Effect of Negative Substrate Bias on the Structure and Properties of Ta Coatings Deposited Using Modulated Pulse Power Magnetron Sputtering

Crystalline phase control is critical for obtaining desired structure and properties of Ta coatings deposited by magnetron sputtering. We have shown the approach to control the alpha and beta Ta phase formations by tuning the negative substrate bias voltage during modulated pulse power (MPP) magnetron sputtering, which generates a large fraction of target metallic ions in the plasma providing enhanced ion bombardment on the growing film. It was found that the peak and mean substrate ion current densities increased rapidly from 42 to 165 mAcm^-2 and 16 to 55 mAcm^-2, respectively, as the negative substrate bias voltage was increased from -20 to -50 V and became saturated with a further increase in the negative substrate bias voltage. As the negative substrate bias voltage was increased from 0 to -100 V, the MPP Ta phase changed from an all beta phase when the bias voltage was at 0 V and a floating bias, to a mixed alpha and beta phases when the bias voltage was in the range of -30 to -40 V, and finally to an all alpha phase when the negative bias voltage was -50 V or greater. In this paper, alpha Ta coating with thicknesses up to 100 μm were successfully deposited using the MPP technique with high deposition rate. The residual stress of the thick Ta coating was measured using an X-ray stress analyzer. The adhesion strength of the thick Ta coating was evaluated using Rockwell-C indentation and scratch tests. The possibility to coat complex-shaped substrates with good coating coverage on the substrate´s surface placed orthogonal to the target has also been demonstrated.