Low temperature Cu-Cu bonding using Ag nanoparticles by PVD

A novel low temperature wafer-level Cu-Cu bonding method using Ag nanoparticles (NP) was proposed and realized in this paper. A bonding structure consisted of Cu bonding pads, TiW barrier/adhesive layer was firstly fabricated on the silicon wafer. Ag NPs were then deposited by physical vapor deposition (PVD) on Cu pads. The morphology of Ag NPs annealed at different temperature was studied. Bonding process was successfully proceeded at 200°C for 10min under the pressure of 20MPa followed by a post-annealing process at 200°C for 1 hour. Die shear test was carried out after bonding process and the shear strength reached 23.59MPa. Scanning electron microscope (SEM) photos of the fracture interfaces were presented and the energy dispersive X-ray (EDX) analysis of the fracture surfaces showed that cracks occurred at the Ag bonded interfaces and TiW/SiO
₂
interfaces. The results mentioned above demonstrated that a novel low temperature short time Cu-Cu bonding was realized by Ag NPs fabricated by PVD.