Influence of Copper Pumping on Integrity and Stress of Through-Silicon Vias

Abstract

The influence of copper pumping on through-silicon vias (TSVs) under thermal loading was investigated using an in situ experimental technique. The morphology of the TSV and its evolution with temperature were observed by scanning electric microscopy, and the process of copper pumping and its damage to the integrity of the TSV were recorded. Some new failure modes were found. The maximum height of pumped copper was as high as $5~\mu \text{m}$ for a single thermal cycle and 25 $\mu \text{m}$ for multiple cycles. The thermal stress of the TSV and its evolution with temperature were then evaluated using a microinfrared photoelastic system. Full-field and real-time measurements were carried out. It was found that copper pumping at high temperature served to release stress and that this stress-free state of the TSV could be maintained. After cooling or annealing, however, the TSV stress again increased.