Quantitative analysis of void initiation in thermo-mechanical fatigue of polycrystalline copper films

Abstract The early stages of thermo-mechanical fatigue in 20-μm-thick copper films are studied using accelerated stress tests on poly‑silicon heater test chips. During loading, the samples are heated up from a base temperature of 100 °C to a maximum temperature of 400 °C within 200 μs with a waiting time of 1 s between subsequent pulses. With applied heating rates up to 106 K/s, followed by studies of microstructural damage after cycle numbers between 0 and 1000, the formation of voids at grain boundaries and triple points is revealed. With image processing on scanning electron microscopy images of stressed samples, void formation and growth as a function of cycle number is quantified. The results from metallography are compared to 3D reconstructions obtained by FIB tomography.