DISLOCATION-FREE SILICON-ON-SAPPHIRE BY WAFER BONDING

A 300 mu m thick silicon wafer with oxide of 200 A in thickness which prevents void formation is sticked with a sapphire wafer at room temperature. To avoid the crack generation of a silicon wafer, a sticked wafer is heated up to 270C for 2 h and then a silicon layer is removed by grinding from 525 mu m to 10 mu m. To remove grinding damage and to further thin the silicon layer to 3 mu m, KOH etching at 80C is used. Finally, to obtain the silicon layer having the thickness range of 0 similar to 3 mu m, polishing is employed. Although the high density of dislocations is observed in the 2.2 mu m thick specimen annealed at 900C for 2 h, however, when the specimen is thinned down to 0.2 mu m, silicon layer becomes dislocation-free, as confirmed by double crystal X-ray topography and transmission electron microscope (TEM). The thin oxide between silicon and sapphire plays an important role in the prevention of diffusion of boron as a contaminant at the bonded interface.