The depth profiles of Ge atoms in SiO2 thin films were investigated by using high-resolution Rutherford back-scattering spectrometry. Samples were prepared by Ge negative ion implantation of 25nm-thick SiO2 films on Si substrates at 10keV to a fluence of 1015/cm2, followed by annealing at various temperatures. As-implanted, and after annealing at below 700C, the depth profiles were Gaussian and corresponded well with the calculated profiles. Joined half-Gaussian curves were fitted to the profiles. The Ge diffusion coefficients were estimated by applying a linear diffusion equation to the fitting curves. These revealed rapid diffusion to the surface side, rather than the interface side. After annealing at 900C, two clear Ge peaks appeared in the high-resolution Rutherford back-scattering spectra for SiO2, with a strong asymmetrical shape at the SiO2/Si interface. Cross-sectional transmission electron microscopic observations revealed that a Ge concentration of about 1at% yielded Ge nanoparticles of about 2nm in diameter. In this low-energy implantation, the vacancies due to implantation were found near to the surface; indicating anisotropic diffusion. At 900C, more normal Ge diffusion behavior was expected to occur, such as strongly anisotropic diffusion in a thin SiO2 film with an interface of crystalline Si.

Thermal Diffusion Behavior of Implanted Germanium Atoms in Silicon Dioxide Film Measured by High-Resolution RBS. N.Arai, H.Tsuji, N.Gotoh, T.Minotani, T.Ishibashi, T.Okumine, K.Adachi, H.Kotaki, Y.Gotoh, J.Ishikawa: Surface and Coatings Technology, 2007, 201[19-20], 8312-6