Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
7882883 | Acta Materialia | 2012 | 11 Pages |
Abstract
Ultrathin films of nickel deposited onto (1Â 0Â 0) 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 6.5Â nm thick Ni film on top of the native oxide was observed regardless of the initial nominal film thickness of either 5 or 15Â 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.
Related Topics
Physical Sciences and Engineering
Materials Science
Ceramics and Composites
Authors
Andrew M. Thron, Peter K. Greene, Kai Liu, Klaus van Benthem,