Method for manufacturing semiconductor substrate and composition

A method for manufacturing a semiconductor substrate, the method comprising:

• applying a composition for forming a resist underlayer film directly or indirectly to a substrate to form a resist underlayer film directly or indirectly on the substrate;
• forming a resist pattern directly or indirectly on the resist underlayer film;
• and
• performing etching using the resist pattern as a mask,
• wherein the composition for forming a resist underlayer film comprises:
• a polymer comprising a repeating unit represented by formula (1):
• in the formula (1), Ar1 is a divalent group comprising an aromatic ring having 5 to 40 ring atoms;
• and R0 is a monovalent group comprising an aromatic ring having 5 to 40 ring atoms and comprises at least one group selected from the group consisting of groups represented by formula (2-1) and groups represented by formula (2-2):
• in the formulas (2-1) and (2-2), R7 is each independently a divalent organic group having 1 to 20 carbon atoms or a single bond;
• and * is a bond with a carbon atom in the aromatic ring;
• and
• a solvent.