Diffusion of Germanium from a Buried SiO₂ Layer and Formation of a SiGe Phase

Ge diffusivity from a buried SiO₂ layer of a silicon-on-insulator (SOI) structure has been studied as a function of annealing temperature. It has been shown that, at an annealing temperature lower than 900°C, almost all Ge is localized in the implantation region of the SiO₂ layer. As the annealing temperature is raised to 1100°C, migration of ion-implanted Ge is accompanied by several processes: diffusion into SiO₂, accumulation at Si/SiO₂ interfaces, diffusion into silicon, and evaporation from silicon. At 1100°C, Ge diffuses from SiO₂ to the bonding interface of the SOI structure with the diffusion coefficient of ~2 × 10⁻¹⁵ cm²/s, which is 2 orders of magnitude higher than its equilibrium value. Depending on the thickness of the silicon layer, formation of a Ge or SiGe phase is detected after annealing at a temperature of 1100°C.