Structural changes during the reaction of Ni thin films with (100) silicon substrates
- Author(s): Thron, Andrew M.
- Greene, Peter K.
- Liu, Kai
- van Benthem, Klaus
- et al.
Published Web Locationhttp://www.sciencedirect.com/science/article/pii/S1359645412000717
Ultrathin films of nickel deposited onto (100) Si substrates were found to form kinetically constrained multilayered interface structures characterized by structural and compositional gradients. The presence of a native SiO2 on the substrate surface in tandem with thickness-dependent intrinsic stress of the metal film limits the solid-state reaction between Ni and Si. A roughly 6.5 nm thick Ni film on top of the native oxide was observed regardless of the initial nominal film thickness of either 5 or 15 nm. The thickness of the silicide layer that formed by Ni diffusion into the Si substrate, however, scales with the nominal film thickness. Cross-sectional in situ annealing experiments in the transmission electron microscope elucidate the kinetics of interface transformation towards thermodynamic equilibrium. Two competing mechanisms are active during thermal annealing: thermally activated diffusion of Ni through the native oxide layer and subsequent transformation of the observed compositional gradient into a thick reaction layer of NiSi2 with an epitaxial orientation relationship to the Si substrate; and, secondly, metal film dispersion and subsequent formation of faceted Ni islands on top of the native oxide layer.