Formation of Ni silicide from Ni(Au) films on (111)Si

Abstract

The solid state reaction between a Ni (7 at. % Au) film and a Si substrate at temperatures ranging from 250 to 800 °C is examined by scanning electron microscopy, x-ray diffraction, and Rutherford backscattering spectrometry. Compared to the usual features for thin film reaction of Ni with Si, we observed the following. (i) The simultaneous growth of Ni2Si and NiSi, and the growth of NiSi at the expense of both Ni2Si and Ni. This is related to Au accumulation in the metal layer. (ii) Au precipitation at 300 °C followed by the dissolution of the clusters thus created above the Au–Si eutectic temperature (370 °C). (iii) A decrease of the temperature of formation of NiSi2 and the appearance of thickness oscillations that are characteristic of nucleation. These different effects are interpreted by taking into account the metallurgy of the system: segregation of Au in the Ni film, Au solubility in the different silicides, change in surface and interface energies, and chemical interactions with Si.