Stefan Bruns¹, Philipp Henning¹, Thomas Melzig¹, Thomas Schütte², Jörg Terhürne³, Michael Vergöhl^1
1Fraunhofer Institute for Surface Engineering and Thin Films IST, Braunschweig, Germany²; PLASUS GmbH, Mering, Germany³; Bte Bedampfungstechnik GmbH, Elsoff, Germany
Nowadays, almost all coating machines for high precision optical interference filters include at least one kind of monitoring which can be based on broad band or single wavelength transmittance or reflectance measurement. The Modular Optical Coating Control Application (MOCCA+) was developed at the Fraunhofer IST for turntable metamode sputtering machines (e.g. EOSS) and includes an interface to the programmable logic controller. All material recipes and stack procedures are stored in a database. Thus, the user does not need to do any further scripting at the user interface of the machine. This helps for quick product feature changes. Once defined a coating batch, only the substrates need to be loaded into the vacuum transfer magazine. From the handling into the machine the process is fully automated up to the final measurement to check the products. We show in situ high resolution characterization including thermal effects on the realized spectra.
The techniques that are used in optical monitoring software may also be transferred to other types of coating machines and adapted to customer needs. Only the sensor changes but the algorithms for security and reinitialization after shutdowns remain the same. Due to the modular structure, e.g. ellipsometry, quartz crystal or plasma optical emission spectroscopy can be integrated. Multi-channel OES measurement and data evaluation along the coating process will be presented. Plasma conditions during different situations like shutter movements and material changes are evaluated up to end of lifetime detection of sputter targets.
Digitizing the whole process chain in one software package allows for data mining and machine learning. The analysis results of measurements connected with machine parameters allow for a closed loop. Thereby, the software can learn during the coating e.g. the actual deposition rate if further layers are deposited by time or is able to include spectral shifts into the calculation.