Transformation from ε-FeSi to β- FeSi2 in RF-sputtered FeSix films

FeSix films were deposited on Si (100) substrates using RF sputtering at room temperature and at 300 °C. After deposition, FeSix films were annealed at 400–900 °C in Ar ambient. XRD measurements revealed that the FeSix films deposited at R. T. for 30 min were completely transformed to β-phase due to annealing at 900 °C for 1 h. On the contrary, the FeSix films deposited at 300 °C for 30 min contained both ε-FeSi and β- FeSi2 after annealing at 900 °C for 1 h. The FeSix films deposited at 300 °C for 3 min were completely transformed to β-phase due to annealing at 800 °C for 1 h. For the FeSix films deposited at 300 °C for 30 min, ε-FeSi transformed to β- FeSi2 in RF-sputtered films due to long time annealing of 10 h. It can be concluded that high-temperature and long-time annealing is necessary for the ε-FeSi bonds in the FeSix films to decompose and for the Fe atoms to be diffused into Si substrates leaving only β-phase FeSi2 in the films.