Positive resist composition and method of forming resist pattern

A positive resist composition comprising a resin component (A) which exhibits increased alkali solubility under action of acid and an acid-generator component (B) which generates acid upon exposure,

• said resin component (A) comprising a structural unit (a1) derived from hydroxystyrene, and a structural unit (a2) represented by general formula (a2-1) or (a2-2) shown below:
• wherein:
• in general formula (a2-1), R represents a hydrogen atom, a halogen atom, a lower alkyl group or a halogenated lower alkyl group;
• R1 and R2 each independently represents a hydrogen atom or a lower alkyl group;
• Y1 represents a lower alkyl group or a monovalent aliphatic cyclic group;
• and nn represents an integer of 0 to 3, and in general formula (a2-2), R is as defined above;
• R3 and R4 each independently represents a hydrogen atom or a lower alkyl group;
• R5 represents an alkylene group or a divalent aliphatic cyclic group;
• Y2 represents a lower alkyl group or a monovalent aliphatic cyclic group;
• and n22 represents an integer of 0 to 3, and
• said acid-generator component (B) comprising an acid generator (B1-i) having at least one anion moiety selected from the group consisting of anion moieties represented by general formulas (b-3), (b-4), and (b-5) shown below:
• wherein:
• in formula (b-3), X″ represents an alkylene group of 2 to 6 carbon atoms in which at least one hydrogen atom has been substituted with a fluorine atom,
• in formula (b-4), Y″ and Z″ each independently represents an alkyl group of 1 to 10 carbon atoms in which at least one hydrogen atom has been substituted with a fluorine atom, and in formula (b-5), U″, V″, and W″ each independently represents an alkyl group of 1 to 10 carbon atoms in which at least one hydrogen atom has been substituted with a fluorine atom,
• an acid generator (B1-ii) having an anion moiety represented by general formula (b-6) shown below:
• [Chemical Formula 3]
• R10″—SO3− (b-6)
• wherein:
• in formula (b-6), R10″ represents a hydrocarbon group which may or may not have a substituent, or
• an acid generator (B1-iii) having a cation moiety represented by general formula (b′-3) shown below:
• wherein:
• in formula (b′-3), R7″ to R9″ each independently represents a phenyl group or naphthyl group that may or may not have a substituent;
• with the proviso that the case where all of R7″ to R9″ represent phenyl groups which do not have a substituent is excluded.