Trapped charge induced gate oxide breakdown

We investigate the physical mechanisms of breakdown in 21A thick silicon dioxide gate oxides in n-channel and p-channel metal-oxide-semiconductor field-effect transistors. The oxide breakdown investigation is based on the direct measurement of the stress-induced charge trapped in the oxide using the direct-current current-voltage technique. The measurements show several parallel breakdown pathways with different oxide field dependence. Direct correlation was found between the steplike increase in the gate current and the oxide-trapped charge. The results point to the multistep character of the oxide breakdown that includes generation of precursor defects by the injection and trapping of either electrons or holes. The weakened defect (breakdown precursor) bonds may be broken by the applied electric field and temperature leading to generation of a conductive percolation path. Time-to-breakdown model is developed taking into the account the oxide field dependence of the different breakdown mechanisms.