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HiPIMS plasmas generate energetic metal ions at the substrate as a majordifference to conventional direct current magnetron sputtering. The origin ofthese ions is still an open issue, which is unraveled by using two fastdiagnostics: time resolved mass spectrometry with a temporal resolution of 2$\mu$s and phase resolved optical emission spectroscopy with a temporalresolution of 1 $\mu$s. A power scan from dcMS-like to HiPIMS plasmas wasperformed, with a 2-inch magnetron and a titanium target as sputter source andargon as working gas. Clear differences in the transport as well in theenergetic properties of Ar$^{+}$, Ar$^{2+}$, Ti$^+$ and Ti$^{2+}$ wereobserved. For discharges with highest peak power densities a high energeticgroup of Ti$^+$ and Ti$^{2+}$ could be identified. A cold group of ions isalways present. It is found that hot ions are observed only, when the plasmaenters the spokes regime, which can be monitored by oscillations in theIV-characteristics in the MHz range that are picked up by the used VI-probes.These oscillations are correlated with the spokes phenomenon and are explainedas an amplification of the Hall current inside the spokes as hot ionizationzones. To explain the presence of energetic ions, we propose a double layer(DL) confining the hot plasma inside a spoke: if an atom becomes ionized insidethe spokes region it is accelerated because of the DL to higher energieswhereas its energy remains unchanged if it is ionized outside. In applying thisDL model to our measurements the observed phenomena as well as severalmeasurements from other groups can be explained. Only if spokes and a doublelayer are present the confined particles can gain enough energy to leave themagnetic trap. We conclude from our findings that the spoke phenomenonrepresents the essence of HiPIMS plasmas, explaining their good performance formaterial synthesis applications.

Origin of the energetic ions at the substrate generated during high power pulsed magnetron sputtering of titanium