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;
• and
• a solvent:
• wherein, in Chemical Formula 1,
• L1, L2, and L3 are each independently a substituted or unsubstituted C1 to C10 alkylene group, a substituted or unsubstituted C1 to C10 heteroalkylene group, a substituted or unsubstituted C3 to C20 cycloalkylene group, a substituted or unsubstituted C2 to C20 heterocycloalkylene group, a substituted or unsubstituted C6 to C20 arylene group, a substituted or unsubstituted C1 to C10 heteroarylene group, a carbonyl group, an ester group, or a combination thereof,
• R is hydrogen, deuterium, a halogen, a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C2 to C20 alkenyl group, a substituted or unsubstituted C2 to C20 alkynyl group, a substituted or unsubstituted C3 to C20 cycloalkyl group, a substituted or unsubstituted C6 to C20 aryl group, a substituted or unsubstituted C1 to C10 heteroalkyl group, a substituted or unsubstituted C2 to C20 heteroalkenyl group, a substituted or unsubstituted C3 to C20 heterocycloalkyl group, or a substituted or unsubstituted C6 to C20 heteroaryl group,
• X1 and X2 are each independently a halogen, a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C1 to C10 heteroalkyl 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, or a substituted or unsubstituted C6 to C20 heteroaryl group, provided that at least one of X1 or X2 is a halogen,
• k is an integer of 1 to 10, and
• * is a linking point.