Composition for resist underlayer film formation, and method of producing semiconductor substrate

A method of producing a semiconductor substrate, the method comprising:

• applying a composition for resist underlayer film formation directly or indirectly on a substrate to form a resist underlayer film;
• applying a composition for metal-containing resist film formation on the resist underlayer film to forcrr a metal-containing resist film;
• exposing the metal-containing resist film to an electron beam or an extreme ultraviolet ray;
• and
• developing the metal-containing resist film exposed,
• wherein the composition for resist underlayer film formation comprises:
• a polysiloxane compound comprising a first structural unit represented by formula (1);
• and
• a solvent,
• wherein, in the formula (1), X represents an organic group comprising at least one structure selected from the group consisting of a hydroxy group, a carbonyl group, and an ether bond;
• a is an integer of 1 to 3, wherein in a case in which a is no R1ss than 2, a plurality of Xs are identical or different from each other;
• R1 represents a halogen atom, a hydroxy group, or a monovalent organic group having 1 to 20 carbon atoms, wherein R1 is a group other than X;
• and b is an integer of 0 to 2, wherein in a case in which b is 2, tA R1s are identical or different from each other, and wherein a sum of a and b is no greater