or radiation. Although the PAG used herein may be any compound capable of generating an acid upon exposure to high-energy radiation, those compounds capable of gener› ating sulfonic acid, imide acid (imidic acid) or methide acid are preferred. Suitable PAGs include sulfouitan salts, iodo› nium salts, sulfonyldiazomethane, N-sulfonyloxyimide, and oxime-O-sulfonate acid generators. Exemplary PAGs are described in JP-A 2008-111103, paragraphs [0122]-[0142] (U.S. Pat. No. 7,537,880). 

[0097] As the PAG used herein, sulfonium salts having the formula (1-1) and iodonium salts having the formula (1-2) are also preferred. 

[0098] 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$_{20 }$ monovalent hydrocarbon group which may contain a heteroatom. Any two ofR 101 , R $^{102 }$and R$^{103 }$may bond together to form a ring with the sulfur atom to which they are attached. The monovalent hydrocarbon group may be straight, branched or cyclic, and examples thereof include those exemplified above for R$^{21 }$to R$^{28 }$in formulae (fl) to (f3). 

[0099] Example of the cation in the sulfonium salt having formula (1-1) are shown below, but not limited thereto. 

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