Formation of FeSi and FeSi₂ films from cis-Fe(SiCl₃)₂(CO)₄ by MOCVD -precursor versus substrate control

The low pressure chemical vapor deposition (LPCVD) reaction of cis-Fe(SiCl₃)₂(CO)₄ yields iron silicides of different composition and texture depending on the substrate. On a (100) Si surface, highly oriented orthorhombic β-FeSi₂ is formed due to lattice matching between Si and β-FeSi₂ (1.4% mismatch). The imprint effect of the (100) Si surface plays a dominant role. On amorphous Pyrex glass substrates, a porous aggregate of polycrystalline cubic FeSi is formed. In this case the film formation process is determined by the decomposition kinetics of the precursor. The mechanism of the iron silicide FeSi formation has been investigated by in situ photoelectron (PE) spectroscopy in the surface controlled regime up to 600°C. The experimental data provide evidence for SiCl₄- and CO-elimination steps involving silylene complexes. The reaction is assumed to occur at the surface via adsorbed intermediates. A density functional theory (DFT) calculation approximated for the gas phase shows the elimination of SiCl₄ to be endothermic by 15.0 kcal mol^-1. The mechanism considered in the calculations involves Cl transfer from Si1 to Si2 of cis-Fe(SiCl₃)₂(CO)₄ accompanied by Fe-Si2 bond fission and formation of [Fe(=SiCl₂)(CO)₄] (calc. energy of activation 47 kcal mol^-1, Fe=Si bond dissociation energy 52 kcal mol^-1).