Monitoring the stress evolution of through silicon vias during thermal cycling with infrared photoelasticity

We have developed a micro-infrared photoelastic system to evaluate the stress of through-silicon-vias (TSV). It was found that the stresses of some TSVs increased after thermal cycling, and the scanning electron microscope revealed that those TSVs with stress increased had Cu filler pumped under thermal loading, but no interfacial fracture were observed. Then the annealed samples were heated up to 400°C and stresses of those TSVs were monitored during thermal cycling in real time mode. It was observed that stress of those TSVs decreased first and then increased again. However, with the continuous increase of temperature, the stress of each TSV finally vanished at different temperatures and their stress-free states were kept until 400C was reached. During and after the cooling process, photo-elastic fringes pattern appeared around each TSV again and some fringes became even brighter than before, which indicated that the stress of some TSVs had increased after experiencing another high temperature cycling.