Anomalous reduction of hot-carrier-induced ON-resistance degradation in n-type DEMOS transistors

Anomalous hot-carrier degradation phenomenon was observed in a 0.5-mu m 12-V n-type drain-extended MOS transistors (N-DEMOS) with various n-type drain-drift (NDD) implant dosage. Under the same stress condition, the device with a higher NDD dosage produces a higher. substrate current, a slightly higher transconductance degradation, but a lower ON-resistance (R-ON) degradation. Two degradation mechanisms are identified from the analysis of the electrical data and two-dimensional device simulations. The first mechanism is hot-electron injection in the accumulation region near the junction of the channel and accumulation regions. The second mechanism is hot-hole injection in the accumulation region near the spacer. This injection of hot holes creates a positive-charge trapping in the gate oxide, resulting in negative mirror charges in the accumulation region that reduces R-ON. The, second mechanism is identified to account for the anomalous lower R-ON degradation.