Defect and microstructural evolution in thermally cycled Cu through-silicon vias

• Three different thermal cycling profiles were used to study Cu TSV reliability.
• RF signal degradation increased with the maximum peak cycling temperatures.
• Cross-sectioning the Cu TSVs revealed void area scaled with cycling temperatures.
• Thermal cycling results in formation of voids, but not growth of preexisting voids.
• Cu grain size/orientation changes were negligible in pre- and post-cycled TSVs.

In this study, the effect of thermal cycling on defect generation, microstructure, and RF signal integrity of blind Cu through-silicon vias (TSVs) were investigated. Three different thermal cycling profiles were used; each differentiated by their peak cycling temperature (100 °C, 150 °C, 200 °C) and the time needed to complete one cycle (cycle time). The study was performed on two Cu TSV wafer sample types; one containing large processing-induced voids (voided sample), the other without (non-voided sample). It was found that the RF signal return loss |S11| of the Cu TSVs increased upon thermal cycling for both the voided and the non-voided sample types. This was attributed to the increase in the void area due to the formation of new voids, rather than the growth of preexisting voids. On the other hand, the grain orientation and grain sizes of the Cu TSVs were found to be unaffected by all studied thermal cycling conditions and sample types.