Chemically amplified positive resist composition and resist pattern forming process

A chemically amplified positive resist composition comprising (A) a photoacid generator and (B) a base polymer containing a polymer adapted to be decomposed under the action of acid to increase its solubility in alkaline developer,

• said photoacid generator (A) containing an onium salt consisting of an anion having the formula (A1) and a cation having the formula (A2):
• wherein n1 is 0 or 1, n2 is 0, 1, 2, 3 or 4, n3 is 0, 1, 2, 3 or 4, with the proviso that when n1=0, 0≤n2+n3≤4, when n1=1, 0≤n2+n3≤6, and n4 is 0 or 1,
• W is a C6-C40 hydrocarbyl group containing at least one aromatic ring, which 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 group, 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;
• when n3 is 2, 3 or 4, 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,
• LA1 and LB1 are each independently a single bond, ether bond, ester bond, amide bond, sulfonate ester bond, sulfonamide bond, carbonate bond or carbamate bond,
• 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 0, 1, 2, 3 or 4, m5 is 0, 1, 2, 3 or 4, m6 is 0, 1, 2, 3, 4, 5 or 6, m7 is 0, 1, 2, 3, 4, 5 or 6, m8 is 0, 1 or 2, m9 is 0, 1 or 2, m10 is 0, 1 or 2, m11 is 0 or 1, m12 is 0, 1, 2, 3 or 4, m13 is 0, 1 or 2, m14 is 0, 1 or 2, with the proviso that when m1=0, 0≤m6+m9≤4, and when m1=1, 0≤m6+m9≤6;
• when m2=0, 0≤m7+m10≤4, and when m2=1, 0≤m7+m10≤6;
• when m3=0, 1≤m4+m5+m8+m14≤4, and when m3=1, 1≤m4+m5+m8+m14≤6;
• when m11=0, 0≤m12+m13≤4, and when m11=1, 0≤m12+m13≤6;
• m4+m12≥1,
• 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;
• when m5 is 2 or more, a plurality of RF2 may be identical or different;
• when m6 is 2 or more, a plurality of RF3 may be identical or different;
• when m7 is 2 or more, a plurality of RF4 may be identical or different,
• R11 to R14 are each independently halogen exclusive of iodine and fluorine, nitro group, cyano group, a C1-C20 hydrocarbyl group which may contain a heteroatom, C1-C20 hydrocarbyloxy group which may contain a heteroatom, C1-C20 hydrocarbylthio group which may contain a heteroatom;
• when m8=2, 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 m9=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 m10=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 m13=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;
• 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, amide bond, sulfonate ester bond, sulfonamide bond, carbonate bond or carbamate bond,
• XL2 is a single bond or a C1-C40 hydrocarbylene group which may contain a heteroatom,
• said polymer comprising repeat units having the formula (B1):
• wherein a1 is 0 or 1, a2 is 0, 1 or 2, a3 is an integer meeting 0≤a3≤5+2(a2)−a4, a4 is 1, 2 or 3,
• RA is hydrogen, fluorine, methyl or trifluoromethyl,
• R21 is halogen, nitro group, carboxy group, an optionally halogenated C1-C6 saturated hydrocarbyl group, optionally halogenated C1-C6 saturated hydrocarbyloxy group, or optionally halogenated C2-C8 saturated hydrocarbylcarbonyloxy group, and
• A1 is a single bond or C1-C10 saturated hydrocarbylene group in which some —CH2— may be replaced by —O—.