Stacking faults and their strain effect at the Si/SiO₂ interfaces of a directly bonded SOI (silicon on insulator)

SOI (silicon on insulator) was fabricated through the direct bonding of a hydrophilic single crystal Si wafer and a thermally oxidized SiO₂ film. The hydrophilic Si was formed by treating the surface with modified SC-1 (NH₄OH:H₂O₂:H₂O) solution. The wafers were directly bonded to each other and were annealed at the temperature of 1200 °C for 1 h. By removing the oxide film, it was possible to examine the stacking faults at the bonding interface and the oxidation interface. The distributions of the stacking faults were showing different behaviors between the bonded and the void regions. While the stacking faults of high density were distributed in the ordered ring-like fashion in the bonded region, the stacking faults of linear orientation were shown in the void region as shown in the thermal oxidation. To investigate the relation between the stacking faults and the lattice deformation at the interface, the lattice strains were measured through CBED (convergent beam electron diffraction) analysis using transmission electron microscopy. It was found that both the thermal and the intrinsic strains were strongly influenced by the stacking faults.