Berlin 2008 – wissenschaftliches Programm

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DF: Fachverband Dielektrische Festkörper

DF 12: Dielectric and ferroelectric thin films and nanostructures II

DF 12.3: Vortrag

Donnerstag, 28. Februar 2008, 11:00–11:20, EB 107

Leakage spot evolution in thin (ZrO₂)_0.8(Al₂O₃)_0.2 -films observed by conductive atomic force microscopy (CAFM) — •Dominik Martin¹, Oliver Bierwagen², Matthias Grube¹, Lutz Geelhaar², and Henning Riechert² — ¹namlab gGmbh, D-01187 Dresden — ²Qimonda, D-81730 Munich

A change from amorphous to nanocrystalline dielectric layers is necessary to achieve dielectric constants >30 as required for future technology nodes. This often leads to significantly higher leakage currents. These were measured in such inhomogeneous samples with a spatial resolution on the nanoscale. CAFM was used to characterize 20 nm-thin (ZrO₂)_0.8(Al₂O₃)_0.2 -films grown by molecular beam deposition. In nanocrystalline samples, there are hillocks at the surface with typical diameters and heights of 30 nm and 3 nm, respectively. An investigation by transmission electron microscopy implies that these hillocks are crystallites that protrude from the surface. CAFM current maps show leakage spots in which the current is significantly higher than in the surrounding matrix. These leakage spots are strongly correlated with the hillocks on the corresponding morphology images, indicating that the formation of crystallites really leads to leakage paths. To distinguish between different transport mechanisms, multiple images of the same area were taken, while the bias-voltage was changed consecutively. By using the entire set of images, IV-curves can be assigned to each location. These show a hysteretic behaviour for all leakage spots. Also, the voltage at which the strong increase in current occurs varies significantly for different leakage spots, i.e. between -1 V and -4 V.