Ellipsometric control of layer thickness during coating of nanolaminate layers

Optical thickness monitoring is implemented in almost all coating machines for high precision optical interference filters. Standard broadband transmittance monitoring comes to the limit of thickness resolution when e.g. nanolaminates are deposited. Ellipsometry is more sensitive for material dispersion and interfaces and gives more detailed information on the layers at the beginning of the stack. On the other hand, transmittance measurements can be used for designs with higher layer count with standard materials. In this contribution we show the integration of a broadband ellipsometer for the determination of thickness and material properties during the growing layers in a magnetron sputtering system with a turntable configuration. The ellipsometric angles Psi and Delta were measured at an angle of incidence of 70° and the deposition process was investigated for Ta2O5 and SiO2. The control substrate passes the measurement position every 240 ms. The triggering was optimized to match the exact position on the moving control substrate. In addition, results for nanolaminates are presented from the combination of amorphous silicon and silicon dioxide. The non-reactive magnetron sputtering process with separate oxidation by plasma source gives smooth surfaces even for sub-nm layers as revealed by TEM measurements. The thicknesses are reproducible and in good agreement with ellipsometry.