Auxiliary capacitor to enhance oscillation in circuit and reduce current onset delay in HiPIMS discharge: Theory, experiment and simulation

In high power impulse magnetron sputtering (HiPIMS) discharge, generally, the current onset lags the applied pulse voltage by a significant time which can reach to several tens of microseconds, especially at a low gas pressure. The existence of this delay will affect the instantaneous and average power, and in turn, it determines the plasma dynamics and the thin film properties. The origin of current onset delay can be traced back to gas breakdown in E × B fields. This work firstly focuses on the theory and model of gas breakdown in the HiPIMS discharge with parallel electrodes. Theoretically, the breakdown voltage of argon in HiPIMS is about −700 V at gas pressure of 0.45 Pa, while it can exceed −1100 V at pressure of 0.4 Pa. To operate the HiPIMS at a low pressure with a short delay time of current onset, the means using an auxiliary capacitor C connected in parallel with plasma between electrodes to enhance oscillation in circuit (named ECO-HiPIMS) is employed, which can generate a high oscillation voltage during the gas breakdown phase. Choosing a suitable capacitor, this oscillation voltage reaches up to −1322 V at applied pulse voltage of −700 V, and in turn, the delay time can be shortened from around 50 μs (in standard HiPIMS) to less than 5 μs. Finally, the plasma dynamics during gas breakdown phase in HiPIMS and ECO-HiPIMS has been investigated by a two-dimension particle in cell/Monte Carlo (2D PIC-MCC) simulation.