A detailed study of yield and reliability for vacuum packages fabricated in a wafer-level Au-Si eutectic bonding process

An Au-Si eutectic wafer-level bonding process was developed for low-temperature vacuum packaging of MEMS devices. Using Au-Si eutectic bonding, devices were encapsulated by bonding a silicon cap wafer to a device wafer. Micromachined Pirani vacuum sensors were encapsulated in order to characterize the packaged pressures. These packages had cavity dimensions of 2.3times2.3 mm with a depth of 90 mum. Yields of 84.6% and 94.1% were achieved in packages with bond ring widths of 100 and 150 mum. With the use of getters and a pre-bond outgassing step, pressures from <3.7 to 23.3 mTorr were achieved. Furthermore, pressures were shown to remain stable to within plusmn2.5 mTorr for over 4 years of testing.