Role of the SiO2 buffer layer thickness in the formation of Si/SiO2/nc-Ge/SiO2 structures by dry oxidation

Nanomemories, containing Ge-nanoparticles in a SiO2 matrix, can be produced by dry thermal oxidation of a SiGe layer deposited onto a Si-wafer with a barrier SiO2 layer on its top. Rutherford backscattering spectrometry has been used to characterize the kinetics of the oxidation process, the composition profile of the growing oxide, the Ge-segregation and its diffusion into the barrier oxide in samples with thin and thick barrier oxide layers. The Ge segregated during the oxidation of the SiGe layer diffuses into the barrier oxide. In the first case the diffusion through the thin oxide is enhanced by the proximity of the substrate that acts as a sink for the Ge, resulting in the formation of a low Ge concentration SiGe layer in the surface of the Si-wafer. In the second case, the Ge-diffusion progresses as slowly as in bulk SiO2. Since barrier oxide layers as thin as possible are favoured for device fabrication, the structures should be oxidized at lower temperatures and the initial SiGe layer thickness reduced to minimize the Ge-diffusion.