The role of gas impurities on the optical properties of sputtered Ti(Al)N coatings

In this study, we investigated the role of impurities, such as H, C, and O on the optical properties of the Ti(Al)N coatings. For comparison, coatings were prepared by direct-current magnetron sputtering (DC-MS) and high-power impulse magnetron sputtering (HiPIMS) at the same average power. The elemental composition of the thin films was measured by elastic recoil detection analysis. Regardless of the deposition technique used, no significant difference in H and C concentrations were found. The analysis showed, that HiPIMS coatings contain less O impurities than the corresponding DC-MS films, despite the lower deposition rate. The reduced residual O content in HiPIMS coatings can be explained by the cleaning effect of the bombarding ions. Moreover, densification effects presumably suppress post-deposition oxidation. Given the reduced O content, HiPIMS films showed higher optical reflectance for the entire measured spectral range.