Dislocation-free formation of relaxed SiGe-on-insulator layers

We demonstrate the fabrication of dislocation-free strain-relaxed SiGe-on-insulator (SGOI) layers as virtual substrates for strained Si-on-insulator (SOI) metal–oxide–semiconductor field-effect transistors (MOSFETs) by forming SiGe-mesa structures and successive oxidation. A pseudomorphic ${\mathrm{Si}}_{\text{0.9}}{\mathrm{Ge}}_{\text{0.1}}$ layer on a SOI layer was etched to form mesa structures. After the oxidation of the mesas, thin (<100 nm) ${\mathrm{Si}}_{\text{0.85}}{\mathrm{Ge}}_{\text{0.15}}$ mesa structures were formed on the buried oxide layer. It was found that the mesas with a diameter smaller than 3 μm were almost completely relaxed after oxidation at 1200 °C, without generating any threading dislocations and crosshatch patterns, which generally exist in the relaxed SiGe layers on bulk Si substrates. The formation of SGOI mesas before oxidation has the potential to provide ideal SGOI virtual substrates for strained SOI MOSFETs.