Low temperature Ag-Ag direct bonding under air atmosphere

Abstract

In this study, sputtered Ag thin films were proposed as bonding materials and Ag‒Ag direct bonding processes were achieved by thermo-compression process at 180–200 ℃ under air atmosphere in short periods. Both results of Ag‒Ag bonding interface and shear strength exhibited excellent bonding quality, which was attributed to the dissociation behavior of Ag2O at elevated temperature under air atmosphere. The dissociation behavior of Ag2O was further investigated using thermogravimetric analysis (TGA) and the results demonstrated that the dissociation temperature is ~175 ℃. The fast surface diffusivity of Ag and the oxide-less surface facilitated the stress-induced migration of Ag atoms during thermo-compression bonding process. The corresponding bonding mechanism of the Ag‒Ag direct bonding processes under air atmosphere was also discussed in details. In addition, the resistance of kelvin structure in test vehicles of Ag‒Ag bonded bumps remained unchanged after temperature cycle test for 1000 cycles, demonstrating good reliability of Ag‒Ag direct bonding.