Sulfonium salt, acid generator, resist composition, photomask blank, and patterning process

A sulfonium salt having the general formula (2):

• wherein A is a monovalent hydrocarbon group having an aromatic ring or alicyclic hydrocarbon structure of at least 5 carbon atoms, R2, R3, and R4 are each independently a substituted or unsubstituted, straight or branched C1-C10 alkyl, alkenyl or oxoalkyl group or a substituted or unsubstituted C6-C18 aryl, aralkyl or aryloxoalkyl group, or at least two of R2, R3, and R4 may bond together to form a ring with the sulfur atom, and n is an integer of 1 to 3.

A chemically amplified resist composition comprising an acid generator capable of generating a sulfonic acid in response to high-energy radiation or heat, said sulfonic acid having the general formula (1a):

• wherein R1 is a straight, branched or cyclic monovalent hydrocarbon group of 1 to 50 carbon atoms which may contain a heteroatom, except vinyl and isopropenyl, and n is an integer of 1 to 3.

A chemically amplified resist composition comprising an acid generator capable of generating a sulfonic acid in response to high-energy radiation or heat, said sulfonic acid having the general formula (2a):

• wherein A is a monovalent hydrocarbon group having an aromatic ring or alicyclic hydrocarbon structure of at least 5 carbon atoms, and n is an integer of 1 to 3.