Controlling the deposition rate during target erosion in reactive pulsed DC magnetron sputter deposition of alumina

Alumina coatings were synthesized by reactive pulsed DC magnetron sputtering in an industrial-scale deposition system. The aim of this study was to investigate the influence of target erosion (racetrack depth) on the deposition rate. Hysteresis curves, showing the cathode voltage as a function of oxygen flow, were mapped out for different target erosion depths and temperatures, revealing significant variations, e.g. in the metallic mode voltage level. Each deposition was made with a fixed cathode voltage and the cathode current was controlled by adjusting the oxygen flow in a feedback loop by means of which a constant power was maintained. Keeping the power constant, this procedure was repeated for various cathode voltages within the hysteresis transition region and at different racetrack depths and deposition temperatures. The corresponding deposition rates were observed to depend mainly on the relative cathode voltage set-point in-between the oxide and metallic voltage levels in the hysteresis region. This result enables control of the deposition rate by maintaining a constant relative cathode voltage as the target erodes.