Evaluation of trap creation and charging in thin SiO2 using both SCM and C-AFM

Conductive atomic force microscopy (C-AFM) and scanning capacitance microscopy (SCM) are used in this work to characterize trap creation and charge trapping in ultra-thin SiO₂. It is found that C-AFM working at normal operational voltages causes severe damage and subsequent negative charge trapping in the oxide. Permanent hillocks are seen in the topography of stressed regions. The height of these features is determined rather by the applied voltage than the electric field. Electrostatic repulsion between tip and sample and Si epitaxy underneath the oxide are the two most probable causes of this feature. The immediate physical damage caused in the oxide during high field C-AFM measurements is a possible showstopper for use of the C-AFM to investigate differences in pristine interface states. SCM operates at lower voltages, yielding less oxide damage and is able to indicate the interface state density variations through hysteresis in the dC/dV vs. V curves.