Wafer Level Surface Activated Bonding Tool for MEMS Packaging

A wafer level surface activated bonding (SAB) tool has been developed for microelectromechanical systems (MEMS) packaging at low temperature. The tool accommodates 8 in. diam wafers. The principle features of the tool are the automatic parallel adjustment for 8 in. wafers to a margin of error within ±1 μm and the X, Y, and θ axis alignments with an accuracy of ±0.5 μm. We have approached a new integration technique for the integration of ionic crystals with transparent and nontransparent thin intermediate layers using this tool. Various sizes of patterned and bare silicon, Al silicate glass, and quartz wafers cleaned by a low energy argon ion source in a vacuum have been successfully bonded by this technique at low temperature. Radioisotope fine leak and vacuum seal tests of sealed silicon cavities show leak rates of 1.0×10−9 and 2.6×10−16 Pa/m3 s, respectively, which are lower than the American military standard encapsulation requirements for MEMS devices in harsh environments. Void-free interfaces with bonding strengths comparable to bulk materials are found. Low adhesion between SAB-processed ionic crystals without adhesive layers is believed to be due to radiation-induced discontinuous polarization. © 2004 The Electrochemical Society. All rights reserved.