Two generations of the EOSS^® coating platform

The production of complex optical coating stacks requires precise interaction between equipment, process control, and monitoring. The EOSS^® platform combines robust system technology with data-driven process control. The CARS process ensures precise oxide layers, while MOCCA^+® monitors deposition rates, stoichiometry, and gradient profiles in real time – delivering reproducible precision optics on an industrial scale. 

A platform for precision optical coatings

EOSS^® (Enhanced Optical Sputtering System) is the industrially proven platform for precision optical coatings developed at Fraunhofer IST. The first generation, implemented as the FHR.Star EOSS^®, introduced key technological concepts: a rotating substrate holder, dual rotatable cylindrical cathodes, and reactive-gas-free mixed-target processes. The upward-facing geometry reduces particle contamination, while integrated in-situ measurement methods enable stable process control. This allows uniformities of more than 99.8 percent to be achieved over periods of several weeks. In this system configuration, double-sided coating is still performed by manually turning the substrates. 

Second Generation: EOSS^®/OPTA X 

The second generation of the platform significantly expands this concept. OPTA X systems enable simultaneous double-sided coating of substrates – a decisive advantage for thin wafers or glass substrates, as well as sensitive optical components. At the same time, longer service life, higher deposition rates, and automated workflows enable stable 24/7 operation with increased throughput.

Digital process control with MOCCA^+® 

The MOCCA^+® software platform complements these system concepts with model- and data-driven control and monitoring of the processes. In-situ measurement techniques such as broadband transmission measurement, optical plasma monitoring, or spectroscopic ellipsometry enable precise control of deposition rate, stoichiometry, and layer thickness distribution.

CARS process for stable oxide layers 

At the heart of this development is the CARS process (Compound-assisted reactive sputtering). In this process, sputtering occurs without reactive gas directly at the cathode, while the chemical reaction for oxide formation takes place spatially separated in a downstream plasma. The result is stoichiometrically precise, low-loss oxide layers with high process stability. 

 This combination of a stable hardware platform and data-driven process control enables scalable precision optics – from wafer-level filters to complex multi-gradient filters for applications in the automotive industry, semiconductor manufacturing, medical engineering, and aerospace.

”With the EOSS^® platform, we combine the highest level of optical precision with industrial productivity. The key lies in the interplay between robust system technology, innovative process concepts, and data-driven process control.”

Dipl.-Phys. Stefan Bruns, Senior Scientist