Positive resist composition for immersion exposure and pattern forming method using the same

1. A positive resist composition, comprising:

(A) a compound capable of generating an acid upon irradiation with actinic rays or radiation;

(B) a resin having a repeating unit containing at least one alicyclic structure, of which solubility in an alkali developer increases under an action of an acid; and

(C) an alkali-soluble resin having a siloxane bond as a main chain;

wherein the alkali-soluble resin (C) is present in the amount from 0.1 to 10 mass % based on the entire solids content of the resist composition.

2. The positive resist composition as claimed in claim 1 , wherein the alkali-soluble resin (C) has a group containing a fluorine atom in a side chain of the alkali-soluble resin (C).

3. The positive resist composition as claimed in claim 2 , wherein in the alkali-soluble resin (C), the fluorine atom is present as a substituent on the carbon atom bonded by a hydroxyl group or as a substituent on the carbon atom adjacent to the carbon atom bonded by a hydroxyl group.

4. The positive resist composition as claimed in claim 1 , further comprising: (D) an organic solvent.

5. The positive resist composition as claimed in claim 1 , further comprising: (E) an organic basic compound.

6. The positive resist composition as claimed in claim 1 , further comprising: (F) a dissolution inhibiting compound.

7. The positive resist composition as claimed in claim 1 , further comprising: (G) a surfactant.

8. The positive resist composition as claimed in claim 1 , further comprising: (H) an alkali-soluble resin.

9. The positive resist composition as claimed in claim 1 , further comprising: (I) an onium carboxylate.

10. A pattern forming method comprising: forming a resist film from the resist composition claimed in claim 1 ; immersion exposing the resist film; and developing the resist film.

11. The positive resist composition as claimed in claim 1 , wherein the alkali soluble resin (C) has an alkali soluble group or a group capable of being solubilized by undergoing hydrolysis with an alkali developer.

12. The positive resist composition as claimed in claim 11 , wherein the alkali soluble resin (C) has an alkali-soluble group selected from the group consisting of a phenolic hydroxyl group, a carboxylic acid group, a fluorinated alcohol group, a sulfonic acid group, a sulfonamide group, and an active methylene group-containing group.

13. The positive resist composition as claimed in claim 12 , wherein the alkali soluble resin (C) has an active methylene group-containining group selected from the group consisting of —C(═O)—CH 2 —C(═O)—,—C(═O)CHR—C(═O)—,—C (═O) —CH(C(═O)) 2 , and —SO 2 —CH 2 —C(═O)—; and,

wherein R is an alkyl group.

14. The positive resist composition as claimed in claim 11 , wherein the alkali soluble resin (C) has a group capable of being solubilized by undergoing hydrolysis with an alkali developer selected from the group consisting of a lactone group, an ester group, a sulfonamide group, and an acid anhydride.