Time evolution of ion energies in HIPIMS of chromium plasma discharge

High power impulse magnetron sputtering (HIPIMS) discharges produce metal ions with energies up to 100 eV and the degree of metal ionization can be up to 90%. The ion energy distribution function (IEDF) of ions in HIPIMS of a chromium target in an argon atmosphere was measured using plasma sampling energy resolved mass spectrometry. The time resolved measurements show that in the pulse-on phase the IEDF of Cr1+ comprises a single high energy group of ions, whereas at the end of the pulse, ions are thermalized due to collisions with Ar and the IEDF comprises both a low energy group of ions and a high energy group of ions. Finally, after 320 mu s from the start of the pulse only a main low energy peak is present. The IEDF of Ar1+ comprises an intense low energy peak and a high energy shoulder, the latter appearing simultaneously with the high energy Cr ions and probably created due to collisions with the hot metal ions. After the pulse only a low energy group of ions of Ar1+ IEDF was detected. The temporal evolution of the total ion density extracted from Langmuir probe measurements is linked with metal ion-to-gas ion ratios giving an insight into the time evolution of deposition fluxes in the plasma. The influence of the time evolution of IEDF and plasma composition on the thin film growth is discussed.