Berlin 2005 – scientific programme

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O: Oberflächenphysik

O 34: Rastersondentechniken II

O 34.8: Talk

Monday, March 7, 2005, 12:30–12:45, TU EB407

Laterally resolved electrical characterization of ultrathin oxides — •Herbert Wormeester, Marko Sturm, Andrey Zinine, Radko Bankras, Jisk Holleman, Jurriaan Schmitz, and Bene Poelsema — MESA+ Institute for Nanotechnology, Universiteit Twente, Enschede, The Netherlands

A non-contact AFM with a conducting tip was used to image both the topography and electrical properties of a 2.5 nm thick aluminumoxide film on Si(001). These films were grown with Atomic Layer Deposition (ALD). Large protrusions are observed on the surface, whose contrast depends on the applied bias voltage. They are the result of an electrostatic interaction between tip and a fixed charge. A quantitative understanding of these features is only feasible if not only the image charge in the tip is evaluated, but also the image of the tip in the silicon is taken into account. The Contact Potential Difference (CPD) of the surface was evaluated with and without the use of lock-in technique (1f signal). The similarities and differences of these measurements will be discussed. A 60 mV change in CPD over the surface was found to correlate with the topography. The local variation of the capacitance (2f signal) was found to negatively correlate with the topography, i.e. a larger height correlates to a lower capacitance. On a siliconoxide film with similar thickness and roughness, a lower variation of the capacitance was found to be uncorrelated with the roughness. These seemingly conflicting results can be attributed consistently to different growth modes of the oxide films.