Nucleation of the ruthenium (Ru) precursor on low-k film surfaces during atomic layer deposition (ALD) of Ru was investigated. The adsorption tendency of the precursor decreased with increasing concentration of methyl groups on the low-k film surface, resulting in poor nucleation of Ru. The electron-deficient hydroxyl groups act as preferential adsorption sites for the electron-rich ligands of the aromatic Ru precursor through the formation of pi-bonds. This leads to the enhanced nucleation of Ru. The roles of the functional groups were corroborated by silylation experiments.