Enhanced Thermoreflectance Imaging of Trench IGBT Devices Using Multi-Focus Optical Reconstruction

Power electronics particularly in electric vehicle applications demand increasingly compact and high-performance components such as Insulated Gate Bipolar Transistors (IGBT). Modern trench IGBT architectures while offering enhanced electrical performance introduce significant challenges for thermal characterization due to their complex three-dimensional geometry and non-planar surfaces. In this work, we present a novel optical image reconstruction method designed to improve the signal-to-noise ratio in thermoreflectance imaging for 3D structures. The method involves generating an optimized optical image at each temperature by combining data acquired at multiple focal planes and under various illumination conditions. A normalized focus criterion is used to select the most in-focus pixels across the image stack enabling the reconstruction of high-quality optical images with an enhanced S/N ratio prior to reflectivity calculation. The approach is applied to two different trench IGBT devices (300A, 1200V) and (200A, 600V) with different structures subjected to a fixed temperature variation. This process results in a more homogeneous and accurate reflectivity map enabling more reliable temperature measurements and supporting improved thermal analysis of advanced power semiconductor devices.