Improving optical thickness monitoring by including systematic and process-influenced transmittance deviations

During optical monitoring using broadband transmittance measurement, the accuracy depends on how both the substrate and the optical path are aligned. We present a correction procedure to improve the accuracy of the monitoring, even if the substrate has features such as absorption or if there is misalignment of the optical path. The substrate in this case can either be a test glass or a product. The algorithm is proven by experimental coatings which were produced with and without the correction. Additionally, the optical monitoring system was also used to perform an in situ quality check. The system allows a detailed spectral analysis of all substrates with a high position resolution. Both plasma and the temperature effects on the central wavelength of a filter are identified. This knowledge enables the optimization of the following runs.