Recent Diagnostic Studies of Unipolar and Bipolar HiPIMS Plasmas

   Using a Langmuir probe LP and laser Thomson scattering LTS, the temporal and spatial evolution of the plasma parameters (densities n_e and n_i, electron temperatures T_e, plasma V_p and floating potentials V_f) have been determined in a magnetron discharge operated in two pulsing regimes, 1) conventional unipolar pulsing and 2) asymmetric bipolar pulsing with a positive “kick” pulse.
   In the former case, LTS and LP methods yield good agreement for the electron properties (n_e, n_i and T_e) during both the main HiPIMS pulse and the long afterglow. In the second case, incorporating the “kick” pulse, LP measurements show a modified behaviour in the plasma, with somewhat raised ne and Te measurements during the voltage “kick” phase together with V_p values rising to values close the applied positive voltage over a period of 10’s of s after the “kick” transition.
   By comparing spatially-resolved LP results from unipolar and bipolar pulsing at the same discharge powers and pressures we see that the presence of the “kick” pulse leads to a re-distribution in ne after termination of the main HiPIMS pulse.
   A discussion of the diagnostic techniques and implications of the results will be given.