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The sulfonium salt having formula (1-1) or iodonium salt having formula (1-2) may be synthesized, for example, by ion exchange with a sulfonium or iodonium salt of weaker acid than the iodinated phenoxy or iodinated phenylalkoxy› containing fluorinated sulfonic acid. Typical of the weaker acid than the iodinated phenoxy or iodinated phenylalkoxy› containing fluorinated sulfonic acid are carboxylic acid, hydrochloric acid and carbonic acid. Alternatively, the sul› fonium or iodonium salt may be synthesized by ion exchange of a sodium salt of an iodinated phenoxy or iodinated phenylalkoxy-containing fluorinated sulfonic acid with a sulfonium or iodonium chloride. 

In the resist composition, the sulfonium salt having for› mula (1-1) or iodonium salt having formula (1-2) is prefer› ably used in an amount of 0.01 to 1,000 parts, more preferably 0.05 to 500 parts by weight per 100 parts by weight of the base polymer, as viewed from sensitivity and acid diffusion suppressing effect. 

## Base Polymer 

Where the resist composition is of positive tone, the base polymer comprises recurring units containing an acid labile group, preferably recurring units having the formula (al) or recurring units having the formula (a2). These units are simply referred to as recurring units (al) and (a2). 

