Thermal source separation for 3D defect localization using independent component analysis (ICA) from time-resolved temperature response (TRTR)

Lock-In Thermography is an established nondestructively operating method for the analysis of failures in microelectronic devices. In recent years a major improvement was achieved allowing the acquisition of the time-resolved temperature responses of weak thermal spots that enhances defect localization in 3D stacked semiconductor architectures. The assessment of a defect's depth based on the numerical estimation of the delay of the thermal response by analyzing the value of the lock-in phase is often prone to thermal noise and parasitic effects. In sample structures that contain partial or full transparence for the infrared signal between the origin and the sample surface, the interference of the direct (radiated) and the conducted signal component largely falsifies the phase value on which the classical depth estimation relies on. In the present study blind source separation by independent component analysis of the thermal signals was successfully applied to allow separation of interfering signal components arising from direct thermal radiation and conductance for a precise estimation of the defect depth.