Nickel film on (001) SiC: Thermally induced reactions

Abstract

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 4He 2+ backscattering spectrometry, X-ray diffraction, secondary ion mass spectrometry, and scanning electron microscopy. Samples are characterized before and after annealing at temperatures of 400–700 oC for 30 min. At 450 oC, 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 450 oC (after 120 min) the Ni 31Si 12 phase starts to form. This is the only detected phase at 500 oC. The Ni 2Si phase, the silicide that is thermodynamically stable with SiC and carbon, forms first at the surface and grows toward the SiC substrate. At 600 oC, this reaction has consumed about half of the Ni 31Si 12 phase and at 700 oC, Ni 2Si 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.