XRD and XPS characterisation of transition metal silicide thin films

Abstract

Binary transition metal silicides based on the systems Ti–Si, Fe–Si, Ni–Si and Cr–Si were fabricated on Si wafers by means of ion-beam co-sputter deposition and subsequent annealing. The crystalline structures of the phases formed were identified from the characteristic patterns acquired by means of X-ray diffraction (XRD) measurements. The phase formation sequences were described by means of the Pretorius' effective heat of formation (EHF) model. For the Ti–Si, Fe–Si and Ni–Si systems, single phase thin films of TiSi2, β-FeSi2 and NiSi2 were generated as the model predicts, while a mixture of CrSi+CrSi2 phases was obtained for the Cr–Si system. The surface chemical condition of individual specimens was analysed by using X-ray photoelectron spectroscopy (XPS). The chemical shifts of transition metal 2p3/2 peaks from their metallic to silicide states were depicted by means of the Auger parameters and the Wagner plots. The positive chemical shift of 2.0eV for Ni 2p3/2 peak of NiSi2 is mainly governed by the initial-state effects. For the other silicide specimens, the initial-state and final-state effects may oppose one another with similar impact. Consequently, smaller binding energy shifts of both negative and positive character are noted; a positive binding energy shift of 0.3eV for the Fe 2p3/2 level was shown for β-FeSi2 and negative binding energy shifts of 0.1 and 0.3eV were determined for CrSi+CrSi2 and TiSi2, respectively.