Microstructural characterization of ordered nickel silicide structures grown on (111) nickel silicide films

The formation processes of epitaxial nickel silicides, resulting from the interaction of nickel silicide films (10 nm-100 nm) on (111) silicon (Si) substrates after furnace annealing, have been studied using transmission electron microscopy (TEM) and x-ray diffraction (XRD) techniques. The formation of type-A epitaxial grains (i.e., grown with the same orientation of the underlying Si substrate) and type-B epitaxial grains (i.e,, rotated by 180 degrees around the surface normal) in ''thick'' epitaxial films (i.e., greater than 35 nm) is proposed to be linked to the formation of a fluorite-based CuPt (Ll(1))-like NiSi phase. This phase is found to be a metastable phase and is believed to be a transitional phase toward the formation of the equilibrium NiSi2 phase in both type-a and type-B orientations. In addition, we have found that a fluorite-based CuPt-like NiSi may even coexist with a fluorite-based CuAu I-like structure. The interrelationship between these two structures is discussed in the context of a displacive transformation process in fee structures as originally proposed by Hansson and Barnes [Acta Metall, 12, 315 (1964)] and Pashley et al. [Philos. Mag. 19, 83 (1969)].