Positive resist composition, pattern forming method using the composition, and compound for use in the composition

A positive resist composition, comprising:

• (A) a compound capable of generating an acid upon irradiation with an actinic ray or radiation;
• (B) a resin capable of increasing a solubility of the resin (B) in an alkali developer by an action of an acid;
• and
• (C) a compound represented by the following formula (I), which decomposes by an action of an acid to generate an acid:
• wherein R1 represents an alkyl group, a cycloalkyl group, an alkoxy group, an aryl group or an aryloxy group;
• R2 represents an alkyl group or a cycloalkyl group;
• R1 and R2 may combine with each other to form a monocyclic or polycyclic hydrocarbon structure;
• each of R3 and R4 independently represents a hydrogen atom or an alkyl group;
• R5 represents a group capable of leaving by an action of an acid;
• X represents —SO2—, —SO— or —CO—;
• and
• Z represents a residue of an organic acid represented by ZH;
• wherein the compound represented by formula (I) is a compound represented by the following formula (II):
• wherein R1 represents an alkyl group, a cycloalkyl group, an alkoxy group, an aryl group or an aryloxy group;
• R2 represents an alkyl group or a cycloalkyl group;
• R1 and R2 may combine with each other to form a monocyclic or polycyclic hydrocarbon structure;
• each of R3 and R4 independently represents a hydrogen atom or an alkyl group;
• Ry1a represents a hydrogen atom, an alkyl group, a cycloalkyl group, an alkoxy group, or an alkylene group bonded to Ry2a;
• Ry2a represents an aryl group or an aryloxy group;
• X represents —SO2—, —SO— or —CO—;
• and
• Z represents a residue of an organic acid represented by ZH.

A compound represented by the following:

• formula (II):
• wherein R1 represents an alkyl group, a cycloalkyl group, an alkoxy group, an aryl group or an aryloxy group;
• R2 represents an alkyl group or a cycloalkyl group;
• R1 and R2 may combine with each other to form a monocyclic or polycyclic hydrocarbon structure;
• each of R3 and R4 independently represents a hydrogen atom or an alkyl group;
• Ry1a represents a hydrogen atom, an alkyl group, a cycloalkyl group, an alkoxy group, or an alkylene group bonded to Ry2a;
• Ry2a represents an aryl group or an aryloxy group;
• X represents —SO2—, —SO— or —CO—;
• and
• Z represents a residue of an organic acid represented by ZH.