Structural properties of ion beam synthezised iron-cobalt silicide

Surface and buried layers of ternary silicide were fabricated by implantation of iron and cobalt into (100) silicon wafers. For the surface layers two sets of samples with different iron to cobalt ratios were prepared. In the first set, cobalt was implanted first followed by iron and the implant order was reversed in the second set. In all cases the total implanted dose (Fe + Co) was kept constant. For the buried ternary silicides two samples were prepared with equal doses of iron and cobalt. In the first sample, cobalt was again implanted first with the implant order being reversed for the second sample. The physical properties of the synthesized layers were investigated by Rutherford backscattering spectrometry (RBS), x-ray photoelectron spectroscopy (XPS) and cross sectional transmission electron microscopy (XTEM). The results indicate that the implantation order is critical to the subsequent development of the synthesized layer. The surface layers with iron implanted first were non-crystalline and showed no significant improvement of crystallinity with increasing anneal temperature. However, the surface layers with cobalt implanted first exhibited a large improvement of crystal quality with increasing anneal temperature. Segregation into separate iron- and cobalt-rich layers was also observed for surface layers where cobalt was implanted first for Co:Fe ratio greater than or equal to 1. The crystalline quality of the buried layers was also determined by the implant order, in a similar way to that for the surface layers.