Growth of beta-FeSi2 films via noble-gas ion-beam mixing of Fe/Si bilayers
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A detailed study of the formation of beta -FeSi2 films by ion-beam mixing of Fe/Si bilayers with noble gas ions is presented. Fe films of 35-50 nm deposited on Si (100) were irradiated with 80-700 keV Ar, Kr, or Xe ions in a wide temperature interval, from room temperature to 600 degreesC. The structures were analyzed by Rutherford backscattering spectroscopy, x-ray diffraction, conversion electron Mossbauer spectroscopy, elastic recoil detection analysis, cross-section high resolution transmission electron microscopy, and energy dispersive x-ray spectroscopy. Already after Xe irradiation at 300 degreesC the whole Fe layer is transformed to a mixture of Fe3Si, epsilon -FeSi, and beta -FeSi2 phases. At 400-450 degreesC, a unique, layer by layer growth of beta -FeSi2 starting from the surface was found. A full transformation of 35 nm Fe on Si to a 105 nm beta -FeSi2 layer was achieved by irradiation with 205 keV Xe to 2x10(16) ions/cm(2), at a temperature of 600 degreesC. The fully ion-b...eam grown layers exhibit a pronounced surface roughness, but a sharp interface to Si. This structure is assigned to a growth of beta -FeSi2 grains in a local surrounding of interdiffused silicon. Rapid diffusion of silicon to the surface was observed during all ion irradiations. Single-phase beta -FeSi2 layers were also synthesized by vacuum annealing for 2 h at 600 degreesC of 35 nm Fe/Si bilayers premixed with Xe at 450 degreesC. In this case, the layers form with a smoother surface topography. It is concluded that ion-beam mixing can be used successfully for growth of beta -FeSi2 layers at moderate temperatures, either directly or combined with postirradiation annealing. (C) 2001 American Institute of Physics.