Pulse repetition frequency control for balancing ionized flux fraction and deposition productivity in chromium HiPIMS

This work addresses one aspect of process control in chromium thin-film deposition by high-power impulse magnetron sputtering (HiPIMS): the influence of pulse repetition frequency under constant pulse energy. In these conditions, the influence of repetition frequency was decoupled from variations in pulse energy, although the average power increased with frequency. The results reveal a transition between two distinct operating regimes. At low repetition frequencies (50-150 Hz), the ionized flux fraction (IFF) increases with frequency, which is consistent with an increasing influence of residual plasma persisting between pulses. However, above a transition region of approximately 200-350 Hz, the IFF approaches a plateau, while both the absolute ionized and neutral chromium fluxes continue to increase with repetition frequency. Consequently, further increases in frequency no longer increase the ionized fraction of the flux reaching the substrate; instead, it enhances the transport of both ionized and neutral sputtered species while maintaining an approximately constant ionized flux fraction. As a result, operating conditions can be selected to maximize the deposition rate without compromising the ionized fraction of the total deposited flux, providing a pathway toward more sustainable PVD processing through shorter deposition times and reduced discharge energy expenditure per unit deposited thickness.