The phenomena of local nucleation and lateral crystal growth of cobalt silicide phases have been investigated with emphasis on a possible reason of the surface roughness and pinholes of the silicide layer. Local nucleation of the CoSi2? grains on the structural defects of the silicon surface is found for the silicide films formed by vacuum annealing the Co/Si(100),(111) structures. Self-sustaining crystallization of CoSi2 phase around a crystal defect is observed. Lateral growth of the silicide crystallites from the Si crystal defects, on the Co-patterned step edge and SiO2 : island steps, indicate that the lateral growth mode is preferable for the silicide phases at Co!Si interface. The silicide film surface and CoSi2/Si interface are much smoother if an additional zircon (Zr) layer is deposited onto the Co film before subsequent annealing. The CoSi2 films were used as a buffer layer for the YBCO/CoSi2/Si and YBCO/CeO2/YSZ/CoSi2/Si/Al2O3 heterostructures in this work. The superconducting transition temperatures of the YBCO films were obtained to be up to 86 K.