COMPOSITION FOR FORMING SILICON-CONTAINING RESIST UNDERLAYER FILM AND PATTERNING PROCESS

A composition for forming a silicon-containing resist underlayer film contains at least one or more kinds of a quaternary ammonium salt shown by the following general formula (A-1), and a thermally crosslinkable polysiloxane (Sx), where Ar1 represents an aromatic group having 6 to 20 carbon atoms, or a heteroaromatic group having 4 to 20 carbon atoms. R11 represents an alkyl group, alkenyl group, oxoalkyl group, or oxoalkenyl group having 1 to 12 carbon atoms, an aryl group having 6 to 20 carbon atoms, or an aralkyl group or aryloxoalkyl group having 7 to 12 carbon atoms. Some or all of hydrogen atoms of these groups are optionally substituted. Z− represents an organic or inorganic anion as a counterion of the quaternary ammonium cation. An object is to provide a silicon-containing resist underlayer film having high effect of suppressing ultrafine pattern collapse and appropriate etching rate in multilayer resist methods.