Copolymer, positive resist composition, and method of forming resist pattern
A copolymer includes a monomer unit (A) represented by formula (I), shown below, and a monomer unit (B) represented by formula (II), shown below, and has a weight-average molecular weight of 230,000 or more. In the formulae, L is a single bond or a divalent linking group, Ar is an optionally substituted aromatic ring group, R 1 is an alkyl group, R 2 is hydrogen, an alkyl group, a halogen atom, a haloalkyl group, a hydroxy group, a carboxy group, or a halocarboxy group, p is an integer of not less than 0 and not more than 5, and in a case in which more than one R 2 is present, each R 2 may be the same or different.
1. A copolymer comprising:
a monomer unit (A) represented by formula (I), shown below,
where, in formula (I), L is a single bond or a divalent linking group and Ar is an optionally substituted aromatic ring group; and
a monomer unit (B) represented by formula (II), shown below,
where, in formula (II), R 1 is an alkyl group, R 2 is hydrogen, an alkyl group, a halogen atom, a haloalkyl group, a hydroxy group, a carboxy group, or a halocarboxy group, p is an integer of not less than 0 and not more than 5, and in a case in which more than one R 2 is present, each R 2 may be the same or different, wherein
the copolymer has a weight-average molecular weight of 230,000 or more, and
a difference between weight-average molecular weight Mw 20 thereof upon exposure with an electron beam irradiation dose of 20 μC/cm 2 and weight-average molecular weight Mw 40 thereof upon exposure with an electron beam irradiation dose of 40 μC/cm 2 is 12,100 or more.
2. The copolymer according to claim 1 , having a weight-average molecular weight of 280,000 or more.
3. The copolymer according to claim 1 , wherein a proportion of components having a molecular weight of less than 50,000 is 20% or less.
4. The copolymer according to claim 1 , wherein a proportion of components having a molecular weight of less than 100,000 is 30% or less.
5. The copolymer according to claim 1 , wherein a proportion of components having a molecular weight of more than 500,000 is 10% or more.
6. The copolymer according to claim 1 , wherein L is a divalent linking group that includes an electron withdrawing group.
7. The copolymer according to claim 6 , wherein the electron withdrawing group is at least one selected from the group consisting of a fluorine atom, a fluoroalkyl group, a cyano group, and a nitro group.
8. A positive resist composition comprising: the copolymer according to claim 1 ; and a solvent.
9. A method of forming a resist pattern comprising:
a step (A) of forming a resist film using the positive resist composition according to claim 8 ;
a step (B) of exposing the resist film; and
a step (C) of developing the resist film that has been exposed using a developer.
10. The method of forming a resist pattern according to claim 9 , wherein the developer includes an alcohol.