BOND STRENGTH OF BONDED SOI WAFERS

We developed a tensile strength measurement technique for bonded silicon-on-insulator (SOI) wafers. After oxidation, wafers are patterned, prior to bonding, to reduce the bonded area. After bonding and grinding, tensile strength is measured by pulling samples perpendicularly to the interface by holders adhesively fixed to the samples. The strength of bonded SOI wafer annealed at 1100-degrees-C for 30 minutes exceeded 2000 kgf/cm2, and samples separated not at the bond interface, but at the Si itself. Both SiO2/Si and SiO2/SiO2 bond strengths increased with annealing temperature. The SiO2/Si bond strength was stronger than that of the SiO2/SiO2 bond for annealing temperatures under 1100-degrees-C. The strengths became equal after 1200-degrees-C annealing. The initial bond strength was maintained in a heat cycle varying from -65-degrees-C to 150-degrees-C in air for five months.