BA: Simulation of a three-zone furnace for ammonothermal crystal growth

4. Dezember 2025

Michael Mischin –

Through a combination of experimental analysis and theoretical modeling, this work contributes to the optimization of fabrication processes in SiC-based power devices. The findings demonstrate the advantages of optical characterization techniques for non-destructive and high-precision measurements of layer thickness to enhance the performance and cost-effectiveness of SiC trench-MOSFETs. Previous research has shown that the optical properties of materials like poly-Si, SiO2, and SiC are crucial for determining layer thickness and optimizing device performance. However, the complex nature of these materials, combined with the requirements of the SiC trench-MOSFET fabrication process, necessitates a thorough investigation of their optical characteristics. Spectroscopic ellipsometry enables the determination of optical parameters, such as refractive index and extinction coefficient and the determination of layer thickness.

Furthermore, the spectroscopic reflectometry is used to measure the polycrystalline silicon (poly-Si) thickness and the reflection of the wafer. By combining the gained refractive index and extinction coefficient with the reflection values, the poly-Si layer thickness can be fitted. Performing these steps on wafers with doped and undoped poly-Si layers, where different thicknesses for the poly-Si layers are analyzed ranging from 60 nm to 1.4 μm, the optical parameters and thicknesses from different characterization methods can be compared. The most accurate optical parameters are gained by integrating the roughness of the wafer into the fitting process. Comparisons showed that a higher poly-Si thickness leads to a higher goodness of fit (GOF), which shows a less accuracy of thickness and optical parameters for thicker layers. Additionally, the refractive index and extinction coefficient of poly-Si are influenced by the thickness of the poly-Si layer.