Backside Thermal Fault Localization Using Laser Scanning Confocal Thermoreflectance Microscopy Based on Auto-Balanced Detection

In this paper, we propose a sensitivity-enhanced thermoreflectance microscopy (TRM) system employing an electronic auto-balancing photoreceiver for effective thermal fault localization through a Si substrate. The proposed system in the auto-balanced detection not only improves the system signal-to-noise ratio (SNR) by approximately five times compared to that achievable via normal detection but also mitigates the inherent system noise, such as pseudothermoreflectance signals, by using the optical zooming. Moreover, temperature variations as small as ~47 mK were detectable under the measurement conditions employed in this paper. Finally, we experimentally demonstrated clear localization of a thermal fault, which was dimly visible in the normal backside detection results, in an optical zoomed thermal image.