Analysis of mechanisms for the enhanced degradation during AC hot carrier stress of MOSFETs

Charge pumping currents were used to monitor the degradation of n-channel MOS transistors under AC stress. The amount of degradation and the degradation mechanisms were found to be strongly dependent on the fall time of the range pulse and on the drain voltage. Different degradation-mode regions are defined in the fall-time-drain-voltage plane: a region where the degradation is quasi-DC, a region where an enhanced degradation occurs, and a region where avalanche multiplication governs the degradation. By measuring the substrate current under the identical conditions as during the stress, a close correlation was found between the substrate current and the degradation. The correlation also holds for drain-voltage conditions where an avalanche multiplication occurs.<>