THE EFFECT OF OXIDE CHARGES AT LOCOS ISOLATION EDGES ON OXIDE BREAKDOWN

The degradation of time dependent dielectric breakdown (TDDB) characte ristics at LOCOS isolation edges has been studied using MOS capacitors with and without field oxide edges under gate electrodes. The wear-ou t mode shifted toward shorter breakdown time by the field oxide etchin g right after the conventional LOCOS process. The increase in leakage current was observed at the isolation edge, so that the current enhanc ement was regarded as one of the main causes of the degradation. The c urrent was reduced by constant current stress, suggesting the neutrali zation of positive charges due to electron trapping. It was, therefore , considered that the current enhancement yielding the degradation was attributed to the buildup of positive charges at the isolation edges. Carrier injection before TDDB tests was, also, found to improve the d egradation of the wear-out mode.