Nitridation of oxide causes to accumulate nitrogen at SiO2/Si interface and prevents the diffusion of boron to the Si substrate surface. This paper shows that in NO annealed oxide, N2post annealing causes degradation such as increasing leakage current and charge trapping. Also, it is found that for a constant current stress the time-to-breakdown in N2post annealed samples is one order of magnitude smaller than that of samples without N2post annealing. These increases of leakage current and charge trapping are found to be due to the penetration of boron into the oxide during subsequent high temperature post N2annealing.