Oxide composition studies of electrochemically grown tantalum oxide on sintered tantalum using XPS depth-profiling and co-relation with leakage properties

Abstract

Chemical structure and leakage properties of electrochemically grown tantalum oxide films on high-surface area tantalum were studied. Tantalum oxide films with different thicknesses were grown on sintered tantalum under potentio-dynamic conditions by modifying the anodization dwell-voltages. X-ray photoelectron spectroscopy depth-profile studies were performed to investigate the surface chemical composition and oxide species of the grown tantalum oxide. Furthermore, the strength of the dielectric film was probed by analyzing the leakage properties of the tantalum oxide of different thicknesses. Different leakage current models were used to identify the plausible defect mechanisms in anodized tantalum oxide films. A mix of the stoichiometric pentavalent oxide and non-stoichiometric sub-oxides were observed in the tantalum oxide film with a distribution gradient along the oxide growth direction. A gradual drop was observed in the content of stoichiometric phase from the oxide surface to the oxide-metal interface irrespective of the oxide thickness. The non-stoichiometric content of oxide gave rise to crystalline nature in the oxide which acted as a catalyst for leakage conduction in oxide dielectrics. The electrode-dielectric interface gave rise to various defect mechanisms which also contributed to leakage in addition to crystalline content in the oxide. To the best of the authors’ knowledge, this is the first scientific reporting on composition and structure of anodically-grown tantalum oxide films on high-surface area tantalum along with identification of mechanisms responsible for their leakage properties.