VOID-FREE SILICON-WAFER-BOND STRENGTHENING IN THE 200-400 DEGREES-C RANGE

Silicon-wafer-bond strengthening in the 200-400-degrees-C range can be successfully applied for wafers having temperature-sensitive device structures. The bond quality and specific surface energy of the bond have been studied experimentally with respect to the surface hydrophilization state. The kinetic bond model of Stengl et al. is applied to low-temperature bond strengthening and agreement between calculated and measured data points is established. Wafer bonding by means of static pressure is shown to be effective in the enhancement of the bond strength by overcoming most of the local waviness during room-temperature wafer bonding. Specific surface energies of 1.9 and 2.3 J/m2 can be reached using surface plasma-activated wafers in bond strengthening at 200 and 400-degrees-C, respectively. A problem in low-temperature wafer-bond strengthening is the voids that are generated in the 200-700-degrees-C range. Our results support the opinion that they are caused by interface water released in the bond reaction. Void-free bond strengthening is possible by the insertion of a shallow groove structure into the silicon or the oxidized silicon surface of one of the wafers.