Ultrathin oxynitride films have been grown on partially strain compensated Si/Si1-x-yGexCy/Si layers by microwave plasma at a low temperature. Significant improvements in charge-to-breakdown (Q(BD)) and charge trapping under static and dynamic electric field stress are observed for O-2/NH3/NO-plasma treated films due to efficient removal of H species from the interface. The trapped charge generation and charge centroid show a frequency dependence for bipolar stress and polarity dependence in case of unipolar stress.