Impact of MEMS Release Process on The Integrity of Cu–Sn SLID Bonds in Vacuum Packaging of Microbolometer Array

This work studies the influence of byproducts from the release process of microbolometer array (MBA) on Cu–Sn solid-liquid diffusion (SLID) bonds. This includes fabricating Si caps and Si substrates featuring Cu/Sn layers electroplated as metal sealing frames. The substrates, imitating dummy readout integrated circuit (ROIC), with and without sacrificial layer used in the MBA fabrication, were exposed to the MBA release process. The metal surfaces were inspected by energy-dispersive X-ray (EDX) spectroscopy before bonding. Hermetic sealing was done by Cu–Sn SLID bonding. The bonded samples were characterized by cross-sectional microscopy, indicating potential impact of surface contamination, particularly with F and O, on the increasing occurrence of voids in final bondlines. This, in turn, has a potential impact on the bond strength of the Cu–Sn SLID bonds, subsequently affecting both the hermeticity and overall reliability of the devices.