Reactive Diffusion in a Ni–Si Bulk Diffusion Couple

Abstract

Reactive diffusion of the Ni–Si system has been studied by using bulk Ni/bulk Si single crystal diffusion couples in the temperature range from 823 to 1023 K. The results were compared with the previous experimental results obtained by using Ni thin film/bulk Si diffusion couples.
In the bulk diffusion couples annealed more than 3.6 ks, Ni₅Si₂, Ni₂Si, Ni₃Si₂ and NiSi were found. The silicides formed in the bulk diffusion couple grew satisfying the parabolic law and square of growth rate, k², of Ni₂Si could be expressed by the following equation:
k²=3.21×10⁻⁷exp(154kJ⁄RT)(m²⁄s).
The value k² obtained by extrapolating the above equation to the lower temperatures ranging from 523 to 603 K is 1⁄10²∼1⁄10⁴ times smaller than the values for Ni₂Si formed in the thin diffusion couples in the temperature range. However, the values of interdiffusion coefficients for the thin couples and bulk couples agree well with each other. The reason for the difference in k² between the thin and bulk samples can be atrributed to the difference of phase layers which are adjacent to the Ni₂Si phase and not to the fast diffusion such as grain boundary diffusion in the thin film diffusion couples.