Chemical amplifying type positive resist composition and sulfonium salt

A chemical amplifying type positive resist composition which comprises:

• (A) an acid generator containing (a) a sulfonium salt represented by the following formula (I):
• wherein Q1 and Q2 each independently represent a straight chain or branched alkyl group having from 1 to 6 carbon atoms or a cycloalkyl group having from 3 to 10 carbon atoms, or Q1 and Q2 form, together with a sulfur atom to which Q1 and Q2 are adjacent, a heteroalicyclic group which may further contain an oxygen atom and a sulfur atom;
• Q3 represents a hydrogen atom, Q4 represents a straight chain or branched alkyl group having from 1 to 6 carbon atoms or a cycloalkyl group having from 3 to 10 carbon atoms, or Q3 and Q4 form, together with a CHC(O) group to which Q3 and Q4 are adjacent, a 2-oxocycloalkyl group;
• and Q5SO3− represents an organosulfonate ion, provided that when Q5 represents a perfluoroalkyl group having from 1 to 8 carbon atoms, there is excluded the case where Q1 represents a straight chain or branched alkyl group having from 1 to 6 carbon atoms, Q2 represents a straight chain or branched alkyl group having from 1 to 6 carbon atoms, or a cycloalkyl group having from 3 to 10 carbon atoms, and Q3 and Q4 represent, together with their adjacent CHC(O) group, a 2-oxocycloalkyl group, and (b) at least one onium salt selected from a triphenylsulfonium salt represented by the following formula (IIa), and a diphenyliodonium salt represented by the following formula (IIb):
• wherein P1 to P5 each independently represent hydrogen, a hydroxyl group, an alkyl group having from 1 to 6 carbon atoms, or an alkoxy group having from 1 to 6 carbon atoms;
• and P6SO3− and P7SO3− each independently represent an organosulfonate ion;
• and
• (B) a resin which has a polymerization unit having a group unstable against an acid, and is alkali-insoluble or -slightly soluble itself, but is converted to alkali-soluble by the action of an acid.