Development of CMOS Compatible Bonding Material and Process for Wafer Level MEMS Packaging Application under Harsh Environment

CMOS compatible metallic hermetic sealing using Al-Ge eutectic alloy for packaging MEMS devices for harsh environments has been developed. The effects of various bonding parameters on the bond quality have been extensively reported. The reliability of this eutectic joint subjected to high operating temperatures involved in deep oil well logging application has been investigated with the specific focus on shear strength and hermeticity. A new configuration for stacking Al-Ge thin films has been demonstrated in order to tackle the issue of loss of Ge prior to bonding since native Ge oxides are soluble in DI water. The impact of solid-state aging prior to Al-Ge eutectic bonding has also been investigated. It has been determined that solid-state aging prior to Al-Ge eutectic bonding is a prerequisite in order to attain a reliable hermetic sealing. Furthermore, the changes in microstructure with respect to thermal aging at 300°C up to 500 hours have also been presented since the minimum requested continuous operating time by the energy industry is 500 hours at 300°C. No thermal degradation of the Al-Ge eutectic joint at 300°C for 500 hours was observed. This could be credited to its composite microstructure. Thus, the overall conclusion of this work is that Al-Ge eutectic bonding is a prospective candidate for this application.