Subpixel Cross Correlation Registration for High Spatial Resolution Thermal Image on IGBT Emitter Metallization by Thermoreflectance Measurements

The technological evolution of high power components involves a strong increase in power densities for smallest structures. It is necessary to determine the thermal constraints because efficiency and reliability are strongly influenced by device self-heating on the micron scale.Thermoreflectance microscopy technique is an optical resolution, non-invasive technique used for quick failure analysis and temperature profiling. It is a non-contact optical method which use the local reflectivity variations induced by heating to measure temperature. Reflectivity variations are determined by image measurements at hot and cold conditions. Due to thermal expansion and drift in apparatus, surface shifts are generally observed. Since measurement is dependent on the change in reflectivity of the materials, these shifts in the image play a huge role in the errors measured.Image registration is therefore mandatory if we want to be able to obtain thermal images without artefacts. Since displacements are not necessarily integer multiples of pixels, a subpixel registration may be necessary in order to further increase measurements spatial resolution. This effort described the effect of subpixel registration on the calculation of reflectivity variation images obtained on IGBT emitter metallization by thermoreflectance.