XPS study of the chemical structure of the nickel/silicon interface

Abstract

The chemical nature of the Ni/Si, Ni/Ni2Si and Si/Ni2Si interfaces have been investigated using x-ray photoelectron spectroscopy. Peak position, line shapes, and envelope intensities are used to probe the compositional structure of these systems. Two approaches have been employed: one approach examines the advancing planar silicide front by dynamically monitoring the in situ formation of Ni2Si. This has the advantage of allowing examination of a realistic interface which is bounded on either side by an extended solid. The second approach follows the development of the Si/Ni interface using UHV depositions of thin layers of Ni on Si <100≳. 4He+ backscattering is used to follow the progression of the thin film reaction and to provide quantitative information on atomic composition. These experiments demonstrate that the Ni/Ni2Si interface consists of a Ni-rich silicide transitional phase while the Si/Ni2Si interface shows a transitional structure which is correspondingly Si-rich. Intensity analysis indicates that these interfacial regions are at least 22 Å wide for α-Si substrates and 9–14 Å wide for crystalline Si. The as-deposited Ni/Si interface cannot be described as a unique single-phase, but rather as a chemically graded transitional region showing a composition which varies from Si-rich to Ni-rich silicides.