Positive resist composition and pattern forming process

A positive resist composition comprising

• (A) a quencher in the form of a sulfonium salt having the following formula (1):
• wherein R1 is fluorine, a C1-C4 alkyl group, C1-C4 alkyloxy group, C2-C4 alkenyl group, C2-C4 alkynyl group, phenyl group, or C1-C20 hydrocarbyloxycarbonyl group, some or all of the hydrogen atoms in the alkyl, alkyloxy, alkenyl, alkynyl, and hydrocarbyloxycarbonyl groups may be substituted by fluorine, chlorine, bromine, iodine, trifluoromethyl, trifluoromethoxy, trifluorothio, hydroxy, cyano, nitro or sulfonyl moiety, some constituent —CH2— in the alkyl, alkyloxy, alkenyl, alkynyl, and hydrocarbyloxycarbonyl groups may be replaced by an ester bond or ether bond, and some or all of the hydrogen atoms in the phenyl group may be substituted by fluorine, C1-C4 fluoroalkyl, C1-C4 fluoroalkyloxy, C1-C4 fluoroalkylthio, cyano or nitro moiety,
• R2 to R4 are each independently halogen or a C1-C20 hydrocarbyl group which may contain at least one atom selected from oxygen, sulfur, nitrogen and halogen, R2 and R3 may bond together to form a ring with the sulfur atom to which they are attached,
• (B) an acid generator in the form of a sulfonium salt consisting of a sulfonate anion having fluorine on the carbon atom at α- and/or β-position of the sulfo group and a sulfonium cation, and
• (C) a base polymer comprising repeat units of at least one type selected from repeat units (a1) having a carboxy group whose hydrogen is substituted by an acid labile group and repeat units (a2) having a phenolic hydroxy group whose hydrogen is substituted by an acid labile group.