Anodic Ta2O5 films with a thickness of 100nm, on polycrystalline Ta, were annealed in ultra-high vacuum at 670 to 800K, for times of up to 2h. The heat-treated layers were characterized by Auger electron spectroscopy sputter depth-profiling. The oxide layers were found to dissolve into the Ta substrate. During dissolution, the oxide thickness decreased linearly with heating time, while the sharp oxide/metal interface broadened only slightly and the Ta2O5 stoichiometry was almost entirely conserved in the residual layers. A model for the dissolution was based upon the generation of mobile O atoms by a dissociation reaction, and rapid O diffusion from the oxide/metal interface and into the Ta substrate. Quantitative evaluations, made using this model, indicated an activation energy of 45.7kcal/mol for O diffusion in Ta2O5.

Dissolution of Anodic Ta2O5 Layers into Polycrystalline Tantalum. J.Giber, H.Oechsner: Thin Solid Films, 1985, 131[3-4], 279-87