Analysis of factors in the nanoscale physical and electrical characterization of high-K materials by conductive atomic force microscope

The conductive atomic force microscope (CAFM) has been shown to be a powerful tool to study the physical and electrical properties of high-k materials on nanoscale. However, such accurate measurements could be altered by external factors. In this work, the main factors affecting CAFM measurements including environmental conditions, tip coating materials and the tip-sample bias are evaluated by analyzing the topographic and current maps performed on HfO2 stacks in different conditions. It is found that environmental conditions have notable effects on the CAFM measurements due to the water meniscus formed by adsorbed water layers on the tip and sample surface in air. And the lateral resolution of the technique can be improved remarkably by measuring in a high vacuum environment. The mechanical and electrical properties of tip coating materials are found to be related to the stability of tip conductivity and the real voltage drop in the stack, hence have a key influence on the current measurement. Moreover, the tip-sample interaction can be altered by the electrostatic force induced by the applied bias, leading to variations of the topographic image of the surface with the bias voltage. Our results indicate that the impact of these factors must be taken into account when performing CAFM measurements under different conditions or comparing the results obtained in different experiments. Copyright © 2014 Taylor & Francis Group, LLC.