This paper presents the characterization of degradation of tunnel oxide during plasma recess of field oxide films for Shallow Trench Isolation (STI) in sub 30 nm flash memory devices. Simple plasma charge damage monitor wafers with Metal-Oxide-Semiconductor (MOS) capacitor structures were used to analyze the mechanisms of degradation of tunnel oxide due to process-induced charging damage. We characterized the gate leakage currents and breakdown voltages of MOS capacitors with area antennas after performing the plasma process for field oxide recess of STI with various etching conditions in a dual-frequency capacitively coupled plasma reactor. The results showed that the degradation was strongly dependent on plasma non-uniformity, which could be improved by optimizing the radio-frequency and biasing power. Especially, we found that RF biasing power caused stress-induced leakage currents due to dielectric breakdown by the leakage current originating from the electrostatic chuck. (C) 2012 Elsevier B.V. All rights reserved.