Diffusion layers and the Schottky-barrier height in nickel silicide—silicon interfaces

New experimental results are presented which suggest that a diffusion layer is always present after forming nickel silicide interfaces at Si surfaces. This layer is a distinct ordered metallic phase having a silicon-rich (Ni${\mathrm{Si}}_2$) stoichiometry which occurs when Ni atoms occupy alternate tetrahedral interstitial voids in the Si lattice. Evidence of this layer is obtained with the use of low-energy electron diffraction, transmission-electron microscopy, and photoelectron emission from interfaces produced at room temperature and higher temperatures at which ${\mathrm{Ni}}_2$Si and NiSi compounds form by selective growth. The invariance of the Schottky-barrier height for Ni silicide interfaces is attributed to this ordered stoichiometric layer. In addition, this interfacial structure appears to have important bearing on planar selective growth processes which occur during the formation of nickel silicide interfaces.