Characterization of Hot-Implanted Fe near the SiO2/Si Interface

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We have investigated nanoparticles formed in the vicinity of a SiO2/Si interface by Fe implantation at substrate temperatures of 300, 600, and 800 °C. The implantation energies are selected to assign peak positions of the implanted Fe profiles at the SiO2/Si interface. The size and crystal orientation of the nanoparticles are confirmed by cross-sectional transmission electron microscopy (TEM) and transmission electron diffraction (TED) analysis. The depth profile of implanted Fe was analyzed by Rutherford backscattering spectroscopy (RBS). It is found in the TEM image of the 300 °C-implanted sample that tiny clusters with a mean diameter of 2.4 nm are grown in the SiO2 layer. In addition, some Fe clusters are precipitated in the vicinity of the SiO2/Si interface. On the other hand, we observe nanoclusters with a mean diameter of 3.2 nm at a certain depth in the SiO2 layer for the 600 °C-implanted sample. Some of the clusters in the SiO2 layer have a crystalline structure of $\alpha$-Fe. Furthermore, $\beta$-FeSi2 with comparatively larger diameters of 5--10 nm is found to precipitate at the SiO2/Si interface from the analysis of TEM and TED images. Most of the implanted Fe atoms are segregated either just on the SiO2 surface or at the SiO2/Si interface in the 800 °C-implantation case. The anomalous diffusion of Fe in the SiO2 layer seems to be explained by the ion-beam-irradiation effect at high temperatures.
2011-03-25