Immersion nickel deposition on blank silicon in aqueous solution containing ammonium fluoride

Immersion deposition of Ni on p-Si (100) blank substrates was carried out in an aqueous NiSO4 solution at a pH value of 8 through displacement reactions. Study of the early deposition stage revealed that incorporation of 2.5 M NH4F in solution promoted Ni nucleation significantly. By adding fluoride, it was observed that metallic Ni was deposited constantly at the expense of Si and the deposition was not self-limited. Sponge-like Ni deposits were observed and it might explain the non-limiting feature of such immersion Ni deposition over Si. Transmission electron microscopic images of Ni/Si cross-sections showed that during the reactions, Si oxide played a role of the intermediate phase. The whole process could have involved successive Si oxidation steps. Eventually the oxide was etched away by fluoride resulting in a nanoporous Ni film.