Resist underlayer composition, and method of forming patterns using the composition

A resist underlayer composition, comprising:

• a polymer including a structural unit that is a reaction product of an isocyanurate compound and a compound having at least one reactive functional group, and
• a solvent,
• wherein:
• the isocyanurate compound is represented by Chemical Formula 1:
• in Chemical Formula 1, R1 to R3 are each independently a substituted or unsubstituted C1 to C30 alkyl group, a substituted or unsubstituted C1 to C30 heteroalkyl group, a substituted or unsubstituted C3 to C30 cycloalkyl group, a substituted or unsubstituted C2 to C30 heterocycloalkyl group, a substituted or unsubstituted C6 to C30 aryl group, or a substituted or unsubstituted C1 to C30 heteroaryl group, provided that at least one of R1 to R3 includes a thiol group substituent,
• the compound having at least one reactive functional group is represented by one of the following Chemical Formula 2-1 to Chemical Formula 2-4:
• in Chemical Formulae 2-1 to 2-4,
• X1 to X4 are each independently CH2, O, or S,
• R11 to R14 are each independently a substituted or unsubstituted C1 to C6 alkenyl group,
• R15 and R16 are each independently hydrogen or a halogen atom, and
• k, l, m, n, o, p, and q are each independently an integer of 0 to 10.