Testglass changer for direct optical monitoring

Abstract

For the production of high performance multilayer systems with tight specifications and large numbers of layers optical monitoring is essential. Substantial progress was achieved by the introduction of direct monitoring on the rotating substrate holder. Pre production analysis by computer simulation of coating processes helps to optimise monitoring strategies and reduces the effort for expensive and time consuming test runs significantly. However not in any case we can find error compensating monitoring strategies. Also we have to deal with error accumulation effects especially with multi layer systems with large number of layers. Changing the monitor glass after the layer stack is deposited partly is a useful method to discontinue accumulation or to simplify the monitoring strategy. A testglass changer which helps to suppress error accumulation was developed and automized. The testglasses are located on the rotating substrate holder which may be a calotte or a plane substrate holder. It combines the advantages of direct monitoring with the flexibility to change testglasses in a fully automatic process. The basic principle will be described. Results of multilayer systems demonstrate the benefits of the newly developed testglass changer.