X-ray photoelectron spectroscopy study of the Ni/Si oxide/Si interface

Abstract

The electronic structure of the Ni/Si oxide/Si interface has been investigated using x-ray photoelectron spectroscopy. This interface represents a more realistic situation encountered in semiconductor device processing technology. Approximately 35 Å of high-purity Ni was sputter deposited on 〈111〉Si (covered with a thin native oxide layer) at room temperature. A sputter profiling technique was employed to determine the composition and reactivity as a function of depth. The measurements show considerable reactivity at the Ni/Si oxide/Si interface, even at room temperature. The Ni 2p3/2 peak exhibits a gradual shift to higher binding energy which indicates that the overlayer cannot be regarded as a single unique nickel silicide phase. The large positive shift of the Ni 2p3/2 and the small shift of the corresponding Si 2p peak suggest that ionicity plays a nominal role in the Ni–Si chemical bond. The valence-band spectra show a dominant 3d-derived feature which gradually shifts to higher binding energy. The observed shifts in the Ni levels are attributed to the change in the electronic configuration of Ni in going from Ni-rich silicide to Si-rich silicide. A study of the composition as a function of depth shows that the Ni/Si oxide/Si interface is not sharply defined due to the interdiffusion of Ni and Si. Thus, the interface is identified as a graded transition region with composition ranging from Ni-rich to Si-rich silicide.