Speaker
Description
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 Urev and “on-time” negative pulse duration neg. The magnetron sputtering discharge was equipped with a Nb target. Based on the knowledge of the IEDF's, the bombarding ion flux density $\Gamma_i$ 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 Urev 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 $\Gamma_i$ 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 neg (from 130 to 40 µs) at a constant discharge power leads to a modest increase in $\Gamma_i$, 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.
