A high-power impulse magnetron sputtering global model for argon plasma-chromium target interactions

A high power impulse magnetron sputtering (HiPIMS) discharge process is analyzed numerically and experimentally so that one may better understand and explain the effect of the pressure and pulse width on HiPIMS discharges and the deposited thin films. For this reason, a time-dependent global plasma model is developed for the ionization region in a HiPIMS discharge of a Cr target in Ar gas. It is based on the solving of a nonlinear equation system composed of the continuity equations of neutral and charged species in the ionization region considered in the reaction scheme. The pulse widths are about tens of microseconds for a frequency cycle of 1KHz. The simulations are performed for a 150W average power and 5-30mTorr pressure range. In these average power and pressure ranges, a double peak of the electron temperature is observed. The high first peak is due to a high rapid increase of negative voltage during the rising time of pulses, while the second one is due to a diminution of the injected gas Ar in the ionization region. On the other hand, gas rarefaction characterized by the diminution of the Ar density during time-on is due to the high ionization degree and the sputtering wind effect. During plasma off, the density of Ar returns to the stationary state corresponding to the initial pressure. In addition, the simulations reveal that the Cr+ population is more important than that of Ar+ caused by the high ionization degree of Cr compared with Ar. This confirms the high ionization degree during time-on, leading to a high efficiency of sputtering of Cr material. However, Cr2+ is still weak. In addition, a good agreement is shown between the calculated time current evolution and the measured one.