SOLID-PHASE EPITAXY AND CHARACTERIZATION OF FESI2 LAYERS ON SI(111)

Beta-FeSi2 films have been epitaxially grown on the Si(111) (7 x 7) reconstructed surface. Fe layers have been deposited at room temperature in an ultrahigh vacuum chamber (base pressure 1-2 x 10(-10) Torr) and then annealed at temperature ranging between 400 and 700-degrees-C. We used low-energy electron diffraction (LEED), Auger spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM) to characterize both the Fe and beta-FeSi2 layers. Monocrystalline Fe films, several hundred angstroms thick, have been obtained, as shown both by LEED and by XRD measurements. Beta-FeSi2 layers (from a few angstroms to thousands of angstroms in thickness) have been studied. For very thin films small, elongated domains oriented along the three <112BAR> directions of the (111) Si substrate have been observed with SEM. The surface becomes very flat and uniform for films as thick as a few hundreds of angstroms. At higher thicknesses surface roughness becomes evident. A strong correlation between SEM and XRD results has been found: good-quality films, from a crystallographic point of view, are obtained in the thickness range that presents flat and homogeneous surfaces, while a textured structure is obtained for a 1000 angstrom thick layer, where the SEM image shows a quite rough surface.