Improved thermoreflectance imaging of trench IGBT via focus and illumination optimized reconstruction

In this paper, we improved the signal-to-noise ratio (S/N) of thermoreflectance images of trench Insulated Gate Bipolar Transistors (IGBT) particularly in low-intensity areas caused by insufficient illumination or defocusing due to topography and depth variations within these components. To enhance and homogenize signal intensity across the entire surface, we accurately determined the focal planes and optimal lighting conditions for each region. Then, before performing reflectivity calculations, we reconstructed a single high intensity optical image by selecting pixels based on their local focus values. This optical image reconstruction ensures a uniform distribution of maximum intensity across the image and significantly improvises the S/N ratio minimizing artifacts in the final reflectivity map. • S/N ratio improved in thermoreflectance images of trench IGBT devices. • Low-intensity zones corrected via focus and illumination optimization. • A single sharp optical image was reconstructed from multiple focal planes. • Uniform high intensity improves reflectivity map quality and accuracy. • Method reduces artifacts due to topography and depth variations.