Positive resist composition and pattern forming method using the same

1. A positive resist composition comprising:

(A) a resin of which solubility in an alkali developer increases under the action of an acid, the resin having a repeating unit represented by formula (I) and a repeating unit represented by formula (IIa),

(B) a compound of generating an acid upon irradiation with actinic rays or radiation, and

(C) an organic basic compound:

wherein

R 1 represents a hydrogen atom, a methyl group, a cyano group, a halogen atom or a perfluoro group,

R 2 represents a non-acid-decomposable group, selected from the group consisting of a halogen atom, a cyclolkyl group, an aryl group, an alkoxy group, an acyl group, —OC(═O)Ra, —OC(═O)ORa, —C(═O)ORa, —C(═O)N(Rb)Ra, —N(Rb)C(═O)Ra, —N(Rb)C(═O)ORa, —N(Rb)SO 2 Ra, —SRa, —SO 2 Ra, —SO 3 Ra and —SO 2 N(Rb)Ra in which Ra represents an alkyl group, a cycloalkyl group or an aryl group and Rb represents a hydrogen atom, an alkyl group, a cycloalkyl group or an aryl group,

X represents a hydrogen atom or an organic group,

m represents an integer of 1 to 4,

n represents an integer of 1 to 4, provided that 2≦n+m≦5,

when m is an integer of 2 to 4, multiple Xs may be the same or different,

when n is an integer of 2 to 4, multiple R 2 s may be the same or different, and

R 1 in formula (IIa) may be the same as or different from R 1 in formula (I), respectively, and X 2 represents a hydrogen atom or an acid-decomposable group.

2. The positive resist composition as claimed in claim 1 , wherein the repeating unit represented by formula (I) is a repeating unit represented by formula (Ia):

wherein

R 1 represents a hydrogen atom, a methyl group, a cyano group, a halogen atom or a perfluoro group,

R 2 represents a non-acid-decomposable group,

X represents a hydrogen atom or an organic group,

n represents an integer of 1 to 4, and

when n is an integer of 2 to 4, multiple R 2 s may be the same or different.

3. The positive resist composition as claimed in claim 1 , wherein the repeating unit represented by formula (I) is a repeating unit represented by formula (Ib):

wherein

R 1 represents a hydrogen atom, a methyl group, a cyano group, a halogen atom or a perfluoro group,

X represents a hydrogen atom or an organic group, and

R 2a and R 2b each independently represents a hydrogen atom or a non-acid-decomposable group, provided that at least one of R 2a and R 2b represents a non-acid-decomposable group.

4. The positive resist composition as claimed in claim 1 , wherein the non-acid-decomposable group represented by R 2 in formula (I) contains an oxygen atom.

5. The positive resist composition as claimed in claim 1 , wherein the non-acid-decomposable group represented by R 2 in formula (I) contains a halogen atom.

6. The positive resist composition as claimed in claim 1 , wherein the resin (A) further contains a repeating unit represented by formula (III):

wherein

R 3 to R 5 each independently represents a hydrogen atom, a fluorine atom, a chlorine atom, a cyano group or an alkyl group, and

X 1 represents a hydrogen atom or an organic group.

7. The positive resist composition as claimed in claim 6 , wherein at least one of X in formula (I), X 2 formula (IIa) and X 1 in formula (III) contains at least one of an alicyclic structure and an aromatic ring structure.

8. The positive resist composition as claimed in claim 1 , wherein the non-acid-decomposable group represented by R 2 in formula (I) is an alkoxy group.

9. The positive resist composition as claimed in claim 1 , which further comprises (D) a surfactant.

10. The positive resist composition as claimed in claim 1 , which comprises (B1) a compound of generating an organic sulfonic acid under the action of actinic rays or radiation as the compound (B).

11. The positive resist composition as claimed in claim 10 , which further comprises (B2) a compound of generating a carboxylic acid under the action of actinic rays or radiation.

12. The positive resist composition as claimed in claim 1 , which further comprises a solvent.

13. The positive resist composition as claimed in claim 12 , wherein the solvent contains a propylene glycol monomethyl ether acetate.

14. The positive resist composition as claimed in claim 13 , wherein the solvent further contains a propylene glycol monomethyl ether.

15. A pattern forming method comprising forming a resist film by using the resist composition claimed in claim 1 , and exposing and developing said resist film.

16. The pattern forming method of claim 15 wherein the resist film is exposed by irradiation of electron beam, X-ray or EUV.

17. The positive resist composition of claim 1 wherein in formula (IIa), X 2 is a hydrogen atom.