High power impulse magnetron sputtering from a chromium target

Abstract

High power impulse magnetron sputtering discharges with a chromium target are studied experimentally. For a given pulse length the deposition rate decreases and the ionized flux fraction increases with increased discharge current density ranging between 0.4 – 1.0 A cm−2. Furthermore, the deposition rate is highest for a pulse length of 50 µs and decreases when shortening the pulses down to 25 µs or increasing the pulse length up to 200 µs. The measured chromium ionized flux fraction ranges between 10% – 50%. The ionized flux fraction is highest for the highest peak discharge current density, and the shortest pulse length studied. In order to understand the experimental findings the discharges were analyzed by applying the ionization region model (IRM). The IRM is a semi-empirical, time-dependent, volume-averaged, plasma chemistry model that covers the ionization region (IR) of the magnetron sputtering discharge and uses the measured cathode voltage and current waveforms as input data. The IRM results indicate that the singly charged chromium ion is the dominant ion in the IR and the discharges operate in metal recycling mode. The ionization probability of the sputtered species increases with increased peak discharge current density. It also increases at first with decreased pulse length, reaches a peak and then decreases with further decrease in the pulse length. The back-attraction probability of the sputtered species decreases with decreasing pulse length, and with increasing peak discharge current density.