The applicability of scanning probe microscopy (SPM) in the time dependent dielectric breakdown (TDDB) characteristics of silicon oxide has been demonstrated. Our study demonstrates that cumulative failure rates by the Weibull plot of TDDB measurement for a 9.5 nm-thick oxide were found to be straight lines and shape parameters were not based on bias voltages, but were almost fixed. These results indicate that failure mode within the limits of these voltage conditions has not changed and the SPM method is applicable to the evaluation of TDDB characteristics of silicon oxides. We also applied this method to oxides on a silicon substrate surface with and without damage by plasma etching. The life expectancy in a real working voltage domain was searched for, and it presumed that a difference arose in these.