Method of producing positive resist composition, positive resist composition, and method of forming resist pattern

1. A method of producing a positive resist composition, comprising a step (I) of passing a positive resist composition, which is obtained by dissolving a resin component (A) that displays increased alkali solubility under action of acid and an acid generator component (B) that generates acid upon exposure in an organic solvent (S), through a filter (f 1 ) equipped with a nylon membrane, wherein

said resin component (A) is a copolymer containing at least two structural units obtained by polymerizing at least one monomer in the presence of acid,

at least one of said monomers is an (α-lower alkyl) acrylate ester, and

said resin component (A) comprises a structural unit (a1) derived from the (α-lower alkyl) acrylate ester within a main chain.

2. A method of producing a positive resist composition according to claim 1 , further comprising a step (II), which is conducted before and/or after said step (I), of passing said positive resist composition through a filter (f 2 ) equipped with a polyethylene or polypropylene membrane.

3. A method of producing a positive resist composition according to claim 1 , wherein said resin component (A) is a copolymer obtained by conducting a polymerization of said monomer in solution, and said solution contains a concentration of acid within a range from 0.1 to 1,000 ppm.

4. A method of producing a positive resist composition according to claim 1 , wherein said resin component (A) is a copolymer comprising a structural unit (a11) derived from an (α-lower alkyl) acrylate ester containing an acid-dissociable, dissolution-inhibiting group, and a structural unit (a2) derived from an (α-lower alkyl) acrylic acid, and

said structural unit (a2) is at least one structural unit selected from the group consisting of structural units (a2″-1) derived from an (α-lower alkyl) acrylic acid produced by dissociation of an ester terminal portion of an (α-lower alkyl) acrylate ester under action of said acid, and structural units (a2″-2) produced by dissociation of an ester terminal portion of a structural unit derived from an (α-lower alkyl) acrylate ester under action of said acid.

5. A method of producing a positive resist composition according to claim 4 , wherein said structural unit (a2) is at least one structural unit selected from the group consisting of structural units (a2″-1-1) derived from an (α-lower alkyl) acrylic acid produced by dissociation, under action of said acid, of said acid-dissociable, dissolution-inhibiting group of an (α-lower alkyl) acrylate ester that gives rise to said structural unit (a11), and structural units (a2″-2-1) produced by dissociation of said acid-dissociable, dissolution-inhibiting group of said structural unit (a11) under action of said acid.

6. A method of producing a positive resist composition according to claim 4 , wherein said structural unit (a11) is a structural unit derived from an (α-lower alkyl) acrylate ester containing an acid-dissociable, dissolution-inhibiting group that comprises an aliphatic cyclic group.

7. A method of producing a positive resist composition according to claim 6 , wherein said structural unit (a11) is at least one structural unit selected from the group consisting of structural units represented by general formulas (a1-1-01) and (a1-1-03) shown below:

(wherein, R represents a hydrogen atom or a lower alkyl group, and R 11 represents a lower alkyl group)

(wherein, R represents a hydrogen atom or a lower alkyl group, and R 2 and R 3 each represent, independently, a lower alkyl group).

8. A method of producing a positive resist composition according to claim 4 , wherein said resin component (A) is a copolymer that further comprises a structural unit (a12) derived from an (α-lower alkyl) acrylate ester that contains a lactone-containing monocyclic or polycyclic group.

9. A method of producing a positive resist composition according to claim 8 , wherein said structural unit (a12) is at least one structural unit selected from the group consisting of structural units represented by a general formula (a2-1) shown below:

(wherein, R represents a hydrogen atom or a lower alkyl group, and R′ represents a hydrogen atom, a lower alkyl group, or an alkoxy group of 1 to 5 carbon atoms).

10. A method of producing a positive resist composition according to claim 4 , wherein said resin component (A) is a copolymer that further comprises a structural unit (a13) derived from an (α-lower alkyl) acrylate ester that contains a polar group-containing aliphatic hydrocarbon group.

11. A method of producing a positive resist composition according to claim 10 , wherein said structural unit (a13) is at least one structural unit selected from the group consisting of structural units represented by a general formula (a3-1) shown below:

(wherein, R represents a hydrogen atom or a lower alkyl group, and j represents an integer from 1 to 3).

12. A method of producing a positive resist composition according to claim 1 , wherein said positive resist composition further comprises a nitrogen-containing organic compound (D).

13. A positive resist composition obtained using a method of producing a positive resist composition according to any one of claim 1 through claim 3 and claim 4 through claim 12 .

14. A method of forming a resist pattern comprising:

forming a resist film on a substrate using a positive resist composition according to claim 13 ;

exposing said resist film; and

developing said resist film to form a resist pattern.