Influence of oxygen co-implantation on germanium out-diffusion and nanoclustering in SiO2/Si films

The thermally activated diffusion of germanium atoms implanted in the middle of SiO ₂ layers has been studied by Rutherford Backscattering Spectroscopy (RBS), X-ray Photoelectron Spectroscopy (XPS), µ-Raman spectroscopy and X-Ray Diffraction (XRD), with and without the presence of co-implanted ¹⁶O ⁻ ions. The important role of implantation-induced defects, in particular atomic recoil of silicon and oxygen atoms, on the well-known asymmetric redistribution of germanium depth-profile is discussed for samples solely implanted with germanium, as a function of the fluence. This is shown how both the stoichiometric state of the implanted SiO ₂ layer and their chemical environment influence the mobility of Ge atoms. For samples co-implanted with oxygen, RBS shows an enhancement of germanium diffusion under thermal activation at 1100 °C as long as the oxygen over-saturation of the SiO ₂ film is not achieved. This change in the germanium diffusion is associated to the formation of GeO _x compounds during the implantation, as shown by XPS measurements. This is responsible, during the annealing step, of the formation of highly mobile GeO at low oxygen fluences and less mobile GeO ₂ at higher fluences. Combination of XRD and µ-Raman analyses is used to highlight the impact of the co-implanted O atoms on the size dispersion of germanium nanocrystals.