Crystallization of NiSix in a Body-Centered Cubic Structure during Solid-State Reaction between an Ultrathin Ni Film and Si(001) Substrate at 150–350 °C

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We investigate ultrathin silicide formation during a solid-state reaction between Ni layers and Si(001) substrates by aberration-corrected electron microscopy. Interdiffusion of two nm thick (equivalent) Ni layers with Si during magnetron-sputter deposition results in an amorphous Ni–Si solid solution. Upon annealing at 150–350 °C, a novel body-centered cubic (bcc) NiSix phase is found to grow epitaxially with a crystallographic relationship {100}<001>bcc-NiSix//{100}<001>Si. bcc-NiSix belongs to the space group I4̅3m (217) with random Ni and Si distribution. The cell parameter is 0.272 nm, which is approximately half that of NiSi2. Further annealing transforms bcc-NiSi to NiSi2 with an activation energy of 0.6 ± 0.1 eV.