Resist underlayer composition and method of forming patterns using the composition

A resist underlayer composition, comprising:

• a polymer comprising a structural unit represented by Chemical Formula 1, a structural unit represented by Chemical Formula 2, a structural unit represented by Chemical Formula 3, or a combination thereof, and a solvent:
• wherein, in Chemical Formula 1 to Chemical Formula 3,
• R1 and R2 are each independently hydrogen, deuterium, a hydroxy group, a halogen atom, a substituted or unsubstituted C1 to C20 alkyl group, substituted or unsubstituted C2 to C20 alkenyl group, a substituted or unsubstituted C2 to C20 alkynyl group, or a combination thereof,
• A is a heterocyclic group including a nitrogen atom in a ring,
• L1 to L7 are each independently a single bond, a substituted or unsubstituted C1 to C10 alkylene group, a substituted or unsubstituted C2 to C10 alkenylene group, a substituted or unsubstituted C2 to C10 alkynylene group, a substituted or unsubstituted C3 to C20 cycloalkylene group, a substituted or unsubstituted C3 to C20 heterocycloalkylene group, a substituted or unsubstituted C6 to C20 arylene group, or a combination thereof,
• X1 to X8 are each independently a single bond, —O—, —S—, —S(═O)—, —S(═O)2—, —C(═O)—, —(CO)O—, —O(CO)O—, —C(═O)NH—, —NRa— (wherein, Ra is hydrogen, deuterium, or a C1 to C10 alkyl group), or a combination thereof,
• Y1 and Y4 are each a group represented by Chemical Formula 4,
• Y2 and Y3 are each independently a hydroxy group, a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C2 to C10 alkenyl group, a substituted or unsubstituted C2 to C10 alkynyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C3 to C20 heterocycloalkyl group, a substituted or unsubstituted C6 to C20 aryl group, a group represented by Chemical Formula 4, or a combination thereof, provided that one or more selected from Y2 and Y3 is a group represented by Chemical Formula 4, and
• * is a linking point:
• wherein, in Chemical Formula 4,
• R3 to R6 are each independently hydrogen, deuterium, a substituted or unsubstituted C1 to C10 alkyl group, substituted or unsubstituted C2 to C10 alkenyl group, a substituted or unsubstituted C2 to C10 alkynyl group, or a combination thereof, and
• * is a linking point.