Fraunhofer Institute for Surface Engineering and Thin Films IST
Interface of MOCCA+® during the coating process.
Development of a fully automated monitoring system to control the production of optical coatings
Challenge
The designs of optical interference filters often consist of a large number of layers. With several hundred individual layers, besides the stability of the coating process itself the layer thicknesses required to achieve the transmittance or reflectance specifications on the product must also be controlled very precisely. The optical monitoring is the key to reach the desired precision and improvements allow for more and more complex filter designs.
Solution
The MOCCA+® system1 (Modular Optical Coating Control Application) consisting of hardware and software has been developed for industrial usage over the past 15 years. The software takes care of all the process steps, from fitting out the system, through process settings and coating-thickness control, to quality control at the end. A broadband spectrometer is used to continuously determine transmission or reflection, from UV to NIR, of the product or a special monitoring substrate. Several times per second, the algorithms determine the time remaining until the layer is complete. MOCCA+® directly communicates with the programmable logic controller (PLC) to control the components of the coating system. The interface of MOCCA+® during the coating process is shown in the first picture below.
Added value
The implementation of taReo as an additional tool into the MOCCA+® software was performed successfully. Proof of concept tests were conducted at the EOSS® coating machine at BTE (see picture below) during normal production. The first very impressive results have been reported at the SVC conference in Washington D.C. in May 20232. Further developments of taReo as well as MOCCA+® offer great opportunities to lower coating thickness errors in complex optical interference filters.
1 S. Bruns et al., Improving optical thickness monitoring by including systematic and process-influenced transmittance deviations, Appl. Opt. 62, B141-B147 (2023
2 Abstract ”Extending the Potential of Optical Monitoring Software by Full Machine Control and Quality Assurance”.
Insights into the project
The project partners
The department ”Optical Systems and Applications” of Fraunhofer Institute for Surface Engineering and Thin Films IST, OTF Studio GmbH, and BTE GmbH cooperate in the development of a fully automated monitoring to control the production of optical coatings:
Fraunhofer IST provides expertise in the development of optimal optical coatings process chains based on a broad spectrum of thin film materials and multilayer coatings. The optical interference filters often consist of many dozens or even hundreds of layers. With several hundred individual layers, the coating process must be kept very stable. The exact thicknesses which are required to achieve the demanding specifications in transmission or reflection on the final product must also be controlled very precisely in each case.
With a broad variety of different vacuum technologies, the BTE team modifies the physical surface properties of glasses, plastics and metals with innovative coating designs so that reflection, transmission and emission behavior meet the requirements of the customers’ applications. Thin dielectric and metallic coatings allow high-precision adjustments of optical surface characteristics.
Team members of OTF Studio have many years of expertise in development of cutting-edge design, characterization, and process-control software. One of the software products, taReo is a powerful tool for support of production of multilayer optical coatings in deposition machines equipped with broadband optical monitoring. taReo algorithms are highly effective, and they need only a fraction of seconds to characterize or re-optimize a coating being produced based on in-situ measurement data flow.
EOSS® coating machine at BTE.
Schematic of a deposition plant equipped with BBM and taReo.
Implementation of taReo into a fully automated deposition process.