Phase separation and layer sequence reversal during silicide formation with Ni-Cr alloys and Ni-Cr bilayers

Abstract

Solid-state reactions of thin films of Ni–Cr alloys, and Ni–Cr bilayers, with Si have been studied by Auger electron spectroscopy and x-ray diffraction. Silicide formation for the alloys which starts at ∼400 °C is completed (after 30 min anneal) for Cr-rich and Ni-rich compositions at 500 and 600 °C, respectively, with phase separation into a NiSi layer near the substrate and a CrSi2 rich layer outside. For the Cr/Ni/Si structure each of the layers reacts independently with Si; structures of Cr/Ni2Si/Si, Cr/NiSi/Si, CrSi2/NiSi/Si, and CrSi2/NiSi2/Si are obtained following 30-min anneals at 300, 400, 500, and 850 °C, respectively. For the Ni/Cr/Si structure for annealing temperatures in the range of 500–750 °C, the inner part of the Cr layer reacts with the substrate to form CrSi2, while the outer part forms a solid solution with Ni; the interaction of this solution with Si results in the inward formation of NiSi and the outward formation of CrSi2. After 850 °C anneal layer sequence reversal is observed, when a NiSi2 layer is formed adjacent to the Si substrate.