The reaction of Co with epitaxial SiGeC/Si layers is investigated and compared to the reaction of Co with SiGe/Si layers. The sequence of phase formation is the same as the reaction of Co with monocrystalline Si, however, cobalt disilicide is formed at much higher temperatures. The presence of C further delays the disilicide formation, as a result of C accumulation at the silicide/substrate interface during the reaction, which blocks the Co diffusion paths. The CoSi2 layers thus formed exhibit a preferential (hOO) orientation. The slow supply of Co atoms to the silicide/Si interface, due to the blocking of Co diffusion paths by Ge and C, is believed to be the reason for this epitaxial alignment. (C) 1997 American Institute of Physics.