Investigation of various phases of Fe–Si structures formed in Si by low energy Fe ion implantation

The compositional phases of ion beam synthesized Fe–Si structures at two high fluences (0.50 × 10¹⁷ atoms/cm² and 2.16 × 10¹⁷ atoms/cm²) were analyzed using X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The distribution of Fe implanted in Si was simulated using a dynamic simulation code (TRIDYN) incorporating target sputtering effects. The Fe depth profiles in the Si matrix were confirmed with Rutherford backscattering spectrometry (RBS) and XPS depth profiling using Ar-ion etching. Based on XPS binding energy shift and spectral asymmetry, the distribution of stable Fe–Si phases in the substrate was analyzed as a function of depth. Results indicate Fe implantation with a fluence of 0.50 × 10¹⁷ atoms/cm² and subsequent thermal annealing produce mainly the β-FeSi₂ phase in the whole thickness of the implanted region. But for the samples with a higher fluence Fe implantation, multiple phases are formed. Significant amount of Fe₃Si phase are found at depth intervals of 14 nm and 28 nm from the surface. Initially, as-implanted samples show amorphous Fe₃Si formation and further thermal annealing at 500 °C for 60 min formed crystalline Fe₃Si structures at the same depth intervals. In addition, thermal annealing at 800 °C for 60 min restructures the Fe₃Si clusters to form FeSi₂ and FeSi phases.