Evaluations of low temperature bonding using Au sub-micron particles for wafer level MEMS packaging

This paper describes wafer level vacuum packaging with sub-micron Au particles for MEMS (micro electro mechanical systems) applications. Low temperature bonding is indispensable for relevant MEMS packaging, and use of sub-micron Au particles are suitable for hermetic seal bonding. For the fabrication of hermetically sealed wafer level packaging, a base silicon wafer and a cap glass wafer were bonded at around 200°C. Before bonding, the surface of seal rings was observed with a laser microscope to investigate the effect of surface roughness for hermeticity. After bonding, bonded wafers were dipped in the hydrofluoroether for 30 min. As a result, surface flatness of Au particles contributed to achieve hermetic sealing. Double seal rings structures were also useful to realize hermetic sealing.