Positive-working resist composition

A positive-working resist composition comprising:

• (A′) a resin which increases in its solution velocity with respect to an alkaline developer when acted upon by an acid wherein
• (i) said resin contains at least one repeating structural unit selected from the group consisting of repeating structural units represented by the following general formulae (Ia) and (Ib) and a repeating structural unit represented by the following general formula (II),
• (ii) said resin contains a group capable of being decomposed by the action of an acid and
• (iii) the content of residual monomers corresponding to the repeating structural units constituting the resin is 0.01 to 4% of the total pattern area as determined by gel permeation chromatography;
• and
• (B) a compound which is capable of generating an acid by irradiation with an active ray or radiation:
• wherein R1 and R2 each independently represent a hydrogen atom, cyano group, hydroxyl group, —COOH, —COOR5, —CO—NHR6, —CO—NH—SO2—R6, alkyl, alkoxy or cyclic hydrocarbon group which may be substituted or —Y group shown below, in which R5 represents an alkyl or cyclic hydrocarbon group which may be substituted or —Y group shown below and R6 represents an alkyl or cyclic hydrocarbon group which may be substituted;
• X represents an oxygen atom, sulfur atom, —NH—, —NHSO2— or —NHSO2NH—;
• A represents a single bond or divalent connecting group:
• —Y:
• wherein R21 to R30 each independently represent a hydrogen atom or an alkyl group which may be substituted;
• and a and b each represent an integer of 1 or 2;
• wherein Z2 represents —O— or —N(R3)— in which R3 represents a hydrogen atom, hydroxyl group or —OSO2—R4, in which R4 represents an alkyl group, haloalkyl group, cycloalkyl group or camphor residue;
• and
• wherein R11 and R12 each independently represent a hydrogen atom, cyano group, halogen atom or alkyl group which may be substituted;
• and Z represents an atomic group containing two connected carbon atoms (C—C) required to form an alicyclic structure which may be substituted.