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-mum 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 (RON) 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 RON. The second mechanism is identified to account for the anomalous lower RON degradation