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The time evolution of the positive ion energy distribution functions (IEDF's) at the substrate position in an asymmetric bipolar high-power impulse magnetron (HiPIMS) system was determined using a gridded energy analyser. This was done for a range of operating conditions, namely the positive voltage U rev  and “on-time” negative pulse duration τ neg . The magnetron was equipped with a Nb target. Based on the knowledge of the IEDF's, the bombarding ion flux density Γ i  and energy flux density Q i  to a grounded surface were calculated. Time-resolved IEDF measurements showed that ions with energies approaching the equivalent of the positive pulse voltage U rev  were generated as the reverse positive voltage phase developed.   On time-average, we observed that increasing the set U rev  value (from 0 to 100 V), resulted in a marginal decrease in the ion flux density Γ i  to the analyser. However, this is accompanied by a 5-fold increase in the ion energy flux density Q i  compared to the unipolar, U rev  = 0 V case. Reducing the negative HiPIMS pulse duration τ neg  (from 130 to 40 µs) at a constant discharge power leads to a modest increase in Γ i , but a 4-fold increase in Q i . The results reveal the benefit of the bipolar HiPIMS technique, in which it is possible to control and enhance the power density of ions bombarding a grounded (or fixed bias) substrate, for potentially better tailoring of thin film properties.

Ion energy analysis of a bipolar HiPIMS discharge using a retarding field energy analyser