Effects of pulse time offset between Cr and Zr dual cathodes in closed-magnetic-field unipolar high-power impulse magnetron sputtering

Abstract

Two cathode (target) materials, Cr and Zr, were paired in a closed-field magnetron dual-cathode configuration and used in unipolar high-power impulse magnetron sputtering (HiPIMS). Two pulse widths (pulse-on durations) and various pulse-time offsets between the negative-voltage pulses of the Cr and Zr targets were investigated by setting the synchronization delay between the HiPIMS power supplies of the two targets at two different Ar pressures. Several trends were observed by analyzing the waveforms of the target discharge current, target discharge voltage, and substrate current. The closed-magnetic-field dual-cathode configuration significantly enhanced the HiPIMS discharge efficiency of the Zr target at all pressures; however, the enhancement for the Cr target was considerably lower. The ion fluxes toward the substrate were influenced by two competing mechanisms. The charged species generated from the previous pulse on one target could be attracted by the subsequent pulse of the adjacent target as a preionized medium to enhance the HiPIMS discharge. However, the fraction of the previously emitted ion flux toward the substrate could be reduced. When a shorter pulse width of 70 μs was applied, the ion flux that reached the substrate was mainly affected by the pulse power of the Zr target, and delaying the pulses of the Cr target with a relatively lower ion yield can achieve a higher ion flux toward the substrate. Increasing the pulse width significantly increased ion fluxes emitted from both the Cr and Zr targets, increasing the total ion flux toward the substrate. The study indicates that for the Cr and Zr dual cathode pair, a pulse time offset of one pulse width plus more than approximately 200 μs would be the most efficient way to obtain the highest ion fluxes toward the substrate and achieve a better film quality.