The Influence of Magnetic Field on the Deposition Rate and Ionized Flux Fraction in HiPIMS Discharges

Abstract

The influence of the magnetic field strength |B| and geometry (degree of balancing) on the axial’ and sideways <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> deposition rate and ionized flux fraction <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$F_{\text{flux}}$</tex> in dc magnetron sputtering (dcMS) and high power impulse magnetron sputtering (HiPIMS) when depositing titanium is explored. We find that the dcMS deposition rate is only 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 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\vert \mathrm{B}\vert, $</tex> the higher was the deposition rate, the lower was the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$F_{\text{flux}}$</tex> . In the fixed peak current mode, both deposition rate and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$F_{\text{flux}}$</tex> increased with decreasing |B|. We observe a significant deposition of the film forming material perpendicular to the target surface. This sideways deposition decreases with increasing axial distance from the target surface. The sideways deposition rate is always the highest in dc operation while it is lower for HiPIMS operation. The magnetic field strength has a strong influence on the sideways deposition rate in HiPIMS but not in dcMS2. Furthermore, in HiPIMS operation the radial ion deposition rate is always at least as large as the axial ion deposition rate, and often around two times higher. Thus there are significantly higher number of ions traveling radially in the HiPIMS discharge. We demonstrate that the total radial flux of film forming material is greater in dcMS compared to HiPIMS for almost all cases investigated. We therefore conclude that the commonly reported reduction of the (axial) deposition rate in HiPIMS compared to dcMS does not seem to be linked with an increase in sideways material transport in HiPIMS.