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

The chemical nature of the Ni/Si, Ni/Ni_(2)Si and Si/Ni_(2)Si 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 Ni_(2)Si. 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 . ^(4)He^+ 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/Ni_(2)Si interface consists of a Ni‐rich silicide transitional phase while the Si/Ni_(2)Si interface shows a transitional structure which is correspondingly Si‐rich. Intensity analysis indicates that these interfacial regions are at least 22 A wide for α‐Si substrates and 9–14 A 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.