Abstract: A silicon-containing composition includes: a polysiloxane including a first structural unit represented by formula (1); and a solvent. X is an alkali-dissociable group; a is an integer of 1 to 3; and when a is 2 or more, a plurality of Xs are the same or different from each other. R1 is a monovalent organic group having 1 to 20 carbon atoms, a hydroxy group, or a halogen atom; b is an integer of 0 to 2; and when b is 2, two R1s are the same or different from each other. a + b is 3 or less.

Abstract: A silicon-containing composition includes: a first polysiloxane; a second polysiloxane different from the first polysiloxane; and a solvent. The first polysiloxane includes a group which includes at least one selected from the group consisting of an ester bond, a carbonate structure, and a cyano group. The second polysiloxane includes a substituted or unsubstituted hydrocarbon group having 1 to 20 carbon atoms.

Abstract: A resist underlayer film-forming composition includes: a polysiloxane compound including a first structural unit represented by formula (1); and a solvent. X represents a group represented by formula (2); a is an integer of 1 to 3; R1 represents a halogen atom, a hydroxy group, or a monovalent organic group having 1 to 20 carbon atoms; and b is an integer of 0 to 2; and a sum of a and b is no greater than 3. R2 represents a monovalent hydrocarbon group having 1 to 20 carbon atoms; n is 1 or 2; R3 represents a hydrogen atom or a monovalent organic group having 1 to 20 carbon atoms; L represents a single bond or a divalent linking group; and * denotes a site bonding to the silicon atom in the formula (1). The composition is suitable for lithography with an electron beam or extreme ultraviolet ray.