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.