Chemically amplified positive resist composition and resist pattern forming process

A chemically amplified positive resist composition comprising (A) a base polymer, (B) a photoacid generator, and (C) a quencher, wherein

• the base polymer (A) contains a polymer comprising phenolic hydroxy-containing units represented by the formula (A1), aromatic ring-containing units represented by any one of the formulae (A2) to (A4), and units containing a phenolic hydroxy group protected with an acid labile group, represented by the formula (A5),
• all repeat units in the base polymer (A) are aromatic ring-containing repeat units,
• the number of halogen atoms in the repeat units in the base polymer (A) is up to 3,
• wherein a1 is an integer satisfying 0≤a1≤5+2(a3)−a2, a2 is an integer of 1 to 3, a3 is an integer of 0 to 2,
• RA is hydrogen, fluorine, methyl or trifluoromethyl,
• X1 is a single bond, *—C(═O)—O— or *—C(═O)—NH—, * designates a point of attachment to the carbon atom in the backbone,
• A1 is a single bond or a C1-C10 saturated hydrocarbylene group in which some —CH2— may be replaced by —O—,
• R1 is halogen, an optionally halogenated C1-C6 saturated hydrocarbyl group, optionally halogenated C1-C6 saturated hydrocarbyloxy group, or optionally halogenated C2-C8 saturated hydrocarbylcarbonyloxy group,
• wherein b and c are each independently an integer of 0 to 4, d1 is an integer of 0 to 5, d2 is an integer of 0 to 2,
• RA is hydrogen, fluorine, methyl or trifluoromethyl,
• X2 is a single bond, *—C(═O)—O— or *—C(═O)—NH—, * designates a point of attachment to the carbon atom in the backbone,
• A2 is a single bond or a C1-C10 saturated hydrocarbylene group in which some —CH2— may be replaced by —O—,
• R2 and R3 are each independently hydroxy, halogen, an optionally halogenated C1-C8 saturated hydrocarbyl group, optionally halogenated C1-C8 saturated hydrocarbyloxy group, or optionally halogenated C2-C8 saturated hydrocarbylcarbonyloxy group,
• R4 is an acetyl group, C1-C20 saturated hydrocarbyl group, C1-C20 saturated hydrocarbyloxy group, C2-C20 saturated hydrocarbylcarbonyloxy group, C2-C20 saturated hydrocarbyloxyhydrocarbyl group, C2-C20 saturated hydrocarbylthiohydrocarbyl group, halogen, nitro group or cyano group, R4 may also be hydroxy when d2 is 1 or 2,
• wherein e1 is an integer satisfying 0≤e1≤5+2(e3)−e2, e2 is an integer of 1 to 3, e3 is an integer of 0 to 2,
• RA is hydrogen, fluorine, methyl or trifluoromethyl,
• X3 is a single bond, *—C(═O)—O— or *—C(═O)—NH—, * designates a point of attachment to the carbon atom in the backbone,
• A3 is a single bond or a C1-C10 saturated hydrocarbylene group in which some —CH2— may be replaced by —O—,
• R5 is halogen, an optionally halogenated C1-C6 saturated hydrocarbyl group, optionally halogenated C1-C6 saturated hydrocarbyloxy group, or optionally halogenated C2-C8 saturated hydrocarbylcarbonyloxy group,
• RAL is an acid labile group of acetal form having the formula (AL-1) when e2=1, RAL is hydrogen or an acid labile group of acetal form having the formula (AL-1), at least one RAL being an acid labile group of acetal form having the formula (AL-1), when e2=2 or 3,
• wherein f1 is an integer of 0 to 2, and f2 is an integer satisfying 0≤f2≤5+2(f1),
• R6 is acetyl, a C1-C20 saturated hydrocarbyl group, C1-C20 saturated hydrocarbyloxy group, C2-C20 saturated hydrocarbylcarbonyloxy group, C2-C20 saturated hydrocarbyloxyhydrocarbyl group, C2-C20 saturated hydrocarbylthiohydrocarbyl group, halogen, nitro or cyano group,
• RL1 is a C1-C30 hydrocarbyl group, and
• the broken line designates a point of attachment.