Oxygen-induced inhibition of noble metal silicide formation: implications for electrode/barrier structures used with perovskite materials

Abstract

We describe how the inhibitory effect of ambient oxygen on silicide formation may be exploited in designing noble metal electrode structures suitable for perovskite-based memory devices. Reactions of Pt and Ir films with substrates of silicon and tungsten silicide (WSi2.8/Si) were examined after anneals in atmospheric pressure ambients of oxygen or nitrogen at temperatures of 640°C for various initial noble metal film thicknesses. Metal/silicon reactions and phase formation were studied by Rutherford Backscattering Spectroscopy, X-ray diffraction, and electrical resistance measurements. While annealing in nitrogen resulted in complete noble metal silicidation in the all samples, some Pt and most to all of the Ir remained after equivalent anneals in oxygen. Oxygen exhibited a greater inhibitory effect on silicidation in thin Ir samples, where no silicide formation was observed. The consistent presence of unreacted noble metal M after oxygen annealing is attributed to the formation of an oxygen-containing M-O-Si barrier which interferes with the silicidation reaction. Qualitative through-film resistance measurements indicate that these in-situ formed M-O-Si barrier layers can be at least moderately conductive, a prerequisite for their possible use as a replacement for deposited barrier materials.