Nickel film on (001) SiC: Thermally induced reactions

The reactions induced in a vacuum furnace (5×10−7 Torr) between an electron-beam-evaporated Ni film a few hundred nm thick and a (001)-oriented (i.e. Si-face-oriented) single crystalline 3C–SiC substrate are investigated by 3.2 MeV 4He2+ backscattering spectrometry, X-ray diffraction, secondary ion mass spectrometry, and scanning electron microscopy. Samples are characterized before and after annealing at temperatures of 400–700oC for 30 min. At 450oC, carbon diffuses throughout the Ni film and forms a carbon-rich layer at the Ni surface of a thickness of a few nm which remains unchanged during subsequent annealing. Some nickel silicides were detected at this initial stage but could not be clearly identified. At 450oC (after 120 min) the Ni31Si12 phase starts to form. This is the only detected phase at 500oC. The Ni2Si phase, the silicide that is thermodynamically stable with SiC and carbon, forms first at the surface and grows toward the SiC substrate. At 600oC, this reaction has consumed about half of the Ni31Si12 phase and at 700oC, Ni2Si is the only silicide in the reacted film. In all the reacted samples the carbon distribution is alike and consists of three distinct layers: a first zone with a constant carbon concentration that extends from near the SiC/silicide interface through most of the films thickness. The second zone is ∼70 nm thick and is deficient of carbon. The third zone is the thin graphite layer at the surface. There is oxygen in the film too, the distribution of which is related increasingly clearly to the carbon profile as the annealing temperature rises.