Structural dependence of breakdown characteristics and electrical degradation in ultrathin RPECVD oxideitride gate dielectrics under constant voltage stress

摘要

The structural dependence of breakdown characteristics and electrical degradation in ultrathin oxideitride (O/N) dielectrics, prepared by remote plasma enhanced chemical vapor deposition, is investigated under constant voltage stress. In the early stage of oxide wearout, soft breakdown is a local phenomenon dominated by the tunneling current. After a given period of stress, a strong channel-length dependence of dielectric breakdown and the corresponding stress-induced leakage current from the evolution of increased tunneling current have been found. Stacked O/N dielectrics with interface nitridation demonstrate improved device performance on subthreshold swing and threshold voltage shifts after stress, indicating the suppression of stress-induced traps at the oxide/Si and oxide/drain interfaces compared to thermal oxides. Experimental evidence shows more severe breakdown and device degradation in the threshold voltage, drain current and transconductance for shorter channel PMOSFETs with O/N dielectrics. These degradations result from the enhancement of hole trapping in the gate-drain overlap region as evidenced by a positive off-state leakage current, which leads to hard breakdown, and the complete failure of device functionality.