Resist composition and pattern forming process

A resist composition comprising a base polymer comprising repeat units (a) having a salt structure consisting of a sulfonic acid anion bonded to a polymer backbone and a sulfonium cation having the formula (1):

• wherein p is 0 or 1, q is an integer of 0 to 4, r is 1 or 2, s is an integer of 1 to 3,
• R1 is a single bond, ether bond, thioether bond or ester bond,
• R2 is a single bond or a C1-C20 alkanediyl group which may contain fluorine or to hydroxy,
• R3 and R4 are each independently a C1-C12 saturated hydrocarbyl group, C2-C8 alkenyl group, C2-C8 alkynyl group or C6-C12 aryl group, which may contain oxygen or sulfur, R3 and R4 may bond together to form a ring with the carbon atom to which they are attached,
• R5 is hydrogen, or a C1-C12, saturated hydrocarbyl group or C6-C18 aryl group, which may contain at least one moiety selected from hydroxy, C1-C6 saturated hydrocarbyloxy, C2-C6 saturated hydrocarbyloxycarbonyl, nitro, cyano, fluorine, chlorine, bromine, iodine, amino, trifluoromethyl, trifluoromethoxy, and trifluoronethylthio, with the proviso that R5 is not hydrogen when R3 is substituted or unsubstituted phenyl,
• R6 is hydroxy, carboxy, nitro, cyano, fluorine, chlorine, bromine, iodine, amino, or a C1-C20 saturated hydrocarbyl group, C1-C20 saturated hydrocarbyloxy group, C2-C20 saturated hydrocarbylcarbonyloxy group, C2-C20 saturated hydrocarbyloxycarbonyl group, or C1-C4 saturated hydrocarbylsulfonyloxy group, which may contain at least one moiety selected from fluorine, chlorine, bromine, iodine, hydroxy, amino and ether bond, and
• R7 is a C1-C20 hydrocarbyl group which may contain a heteroatom, in case of s=1, two groups R may be the same or different and may bond together to form a ring with the sulfur atom to which they are attached.