Positive resist composition and method of forming pattern using the same

1. A positive resist composition comprising (A) a resin that increases solubility in a developing solution by the action of an acid and comprises (a) a repeating unit containing a group that is decomposed by the action of an acid to become alkali-soluble, (b) a repeating unit containing an alicyclic lactone structure, (c) a repeating unit containing an alicyclic structure substituted with a hydroxy group and (d) a methacrylic acid repeating unit, wherein an amount of the methacrylic acid repeating unit is from 5 to 18% by mole based on the total repeating units of the resin, and (B) a compound that generates an acid upon irradiation of an actinic ray or radiation.

2. The positive resist composition as claimed in claim 1 , wherein the repeating unit (a) containing a group that is decomposed by the action of an acid to become alkali-soluble contains an alicyclic structure.

3. The positive resist composition as claimed in claim 2 , wherein the repeating unit (a) containing a group that is decomposed by the action of an acid to become alkali-soluble is represented by the following formula (I):

wherein R 2 represents a hydrogen atom or a methyl group; A represents a single bond or a connecting group; and ALG represents a group containing an alicyclic hydrocarbon represented by any one of the following formulae (pI) to (pV):

wherein R 11 represents a methyl group, an ethyl group, a n-propyl group, an isopropyl group, a n-butyl group, an isobutyl group or a sec-butyl group, Z represents an atomic group necessary for forming an alicyclic hydrocarbon group together with the carbon atom, R 12 to R 16 each independently represent a straight chain or branched alkyl group having from 1 to 4carbon atoms or an alicyclic hydrocarbon group, provided that at least one of R 12 to R 14 or either R 15 or R 16 represents an alicyclic hydrocarbon group; R 17 to R 21 each independently represent a hydrogen atom, a straight chain or branched alkyl group having from 1 to 4 carbon atoms or an alicyclic hydrocarbon group, provided that at least one of R 17 to R 21 represents an alicyclic hydrocarbon group and that either R 19 or R 21 represents a straight chain or branched alkyl group having from 1 to 4 carbon atoms or an alicyclic hydrocarbon group; R 22 to R 25 each independently represent a hydrogen atom, a straight chain or branched alkyl-group having from 1 to 4 carbon atoms or an alicyclic hydrocarbon group, provided that at least one of R 22 to R 25 represents an alicyclic hydrocarbon group, or R 23 and R 24 may be combined with each other to form a ring.

4. The positive resist composition as claimed in claim 1 , wherein an acid value of the resin (A) is from 0.2 meq/g to 0.9 meq/g.

5. The positive resist composition as claimed in claim 1 , wherein a content of the repeating unit (a) having an acid-decomposable group is from 18 to 55% by mole based on the total repeating units of the resin (A).

6. The positive resist composition as claimed in claim 1 , wherein a content of the repeating unit (b) having an alicyclic lactone structure is from 15 to 60% by mole based on the total repeating units of the resin (A).

7. The positive resist composition as claimed in claim 1 , wherein a content of the repeating unit (c) having an alicyclic structure substituted with a hydroxy group is from 5 to 40% by mole based on the total repeating units of the resin (A).

8. A method of forming a pattern comprising a step of forming a resist film with the positive resist composition as claimed in claim 1 , a step of exposing the resist film, and a step of developing the exposed resist film.

9. The positive resist composition as claimed in claim 1 , wherein the alicyclic lactone structure in the repeating unit (b) is selected from the group consisting of a cyclohexane lactone, a norbornane lactone, and an adamantane lactone.