Interfacial reactions in Ni/amorphous-Si multilayers

Abstract

Ni/amorphous-Si multilayers (Ni/a-Si) were prepared by ion beam sputtering. The interfacial reactions in Ni/a-Si multilayers were studied by transmission electron microscopy and in situ X-ray diffraction. An amorphous NiSi phase (a-(Ni,Si)) is the first phase formed in the Ni and a-Si interfacial reaction. In as-deposited Ni/ASi multilayers with short modulation period ( L = 4.8 nm), the uniform a-(Ni,Si) phase forms at least in the composition range 25–62 at.% Ni, which is consistent with predictions from the calculated Gibbs free energy diagram. The mechanism that controls phase selection in Ni/a-Si interfacial reactions is discussed using nucleation theory. A nucleation controlled model for phase selection is proposed. For polycrystalline Ni and a-Si multilayers with larger modulation period ( L = 16.0 nm), amorphization is found to occur both at the Ni-a-Si interfaces, according to planar-layer growth model, and along the Ni crystallite grain boundaries in the Ni sublayer. An amorphous growth model is suggested to explain the amorphization reaction in Ni/a-Si multilayers.