Influence of thinSiO2interlayers on chemical reaction and microstructure at the Ni/Si(111) interface

Surface electron spectroscopies (Auger electron spectroscopy and ultraviolet photoemission spectroscopy) and electron microscopy (scanning and transmission) have been used to study the influence of interfacial ${\mathrm{SiO}}_2$ on the reactivity of the Ni/Si(111) interface. Iterated Ni depositions (up to ∼75 Å thick), at room temperature, on Si oxide layers of various thicknesses [grown on Si(111)] were made in ultrahigh vacuum and followed by in situ annealing up to 900 °C. It was found that Ni initially agglomerates into islands at room temperature and above. Furthermore, at elevated temperatures the Ni reacts with the underlying Si through pinholes in the oxide to form ${\mathrm{NiSi}}_2$. A higher temperature was required to initiate the silicide formation reaction for thicker ${\mathrm{SiO}}_2$ layers, suggesting that the reaction is limited by mass transport through pinholes in the oxide. Direct Ni-${\mathrm{SiO}}_2$ interaction, in contrast, is rather limited. Some ${\mathrm{SiO}}_2$ decomposition may take place at elevated temperatures and at such favorable sites as pinholes and structural defects in the oxide or areas adjacent to silicides. The low Schottky-barrier height found for reacted contacts (0.60±0.04 eV) was comparable to that obtained at nonperfect, oxide-free Ni silicide/n-type Si(111) interfaces.