Chemically amplified resist composition and pattern forming process

A chemically amplified resist composition comprising

• (A) a polymer comprising repeat units having the formula (a1) and being free of repeat units adapted to generate acid upon light exposure,
• (B) a photoacid generator containing a fluoroalkane sulfonic acid anion having an aromatic ring structure substituted with iodine or iodine and bromine, and
• (C) an organic solvent,
• wherein a1 is 0 or 1, a2 is 0, 1, 2 or 3 when a1=0 and a2 is 0, 1, 2, 3, 4 or 5 when a1=1,
• RA is hydrogen, fluorine, methyl or trifluoromethyl,
• X1 is a single bond, *—C(═O)—O— or *—C(═O)—N(H)—, * designates a point of attachment to the carbon atom in the backbone,
• X2 is a single bond, a C1-C4 aliphatic hydrocarbylene group, carbonyl, sulfonyl or a group obtained by combining the foregoing,
• X3 and X4 are each independently oxygen or sulfur, with the proviso that X2 and X4 are attached to adjacent carbon atoms on the aromatic ring,
• R1 and R2 are each independently hydrogen or a C1-C20 hydrocarbyl group which may contain a heteroatom, R1 and R2 may bond together to form a ring with the carbon atom to which they are attached,
• R3 is halogen, hydroxy, cyano, nitro, pentafluorosulfanyl, a C1-C20 hydrocarbyl group which may contain a heteroatom, C1-C20 hydrocarbyloxy group which may contain a heteroatom, C2-C20 hydrocarbyloxycarbonyl group which may contain a heteroatom, C1-C20 hydrocarbylthio group which may contain a heteroatom, or —N(R3A)(R3B), wherein R3A and R3B are each independently hydrogen or a C1-C6 hydrocarbyl group;
• when a2 is 2 or more, a plurality of R3 may be identical or different and a plurality of R3 may bond together to form a ring with the carbon atoms in the aromatic ring to which they are attached.