Synchrotron-based investigation of iron precipitation in multicrystalline silicon

We report on investigations of the precipitation of iron in block-cast multicrystalline silicon using the techniques of X-ray beam induced current, X-ray fluorescence microscopy and X-ray absorption microspectroscopy. The samples studied were intentionally contaminated with iron and annealed at temperatures between 850 and 1050 ∘C. Annealing at 950 ∘C was found to lead to well detectable iron precipitation inside the grains and at grain boundaries. Small only iron clusters were detected after the 850 ∘C anneal while no iron clusters were found after the 1050 ∘C treatment. X-ray absorption near edge structure analyses of the iron clusters revealed mostly iron silicide and in one case iron oxide. Under the given condition at the beamline, the detection sensitivity for iron was estimated to be 4×107 atoms, corresponding to a spherical FeSi2 particle of 40 nm radius.