Investigation on the Growth Initiation of Ru Thin Films by Atomic Layer Deposition

Ru thin films were grown on Au, Pt, TiN, TiO2, and SiO2 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.