Germanium movement mechanism in SiGe-on-insulator fabricated by modified Ge condensation

The movement of Ge during Ge condensation in SiGe-on-insulator (SGOI) fabrication is studied based on the competition between the diffusion of Ge atoms and accumulation of Ge atoms. The diffusion of Ge atoms overwhelms the Ge accumulation at the top thermal oxide∕SiGe interface, resulting in a flat Ge profile in the SGOI layer. However, the opposite result is found at the bottom SiGe∕buried-oxide (BOX) interface. The Ge diffusion towards the BOX is blocked because of the much smaller diffusion coefficient of Ge in the BOX than that in the SiGe layer. The Ge accumulation effects are more dominant than the diffusion of Ge, and so Ge atoms pile up near the BOX giving rise to an abrupt profile. The disappearance of the SiGe lattice structure near the SiGe∕BOX interface is also found in the sample oxidized for a longer time due to the reduction of the melting point of SiGe alloys with higher Ge fractions.