Positive resist composition, method of forming resist pattern using the same, and polymeric compound

A positive resist composition comprising:

• a base component (A) which exhibits increased solubility in an alkali developing solution under the action of acid;
• an acid-generator component (B) which generates acid upon exposure;
• and an organic solvent (S), the base component (A) and the acid-generator component (B) being dissolved in the organic solvent (S),
• the base component (A) comprising a polymeric compound (A1) comprised of:
• a structural unit (a0) represented by general formula (a0-1) shown below,
• a structural unit (a1) derived from an acrylate ester containing an acid dissociable, dissolution inhibiting group, and
• a structural unit (a5) represented by general formula (a5-1) shown below:
• wherein R1 represents a hydrogen atom, a lower alkyl group of 1 to 5 carbon atoms or a halogenated lower alkyl group of 1 to 5 carbon atoms;
• R2 represents a divalent linking group;
• and R3 represents a cyclic group containing —SO2— within the ring skeleton thereof;
• and
• wherein R represents a hydrogen atom, a lower alkyl group of 1 to 5 carbon atoms or a halogenated lower alkyl group of 1 to 5 carbon atoms;
• Y1 represents an aliphatic hydrocarbon group which may have a substituent;
• Z represents a monovalent organic group;
• a represents an integer of 1 to 3, and b represents an integer of 0 to 2, with the provision that a+b=1 to 3;
• and each of c, d and e independently represents an integer of 0 to 3.