STM observation of nickel silicides on Si(001)

The formation of NiSi2 on the clean 2 x 1 and the hydrogen-terminated Si(001) substrates has been examined and compared by using scanning tunneling microscopy. The deposited Ni atoms form clusters on both substrates at room temperature. After annealing at elevated temperatures, the clusters coalesce and inhomogeneous surface morphology of the NiSi2 is obtained in the case of the deposition onto the clean surface, due to immediate Ni diffusion into the bulk Si. In contrast, the NiSi2 films formed by using the hydrogen-terminated surface have a large flat morphology. This is explained as being the result of the enhanced "in-plane" nickel diffusion and the blocking of inter-diffusion by the existence of stable Si-H bonds formed on the surface.