Low-temperature MEMS process using plasma activated Silicon-On-Silicon (SOS) bonding

This paper explores the use of dielectric barrier discharge (DBD) surface activated low-temperature wafer bonding in MEMS device fabrication. Characterization of the DBD surface treatment process is included as well as analysis of the optimal bonding conditions. A new high aspect-ratio MEMS technology based on bonding two silicon wafers with an intermediate silicon dioxide layer at 400degC is presented. This silicon-on-silicon (SOS) process requires three masks and provides several advantages compared with silicon-on-glass (SOG) and silicon-on- insulator (SOI) processes, including better dimensional and etch profile control of narrow and slender MEMS structures. This is demonstrated by fabricating a 5 mum wide 30 mm long beam. Additionally, by patterning the intermediate SiO₂ insulation layer before bonding, footing is reduced without any extra processing, as compared to both SOG and SOI. All SOS process steps are CMOS compatible.