Positive resist composition

1. A positive resist composition, comprising:

(A) a phenolic polymer having a property of being insoluble or hardly soluble in an aqueous alkali solution and becoming soluble in an aqueous alkali solution by the action of an acid, in which the phenolic polymer includes a repeating unit containing at least one selected from the group consisting of an acetal-protected phenolic hydroxyl group, a ketal-protected phenolic hydroxyl group, a tertiary ester-protected carboxyl group and a tetrahydropyranyl-protected carboxyl group; and

(B) a compound represented by the following formula (I) and capable of generating an acid upon irradiation with one of actinic rays and radiation;

wherein R 1 to R 5 each independently represents a hydrogen atom, a nitro group, a halogen atom, an alkyl group, an alkoxy group, an alkyloxycarbonyl group, an aryl group or an acylamino group, and at least two of R 1 to R 5 may combine to form a ring; R 6 and R 7 each represents a hydrogen atom; Y 1 and Y 2 each independently represents an alkyl group, an alkenyl group or an aryl group, Y 1 and Y 2 may combine to form a ring together with S + , provided that at least one of Y 1 and Y 2 is an aryl group; at least one of R 1 to R 5 and at least one of Y 1 and Y 2 may combine to form a ring; the compound (B) may have at least two structures represented by formula (I) by being combined via a linkage group at any site selected from the group consisting of R 1 to R 5 , Y 1 and Y 2 ; and X − represents an alkanesulfonic acid anion containing at least 3 carbon atoms, a benzenesulfonic acid anion having at least one substituent selected from the group consisting of a halogen atom, a halogen-substituted alkyl group or an alkyl group containing at least two carbon atoms, a naphthalenesulfonic acid anion, an anthracenesulfonic acid anion and a camphorsulfonic acid anion.

2. The positive resist composition as described in claim 1 , which further comprises (D) a nitrogen-containing basic compound.

3. The positive resist composition as described claim 1 , which further comprises a compound capable of generating an acid upon irradiation with one of actinic rays and radiation, in which the compound is not the compound represented by formula (I).

4. The positive resist composition as described in claim 1 , wherein the phenolic polymer (A) represents a phenol resin, a novolak resin, or a polymer containing hydroxystyrene units in the molecule, each of polymers having: a property of being insoluble or hardly soluble in an aqueous alkali solution and becoming soluble in an aqueous alkali solution by the action of an acid; and including a repeating unit containing at least one selected from the group consisting of an acetal-protected phenolic hydroxyl group, a ketal-protected phenolic hydroxyl group, a tertiary ester-protected carboxyl group and a tetrahydropyranyl-protected carboxyl group.

5. The positive resist composition as described in claim 1 , wherein the phenolic polymer (A) represents a polymer containing hydroxystyrene units in the molecule, the polymer having: a property of being insoluble or hardly soluble in an aqueous alkali solution and becoming soluble in an aqueous alkali solution by the action of an acid; and including a repeating unit containing at least one selected from the group consisting of an acetal-protected phenolic hydroxyl group, a ketal-protected phenolic hydroxyl group, a tertiary ester-protected carboxyl group and a tetrahydropyranyl-protected carboxyl group.

6. The positive resist composition as described claim 1 , which further comprises at least one of a fluorine-containing surfactant, a silicon-containing surfactant and a surfactant containing both fluorine and silicon atoms.