The epitaxial nature of the CoSi2formed on the (100)Si substrate as a result of annealing a Co/Ta bilayer at 500–1000 °C for 20 s in N2atmosphere is described. At the early stage of annealing, diffusion of Co and Si occurs across the interlayed Ta layer, first forming a CoSi layer on the Si substrate. After that, CoSi2grains nucleate at the CoSi/Si interface and grow laterally parallel to the surface. Due to a difference in mobility the CoSi2grains at the interface of the CoSi/Si impede the interface movement, leading the facet formation. Even after annealing below 600 °C, the epitaxial CoSi2grains are nucleated at the limited area of the nonepitaxial CoSi/Si interface and the faceted corner, and grow laterally along the Si surface. By increasing the annealing temperature, the epitaxiality of CoSi2improves due to the increased lateral growth rate of the CoSi2. However, annealing above 900 °C impairs the CoSi2crystallinity because the interlayered Ta loses its function as a diffusion barrier due to the formation of the TaSi2. ©1995 American Institute of Physics.