Wafer-scale spontaneous bonding of silicon wafers by argon-beam surface activation at room temperature

We have developed a wafer-scale direct bonding method at room temperature. Four-inches Si wafers are bonded in vacuum after Ar-beam sputter-etching. In situ infrared observation indicates that the bonding is achieved spontaneously when two wafers are mated. The specimens bonded at room temperature are so strong that bulk fracture is observed after tensile test. The bonding strength is almost uniform over the 4-in. wafer area. These results demonstrate that neither heat treatment nor applying pressure is required in this bonding method. It is expected that this method provides low-damage assembly and packaging processes suitable for delicate micro-structures.