IN-SITU TRANSMISSION ELECTRON-MICROSCOPY OBSERVATIONS OF SILICIDATIONPROCESSES FOR COBALT THIN-FILMS DEPOSITED ON SILICON

Morphological evolution associated with silicidation of Co thin films deposited on (100) and (111) Si substrates has been followed using tra nsmission electron microscopy with in situ thermal annealing from ambi ent temperature up to 850 degrees C. Noticeable structural changes ass ociated with the formation of CoSi2 occur at temperatures as low as 40 0 degrees C and the reaction is essentially complete at about 500 degr ees C. Prolonged heating above 500 degrees C leads to CoSi2 grain grow th and coalescence and, finally, to pinholes formation. Silicidation o f Co films on (100) and (111) Si substrates follows the same pattern. The morphology of films annealed in situ is similar to those annealed ex situ except that the Si/CoSi2 interface appears to be much rougher. This behavior is associated with the specific geometry of cross-secti onal TEM specimens, where surface diffusion dominates bulk diffusion. Very thin Co films, which have less contribution from surface diffusio n than thicker films, are ideal for studying dynamic phenomena at Co/S i reactive interfaces.