Annealing of the Co/Hf bilayer on single Si, polycrystalline Si and SiO2

Silicidation of the Co/refractory metal/Si system in which the refractory m etal is used as an epitaxy promoter for CoSi2 has recently received much at tention. Hf is one of the candidates for the epitaxy promoter of cobalt sil icide like Ti. In this paper, we investigated the layer structures of the C o/Hf bilayer on various substrates like single (100)Si, polycrystalline Si and SiO2 after rapid thermal annealing. Epitaxy of CoSi2 was obtained on (1 00)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 silicidatio n of Co/Hf/(100)Si. The existence of Co-HF compounds is helpful in the form ation of epitaxial CoSi2 since they retard the diffusion of cobalt and sili con atoms. The transition temperatures of cobalt silicides in the Co/Hf/pol y-Si system were found to be lower than those in the Co/Hf/(100)Si system. The reaction between the metal and the spacer SiO2 during silicidation is a matter of concern since any conducting residue of this reaction could degr ade oxide integrity or produce bridging. In the Co/Hf/SiO2 system Hf oxides formed as a result of the reaction between Hf and SiO2 but a conducting ma terial like HfSi2 was not found to form after annealing. Considering the te mperature at which epitaxial CoSi2 forms along with the one from which the SiO2 substrate starts collapsing we may conclude that the optimum silicidat ion annealing temperature for Co/Hf/Si is 600 degrees C. (C) 2000 Elsevier Science B.V. All rights reserved.