Bombardment-induced silicide formation at rhenium-silicon interfaces studied by XPS and TEM

Abstract

For further evaluation of photoemission properties of argon ion bombarded rhenium-silicon thin films pure element Re(21 nm) / Si(39 nm) / Re(21 nm) layer sandwiches were investigated on Si(111) substrates. TEM cross sectioning revealed abrupt interfaces between the polycrystalline Re layers and the amorphous Si layer in the as-deposited sample. In XPS sputter depth profiling the interfaces were severely broadened. This is not just a result of the finite electron escape depth together with atomic mixing and preferential sputtering which was demonstrated with the dynamic Monte Carlo simulation program T-DYN, but mainly caused by topographic effects and silicide formation. Factor analysis of XPS spectra results in two Re-Si principal components which can be ascribed to silicide bonding. Accordingly the valence band changes are caused by different bonding configurations. Bombardment-induced silicide formation is proved by TEM investigations of a selected cross-sectioned sandwich. Due to preferential bombardment-induced effects Re₂Si is formed at the Re/Si interfaces in contrast to the ReSi₂ growth on thermal heating. This is discussed in terms of the interface composition and the effective heat of formation (EHF) model.