PHASE FORMATION IN FE-SI THIN-FILM DIFFUSION COUPLES

The formation of FeSi2, as well as other iron silicides, from solid-st ate reactions of Fe thin films on Si substrates has been investigated. Iron layers, approximately 50 nm thick, were deposited by electron be am evaporation on [100] oriented Si substrates. Silicon (almost-equal- to 35 nm) and SiO2 (almost-equal-to 170 nm) layers were deposited on t op of the Fe layer in the same evaporator without breaking the chamber vacuum. SiO2 acted as a protective layer during subsequent annealing in a nitrogen ambient. All annealed samples were examined using X-ray diffraction and transmission electron microscopy (TEM). Both plan view and cross section specimens were prepared for TEM. Detailed phase ana lysis was accomplished through the various electron diffraction and X- ray microanalysis techniques available with the TEM. Silicon dissolved readily in Fe, at temperatures lower than 300-degrees-C, up to the so lubility limit of almost-equal-to 26 at%Si. FeSi formation followed (3 50-degrees-C), with semiconducting FeSi2 forming at 500-degrees-C. The Fe - amorphous Si interface was more reactive, with silicide formatio n occurring at lower annealing temperatures (300-degrees-C). There was also evidence that FeSi2 formed directly from alpha-Fe and amorphous Si.