Copper pumping behaviors of TSV and experimental investigations of the mechanism

Abstract

Through-silicon-Vias (TSV) is a key component of 3D packaging, its reliability is the core concern of engineers. Annealing is usually though to be an effective way to remove the residual stress in TSV, however, it was reported that copper pumping occurred during this process, while the interface of copper filler and Silicon chip was kept intact, and we have shown that residual stress of TSV was increased rather than decreased after annealing due to copper pumping. Besides the case of annealing, copper pumping also occurred during thermal cycling, and the pumped height increased with the number of cycles, the RDL was even broken by over large plastic deformation caused by copper pumping. In this paper, the micro-mechanism of the copper pumping was investigated with the aid of experiment and theoretical analysis. Signal of acoustic emission was monitored during the annealing of TSV and no obvious signal due to plastic deformation was found. Then it was suggested that creep of interfacial layer between copper filler and silicon chip should be responsible for the copper pumping.