Microstructure of β-FeSi₂ thin films prepared by pulsed laser deposition

Iron disilicide thin films were prepared by pulsed laser deposition (PLD) on Si (100) substrates using a FeSi₂ alloy target. Droplet-free films could be deposited at a fluence between 2 and 4 J/cm² using a 193-nm laser. Polycrystalline films of β-FeSi₂ phase could be formed even at a substrate temperature of 20 °C. In addition to the β-FeSi₂ phase, the FeSi phase was observed for substrate temperatures between 400 and 600 °C. This is attributed to the mobility enhancement of Si atoms. At 700 °C, the FeSi phase disappeared and β-FeSi₂ single-phase films having a columnar structure were grown due to the mobility enhancement of both the Fe and Si atoms. At the substrate temperatures of less than 600 °C, the lattices of β-FeSi₂ were distorted. At substrate temperatures higher than 700 °C, the lattice constants approached the bulk values. The films deposited at more than 700 °C were grown epitaxially on Si(100) with the relation of β-FeSi₂ (041) or (014) ∥ Si (220) at the beginning of deposition. As the film thickness increases, the epitaxial growth becomes disordered and finally becomes non-oriented near the film surface. For all films deposited at various substrate temperatures, the stoichiometry was constant in the depth direction. Thus, it is suggested that Si atoms from the substrate hardly diffused into the film. The generation of iron disilicide in the PLD deposition mechanism is also discussed.