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A high power impulse magnetron sputtering (HiPIMS) discharge assisted by a dc pre-ionizer operating at low pressure has been investigated using the Langmuir probe technique as well as energy-resolved mass spectrometry. It was found that the background plasma with densities of about 1 × 109 cm-3 provided by the dc pre-ionizer can reduce the ignition delay time of the HiPIMS plasma from more than 50 μs to less than 5 μs at a working pressure of about 0.1 Pa. Furthermore, the technique of super-imposing HiPIMS with the dc discharge can be readily employed with a low self-sputtering yield target (Ti) at a working pressure of 0.08 Pa, with a pulse width and a repetition frequency of 100 μs and 100 Hz, respectively. This leads to a power density of 450 Won 2 at the target. At these operating conditions, the probe measurements showed a high-density plasma 6 cm in front of the target. The maximum electron density was found to be 8 × 1011 cm-3, with an effective electron temperature of about 3-4 eV. A study of the ion mass distribution revealed that the intensity of Ti2+ ions is larger than the peak of Ti+ in low-pressure operation. Moreover, the number of metal ions in the high-energy tail of the ion energy distribution function increased with a decreasing pressure from 0.5 to 0.08 Pa.

By using a time-resolved Langmuir probe, the temporal evolution of plasma parameters (including the electron energy distribution function) in a preionised HiPIMS discharge were investigated for a number of discharge conditions. Assistance from a DC preioniser circuit providing the remnant and ‘active’ charge particles for the subsequence pulse with the delay time of plasma build-up being decreased dramatically to T de

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−, , TiO−, and ions and their respective energy spectra are presented. The oxygen negative ion (O− and ) 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 × 10−19 m2 for O− interacting with the background gas mixture.

Using a biased quartz crystal microbalance in combination with a gridded electrode, the ionized metal flux fraction in a high power impulse magnetron sputtering (HiPIMS) discharge operated with a titanium target has been investigated. The average discharge power was controlled by varying three different parameters; initial target voltage, pulse width and pulse frequency. The average discharge power was varied from 0.3 to 1.3 kW and irrespective of the power control method used an associated decrease in the flux fraction (from 50% to 30%) was observed. The mechanisms responsible for this decrease in the time-averaged flux fraction of metal ions are discussed.