Direct optical monitoring on the rotating substrate holder

Single wavelength optical monitoring is frequently applied in large box coaters. In state‐of‐the‐art optical coating systems a testglass changer with stationary test glasses is used for thickness monitoring while the substrates are located on a rotating substrate holder. The accuracy of this so‐called indirect monitoring technique is mainly limited by variations of the tooling factor. Direct monitoring on a substrate which is located on the rotating substrate holder avoids these errors and takes advantage of automatic thickness error compensation effects. The paper reports substantial progress which has been achieved for coating systems with large area substrate holders (up to ∅︁ 1500 mm). Intermittent monitoring on a substrate or a witness was applied. This technique enables rapid prototyping with tight specifications and high yields in large area batch coaters. Application results of challenging optical multilayer systems are clearly demonstrating the potential of this powerful monitoring technique. The monitoring capability was investigated for a lot of different layer systems such as dielectric mirrors, anti‐reflection coatings, sophisticated edge filters, polarizer coatings, beam splitters, multiple cavity band‐pass filters and notch filter coatings. Strong coincidence of theory with experiment was achieved with plasma ion assisted deposition (PIAD) and magnetron sputtering. Reproducibility experiments have clearly shown the benefits of this monitoring technique.