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

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 Ni2SL 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>. 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/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 A wide for a -Si substrates and 9-14 A wide for crystalline SL The as-deposited Ni/Si interface cannot be described as a unique singlephase, but rather as a chemically graded transitional region showing a composition which varies from Si-rich toNi-rich silicides.