Resist underlayer composition and method of manufacturing semiconductor integrated circuit devices using the same

A resist underlayer, comprising:

• a resist underlayer polymer formed by cross-linking an organosilane condensation polymerization product including about 10 to about 40 mol % of a structural unit represented by Chemical Formula 1:
• wherein, in Chemical Formula 1,
• ORG is selected from the group of:
• a C6 to C30 functional group including a substituted or unsubstituted aromatic ring,
• a C1 to C12 alkyl group,
• and —Y—{Si(OR)3}a,
• R is a C1 to C6 alkyl group,
• Y is a linear or branched substituted or unsubstituted C1 to C20 alkylene group, or a C1 to C20 alkylene group including in a main chain a substituent selected from the group of an alkenylene group, an alkynylene group, an arylene group, a heterocyclic group, a urea group, an isocyanurate group, and a combination thereof, and
• a is 1 or 2.