Sputtering platform for double-sided precision optical coatings

Market drivers for the increasing demand for optical interference coatings on planar substrates and lenses include data communication systems and consumer electronics. Magnetron sputtering can deliver environmentally stable coatings with high throughput. Low defect densities combined with high stability of the process and coating system enable complex optical layer designs with very accurate reproducibility. Cylindrical targets are well known for coatings on large area such as window glass, but are rarely used for coating stacks with high layer counts. With the OPTA X, we are introducing a rotary target-based platform that takes advantage of the long-term stable deposition rate and high material utilization of these sputtering sources. Cylindrical targets have almost no re-deposition zone and no deep racetracks due to rotation. This strongly reduces the potential of particle generating arcs that are caused by surface charges in oxidized target areas. We also use substoichiometric target material sputtered in a pure argon atmosphere without the need for further reactive gas process control. Oxidation is performed by a plasma source in a pressure-separated plasma oxidation zone. The platform can be equipped with sputter sources in a sputter-up or sputter-down configuration or in a combination of both. Interesting applications for double-sided filter coatings include beam splitters for aerospace applications or filter deposition on thin glass substrates to compensate for layer stresses and associated geometric deformations. The elimination of substrate flipping for double-sided coatings also enables shorter production times and offers potential for cost savings.
In this paper, we are presenting preliminary optical properties as well as deposition rates of SiO2 and Nb2O5 oxide films. Furthermore, we are showing results of optical single layers as well as examples of filter coatings prepared by broadband transmittance monitoring and process control.