Formation and stability of NiSi in the presence of Co and Fe alloying elements

The formation and degradation of NiSi in the presence of Co and Fe alloying elements have been investigated. Alloyed Ni layers were characterized with in situ techniques to determine the stability of the NiSi phase on single crystalline and on polycrystalline Si substrates. It is shown that the phase stability is decreased with the addition of Co or Fe. The formation of the NiSi(2) phase on Si(100) is initiated at a temperature that is more than 200 degrees C lower for the Ni alloys than for a reference Ni layer. Thereby a few percent of Co or Fe results in the formation of a polycrystalline NiSi(2) phase on a single crystalline substrate. The low formation temperature of the NiSi(2) phase in the presence of Co or Fe can be attributed to a mixing entropy effect. The morphological stability of the silicide films on Si(100) and on polycrystalline Si is improved due to the early formation of NiSi(2) and is related to an increased film thickness and also to a higher deformation temperature for the poly-Si.