Low-temperature silicon wafer-to-wafer bonding using gold at eutectic temperature

Abstract

Micromechanical smart sensor and actuator systems of high complexity become commercially viable when realized as a multi-wafer device in which the mechanical functions are distributed over different wafers and one of the wafers is dedicated to contain the readout circuits. The individually-processed wafers can be assembled using wafer-to-wafer bonding and can be combined to one single functional electro-mechanical unit using through-wafer interconnect, provided that the processes involved comply with the constraints imposed by the proper operation of the active electrical and micromechanical subsystems. This implies low-temperature wafer-to-wafer bonding and through-wafer interconnect. Au/Si eutectic bonding has been investigated as it can conveniently be combined with bulk-micromachined through-wafer interconnect. The temperature control in eutectic bonding has been shown to be critical.