Interfacial reactions in Ni/6H-SiC at low temperatures

We report the reaction between thin Ni films and 6H-SiC substrates at relatively low temperatures (<550°C) and the diffusion behavior of carbon during silicide formation. The phase transformation and distribution of chemical constituents were investigated using transmission electron microscopy. About 60 nm of Ni was deposited on 6H-SiC using an e-beam evaporator, and samples were then annealed using a rapid thermal annealing process. In a Ni/SiC sample annealed at 450°C, while there are no Ni-silicides present, a graphite inter layer is formed between the SiC substrate and Ni. In addition, Si is released by SiC decomposition diffusing to the Ni layer to form a Ni(Si) solid solution. As the annealing temperature increases to 550°C, a phase transformation begins, with the Ni-silicides going from Ni₃Si to Ni₃₁Si₁₂ and N₂Si over time. At the very beginning of the Ni/SiC reaction, carbon atoms liberated from SiC diffuse through un-reacted polycrystalline Ni towards the external surface and form a graphite layer. During the silicidation reaction, carbon atoms (a decomposition product formed after the Ni/SiC reaction) are distributed inside the silicide layer and precipitate in the form of graphite.