Formation, oxidation, electronic, and electrical properties of copper silicides

Abstract

The solid state reaction between copper and silicon has been studied using Rutherford backscattering, glancing‐angle x‐ray diffraction, scanning electron microscopy, and x‐ray photoemission spectroscopy. Schottky‐barrier‐height measurements on n‐type Si (100) have also been performed in the temperature range of 95–295 K with the use of a current‐voltage technique. The results show that a metal‐rich compound with a composition in the Cu₃Si range forms at low temperatures (473 K). The electronic properties of the compound are dominated by the hybridization between the Cu(d) and Si(p) valence states. A direct consequence of this hybridization is the peculiar oxidation behavior of the compound surface; both Cu and Si have been found to oxidize at room temperature. The oxidation of Si in the silicide is enhanced as compared with the oxidation of the elemental single‐crystalline Si surface. Upon annealing the oxidized surface, a solid state reaction takes place: Cu₂O disappears and a thicker SiO₂ layer grows, owing to the large difference in free energies of formation between SiO₂ and Cu₂O. The n‐type barrier height of 0.79 eV for both the as‐deposited metal and the metal‐rich silicide phase decreases with increasing temperature with a coefficient close to the temperature coefficient of the indirect energy gap in Si. These results suggest that the Fermi level at the interface is pinned relative to the valence‐band edge, independent of temperature.