Low temperature Cu-Cu bonding using tin nanoparticles fabricated by high pressure magnetron sputtering

A low temperature wafer-level Cu-Cu bonding method using Sn 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. Sn NPs were then deposited by high pressure physical vapor deposition (PVD) on Cu pads. The morphology of Sn NPs was studied. Bonding process was successfully proceeded at 200°C for 3min under the pressure of 40MPa. Shear tests were performed after bonding, and the influence of annealing time on shear strength were assessed. The average shear strength without annealing process reached 16.46MPa. Transmission electron microscope (TEM) photos of the fracture interfaces were presented and the energy dispersive X-ray (EDX) analysis of the fracture surfaces showed that Sn has already diffused in Cu. The results mentioned above demonstrated that a robust low temperature short time Cu-Cu bonding was realized by Sn NPs fabricated by PVD.