Study of the initial stage of electroless Ni deposition on Si (100) substrates in aqueous alkaline solution

We investigated electroless nickel deposition in aqueous alkaline solution with and without conventional palladium catalyzation and found that nickel deposition was initiated and sustained on silicon substrates even without the palladium nuclei activation of the surface. But the resulting quality of the nickel film was not as good as the one with the prior activation. The reason was observably directed to the initial stage of the deposition processes. Nickel deposits nucleation on silicon surface was considered crucial for subsequent achievement of a well adhered, least damage influenced film. Effects of ammonia fluoride, nickel ion concentration and bath temperature in the aqueous nickel bath without reducing agent were studied over the nucleation results. The existence of fluorine ions in the solution increased the density of nickel nuclei particles and refined nickel particle sizes to the most extent, while concentrated nickel bath enhanced the nucleation as well. Consequently the improved quality of nickel film that was obtained from the electroless baths can be attributed to the fine and dense nickel particles formed in the initial stage by virtue of the fluorine ion, concentrated nickel ion and elevated temperature.