Observation of a periodic runaway in the reactive Ar/O₂ high power impulse magnetron sputtering discharge

This paper reports the observation of a periodic runaway of plasma to a higher density for the reactive discharge of the target material (Ti) with moderate sputter yield. Variable emission of secondary electrons, for the alternating transition of the target from metal mode to oxide mode, is understood to be the main reason for the runaway occurring periodically. Increasing the pulsing frequency can bring the target back to a metal (or suboxide) mode, and eliminate the periodic transition of the target. Therefore, a pulsing frequency interval is defined for the reactive Ar/O₂ discharge in order to sustain the plasma in a runaway-free mode without exceeding the maximum power that the magnetron can tolerate.