Deposition mechanism of Ni on Si(100) surfaces in aqueous alkaline solution

The spontaneous deposition process of Ni on Si(100) surface in aqueous alkaline solution was investigated by electrochemical measurements and in situ attenuated total reflection Fourier transform infrared spectroscopy (ATR FTIR). The open circuit potential (OCP) profile revealed that the deposition reaction was self-terminated as the potential steeply shifted in the positive direction after a certain immersion time. Auger depth profiles of specimens after the termination of the deposition reaction indicated that the surface was not completely covered by Ni. To clarify the deposition behavior, anodic reaction of Si in an aqueous alkaline solution containing no Ni ions was investigated by in situ ATR FTIR and electrochemical measurements. It was found that the deposition reaction was initiated by the formation of suboxide species of Si at the surface. This suboxide species served as "reductant" for Ni ions. Subsequently, the anodic reactions such as the oxidation of suboxide species and the anisotropic etching to 〈111〉 direction proceeded spontaneously. When 〈111〉 oriented microfacets were formed, the surface was passivated with silicon dioxide. Because of the silicon dioxide insulating properties, the electron generation by Si oxidation is inhibited, and then, the OCP sharply shifted in the positive direction. Apparently, the formation of 〈111〉 oriented microfacets at the surface led to the self-termination of the Ni deposition process. This study shows that the overall deposition reaction of Ni is significantly affected by the anodic reaction of Si, including the oxidation and the anisotropic etching.