Implanted noble gas atoms as diffusion markers in silicide formation

Abstract

Implanted noble gas atoms of Ar and Xe have been used as diffusion markers in growth studies of silicides formed by reacting metal films with silicon substrates. MeV 4He ion backscattering has been used to determine the displacement of the markers. Two approaches were used: either the silicon samples were implanted with Xe or Ar and then covered with a thin layer of metal, or the metal layer was implanted with the marker. When the sample was heated to form the silicide layer, the displacement of the marker relative to the surface determined the identity of the diffusing species. Diffusion markers have been used in growth studies of six silicides: Ni2Si, Mg2Si, FeSi, VSi2, TiSi2 and Pd2Si. We found that Si atoms are the predominant moving species in diffusion in VSi2, TiSi2 and FeSi, while Ni atoms are the moving species in Ni2Si and Mg in Mg2Si. In Pd2Si, both Pd and Si are diffusing species with Si the faster of the two. Chemical effects can play a role in marker studies. In the thermal oxidation of Si, the displacement of Xe markers is consistent with the fact that oxygen is the moving species. Implanted As, on the other hand, accumulates at the Si-SiO2 interface. Therefore, it is necessary to choose markers which are chemically inert. © 1975.