Interfacial structure and strength of silicon-silicon diffusion bonds

Silicon wafers were bonded in air at various temperatures up to 1200 degrees C. The resultant interfacial structures were analysed using transmission electron microscopy, parallel electron energy loss spectroscopy, and energy dispersive X-ray spectroscopy, and relationships between the bonding strength and bonding parameters (bonding temperature and bonding time) were determined. When the specimen was prebonded at room temperature before heat treatment, the bonding strength was higher than in those specimens without prebonding. The shear strength increased with bonding temperature, and approached the maximum of 18 and 9 MN m(-2) for specimens bonded at 1000 degrees C for 1.5 h with and without prebonding, respectively. In specimens bonded at 1000 degrees C ol less after prebonding, a layer of silicon dioxide existed at the interface, and the thickness of the silicon oxide layer increased with bonding temperature. When the specimen was bonded at 1200 degrees C, no oxide layer was observed at the interface because of decomposition of the oxide layer. The relationship between the temperature dependence of the bonding strength and the chemical reaction at the interface was discussed. The formation and decomposition processes of the oxide layer were also discussed.