Lattice and grain boundary self-diffusion in Ni2Si: Comparison with thin-film formation

Abstract

The Ni2Si lattice and grain boundary self-diffusion parameters have been studied using radiotracers 63Ni for Ni diffusion, 68Ge for Si diffusion, conventional sectioning techniques, and bulk specimens. The results obtained show that Ni diffuses faster than Ge(Si) in the lattice (and in the grain boundaries) of Ni2Si, in agreement with the structure of this silicide. The activation energies for Ni lattice and grain boundary diffusion are respectively 2.48 eV (measured between 650 and 910 °C) and 1.71 eV (530–710 °C). These values are comparable to those obtained in pure metals of similar melting temperature. They suggest that Ni diffuses on its own sublattice by a vacancy mechanism. Grain boundary diffusion in this intermetallic compound appears as a very efficient process for mass transport at low temperature. A quantitative comparison with the kinetic of formation of Ni2Si (by solid state reaction between a Ni film and a Si substrate) indicates that the growth of thin films is controlled by the diffusion of Ni along the silicide grain boundaries. This mechanism explains the rapidity of the formation and its low activation energy (≊1.6 eV).