Improvement of phase detection sensitivity of thermal microscope by controlling thermal conductivity of reflective film

Abstract

We used the periodic heating thermoreflectance (TR) method with micro-scale spatial resolution to measure thin films of Al and Mo. The TR method evaluates the phase lag of the thermoreflectance signal (TR signal) from the sample of the detection laser to the periodically modulated heating laser. In this paper, the effects of different physical properties of the thin film are evaluated from simulations and measurements using 3D heat conduction analysis. In the simulations, the beam diameter was measured by image processing in order to approximate the actual measurement conditions. Comparing the simulation results with the measurement results, the frequency dependence of the thermal diffusion length was confirmed for Mo thin film samples, but for Al thin film samples, Si and Ge showed different frequency characteristics from the simulation results. In actual measurements, the YSZ and pyrex of Al thin film did not show any difference in phase delay between the samples compared to that of Mo thin film. Future work includes finding measurement conditions that are compatible with the reflection coefficient of Al thin film and evaluating the TR signal.