Structural changes during the reaction of Ni thin films with (100) silicon substrates

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

Direct observation of preferential heating near grain boundaries in patterned silicide films

Heat generation in silicide stripes is studied using scanning thermal expansion microscopy. Local hot spots in the lithographically patterned silicide stripes can be imaged with high spatial resolution (around 20 nm). On the micrometer scale the enhancement of temperature can be linked to pronounced depressions appearing in the film topography, resulting in current crowding. On the submicrometer scale hot spots appear that do not correlate with large thickness variations and can be accounted for by crystallographic silicide grain boundaries with a locally enhanced resistivity. Our experimental approach, which enables to monitor local heating with submicrometer spatial resolution, provides a sensitive method to monitor device reliability. (C) 2010 American Institute of Physics. [doi:10.1063/1.3475506]status: publishe

Study of CoSi2 Formation from a Co-Ni Alloy

CoSi formation from Co–Ni alloys with 25 and 10% Ni content was investigated. Samples with various 2 Co–Ni /Ti stacks were characterized by four-point probe, AES, XRD, RBS and TEM. Light scattering measurements were carried out for roughness evaluation. Stress build-up was estimated from room temperature measurements of wafer curvature. It was found that Co disilicide formation temperature decreases with an increase of the Ni percentage. CoSi growth at temperatures around 450–5008C depending on Ni concentration 2 and Ti cap thickness was observed. Sheet resistance of 5–6.5 V/ sq. was measured for various Co–Ni / Ti compositions. CoSi (220) and CoSi (111) peaks were detected on XRD spectra for both Ni-rich and Ni-poor 2 2 layer. Stress values of 0.9–1.9 GPa were calculated for silicidation of various Co–Ni /Ti stacks. The roughness of the silicide film was found to be dependent on Ni concentration, Ti cap thickness and anneal temperature

Study of thermal stability of nickel silicide by X-ray reflectivity

The thermal stability of Ni silicide, in comparison to the more conventionally used Co silicide, is studied by X-ray reflectivity. These data were complemented by sheet resistance measurements, transmission electron microscopy, time-of-flight Rutherford backscattering spectrometry, X-ray diffraction and time-of-flight elastic recoil detection analysis. (c) 2005 Published by Elsevier B.V