Lawrence Berkeley National Laboratory

The commonly used current-voltage characteristics are found inadequate for describing the pulsed nature of the high power impulse magnetron sputtering (HIPIMS) discharge, rather, the description needs to be expanded to current-voltage-time characteristics for each initial gas pressure. Using different target materials (Cu, Ti, Nb, C, W, Al, Cr) and a pulsed constant-voltage supply it is shown that the HIPIMS discharges typically exhibit an initial pressure dependent current peak followed by a second phase that is power and material dependent. This suggests that the initial phase of a HIPIMS discharge pulse is dominated by gas ions whereas the later phase has a strong contribution from self-sputtering. For some materials the discharge switches into a mode of sustained self-sputtering. The very large differences between materials cannot be ascribed to the different sputter yields but they indicate that generation and trapping of secondary electrons plays a major role for current-voltage-time characteristics. In particular, it is argued that the sustained self-sputtering phase is associated with thegeneration of multiply charged ions because only they can cause potential emission of secondary electrons whereas the yield caused by singly charged metal ions is negligibly small.