Formation of epitaxial β-FeSi₂ films on Si(001) as studied by medium-energy ion scattering

Ultrathin (∼1.3 nm) epitaxial films of β-FeSi2 were grown on Si(001) by room temperature (RT) deposition of Fe followed by annealing. During the various stages of the growth process, the lattice structure, composition, and morphology of the films were investigated by medium-energy ion scattering in conjunction with shadowing and blocking. At RT, the deposited Fe reacts with the Si(001) substrate and forms a continuous film of average composition FeSi. After annealing to 670 K, a conversion into β-FeSi2 has taken place and the film is no longer continuous. Further annealing at higher temperatures results in the formation of islands of increasing height. The β-FeSi2 films grown are composites of two azimuthal orientations with respect to the substrate: The predominant A orientation with β-FeSi2 [010]∥ Si〈110〉 and the B orientation with β-FeSi2 [010] ∥ Si〈100〉. The lattice strain in the films is partially relaxed. At the interface, the Fe atoms are found to be displaced from bulk lattice sites. These displacements are thought to be associated with the formation of atomic bonds at the interface of the dissimilar β-FeSi2(100) and Si(001) lattices.