On the film density using high power impulse magnetron sputtering

The influence on thin film density using high power impulse magnetron sputtering (HiPIMS) has been investigated for eight different target materials (Al, Ti, Cr, Cu, Zr, Ag, Ta, and Pt). The density values as well as deposition rates have been compared to results obtained from thin films grown by direct current magnetron sputtering (DCMS) under the same experimental conditions. Overall, it was found that the HiPIMS deposited coatings were approximately 5-15% denser compared to the DCMS deposited coatings. This could be attributed to the increased metal ion bombardment commonly seen in HiPIMS discharges, which also was verified using a global plasma model to assess the degree of ionization of sputtered metal. One key feature is that the momentum transfer between the growing film and the incoming metal ions is very efficient due to the equal mass of film and bombarding species, leading to a less pronounced columnar microstructure. As expected the deposition rates were found to be lower for HiPIMS compared to DCMS. For several materials this decrease is not as pronounced as previously reported in the literature, which is shown in the case of Ta, Pt, and Ag with rate_HiPIMS/rate_DCMS~70-85%, while still achieving denser coatings.