Calibration procedure for temperature measurements by thermoreflectance under high magnification conditions

We show that, in thermoreflectance measurements under high focusing conditions, the signal is not only due to the surface temperature variations. Indeed, the reflected light from the device under test interferes with the incoming one, making a parasitic Fabry-Pérot. Besides, the motion of the sample surface induced, for example, by Joule heating, can produce an additional signal superimposed on the thermoreflectance one. Consequently, reliable thermoreflectance measurements under high focusing conditions, and particularly their calibration, demand a control of the distance between the objective and the sample. Using a servo loop to maintain the distance between the objective and the device constant, thermoreflectance measurements have been made in transient regime on an electronic device and the thermoreflectance coefficient of gold has been deduced