Positive resist composition and method of forming resist pattern

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

• said resin component (A) containing a polymer comprising:
• a core portion represented by formula (1) shown below;
• and
• arm portions that are bonded to the core portion and are also composed of a polymer chain obtained by an anionic polymerization method, wherein said arm portions have a structural unit derived from a hydroxystyrene derivative,
• PX—Y)a (1)
• wherein P represents an a-valent organic group;
• a represents an integer of 3 to 20;
• Y represents an arylene group or an alkylene group of 1 to 12 carbon atoms;
• and X represents any one of the linking groups represented by formulas (2) to (5) shown below which can be cleaved under action of acid,
• wherein R1 and R2 each independently represents a linear, branched or cyclic alkyl group of 1 to 12 carbon atoms which may be substituted with alkoxy group, hydroxyl group, a halogen atom or an epoxy group, an aryl group which may be substituted with alkoxy group, hydroxyl group, a halogen atom or an epoxy group, alkoxy group or a hydrogen atom;
• R3 and R4 each independently represents a linear, branched or cyclic alkyl group of 1 to 12 carbon atoms which may be substituted with alkoxy group, hydroxyl group, a halogen atom or an epoxy group;
• and
• R5 represents a linear, branched or cyclic alkylene group of 1 to 12 carbon atoms which may be substituted with alkoxy group, hydroxyl group, a halogen atom or an epoxy group, an arylene group which may be substituted with alkoxy group, hydroxyl group, a halogen atom or an epoxy group, or a single bond.

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

• said resin component (A) containing a polymer comprising:
• a core portion represented by formula (1) shown below;
• and
• arm portions that are bonded to the core portion and are also composed of a polymer chain obtained by an anionic polymerization method,
• PX—Y)a (1)
• wherein P represents an a-valent organic group;
• a represents an integer of 3 to 20;
• Y represents an arylene group or an alkylene group of 1 to 12 carbon atoms;
• and X represents any one of the linking groups represented by formulas (2) to (4) shown below which can be cleaved under action of acid,
• wherein R1 and R2 each independently represents a linear, branched or cyclic alkyl group of 1 to 12 carbon atoms which may be substituted with alkoxy group, hydroxyl group, a halogen atom or an epoxy group, an aryl group which may be substituted with alkoxy group, hydroxyl group, a halogen atom or an epoxy group, alkoxy group or a hydrogen atom.