BIPOLAR STRESSING, BREAKDOWN, AND TRAP GENERATION IN THIN SILICON-OXIDES

Thin silicon oxide films were stressed with bipolar pulses in which the magnitudes of both the positive and negative pulses were independently varied. The time-to-breakdown, the charge-to-breakdown, and the number of traps generated inside of the oxides during the stresses were measured and compared with oxides that had been stressed with unipolar pulses or stressed with constant dc voltages. For the bipolar stresses it was found that the time-to-breakdown, the charge-to-breakdown, and the number of traps generated inside of the oxide all increased as the magnitude of the opposite polarity, nonstressing pulse was increased, until the opposite polarity pulse became large enough to become the stressing pulse. The time-to-breakdown reached a maximum when the magnitude of the stressing pulse was approximately 1 V larger than the magnitude of the nonstressing pulse. The model that was used to explain these increases involved generation of traps inside of the oxide and the lack of spatial correlation between the traps generated by injection from one interface with the traps generated by injection from the other interface.