Deposition of titanium oxide films by reactive High Power Impulse Magnetron Sputtering (HiPIMS): Influence of the peak current value on the transition from metallic to poisoned regimes

Abstract

In this study, reactive High Power Impulse Magnetron Sputtering (HiPIMS) experiments were carried out to synthesize titanium oxide films, using a 45×15cm² titanium target in Ar/O2 gas mixtures. The deposition process was studied as a function of the peak current (ipeak) at constant voltage during the pulse (1kV) and constant average power (Pav). As the oxygen flow was increased, ipeak was kept constant (160, 300 or 400A) by adjusting the pulse duration and the average power (2 or 4kW) by adjusting the pulse repetition frequency. For all experimental conditions, an abrupt transition from metallic towards poisoned regimes was observed. The transition curves exhibit hysteresis. As ipeak is increased from 160A to 450A, for Pav=4kW, the oxygen content (Ω) in the Ar/O2 mixture needed to poison the target surface was reduced from Ω=11.5% to Ω=8.5%. These values are much smaller than those recorded for DC magnetron sputtering (DCMS) (Ω=42%) and pulsed DCMS (Ω=36%) experiments carried out at the same power. These results are explained by the enhancement of the ionization and dissociation rates of oxygen molecules with the increase of ipeak.X-ray fluorescence data show that the higher is ipeak, the lower is the deposition rate (RD). Therefore, both the deposition and poisoning processes depend on ipeak. According to X-ray diffraction data, for DCMS, the films are amorphous and for HiPIMS the phase constitution evolves from an anatase/rutile mixture to pure rutile as ipeak is increased.