Investigation of Al and Ge surfaces for Al-Ge wafer level eutectic bonding

Metal based wafer level eutectic bonding has been developed for hermetic sealing providing consistent gas environment for MEMS Silicon (Si) sensor devices as well as protecting the MEMS structure. The use of Aluminum (Al) and Germanium (Ge) materials for bonding has advantages as these materials are CMOS compatible with Al conventionally used for wire bonding and metal pads, and Ge for creating SiGe CMOS devices. Al-Ge bonding is also comparatively low cost compared to gold and silicon (Au-Si) bonding. For successful eutectic mixture during bonding process, the two metal surfaces on both sides of the wafers to be bonded have to be cleaned and cleared of native oxides and contaminants. This work examines the Al and Ge surfaces prior to bonding that affects the formation of Al-Ge eutectic reaction.