Study of Ge loss during Ge condensation process

Ge loss during Ge condensation process was investigated by transmission electron microscopy, Raman spectroscopy, secondary ion mass spectrometry and Rutherford backscattering spectrometry. This work reveals that Ge loss can be attributed to the Ge oxidation at SiO2/SiGe interface, Ge diffusion in SiO2 layers and Ge trapped at buried SiO2/Si interface. During Ge condensation process, with the increase of the Ge content, the Si atoms become insufficient for selective oxidation at the oxide/SiGe interface. Consequently, the Si and Ge are oxidized simultaneously. When the Ge composition in SiGe layer increases further and approaches 100%, the Ge atoms begin to diffuse into the top SiO2 layer and buried SiO2 layer. However, the X-ray photoelectron spectrometry analysis manifests that the chemical states of the Ge in top SiO2 layer are different from those in buried SiO2 layer, as the Ge atoms diffused into top SiO2 layer are oxidized to form GeO2 in the subsequent oxidation step. With the increase of the diffusion time, a quantity of Ge atoms diffuse through buried SiO2 layer and pile up at buried SiO2/Si interface due to the interfacial trapping. The SiO2/Si interface acts like a pump, absorbing Ge from a Ge layer continuously through a pipe-buried SiO2 layer. With the progress of Ge condensation process, the quantity of Ge accumulated at SiO2/Si interface increases remarkably.