Structural evolution upon thermal annealing for Fe ion irradiated Si(100)

Off-normal irradiation of Si(100) by Fe ions leads to the surface patterning. In order to understand the mechanism of pattern formation, chemical reactions between Fe and Si atoms have to be considered to influence the surface instability required for pattern formation. Since the as-irradiated surface area is amorphous, we examined the recrystallization process of the Fe-Si layer formed by off-normal 20 keV irradiation using a Si(100) substrate comparing the effect of low (1X10^16 ions cm^-2) and high (5x10^17 ions cm-2) fluencies, where only the higher fluence leads to patterned surface. The samples were annealed up to a temperature of 800°C and characterized by in-situ grazing incidence X-ray diffraction (GI-XRD). Depth profiling by GI-XRD confirmed that ε-FeSi was formed close to the surface changing to a ß-FeSi2 phase with lower Fe content at larger depths. While the polycrystalline ß-FeSi2 phase dominates for higher ion fluencies, a nearly equal ratio between ε-FeSi and ß-FeSi2 is found for lower ones. Our results suggest that phase distribution is related to the Fe concentration profile and can be considered as the relevant factor in the process of pattern formation.