TEM analysis of (Ni,Fe)Si2 precipitates in Si

The present article provides evidence that Fe impurity atoms in silicon can be gathered by NiSi2 precipitates at temperatures near RT via solid-state diffusion. Mixtures of silicon and suicide grains, resulting from annealing at 800-900 degrees C, were analysed. High supersaturation (about 10(19)-10(20) atoms/cm(3)) of metal impurities in Si was achieved locally by incorporation of nickel and iron atoms from silicide grains into silicon grains during ion milling for TEM specimen preparation. Consequently, particles with local densities of 10(13)-10(14) precipitates/cm(3) and average volumes of 10(-18)-10(-16) cm(3) formed via diffusion and precipitation. Precipitates with an irregular octahedra shape and platelet-like habit were found at dislocations. Less frequently, precipitates with a regular octahedra shape were observed in undisturbed matrix. HRTEM images and SAD patterns demonstrate that all precipitates have NiSi2 structure. Ni contents were detected for all precipitates by EDX analysis, but accumulated amounts of Fe could only be proven for some precipitates at dislocations. Quantitative EDX-analysis revealed Fe/(Fe + Ni) ratios between 16 and 30 at% for these ternary precipitates. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim