Resist composition and pattern forming process

A resist composition comprising an acid generator containing a sulfonium salt containing a sulfonic acid anion having a carbon atom to which an iodine atom is bonded and a sulfonium cation having formula (1):

• wherein p, q, and r are each independently an integer of 0 to 3, and s is 1 or 2, provided that 1≤r+s≤3,
• R1 is a halogen atom, a trifluoromethyl group, a trifluoromethoxy group, a trifluoromethylthio group, a nitro group, a cyano group, —C(═O)—R5, —O—C(═O)—R5, or —O—R5,
• R2 and R3 are each independently a halogen atom, a trifluoromethyl group, a trifluoromethoxy group, a trifluoromethylthio group, a nitro group, a cyano group, —C(═O)—O—R4, —C(═O)—R5, —O—C(═O)—R5, —O—C(═O)—O—R5, or —O—R5,
• R4 is a C1-C10 aliphatic hydrocarbyl group, a C6-C12 aryl group, or a C4-C12 heteroaryl group, some or all of hydrogen atoms of these groups may be substituted with a halogen atom other than an iodine atom, a hydroxy group, a cyano group, a nitro group, a halogenated alkyl group, a halogenated alkoxy group, or a halogenated alkylthio group, and some of —CH2— of these groups may be substituted with an ether bond, an ester bond, a carbonyl group, or a sulfonic ester bond, provided that R4 is not an acid labile group,
• R5 is a C1-C10 hydrocarbyl group, and
• Z1 and Z2 are each independently a hydrogen atom, a halogen atom, a trifluoromethyl group, a trifluoromethoxy group, a trifluoromethylthio group, a nitro group, a cyano group, —C(═O)—O—R4, —C(═O)—R5, —O—C(═O)—R5, —O—C(═O)—O—R5, or —O—R5, and Z1 and Z2 may together form a single bond, an ether bond, a carbonyl group, —N(RN)—, a sulfide bond, or a sulfonyl group, wherein RN is a hydrogen atom or a C1-C6 saturated hydrocarbyl group.