Nucleation of Nickel Disilicide Precipitates in Float-Zone Silicon: The Role of Vacancies

Nickel is one of the fast diffusion transition metal impurities in silicon that tends to form precipitates during cooling from processing temperature. The typically observed NiSi2 plate-shaped precipitates are well-understood from structural and electrical perspectives with the exception of the initial stages of particle nucleation. Herein, the fact that excess vacancies bound into nitrogen-vacancy complexes react with interstitial nickel to form substitutional nickel atoms, Ni-s is exploited. Furthermore, excess vacancies can be removed by thermal annealing thus providing a scheme, where nickel precipitation can be studied with and without the presence of Ni-s. It is shown by deep-level transient spectrocopy (DLTS) that Ni-s considerably enhances nickel precipitate nucleation by reducing the nucleation barrier by about 1.7 eV and that Ni-s is consumed by precipitate formation. Simple energy considerations and an atomistic model of particle nucleation will be discussed.