Growth of beta-FeSi2 films via noble-gas ion-beam mixing of Fe/Si bilayers

A detailed study of the formation of beta -FeSi2 films by ion-beam mixing o f Fe/Si bilayers with noble gas ions is presented. Fe films of 35-50 nm dep osited 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 struc tures were analyzed by Rutherford backscattering spectroscopy, x-ray diffra ction, 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 3 00 degreesC the whole Fe layer is transformed to a mixture of Fe3Si, epsilo n -FeSi, and beta -FeSi2 phases. At 400-450 degreesC, a unique, layer by la yer growth of beta -FeSi2 starting from the surface was found. A full trans formation of 35 nm Fe on Si to a 105 nm beta -FeSi2 layer was achieved by i rradiation with 205 keV Xe to 2x10(16) ions/cm(2), at a temperature of 600 degreesC. The fully ion-beam grown layers exhibit a pronounced surface roug hness, but a sharp interface to Si. This structure is assigned to a growth of beta -FeSi2 grains in a local surrounding of interdiffused silicon. Rapi d diffusion of silicon to the surface was observed during all ion irradiati ons. Single-phase beta -FeSi2 layers were also synthesized by vacuum anneal ing 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.