Reliability and Characterization of Micro-Packages in a Wafer Level Au-Si Eutectic Vacuum Bonding Process

A Au-Si eutectic vacuum packaging process was evaluated using high sensitivity poly-Si Pirani vacuum sensors. Encapsulation of devices was achieved by bonding a silicon cap wafer to a device wafer using a Au-Si eutectic solder at above 390°C in a vacuum bonder. The Au-Si eutectic solder encircled the devices, providing an airtight seal. The Pirani gauges were encapsulated and tested over a period of several months in order to determine base pressures and leak/outgassing rates of the micro-cavities. Packaged devices without getters showed initial pressures from 2 to 12 Torr with initial leak/outgassing rates of −0.073 to 80 Torr/year. Using getters, pressures as low as 5 mTorr have been achieved with leak/outgassing rates of <10 mTorr/year. Trends in pressure over time seem to indicate outgassing (desorption of atoms from inside of the microcavity) as the primary mechanism for pressure change over time.