Fraunhofer Institute for Surface Engineering and Thin Films IST
SEM image of a diamond coating on a silicon substrate with a native oxide layer. The grain size and roughness of the growing polycrystalline diamond coating increase with the thickness of the coating.
Determination of optical constants of large-area diamond coatings
Project SemiProcessing
Characterization of large-area diamond coatings
Large-area diamond coatings offer great potential for industrial applications – but place high demands on quality assurance and process control. A homogeneous film thickness and reproducible material properties across the entire wafer are crucial. This requires precise knowledge of the optical constants of diamond over a broad wavelength range. Conventional optical measurement methods provide valuable information, but they reach their limits as stand-alone methods, particularly when dealing with rough, polycrystalline layers and complex multilayer systems.
Fraunhofer IST’s holistic measurement approach
By strategically combining multiple measurement methods, significantly more robust and reliable conclusions about layer properties can be drawn. Fraunhofer IST has developed an integrated measurement and evaluation approach that combines spectral photometry and angle-resolved ellipsometry. All measurement data are simultaneously evaluated using a global modeling method. A specially developed multilayer model realistically represents diamond layers, including roughness, and integrates established optical material data. The simultaneous analysis of all measurement parameters enables significantly higher accuracy than traditional individual measurements and generates reliable process data. After determining the optical dispersion, large-area substrates can be characterized quickly and efficiently using reflection mapping, even for wafers up to 300 mm in diameter.
Efficient wafer characterization with high added value
Customers benefit from reduced measurement times, improved process control, and targeted optimization of layer homogeneity. The method thus provides a robust foundation for stable coating processes as well as for high-performance and durable diamond coatings in industrial applications.
Insights into the project
Schematic representation of a diamond layer on a silicon substrate with a native oxide layer. The grain size and roughness of the growing polycrystalline diamond layer increase with the thickness of the layer.
Example of a measured reflectance spectrum at a measurement point in the mapping, in the wavelength range from 250 to 1200 nm, with a fitted curve to determine the film thickness and roughness. To illustrate the range perceivable by the human eye, a color bar showing the visible spectrum is also displayed.
Comparison of a non-optimized and an optimized coating process. On the left in each case is a diamond-coated silicon wafer (300 mm), and on the right is the corresponding film thickness distribution (same film thickness scale for both wafers).
In the non-optimized process (left), the film thickness lies within the Min/Max range (913 nm/1081 nm), while in the optimized process (right), it lies within the Min/Max range (1013 nm/1059 nm). The greatest deviations occur at the wafer edges in each case.