US Patent 7964331 Positive resist composition and method of forming resist pattern

A positive resist composition including a resin component (A) which exhibits increased alkali solubility under action of acid and an acid-generator component (B) which generates acid upon exposure, the resin component (A) including: a polymer (A1) including a structural unit (a0) represented by general formula (a0) shown below and no structural unit (a1) derived from an acrylate ester containing an acetal-type acid dissociable, dissolution inhibiting group, exclusive of the structural unit (a0), and a polymer (A2) including the structural unit (a1) and no structural unit (a0).