Resist composition and pattern forming process

A resist composition comprising a base polymer and an acid generator containing a sulfonium salt having the formula (1) or an iodonium salt having the formula (2):

• wherein m is an integer of 1 to 3, n is an integer of 1 to 3,
• XBI is bromine or iodine,
• R is a C1-C20 (m+1)-valent aliphatic hydrocarbon group which may contain at least one selected from fluorine, chlorine, a hydroxyl group, a carboxyl group, a C6-C12 aryl group, an ether bond, an ester bond, a carbonyl group, an amide bond, a carbonate group, a urethane bond, or a urea bond,
• L1 is a C1-C20 hydrocarbylene group which may contain a single bond or a heteroatom when n is 1, or a C1-C20 (n+1)-valent hydrocarbon group which may contain a heteroatom when n is 2 or 3,
• L2 is a single bond, an ester bond, or an ether bond,
• L3 is a single bond or a C1-C10 aliphatic hydrocarbylene group,
• Rf1 to Rf4 are each independently hydrogen, fluorine, or a trifluoromethyl group, at least one of Rf1 to Rf4 being fluorine or a trifluoromethyl group, Rf1 and Rf2, taken together, may form a carbonyl group,
• R1 to R5 are each independently a C1-C20 hydrocarbyl group which may contain a heteroatom, and R1 and R2 may bond together to form a ring with the sulfur atom to which they are attached.