Quantitative Thermoreflectance Imaging: Calibration Method and Validation on a Dedicated Integrated Circuit

We have developed a charge-coupled device-based thermoreflectance microscope which can deliver thermal images of working integrated circuits. However, in any thermoreflectance experiment, the coefficient linking reflectance variations to temperature is different for each material. Calibrations are therefore necessary in order to obtain quantitative temperature imaging on the complex surface of an integrated circuit including several materials such as aluminium and polysilicon. We propose here a system using a Peltier element to control the temperature of the whole package in order to obtain calibration coefficients simultaneously on all the materials visible on the surface of the circuit. Under high magnifications, vertical and lateral movements associated to thermal expansion are corrected using respectively a piezo electric displacement and a software image shifting. The thermoreflectance temperature measurements calibrated with this method are compared to the temperatures measured with separately calibrated thermocouples and diodes, and to a finite elements simulation.