First phase nickel silicide nucleation and interface structure at Si(100) surfaces

Abstract

Photoemission and work function measurements are used to investigate the formation and structure of Ni–Si(100) interfaces at 300 K. For Ni coverages θ≲0.5 Å (4.6×1014/cm2) a chemisorbed phase of Ni surface atoms forms. This chemisorbed phase persists to coverages θ≂2 Å; but also in this coverage range, a diffusion layer forms in the Si lattice. At θ≊1.5 Å the surface composition closely resembles NiSi. Addition of more Ni atoms (θ≥1.5 Å) initiates nucleation of Ni2Si. The growth of this phase continues up to θ≊1.5 Å where silicide formation stops. Additional Ni atoms deposit as a pure Ni overlayer. These results yield a model for Ni–Si interfaces formed at room temperature which consists of a shallow diffusion layer of Ni atoms in the Si lattice, a very thin (1.5-Å thick) interface having NiSi chemical characteristics, a Ni2Si phase (15-Å thick) of relatively uniform stoichiometry followed by a Ni layer.