Low-temperature plasma anodization of tantalum silicides

Abstract

The low-temperature plasma anodization of cosputtered Ta silicide has been studied. The anodization parameters, oxide growth rate, electric field, and faradic efficiency showed a strong dependence on the silicide formation (with or without annealing). Rutherford backscattering techniques were employed to characterize the oxide films and it was found that the plasma oxides grown on as-deposited silicide are of uniform composition in the oxide bulk, but the near-surface region shows a slight Si oxide enrichment, and, thus, a Ta oxide depletion. On the contrary, for annealed (950 °C) silicides, when the hexagonal Si-enriched TaSi2 phase is formed, a high-surface enrichment in Ta oxide is observed in the plasma grown oxides. The insulating properties of the oxide films as determined by capacitance, electrical conductivity, and dielectric strength measurements also depend on the silicide formation, and these properties were correlated to the cation depth distributions in the oxide mixtures. A spectacular difference in the dielectric constant has been found between oxide formed on an as-deposited layer (∼12) and on an annealed one (∼6). This is a consequence of continuous (although nonconstant) cation’s mixture in the first case and layered structure in the second.