Mass spectrometry diagnostics of short-pulsed HiPIMS discharges

Abstract

Time-resolved mass spectrometry (MS) study of a high-power impulse magnetron sputtering discharge (HiPIMS) operating in the ‘short-pulse’ regime (5 µs) at 1 kHz of the repetition frequency is undertaken. Several time-resolved effects related to both Ti+ and Ar+ ion energy distribution functions (IEDF) are found. In particular, the dynamics of both the low- (0–5 eV) and high- (5–30 eV) energy regions presented in Ti+ IEDFs is clarified. According to our results the sputtered and ionized Ti arrive at the virtual substrate position in the form of two waves, with the first one representing the high-energy Ti+, and the second one responsible for the low-energy Ti+. An essential decrease in the population of the energetic Ti+ group is observed at the moment of the arrival of the low-energy group, which is explained by the charge exchange processes, as well as by the refilling process afterwards. The role of Ar metastables presumably generated at the end of the plasma pulse for further Ti ionization is stressed as well. The time-averaged IEDFs for Ti+ and Ar+ are additionally analysed. The effective ion temperatures are calculated for these species for the above-mentioned energy ranges. A considerable increase in the effective ion temperature for the high-energy Ti+ is found, which is directly related to the elevation of the high-energy tail in the time-averaged IEDFs with increasing discharge voltage. Possible mechanisms for such an elevation are discussed.