Chemically amplified negative resist composition and resist pattern forming process

A chemically amplified negative resist composition comprising

• (A) an acid generator containing an onium salt having the formula (A):
• wherein X1 and X2 are each independently methylene, propane-2,2-diyl or ether bond,
• L is a single bond, ester bond, sulfonic acid ester bond, carbonate bond or carbamate bond,
• R1 and R2 are each independently a C1-C20 monovalent hydrocarbon group which may contain a heteroatom,
• m1 and m2 are each independently an integer of 0 to 2, m3 is 0 or 1, n1 is an integer satisfying 1≤n1≤5+2m1, n2 is an integer satisfying 0≤n2≤4+2 m2, n3 is an integer satisfying 0≤n3≤8+4 m3,
• A+ is a sulfonium cation having the formula (A-A), an iodonium cation having the formula (A-B), or an ammonium cation having the formula (A-C):
• wherein R3A, R3B, R3C, R4A, R4B, R5A, R5B, and R5C are each independently a C1-C20 monovalent hydrocarbon group which may contain a heteroatom, R5D is hydrogen or a C1-C20 monovalent hydrocarbon group which may contain a heteroatom, any two of R3A, R3B and R3C or any two of R5A, R5B, R5C and R5D may bond together to form a ring with the sulfur or nitrogen atom to which they are attached, and
• (B) a base polymer containing a polymer comprising recurring units having the formula (B1):
• wherein RA is hydrogen, fluorine, methyl or trifluoromethyl,
• R11 is each independently halogen, an optionally halogenated C2-C8 acyloxy group, optionally halogenated C1-C6 alkyl group, or optionally halogenated C1-C6 alkoxy group,
• A1 is a single bond or C1-C10 alkanediyl group in which an ether bond may intervene in a carbon-carbon bond,
• t1 is 0 or 1, x1 is an integer of 0 to 2, a is an integer satisfying 0≤a≤5+2x1−b, and b is an integer of 1 to 3.