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Diamond coatings are considered a key technology for numerous industrial applications – from power electronics to optics to sensors. To enable these high-performance coatings to fully realize their potential, uniformity is crucial. Researchers at the Fraunhofer Institute for Surface Engineering and Thin Films IST have developed a new measurement and analysis method that allows the optical constants of large-scale diamond films to be determined with high precision and efficiency.
Uniformity of polycrystalline diamond coatings is a critical quality factor for their functionality and service life. However, conventional measurement methods reach their limits when measuring large-scale substrates, such as silicon wafers with diameters up to 300 millimeters. Material inhomogeneities, surface roughnesses, and complex layer structures make it difficult to obtain reliable measurements and cause the process control to be time-consuming and intensive.
Fraunhofer IST therefore takes a holistic approach and combines various measurement methods: Spectral photometry is used to examine how strongly a surface reflects or transmits light at different wavelengths. Depending on the material and layer thickness, the spectral reflection and transmission characteristics change. In addition, angle-dependent ellipsometry is used as a complementary method. It records how the state of polarized light changes after reflection at different angles of incidence and – like spectral photometry – enables the determination of the refractive index, extinction coefficient, and film thickness. Both measurement methods are based on different measurement principles and react with varying sensitivity to the film parameters. When combined, they therefore provide a significantly more robust and accurate characterization of the layers. Instead of evaluating the measurements individually, they are analyzed simultaneously at Fraunhofer IST using a global modeling approach. The basis is a specially developed multilayer model that realistically represents the polycrystalline diamond layer, including its roughness, and incorporates known optical material data. “By simultaneously evaluating all measurement data, we achieve significantly higher accuracy than with conventional individual measurements and can precisely determine the optical dispersion and other relevant coating parameters,” explains Dr. Volker Sittinger, Head of department “Diamond-based Systems” at Fraunhofer IST, highlighting the unique selling point of the new simultaneous fitting method.
The key advantage: Once the dispersion and all optical data have been reliably determined, the most time-consuming part of the analysis is complete, as there is no longer a need to tediously remeasure all data at every single point. Instead, a simple and quick reflectance measurement, applied to numerous measurement points across the entire surface, is sufficient to determine, for example, the film thickness and the resulting uniformity of the coating. This so-called reflection mapping allows efficient characterization of large-area diamond coatings.
For industrial customers, this means significantly reduced measurement time, improved process control, and the ability to specifically evaluate and optimize layer homogeneity over large areas. Using diamond-coated 300-mm silicon wafers as an example, it was demonstrated that improved process control can significantly reduce variations in film thickness. Thus, the method directly contributes to higher production quality and provides the foundation for high-performance and durable diamond coatings.
“With the measurement approach, we offer our partners a powerful solution for quality and process control in modern diamond coating systems. This fast, robust, and automatable method helps companies accelerate development and production processes, reduce scrap, and sustainably increase the reliability of their products,” explains Sittinger.
https://www.ist.fraunhofer.de/en/press-media/2026/precise-measurement-for-better...
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Elektrotechnik, Maschinenbau, Physik / Astronomie, Werkstoffwissenschaften
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