Aligned room-temperature bonding of silicon wafers in vacuum by argon beam surface activation

A precise aligned wafer bonding process without any heat treatments, pressure, high-voltage application or intermediate adhesive layers has been developed. Surface treatment by argon beam and bonding in a high-vacuum environment enable the formation of strong direct bonding between silicon wafers at room temperature. In order to apply this method to the bonding of prefabricated microelectromechanical systems (MEMS) wafers, we have developed a bonding apparatus with instrumentation for precise alignment in vacuum. Silicon wafers of 100 mm diameter with line-and-space patterns were successfully bonded with alignment accuracies of better than 2 mum. This process is expected to provide a very low-damage assembling and packaging process for MEMS structures.