IRON SILICIDE FORMATION BY PRECIPITATION IN A SILICON BICRYSTAL

Segregation and precipitation of iron in a Sigma = 25 silicon bicrysta l have been carefully investigated by means of high resolution electro n microscopy and energy dispersive X-rag analyses; in combination with capacitance and electron beam induced current measurements. After int entional incorporation of iron in the bicrystal by a simple heating pr ocedure, it was shown that a non-equilibrium segregation of iron has o ccurred after rapid cooling whereas iron precipitates have been produc ed upon slow cooling. The silicides are formed mainly at the grain bou ndary area and they were found to belong to the epsilon-FeSi cubic or alpha-FeSi2 tetragonal phases. Each precipitate is simply oriented wit h respect to one of the two grains without any preference between them . The orientation relationships were found in perfect agreement with t hose observed for the corresponding iron silicides that are epitaxiall y grown on oriented silicon substrates. Barrier and recombinative effe cts on the contaminated (1200 degrees C) and slowly cooled samples hav e been detected. These effects have been associated with the formation of iron silicides at the grain boundary.