Sulfonium salt and use thereof

A chemical amplifying type positive resist composition comprising:

• a resin which contains a structural unit having a group that is unstable to acid and which is insoluble or slightly soluble by itself in an aqueous alkali, but becomes soluble in the aqueous alkali by an action of acid;
• and a sulfonium salt represented by the following formula (I):
• 24
• wherein Q1, Q2 and Q3 each independently represent hydrogen, hydroxy, alkyl having 1 to 6 carbon atoms, or alkoxy having 1 to 6 carbon atoms, but all of Q1, Q2 and Q3 are not the same;
• and Q4 and Q5 each independently represent perfluoroalkyl having 1 to 8 carbon atoms.

A polymerization initiator composition comprising a sulfonium salt represented by the following formula (I):

• 29
• wherein Q1, Q2 and Q3 each independently represent hydrogen, hydroxy, alkyl having 1 to 6 carbon atoms, or alkoxy having 1 to 6 carbon atoms, but all of Q1, Q2 and Q3 are not the same;
• and Q4 and Q5 each independently represent perfluoroalkyl having 1 to 8 carbon atoms;
• and a sensitizer.