Investigation on the growth initiation of Ru thin films by atomic layer deposition

Ru thin films were grown on Au, Pt, TiN, TiO₂, and SiO ₂ substrates by atomic layer deposition using 2,4- (dimethylpentadienyl)(ethylcyclopentadienyl)Ru (DER) dissolved in ethylcyclohexane at a concentration of 0.2 M as the Ru precursor and O ₂ as the reactant. There was a long incubation time for Ru film deposition on TiN and SiO₂ due to the weak interaction between DER and the covalent bonds in TiN and SiO₂. On the other hand, the Ru films on TiO₂ exhibited a shorter incubation time. There was a negligible incubation time for Ru film deposition on Au and Pt due to the strong interactions between the DER precursor and metallic surfaces, resulting in a smooth surface morphology and strong c-axis texture. A continuous Ru film, not an island-shaped film, was formed on Au, which does not catalytically dissociate molecular oxygen, even at a film thickness of 1 nm. Therefore, the initial growth of Ru thin films was determined by the adsorption of the metal precursor not the catalytic dissociation of molecular oxygen.