Annealing of the Co/Hf bilayer on single Si, polycrystalline Si and SiO(2)

Silicidation of the Co/refractory metal/Si system in which the refractory metal is used as an epitaxy promoter for CoSi(2) has recently received much attention. Hf is one of the candidates for the epitaxy promoter of cobalt silicide like Ti. In this paper, we investigated the layer structures of the Co/Hf bilayer on various substrates like single (100)Si, polycrystalline Si and SiO(2) after rapid thermal annealing. Epitaxy of CoSi(2) was obtained on (100)Si by annealing Co/Hf/(100)Si. Co-Hf compounds seem to play an important role of barriers against the reaction between Co and Si during silicidation of Co/Hf/(100)Si. The existence of Co-Hf compounds is helpful in the formation of epitaxial CoSi(2) since they retard the diffusion of cobalt and silicon atoms. The transition temperatures of cobalt silicides in the Co/Hf/poly-Si system were found to be lower than those in the Co/Hf/(100)Si system. The reaction between the metal and the spacer SiO(2) during silicidation is a matter of concern since any conducting residue of this reaction could degrade oxide integrity or produce bridging. In the Co/Hf/SiO(2) system Hf oxides formed as a result of the reaction between Hf and SiO(2) but a conducting material like HfSi(2) was not found to form after annealing. Considering the temperature at which epitaxial CoSi(2) forms along with the one from which the SiO(2) substrate starts collapsing we may conclude that the optimum silicidation annealing temperature for Co/Hf/Si is 600 degrees C.