Resist underlayer film-forming composition

A resist underlayer film-forming composition comprising:

• a thermal acid generator represented by formula (I) below;
• a polymer (G) which is a novolac resin comprising:
• (i) a unit structure having an optionally substituted aromatic ring, and
• (ii) a unit structure containing:
• an optionally substituted aromatic cyclic organic group;
• an optionally substituted non-aromatic monocyclic organic group;
• or an optionally substituted, 4—to 25-membered bicyclic, tricyclic, or tetracyclic organic group containing at least one non-aromatic monocyclic ring;
• the unit structure (i) and the unit structure (ii) being bonded to each other via a covalent bond between a carbon atom on the aromatic ring of the unit structure (i) and a carbon atom on a non-aromatic monocyclic ring of the unit structure (ii);
• and
• a solvent,
• [Chem. 92]
• (A—SO3)−(BH)+ (1)
• [in formula (I),
• A is an optionally substituted, linear, branched, or cyclic, saturated or unsaturated, aliphatic hydrocarbon group;
• an optionally substituted aryl group;
• or an optionally substituted heteroaryl group;
• and
• B is a base having a pKa of 6.5 or more].