Tantalum Ion Transport Number during the Anodic Oxidation of Beta‐Tantalum Films

Abstract

In this study Rutherford backscattering has been used to determine the tantalum ion transport number during the anodic oxidation of beta-tantalum films. The required marker is the argon uniformly incorporated in tantalum during sputtering. The transport number for Ta +~ ions for beta-tantalum anodic oxidation is 0.25 • 0.02 at 1 mA/cm 2 and 23.5~C, and there is a weak dependence on the electric field used during the oxide growth. These results are identical to that obtained for bulk alpha-(bcc) -tantalum, which may indicate that the transport number is not controlled by the crystal structure associated with the metal-oxide interface. For metal films which are anodized completely through to the substrate, there is an apparent 1% tantalum excess in the outer portion of the oxide. This effect may be associated with the argon incorporation in the oxide, or a nonequilibrium ratio of Ta/O, or a low atomic weight impurity.