Study of breakdown in ultrathin gate dielectrics in nanoscale MOSFETs

Progressive breakdown has been found to provide an extra post-breakdown reliability margin for devices with ultrathin gate oxide. It is primarily constituted by two major regions, which are digital and analog breakdown. In this project, the progressive breakdown in the ultrathin gate oxide is thoroughly characterized and studied using different novel approaches. A K-cyc1e multiple-stage constant-voltage stress has been employed to study the behaviors of the gate leakage current (Ig) at different stages of the progressive breakdown under various conditions. A critical gate voltage (Vcrit) is found to demarcate the evolution of Ig during the progressive breakdown. For a gate voltage (Vg ) smaller than Vcrit, the digital breakdown dominates for which Ig digitally fluctuates with no apparent net increase. For Vg larger than Vcrit, Ig rapidly evolves into a stable high leakage state, indicating that the analog breakdown starts to prevail. The transition of the digital breakdown into the analog breakdown is irreversible. This transition can rarely occur if Vg does not exceed Vcrit. This brings a significant impact on the degradation rate of Ig (dIg/dt) at nominal operating voltages (Vop).DOCTOR OF PHILOSOPHY (EEE