Low Temperature Au-Au Bonding Using Ag Nanoparticles as Intermediate

In this work, we propose a novel Au-Au bonding approach using silver nanoparticles (Ag NPs) prepared by high-pressure magnetron sputtering method as a surface modification layer to accomplish time-saving and low-temperature bonding. The diced silicon chips with 100 nm Cr and 200 nm Au are bonded via Ag NPs at 200°C for 3 mins under the pressure of 30 MPa. After the bonding process, shear strength of bonding pairs is tested, and the fracture surfaces are observed using SEM along with EDS. Testing results show that average bonding strength above 10 MPa is achieved. Observations from fracture surfaces illustrate that the fracture happens at SiO
₂
/Cr interfaces, which indicates the bonding strength is stronger than the adhesive strength of SiO
₂
/Cr. In addition, the bonding interfaces are investigated by TEM. The TEM cross-section images of the bonding interfaces present no cracks or voids, which further confirms the seamless Au-Au bonding through Ag NPs. It can be concluded that Au and Ag atoms inter-diffuse sufficiently with negligible oxides, and recrystallization has occurred at the original surfaces. Interdiffusion of Au and Ag atoms, together with grain growth at the bonding interfaces contributes to the robust Au-Au bonding.