Effect of the target bias voltage during off-pulse period on the impulse magnetron sputtering

Abstract

With a high-power impulse magnetron sputtering (HiPIMS) apparatus, it has been studied how the target bias voltage during the off-pulse period affects the stability of the generated plasma. We have prepared an electrical pulse power source which can control the target voltage during the pulse off period, in addition to the pulse voltage, repetition frequency and a duty ratio of the pulse. Time-resolved current-voltage characteristic was monitored by an oscilloscope, and plasma generation behavior was elucidated. With titanium target and at Ar gas pressures of 0.6–5 Pa, pulse-off bias voltage was changed between −300 and +100 V, and the I-V characteristics were recorded. On increasing the negative bias voltage, the time at which the target current began to rise was gradually delayed. And at a certain voltage, the delay suddenly disappeared. This voltage was found to be the sustain voltage of the dc discharge in the same condition. Applying positive bias voltage resulted in a much longer delay. These results suggest that the minimal discharge during the pulse-off period helps the initiation of high-density plasma, while the bias voltage which can not maintain the plasma contrarily hampers it.