Composition, method of producing substrate, and polymer

A composition comprising:

• a polymer comprising:
• a structural unit comprising a ring structure;
• and a functional group capable of bonding to a metal atom;
• and
• a solvent,
• wherein an atom chain constituting the ring structure constitutes a part of a main chain of the polymer, and
• wherein the structural unit is represented by formula (1):
• wherein, in the formula (1), R1 to R6 each independently represent a hydrogen atom, a halogen atom, or a monovalent organic group having 1 to 10 carbon atoms;
• R7 represents a hydrogen atom or a monovalent organic group having 1 to 10 carbon atoms;
• and p is an integer of 0 to 4, wherein in a case in which p is 1, R8 represents a halogen atom, a hydroxy group, or a monovalent organic group having 1 to 20 carbon atoms, and wherein in a case in which p is no less than 2, a plurality of R8s are identical or different from each other and each represent a halogen atom, a hydroxy group, or a monovalent organic group having 1 to 20 carbon atoms, or at least two of the plurality of R8s taken together represent a ring structure having 4 to 20 ring atoms together with the carbon chain to which the at least two of the plurality of R8s bond.