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

High power impulse magnetron sputtering (HiPIMS) is an ionized physical vapour deposition technique. While HiPIMS provides a high flux of metal ions to the substrate, the disadvantage is a reduced deposition rate compared to direct current magnetron sputtering (dcMS) at equal average power. This is mainly due to the high target back-attraction probability of the metal ions with typical values in the range 70%–90% during the pulse. In this work, we investigate how to reduce this effect by quantifying the contribution of the metal ion flux after each HiPIMS pulse, a period also known as afterglow. Without a negative potential on the target at this stage of the HiPIMS process, the back-attracting electric field disappears allowing remaining ions to escape the ionization region. In order to analyze the fate of the film-forming ions, we extend the time-dependent ionization region model (IRM) by adding consideration of an afterglow. This approach allows to distinguish between fluxes from the ionization region during the pulse and during the afterglow. We show that by shortening the pulse length of a titanium HiPIMS discharge, the contribution to the outward flux of film-forming species from the afterglow increases significantly. The IRM predicts a gain in deposition rate of 46% and 47% for two discharges with different peak discharge currents, when using 40 μ s compared to 100 μ s-long pulses at the same average power. This is without compromising the ionized flux fraction that remains constant for the range of pulse lengths investigated here.

In high power impulse magnetron sputtering (HiPIMS) operation, there are basically two goals: a high ionized flux fraction of the sputtered target material and a high deposition rate. In this work, it is demonstrated that the former always comes at the cost of the latter. This makes a choice necessary, referred to as the HiPIMS compromise. It is here proposed that this compromise is most easily made by varying the discharge current amplitude, which opens up for optimization of additionally four external process parameters: the pulse length, the working gas pressure, the magnetic field strength, and the degree of magnetic unbalance to achieve the optimum combination of the ionized flux fraction and the deposition rate. As a figure of merit, useful for comparing different discharges, (1−βt) is identified, which is the fraction of ionized sputtered material that escapes back-attraction toward the cathode target. It is shown that a discharge with a higher value of (1−βt) always can be arranged to give better combinations of ionization and deposition rate than a discharge with a lower (1−βt). Maximization of (1−βt) is carried out empirically, based on data from two discharges with Ti targets in Ar working gas. These discharges were first modeled in order to convert measured plasma parameters to values of (1−βt). The combined effects of varying the different process parameters were then analyzed using a process flow chart model. The effect of varying the degree of unbalance in the studied range was small. For the remaining three parameters, it is found that optimum is achieved by minimizing the magnetic field strength, minimizing the working gas pressure, and minimizing the pulse length as far as compatible with the requirement to ignite and maintain a stable discharge.

The magnetic field is a key feature that distinguishes magnetron sputtering from simple diode sputtering. It effectively increases the residence time of electrons close to the cathode surface and by that increases the energy efficiency of the discharge. This becomes apparent in high power impulse magnetron sputtering (HiPIMS) discharges, as small changes in the magnetic field can result in large variations in the discharge characteristics, notably the peak discharge current and/or the discharge voltage during a pulse. Here, we analyze the influence of the magnetic field on the electron density and temperature, how the discharge voltage is split between the cathode sheath and the ionization region, and the electron heating mechanism in a HiPIMS discharge. We relate the results to the energy efficiency of the discharge and discuss them in terms of the probability of target species ionization. The energy efficiency of the discharge is related to the fraction of pulse power absorbed by the electrons. Ohmic heating of electrons in the ionization region leads to higher energy efficiency than electron energization in the sheath. We find that the electron density and ionization probability of the sputtered species depend largely on the discharge current. The results suggest ways to adjust electron density and electron temperature using the discharge current and the magnetic field, respectively, and how they influence the ionization probability.

We study the microstructure and magnetic properties of Ni ₈₀ Fe ₂₀ thin films grown by high power impulse magnetron sputtering (HiPIMS), and compare with films grown by dc magnetron sputtering (dcMS). The films were grown under a tilt angle of 35° to identical thickness of 37 nm using both techniques, at different pressure (0.13–0.73 Pa) and substrate temperature (room temperature and 100 °C). All of our films display effective in-plane uniaxial anisotropy with square easy axis and linear hard axis magnetization traces. X-ray diffraction reveals that there is very little change in grain size within the pressure and temperature ranges explored. However, variations in film density, obtained by x-ray reflectivity measurements, with pressure have a significant effect on magnetic properties such as anisotropy field ( H _k ) and coercivity ( H _c ). Depositions where adatom energy is high produce dense films, while low adatom energy results in void-rich films with higher H _k and H _c . The latter applies to our dcMS deposited films at room temperature and high pressure. However, the HiPIMS deposition method gives higher adatom energy than the dcMS and results in dense films with low H _k and H _c . The surface roughness is found to increase with increased pressure, in all cases, however it showed negligible contribution to the increase in H _k and H _c .

Background: Oblique angle deposition is known for yielding the growth of columnar grains that are tilted in the direction of the deposition flux. Using this technique combined with high-power impulse magnetron sputtering (HiPIMS) can induce unique properties in ferromagnetic thin films. Earlier we have explored the properties of polycrystalline and epitaxially deposited permalloy thin films deposited under 35° tilt using HiPIMS and compared it with films deposited by dc magnetron sputtering (dcMS). The films prepared by HiPIMS present lower anisotropy and coercivity fields than films deposited with dcMS. For the epitaxial films dcMS deposition gives biaxial anisotropy while HiPIMS deposition gives a well-defined uniaxial anisotropy.Results: We report on the deposition of 50 nm polycrystalline nickel thin films by dcMS and HiPIMS while the tilt angle with respect to the substrate normal is varied from 0° to 70°. The HiPIMS-deposited films are always denser, with a smoother surface and are magnetically softer than the dcMS-deposited films under the same deposition conditions. The obliquely deposited HiPIMS films are significantly more uniform in terms of thickness. Cross-sectional SEM images reveal that the dcMS-deposited film under 70° tilt angle consists of well-defined inclined nanocolumnar grains while grains of HiPIMS-deposited films are smaller and less tilted. Both deposition methods result in in-plane isotropic magnetic behavior at small tilt angles while larger tilt angles result in uniaxial magnetic anisotropy. The transition tilt angle varies with deposition method and is measured around 35° for dcMS and 60° for HiPIMS.Conclusion: Due to the high discharge current and high ionized flux fraction, the HiPIMS process can suppress the inclined columnar growth induced by oblique angle deposition. Thus, the ferromagnetic thin films obliquely deposited by HiPIMS deposition exhibit different magnetic properties than dcMS-deposited films. The results demonstrate the potential of the HiPIMS process to tailor the material properties for some important technological applications in addition to the ability to fill high aspect ratio trenches and coating on cutting tools with complex geometries.