Atomic layer deposition of Ru thin films using (2,4-dimethyloxopentadienyl)(ethylcyclopentadienyl)Ru and the effect of ammonia treatment during the deposition

Abstract

In this study, ruthenium (Ru) thin films were grown on Ta₂O₅, Si, Ru, and Pt substrates (Ta₂O₅, Ru, and Pt are thin films, and Si is a bulk wafer) through atomic layer deposition (ALD) using (2,4-dimethyloxopentadienyl)(ethylcyclopentadienyl)Ru [Rudense®] and oxygen as the Ru precursor and the reactant, respectively, at substrate temperatures ranging from 250 °C to 270 °C and ALD chamber pressures ranging from 0.5 Torr to 2.5 Torr. The Ru films showed a high growth rate of 0.83 Å cy⁻¹ except on Pt substrates and negligible incubation cycles. Ru metallic phases were confirmed via resistivity and crystalline structure analyses. A different preferred crystalline orientation of the Ru films was obtained on Pt substrates as compared to other substrates, which resulted in lower growth rates. A smooth and uniform surface was obtained at low thickness; however, the surface morphology abruptly deteriorated as the thickness of the Ru films increased on the Ta₂O₅ and Si substrates, which was not the case for metallic substrates. Ammonia (NH₃) treatment was adopted to enhance the surface morphology of the Ru films by suppressing excessive growth of the RuO_x layer, where the adsorbed nitrogen atoms inhibited excessive chemical adsorption of the precursor molecules. The surface roughness and the number of protrusions decreased with appropriate NH₃ treatment, while the structural and chemical properties of the metallic Ru films remained unaffected.