Onium salt, chemically amplified resist composition, and pattern forming process

An onium salt consisting of a cation having the formula (1A) and an anion having the formula (1B):

• wherein p is 1, 2, or 3, n1 is 0 or 1, n2 is 1 or 2, n3 is 0, 1, 2, or 3, meeting 1≤n2+n3≤5 in case of n1=0 and 1 n2+n3 7 in case of n1=1,
• R1 is halogen, cyano, hydroxy, carboxy, a C1-C20 hydrocarbyl group which may contain a heteroatom, a C1-C20 hydrocarbyloxy group which may contain a heteroatom, a C1-C20 hydrocarbylthio group which may contain a heteroatom, or a C2-C20 hydrocarbyloxycarbonyl group which may contain a heteroatom, and when n3 is 2 or 3, a plurality of R1 may be identical or different and two R1 may bond together to form a ring with the carbon atoms to which they are attached,
• R2 is halogen or a C1-C30 hydrocarbyl group which may contain a heteroatom, when p is 1, two R2 may be identical or different, and any two of three substituents bonded to S+ may bond together to form a ring with the sulfur atoms to which they are attached;
• wherein n11 is 0 or 1, n12 is 1, 2, 3, or 4, n13 is 0, 1, or 2, n14 is 0, 1, 2, 3, or 4, meeting 2≤n12+n13+n14≤5 in case of n11=0 and 2≤n12+n13+n14≤7 in case of n11=1,
• LA is a single bond, oxygen, sulfur, ester bond or carbonate bond,
• R3 is hydrogen or a C1-C20 hydrocarbyl group which may contain a heteroatom when LA is a single bond, and hydrogen, a C1-C20 hydrocarbyl group (exclusive of acid labile group) which may contain a heteroatom, or acid labile group when LA is oxygen, sulfur, ester bond or carbonate bond, and
• R4 is halogen exclusive of iodine, a nitro group, cyano group, C1-C20 hydrocarbyl group which may contain a heteroatom, C1-C20 hydrocarbyloxy group which may contain a heteroatom, or C1-C20 hydrocarbylthio group which may contain a heteroatom.