Sulfonium salt-containing polymer, resist composition, patterning process, and sulfonium salt monomer and making method

A polymer comprising recurring units having the general formulae (1a), (2), and (3):

• wherein
• R1 is hydrogen, fluorine, methyl or trifluoromethyl,
• R2, R3, and R4 are each independently a substituted or unsubstituted, straight or branched C1-C10 alkyl, alkenyl or oxoalkyl group, a substituted or unsubstituted C6-C18 aryl, aralkyl or aryloxoalkyl group, or 4-fluorophenyl group, any two of R2, R3, and R4 may bond together to form a ring with the sulfur atom, with the proviso that at least one of R2, R3, and R4 is a 4-fluorophenyl group,
• n is an integer of 0 to 2,
• R8 is hydrogen or a C1-C10 alkyl group,
• p is 0 or 1,
• B is a single bond or a C1-C10 divalent organic group which may be substituted with an oxygen atom,
• a is an integer of 0 to 3,
• b is an integer of 1 to 3, and
• X is an acid labile group.