Low Temperature Fine-Pitch Wafer-Level Cu-Cu Bonding Using Nanoparticles Fabricated by PVD

Wafer-level Cu-Cu bonding with fine-pitch interconnection was realized with Copper nanoparticles (Cu NPs) fabricated by physical vapor deposition (PVD). Test vehicle design with 20μm fine-pitch Cu pad was introduced. Al wiring and TiW/Cu pads were fabricated on the silicon wafer. Cu NPs were then deposited on the substrate as surface modification by high pressure magnetron sputtering, and the morphology of Cu NPs was inspected by atomic force microscope (AFM). The wafer bonding process was accomplished at 200°C for 3min under the pressure of 40MPa, and the bonded wafers were diced into chips. Die shear test was carried out and an average strength of 18.50MPa was reached. The fracture surface after shear test was analyzed and mixed failure mode was observed. The cross-sectional view of the 20μm fine-pitch Cu-Cu interconnection with Cu NPs was inspected by scanning electron microscope (SEM). These results demonstrated a reliable low temperature Cu-Cu bonding method was realized and it might be a promising technique for fine-pitch 3D integration.