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 | B | and geometry (degree of balancing) on the deposition rate and ionized flux fraction F flux 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 | B | decreased. In contrast, when operating the HiPIMS discharge in fixed peak current mode, the deposition rate increased only slightly with decreasing | B | . In fixed voltage mode, for weaker | B | , the higher was the deposition rate, the lower was the F flux . In the fixed peak current mode, both deposition rate and F flux increased with decreasing | B | . Deposition rate uniformity measurements illustrated that the dcMS deposition uniformity was rather insensitive to changes in | B | 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 | B | and in particular the magnetic field topology. We related the measured quantities, the deposition rate and ionized flux fraction, to the ionization probability α t and the back attraction probability of the sputtered species β t . We showed that the fraction of the ions of the sputtered material that escape back attraction increased by 30% when | B | was reduced during operation in fixed peak current mode while the ionization probability of the sputtered species increased with increasing | B | , due to increased discharge current, when operating in fixed voltage mode.

Oblique angle deposition of nickel thin films by high-power impulse magnetron sputtering

“…There have been a few investigations on this matter that all agree that the magnetic field plays a significant role in the profile of deposition. We have recently shown that, depending on the stationary magnetic field configuration, HiPIMS deposition may result in a more uniform film thickness than dcMS deposition [31]. Furthermore, Qiu et al [56] showed that the target voltage, magnetic field strength and geometry can affect the shape of the racetrack and the target utilization.…”

“…On the other hand, it has been demonstrated that a small decrease in the magnetic field strength in the HiPIMS process can lead to a significant increase in the deposition rate in that case [28–29]. We have recently reported an increase by a factor of 2 and 2.6 of the HiPIMS deposition rate by 83% and 53% weakening of the magnetic field strength (at racetrack) using vanadium [30] and titanium [31] targets, respectively. Thus, utilizing HiPIMS for the deposition of ferromagnetic material can be very beneficial.…”

On the electron energy distribution function in the high power impulse magnetron sputtering discharge

“…The ionized flux fraction F flux and the deposition rate were measured at 30 mm above the racetrack using a gridless ion meter [82]. For details on the experiments and the magnetic field topology, see Hajihoseini et al [80]. The discharge was generated using a magnetic field configuration denoted C0E0 [80], which indicated that both the center and edge magnets sit next to the back of the cathode target and give the highest magnetic field strength (parallel to the target surface) in the cathode target vicinity just above the target racetrack.…”

“…The EEDF is discretized using non-equal energy intervals [38] between 0 eV and a value above the energy that corresponds to the sheath voltage eV SH . The secondary electrons are injected into the discharge volume at an [80], the IRM fitting parameters [31], and the energy discretization parameters for OBELIX. energy close to the energy corresponding to the sheath voltage…”

Engineered ion-bombardment as a tool in thin film deposition

“…[71]. Several published works have tried to address this problem by modifying the magnetic field strength and orientation of either the magnetron or that of an external magnetic field [74][75][76][77][78]. Another simpler way to increase the deposition rate in HiPIMS is to modify the pulse parameters, e.g.…”