Examples were presented in order to illustrate that transition metal impurities could be extrinsically gettered during low-temperature processing; even when they were present as traces. Samples of Si/Si(Ge)/Si epitaxial heterostructures which contained interfacial misfit dislocations were studied by using cross-sectional analytical transmission electron microscopy after annealing (700C, vacuum). In one example, trace Fe precipitates (about 6.5nm in diameter) which segregated at an end-on misfit dislocation were analyzed by using nanoprobe X-ray spectroscopy, combined with high-resolution lattice imaging. The Fe-containing precipitate was cubic and was epitaxially aligned with the host Si crystal. In another example, trace Cu precipitates (about 0.5 in diameter) with a disk-like morphology were observed along a misfit dislocation segment. It was concluded that these results demonstrated the effectiveness of misfit dislocations as extrinsic gettering sites at very low impurity levels.

D.M.Lee, G.A.Rozgonyi: Applied Physics Letters, 1994, 65[3], 350-2