Positive resist composition and method of forming a resist pattern using the same

A positive resist composition comprising:

• (A) a resin which comprises a repeating unit having at least two groups represented by the following general formula (Z) and at least one repeating unit selected from the group consisting of repeating units represented by the following general formulae (II) to (V), the resin increasing the solubility in an alkaline developing solution by the action of an acid;
• and
• (B) at least one compound which generates an acid by the action of actinic rays or a radiation:
• in general formula (Z),
• R50 to R55 each independently represents a hydrogen atom, a fluorine atom, or an alkyl group, provided that at least one of R50 to R55 is either a fluorine atom or an alkyl group in which at least one of the hydrogen atoms has been replaced by a fluorine atom, and
• Y's each independently represent a hydrogen atom or an organic group;
• in general formula (II),
• Rb and Rb′ each independently represents a hydrogen atom, a halogen atom, or an organic group,
• L3 represents a single bond or a bivalent connecting group, A1 represents a partial structure represented by the following general formula (A1), and
• r represents 0 or 1;
• in general formula (III),
• R6 to R8 each independently represents a hydrogen atom, a fluorine atom, a chlorine atom, a cyano group, or an alkyl group in which at least one of the hydrogen atoms has been replaced by a fluorine atom, provided that at least one of R6 to R8 is not a hydrogen atom, and
• A1 represents a partial structure represented by tile following general formula (A1);
• in general formula (IV),
• R9 to R11 each independently represents a hydrogen atom, a fluorine atom, a chlorine atom, a cyano group, or an alkyl group in which at least one of the hydrogen atoms has been replaced by a fluorine atom, provided that at least one of R9 to R11 is not a hydrogen atom,
• Ra represents a hydrogen atom, an alkyl group, a cycloalkyl group, an aryl group, or an aralkyl group, and
• A1 represents a partial structure represented by the following general formula (A1);
• in general formula (V),
• R12 to R14 each independently represents a hydrogen atom, a fluorine atom, a chlorine atom, a cyano group, or an alkyl group in which at least one of the hydrogen atoms has been replaced by a fluorine atom,
• Y1, represents a single bond, —O—, or —N(Ra)—, wherein Ra represents a hydrogen atom, an alkyl group, a cycloalkyl group, an aryl group, or an aralkyl group, and
• A1 represents a partial structure represented by the following general formula (A1);
• and
• in general formula (A1),
• R4a and R5a each independently represents an alkyl group,
• Z1 represents an alicyclic hydrocarbon group having a valence of p+1,
• L2 represents a single bond or a methylene group,
• X represents a hydroxy group, a cyano group, an alkoxy group, or an alkyl group, provided that at least one of the X's is not an alkyl group,
• when two or more L2's and two or more X's are present in the partial structure, the L2's and the X's each may be the same or different,
• m represents 0 or 1, and
• p represents an integer of 1 to 4.