Origin of the Delayed Current Onset in High-Power Impulse Magnetron Sputtering

Abstract

Repetitive pulses of voltage and current are applied in high power impulse magnetron sputtering. The current pulse usually lags the applied voltage by a significant time, which in some cases can reach many 10s of microseconds. The current time lag is generally highly reproducible and jitters less than 1% of the delay time. This work investigates the time lag experimentally and theoretically. The experiments include several different target and gas combinations, voltage and current amplitudes, gas pressures, pulse repetition rates, and pulse durations. It is shown that in all cases the inverse delay is approximately proportional to the applied voltage, where the proportionality factor depends on the combination of materials and the conditions selected. The proportionality factor contains the parameters of ionization and secondary electron emission. The statistical time lag is negligible while the formative time lag is large and usually dominated by the ion motion (inertia), although, at low pressure, the long free path of magnetized electrons causing ionization contributes to the delay.

Plasma potential mapping of high power impulse magnetron sputtering discharges

“…This indicates that a weak plasma is already present and developing at an early stage, before 0 t  , in agreement with previous considerations of plasma onset. 45 A shift to negative plasma potential (Fig. 7) can be explained by the removal of ionsdue to acceleration in the electric field-leaving behind the confined, drifting and accumulating electrons.…”

“…5, as opposed to the time when the voltage is applied to the target. This kind of 0 t  definition was adopted in order to eliminate the issues associated with the jitter caused by the statistical time delay 45 of the measurable discharge current onset. This approach allowed us to meaningfully average the measured signals of currents and voltages using 100 discharge pulses per location.…”

A review comparing cathodic arcs and high power impulse magnetron sputtering (HiPIMS)

“…With plasma already present at the beginning of each pulse, the current can rise faster, and the peak current can be higher [185]. Higher power density leads to a greater degree of ionization and the formation of multiple charge states [87,181,[186][187][188][189].…”

High power impulse magnetron sputtering discharge

“…95,134 Yushkov and Anders 138 explore this phenomena both experimentally and theoretically. The delay of current onset consists of a statistical time lag t s and the formative time lag t f or…”

“…By treating the initiation of the discharge as a vacuum breakdown Yushkov and Anders 138 derive an equation for the formative time lag,…”