Nickel diffusion and silicide island formation on silicon (111)

Crystalline nickel disilicide islands have been observed on the Si(111) surface by atomic force microscopy (AFM). The nickel disilicide islands coalesce following a high temperature anneal (≈1260K). The islands differ from those formed at lower temperature in both shape and orientation. To explain the differences, we discuss kinetically limited growth accompanying phase and surface segregation of Ni from the bulk silicon wafer, and condensation of a Ni-rich NiSi_2-x liquid phase at the surface. Condensation from the liquid phase to NiSi₂ is concluded to be responsible for the structure of the crystallites. High temperature growth conditions lead preferentially to A-type (non-twinned) silicide structures.