Kinetics of Ge diffusion, desorption and pit formation dynamics during annealing of Si0.8Ge0.2/Si(001) virtual substrates

Thermal stability of Si0.8Ge0.2/Si(001) virtual substrates (VS) is studied as a function of annealing temperature and time by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Two regimes describing different Ge behavior are observed when the Si0.8Ge0.2 VS is annealed. Heating the substrate from room temperature to 500 °C results in some degree of Ge segregation. The surface morphology however remains relatively smooth and there is no formation of 3D islands on the surface. Above 500 °C, Ge is preferentially lost from the surface and microscopic pits with edges aligned along 〈110〉 azimuth are formed. As temperature increases, Ge% decreases and the size of pits also increases. The decrease in Ge% and the formation of holes at the surface are attributed to Ge desorption from the surface. A kinetic model involving diffusion and desorption processes is proposed to describe the Ge behavior and pits formation in this regime.