DEPENDENCE OF THE STRUCTURAL AND ELECTRICAL PROPERTIES OF ULTRATHIN COBALT SILICIDE FILMS ON FORMATION CONDITIONS.

We have studied the dependence of the electrical and structural properties of ultrathin cobalt silicide films on the annealing temperature and deposited Co thickness. If less than 10angstrom of Co is deposited, epitaxial type B CoSi sub 2 forms immediately. As the deposited thickness approaches 10angstrom, small amounts of Co sub 2 Si are observed. If greater than 10angstrom of Co is deposited, epitaxial Co sub 2 Si forms at room temperature, which proceeds either via the reaction Co sub 2 Si->Co Si->CoSi sub 2 or via Co sub 2 Si->CoSi sub 2 during annealing. In these thicker films our results suggest that the formation of type A CoSi sub 2 is correlated with the presence of Co sub 2 Si; the occurrence of type B Co Si sub 2 is correlated with the presence of CoSi as an intermediate phase. Both film thickness and reaction temperature strongly influence the electrical transport in these films such that very high resistivities are encountered when films either become very thin or are reacted at low temperatures. In the former case the size effect is responsible whereas in the latter the transport properties are dominated by extensive atomic-scale disorder.