Negative ion energy distributions in reactive HiPIMS

Energy-resolved mass spectrometry has been used to measure the time-averaged energy and mass distributions of negative ion species in high power impulse magnetron sputtering (HiPIMS) of titanium in an argon/oxygen gas mixture for a number of different discharge conditions. The discharges were found to contain O-, O-2(-), TiO-, TiO2- and TiO3- ions and their respective energy spectra are presented. The oxygen negative ion (O- and O-2(-)) energy distributions exhibit three broad energy populations (low, medium and high energy) and their origin is discussed. The high-energy peak is found to coincide with a value corresponding to the absolute target potential during the stable on-phase of the HiPIMS pulse. The shape of the high-energy population of O- ions is compared with both a theoretical Thompson energy distribution of sputtered particles and a current-weighted target potential distribution function. A study of the attenuation of high-energy O- ions as a function of the pressure-distance product has been performed. An exponential decrease in intensity of the high-energy O- ions with an increasing pressure-distance product in the substrate region is observed, yielding an effective total cross section of 2.2 x 10(-19) m(2) for O- interacting with the background gas mixture.