Abstract
The fundamental properties of the binary disilicides CoSi2 and FeSi2 have been extensively studied. Epitaxial CoSi2 can be formed on silicon, however, it is very difficult to form epitaxial FeSi2 on silicon substrates. With the aim to improve the epitaxial quality of FeSi2 and also to study the effect of the incorporation of Fe(Co) into CoSi2(FeSi2), ternary Fe-Co silicides are explored. This thesis reports a study of the structural and electrical characterisation of surface and buried ternary Fe-Co silicide layers in Si(100) fabricated by ion beam synthesis (IBS). In all cases two sets of samples were prepared, with Fe implanted first followed by Co in the first set and the implant order was reversed in the second set. Rutherford Backscattering spectrometry, four point probe measurements, cross-sectional transmission electron microscopy (XTEM), secondary ion mass spectrometry (SIMS) and x-ray photoelectron spectroscopy (XPS) were used to assess the synthesised material. The surface layers can be grouped into three structural classes determined by the composition. The Fe(Co) rich layers were found to have the FeSi2(CoSi2) structure for both implant orders. However, the layer morphology of the samples containing approximately equal amounts of Fe and Co was determined by the implant order. When Fe was implanted first the layers were non-crystalline and annealing had no significant effect on the crystal quality. However, when Co was implanted first epitaxial layers were formed after implantation and there was a significant improvement in the crystal quality with increasing anneal temperature. Phase separation into Fe and Co rich regions running parallel to the sample surface was observed upon annealing of the sample containing approximately equal amounts of Fe and Co, when Co was implanted first. For both implant orders the sheet resistance increased with increasing Fe content. Also for the Fe rich samples the phase transition from the ? to the a phase decreased with increasing Co content. The crystal quality of the buried layers was also determined by the implant order, however phase separation was not observed upon annealing of the samples with Co implanted first. The effects of the implantation energy, implantation temperature, intermediate anneals and the annealing temperature and time on the morphology of the surface layers containing approximately equal amounts of Fe and Co were also examined.