Bottom resist layer composition and patterning process using the same

A bottom resist layer composition for a multilayer-resist film used in lithography comprising, at least, a polymer comprising a repeating unit represented by the following general formula (1),

• wherein R1 represents a hydrogen atom or an acid labile group;
• X represents any one of a single bond, —Y—C(═O)—, and a linear or branched alkylene group having 1-4 carbon atoms;
• Y represents a single bond or a linear or branched alkylene group having 1-4 carbon atoms;
• Z represents any one of a methylene group, an oxygen atom, and a sulfur atom;
• R2 and R3 independently represent an alkyl group, an alkoxy group, an acetoxy group or an alkoxycarbonyl group each having 1-4 carbon atoms, or an aryl group having 6-10 carbon atoms;
• R4 represents an alkyl group having 1-4 carbon atoms or an aryl group having 6-10 carbon atoms;
• R5 represents a pyrene, fluorene, phenanthrene, chrysene, naphthacene, pentacene, or acenaphthene in which hydrogen atoms in part or in entirety may optionally be substituted with a halogen;
• n represents an integer of 0 to 4;
• p and q independently represent an integer of 0 to 6;
• R6 represents a hydrogen atom or a methyl group;
• and
• a, b, c, d, and e satisfy 0<a<1.0, 0≦b≦0.9, 0≦c≦0.9, 0≦d≦0.9, 0≦e≦0.9, and 0<b+c+d+e<1.0.