US Patent 7803512 Positive resist composition and method of forming resist pattern

A positive resist composition that includes a resin component (A) that exhibits increased alkali solubility under the action of acid, and an acid generator component (B) that generates acid on exposure to radiation, wherein the component (A) includes a structural unit (a1) represented by a general formula (a1-2) or (a1-4), a structural unit (a2) derived from an acrylate ester that contains a lactone-containing monocyclic or polycyclic group, and a structural unit (a3), which is different from the structural unit (a1) and the structural unit (a2), and is derived from an acrylate ester that contains an aliphatic cyclic group-containing non-acid-dissociable, dissolution-inhibiting group and contains no polar groups, and the component (B) includes an onium salt (B1) having an anion portion represented by a formula: R41—SO3−.