From independent thickness monitoring to adaptive manufacturing: advanced deposition control of complex optical coatings

Ever increasing demands in the field of optical coating systems with highest complexity impose new challenges on the development of advanced deposition techniques with increased stability, and especially on the corresponding precise thickness monitoring strategies. Most of the classical thickness monitoring concepts employed in industrial production, which are based on quartz crystal or optical monitoring, are presently operated near to their precision limits. However, resulting from extensive research activities, monitoring concepts could be significantly extended during the last years. On the one hand, newly developed hybrid process control algorithms combine the information of the optical and non-optical sensors to achieve a higher precision and fault-tolerance. On the other hand, independent thickness monitors are integrated in flexible manufacturing concepts which include adapted computational manufacturing tools as well as specific re-calculation and design re-optimization modules. Computational manufacturing allows for a design pre-selection prior to deposition with essentially improved certainty which could not be achieved with classical error analysis until now. In contrast, the re-calculation and re-optimization modules are on-line tools that monitor the running deposition process. In case of critical deviations, a fully automated modification of the residual design assures a successful achievement of specifications under the chosen monitoring technique.