Estimating the Number of Defects in a Single Breakdown Spot of a Gate Dielectric

Conduction Atomic Force Microscopy (CAFM) is used to locally stress a 3.5 nm thick SiO2 film to induce soft dielectric breakdown (SBD). The tip-to-surface adhesion and current-voltage ( I-V ) characteristic at the breakdown location are measured by the CAFM before and after the SBD event. The adhesion force is enhanced after SBD because oxygen ion and charged defects are created at the SBD location during stressing which increases the adhesion via image charge forces. We show that the change in adhesion force, supported by charge transport modeling of the I-V data, can be effectively used to estimate the density and number of defects (~20-30) generated during SBD at a single breakdown spot. The information could be useful to assess the post-breakdown reliability and performance variability of the device.