The Effect of Magnetic Field Strength and Geometry on the Deposition Rate and Ionized Flux Fraction in the HiPIMS Discharge

Abstract

We explored the effect of magnetic field strength (Formula presented.) and geometry (degree of balancing) on the deposition rate and ionized flux fraction (Formula presented.) in dc magnetron sputtering (dcMS) and high power impulse magnetron sputtering (HiPIMS) when depositing titanium. The HiPIMS discharge was run in two different operating modes. The first one we refer to as “fixed voltage mode” where the cathode voltage was kept fixed at 625 V while the pulse repetition frequency was varied to achieve the desired time average power (300 W). The second mode we refer to as “fixed peak current mode” and was carried out by adjusting the cathode voltage to maintain a fixed peak discharge current and by varying the frequency to achieve the same average power. Our results show that the dcMS deposition rate was weakly sensitive to variations in the magnetic field while the deposition rate during HiPIMS operated in fixed voltage mode changed from 30% to 90% of the dcMS deposition rate as (Formula presented.) decreased. In contrast, when operating the HiPIMS discharge in fixed peak current mode, the deposition rate increased only slightly with decreasing (Formula presented.). In fixed voltage mode, for weaker (Formula presented.), the higher was the deposition rate, the lower was the (Formula presented.). In the fixed peak current mode, both deposition rate and (Formula presented.) increased with decreasing (Formula presented.). Deposition rate uniformity measurements illustrated that the dcMS deposition uniformity was rather insensitive to changes in (Formula presented.) while both HiPIMS operating modes were highly sensitive. The HiPIMS deposition rate uniformity could be 10% lower or up to 10% higher than the dcMS deposition rate uniformity depending on (Formula presented.) and in particular the magnetic field topology. We related the measured quantities, the deposition rate and ionized flux fraction, to the ionization probability (Formula presented.) and the back attraction probability of the sputtered species (Formula presented.). We showed that the fraction of the ions of the sputtered material that escape back attraction increased by 30% when (Formula presented.) was reduced during operation in fixed peak current mode while the ionization probability of the sputtered species increased with increasing (Formula presented.), due to increased discharge current, when operating in fixed voltage mode.