Defects in thin film oxides
Thin films of HfO2 on silicon were probed via conductive, contact afm and defects were identified by high leakage currents. (a) The same region was imaged over a range of tip bias to create a map of leakage current and identify defects. (b) High-resolution image of one defect. Features <5 nm in size can be resolved. (c ) A-B cross section from (b).
Analysis of the higher-than-expected spatial resolution showed that stress concentrations in the contact zone yielded a “focusing” of the current. Stresses under the tip lead to increased conductivity below the surface, as shown in (d). If the combination of tip an load are in the gray region of the chart, then the silicon undergoes a semiconducting-t0-metal transition. Alternatively, pressure-induced bandgap narrowing can increase conductivity if the dopant density in the substrate is sufficiently high. (e) Another high-resolution leakage current map.
[Nikiforov, Brukman, and Bonnell, Applied Physics Letters 93, 181101(2008)]