Low-temperature glass bonding for sensor application using boron oxide thin films

Low-temperature glass bonding of silicon, silicon dioxide and silicon nitride is described. Boron oxide was used as the intermediate glass layer at a bonding temperature of 450°C. First experiments indicate that due to reflow and deformation of the molten glass layer, bonding over metal patterns is possible, e.g. aluminium or chromium/gold. No voids are observed by examination of cleaved cross sections using optical microscopy or by IR transmission of bonded wafers. Scanning acoustic tomography, however, revealed regions of good, as well as regions of bad bonding quality. Bonding at low temperatures, with less critical demands for surface flatness, and the possibility of metalized electrical feedthrough will offer more process flexibility in the fabrication of sensors and actuators.