Method For Forming Resist Underlayer Film And Patterning Process

A method for forming a resist underlayer film on a substrate, the method comprising the steps of:

• (i) forming an underlayer-film-precursor film by applying a composition for forming a resist underlayer film onto the substrate, the composition containing (A) a polymer and (B) an organic solvent, and subjecting the composition to heat treatment at a temperature of 100° C. or higher and 800° C. or lower for 10 seconds to 7,200 seconds to cure the composition;
• and
• (ii) forming a resist underlayer film by subjecting the substrate having the underlayer-film-precursor film formed to plasma irradiation,
• wherein the polymer (A) contains a constitutional unit represented by the following general formula (1) and has a weight-average molecular weight of 2,500 to 20,000 as measured by gel permeation chromatography in terms of polystyrene,
• wherein Ar1 and Ar2 each independently represent a substituted or unsubstituted benzene ring or a substituted or unsubstituted naphthalene ring, X represents a structure represented by the following general formula (1A), Y represents a divalent organic group having 6 to 50 carbon atoms, and “k” represents 0 or 1,
• wherein “n1” represents 0 or 1, “n2” represents 1 or 2, R2 represents a hydrogen atom or an organic group having 1 to 10 carbon atoms or has a structure represented by one of the following general formulae (1B), R3 represents a hydrogen atom, a linear, branched, or cyclic alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 10 carbon atoms, or a group represented by the following general formula (1C), “n3” represents 0, 1, or 2, “*” represents an attachment point to the methylene group, and “**” represents an attachment point to the quaternary carbon atom of the fluorene,
• wherein “*” represents an attachment point to the oxygen atom, RA represents a divalent organic group having 1 to 10 carbon atoms, and RB represents a hydrogen atom or a monovalent organic group having 1 to 10 carbon atoms,
• wherein R4 represents a hydrogen atom or a saturated or unsaturated hydrocarbon group having 1 to 10 carbon atoms, a hydrogen atom on the benzene ring in the formula optionally being substituted with a methyl group or a methoxy group.