The purpose of the present invention is to provide: a method for manufacturing a
semiconductor substrate using a composition from which a film having excellent
etching resistance,
heat resistance, and bending resistance can be formed; a composition; a
polymer; and a method for producing a
polymer. This method for manufacturing a
semiconductor substrate comprises: a step for applying a
resist underlayer film-forming composition directly or indirectly to a substrate; a step for forming
resist patterns directly or indirectly on the
resist underlayer film formed in the application step; and a step for performing
etching using the resist patterns as masks, wherein the resist underlayer film-forming composition contains a
solvent and a
polymer having a repeating unit represented by formula (1). (In formula (1), Ar1 is a
divalent group having an aromatic ring with 5-40 membered rings. R0 is a group represented by formula (1-1) or (1-2).) (In formula (1-1) or (1-2), X1 and X2 are each independently a group represented by formula (i), (ii), (iii), or (iv). * is a
dangling bond to the
carbon atom in formula (1). Ar2, Ar3, and Ar4 are each independently a substituted or unsubstituted aromatic ring with 6-20 membered rings, which forms a condensed ring structure together with adjacent two carbon atoms in formulae (1-1) and (1-2).) (In formula (i), R1 and R2 are each independently a
hydrogen atom or a C1-C20 monovalent
organic group. In formula (ii), R3 is a
hydrogen atom or a C1-C20 monovalent
organic group. R4 is a C1-C20 monovalent
organic group. In formula (iii), R5 is a C1-C20 monovalent organic group. In formula (iv), R6 is a
hydrogen atom or a C1-C20 monovalent organic group.)