The oxidation process and dissipation factor of Al/Ta/Hf multilayered anodized thin‐film capacitors

Abstract

AbstractIt is known that the anodic oxidation of Hf proceeds by the diffusion of anions into Hf thin film and is affected by the other overlayered films existing on Hf in multilayered anodized thin‐film capacitors. to characterize multilayered thin oxide film structures necessary for the fabrication of high‐quality capacitors, a correlation between dissipation factor and oxidation process has been investigated as a function of anodization voltage and thinfilm thicknesses of Al/Ta/Hf and Ta/Al/Hf multilayers.The results indicate that thin‐film capacitors with low dissipation factor can be obtained by anodizing Al/Ta/Hf thin films so long as their original multilayered structures are maintained during anodization and the Ta intermediate layer acts as a transport medium of oxygen ions for the bottom Hf layer. With increasing anodization voltage, Ta ions migrate toward the surface of the multilayer, which alters the original multilayered structure and contributes to higher dissipation factor.When the intermediate layer is Al such as in the case of Ta/Al/Hf multilayer capacitors, the flow of oxygen ions to the bottom Hf layer is restricted during anodization by the formation of an oxidized Al layer and this makes the dissipation factor higher. It has been concluded that in order to fabricate thin‐film capacitors with low dissipation factor, it is vital to have the presence of an intermediate layer such as Ta which has a lower heat of formation for oxidation than Hf.