Quantitative thermal imaging by synchronous thermoreflectance with optimized illumination wavelengths

Using thermoreflectance microscopy with a camera, we have designed a system which delivers submicronic images of the alternative temperature variations in integrated circuits working in a modulated regime. A careful choice of the illumination wavelength permits us to highlight the heating in chosen parts of the sample and to optimize the thermoreflectance signal. We measure and explain the modifications of the photothermal response which are induced by the presence of a passivation layer. A calibration conducted on various materials with a thermocouple gives access to the absolute alternative temperature variations in integrated circuits working at frequencies between 0.1 Hz (quasipermanent regime) and 5 MHz.