Underlayer film-forming composition, pattern-forming method, copolymer, and monomer for underlayer film-forming composition

A copolymer containing:

• (a) a unit derived from a sugar derivative;
• (b) a unit derived from a compound having a light antireflection function;
• and
• (c) a unit derived from a compound capable of cross-coupling the copolymer,
• wherein the unit derived from a sugar derivative (a) is at least one selected from a unit derived from a pentose derivative and a unit derived from a hexose derivative.

A monomer for an underlayer film-forming composition, which is represented by the following formula (1′) or the following formula (2′):

• wherein, in formula (1′), each R1 independently represents a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, an alkyl group, an acyl group, an aryl group, a trimethylsilyl group, or a phosphoryl group, and a plurality of R1 may be the same or different;
• R′ represents a hydrogen atom, —OR11, or —NR122;
• R″ represents a hydrogen atom, —OR11, —COOR13, or —CH2OR13, provided that R11 represents a hydrogen atom, an alkyl group, an acyl group, an aryl group, a trimethylsilyl group, or a phosphoryl group, R12 represents a hydrogen atom, an alkyl group, a carboxyl group, or an acyl group, a plurality of R12 may be the same or different, and R13 represents a hydrogen atom, an alkyl group, an acyl group, an aryl group, a trimethylsilyl group, or a phosphoryl group;
• R5 represents a hydrogen atom or an alkyl group;
• and
• each Y1 independently represent a single bond or a linking group;
• wherein, in formula (2′), each R201 independently represents a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, an alkyl group, an acyl group, an aryl group, a trimethylsilyl group, or a phosphoryl group, and a plurality of R201 may be the same or different;
• R′ represents a hydrogen atom, —OR11, or —NR122;
• and
• R″ represents a hydrogen atom, —OR11, —COOR13, or —CH2OR13, provided that R11 represents a hydrogen atom, an alkyl group, an acyl group, an aryl group, a trimethylsilyl group, or a phosphoryl group, R12 represents a hydrogen atom, an alkyl group, a carboxyl group, or an acyl group, a plurality of R12 may be the same or different, and R13 represents a hydrogen atom, an alkyl group, an acyl group, an aryl group, a trimethylsilyl group, or a phosphoryl group.