ATOM-PROBE STUDY OF THE EARLY STAGE OF SILICIDE FORMATION. II. Ni-Si SYSTEM.

Silicon-deposited Ni tips were heated at various temperatures up to 1000 K and structures and compositions of thin Ni silicide layers formed in situ were investigated by the atom probe and the field ion microscope (FIM). Although a mixed layer of Ni and Si was formed even at 80 K, FIM images of an ordered silicide structure were observed after heating the tip above 900 K. It was noticed that the evaporation field of the ordered silicide is significantly higher than those of Ni and Si, possibly due to a strong binding force among the constituting atoms. Since Ni is the major moving species, the Ni concentrations in the thin silicide layers were found to be as high as Ni//4Si near the surface and decreased to NiSi at the boundary of the silicide and the substrate Ni.