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

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

• wherein n1 is 0 or 1, n2 is an integer of 0 to 4, n3 is an integer of 0 to 4, n2+n3 is from 0 to 4 when n1-0 and n2+n3 is from 0 to 6 when n1=1, n4 is 0 or 1,
• W is a C6-C40 hydrocarbyl group which contains at least one aromatic ring and may contain a heteroatom,
• RF1 is fluorine, a C1-C6 fluorinated saturated hydrocarbyl group, C1-C6 fluorinated saturated hydrocarbyloxy group, or C1-C6 fluorinated saturated hydrocarbylthio group,
• R1 is halogen exclusive of fluorine, nitro, a 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, with the proviso that a plurality of R1 may be identical or different and a plurality of R1 may bond together to form a ring with the carbon atoms to which they are attached, when n3 is 2, 3 or 4,
• LA1 and LB1 are each independently a single bond, ether bond, ester bond, sulfonate ester bond, amide bond, sulfonamide bond, carbonate bond or carbamate bond, and
• XL1 is a single bond or a C1-C40 hydrocarbylene group which may contain a heteroatom,
• wherein m1 is 0 or 1, m2 is 0 or 1, m3 is 0 or 1, m4 is an integer of 0 to 4, m5 is an integer of 0 to 4, m6 is an integer of 0 to 6, m7 is an integer of 0 to 6, m8 is an integer of 0 to 2, m9 is an integer of 0 to 2, m10 is an integer of 0 to 2, m11 is 0 or 1, m12 is an integer of 0 to 4, m13 is an integer of 0 to 2, m14 is an integer of 0 to 2, m6+m9 is from 0 to 4 when m1=0, m6+m9 is from 0 to 6 when m1=1, m7+m10 is from 0 to 4 when m2-0, m7+m10 is from 0 to 6 when m2=1, m4+m5+m8+m14 is from 1 to 4 when m3=0, m4+m5+m8+m14 is from 1 to 6 when m3=1, m12+m13 is from 0 to 4 when m11=0, m12+m13 is from 0 to 6 when m11=1, m4+m12 is 1 or greater,
• RF2 to RF4 are each independently fluorine, a C1-C6 fluorinated saturated hydrocarbyl group, C1-C6 fluorinated saturated hydrocarbyloxy group, or C1-C6 fluorinated saturated hydrocarbylthio group, with the proviso that a plurality of RF2 may be identical or different when m5 is 2 or more, a plurality of RF3 may be identical or different when m6 is 2 or more, and a plurality of RF4 may be identical or different when m7 is 2 or more,
• R11 to R14 are each independently halogen exclusive of iodine and fluorine, nitro, cyano, a 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, with the proviso that two R11 may be identical or different and two R11 may bond together to form a ring with the carbon atoms to which they are attached, when m8=2, two R12 may be identical or different and two R12 may bond together to form a ring with the carbon atoms to which they are attached, when m9=2, two R13 may be identical or different and two R13 may bond together to form a ring with the carbon atoms to which they are attached, when m10=2, two R14 may be identical or different and two R14 may bond together to form a ring with the carbon atoms to which they are attached, when m13=2,
• the aromatic rings directly bonded to S+ in the sulfonium cation may bond together to form a ring with S+,
• LA2 and LB2 are each independently a single bond, ether bond, ester bond, sulfonate ester bond, amide bond, sulfonamide bond, carbonate bond or carbamate bond, and
• XL2 is a single bond or a C1-C40 hydrocarbylene group which may contain a heteroatom.