X‐ray diffraction was performedinsituduring annealing of a Co/Ti/Si(001) multilayer, which produced an epitaxial CoSi2layer. The results indicate that the Ti layer did not stay intact during the reaction, and thus could not act like a membrane, moderating Co/Si interdiffusion. Strongly textured phases (M) formed prior to CoSi2nucleation, and was unobservable upon completion of the anneal. Nucleation and growth of CoSi2on Si(001) took place in the presence ofM, new Co‐Ti‐(O) phases that were located at the metal/Si interface, and thusMmight play an important role in the perfection of the silicide. ©1995 American Institute of Physics.