Impacts of Gate Electrode Materials on Threshold Voltage (V{sub}(th)) Instability in nMOS HfO{sub}2 Gate Stacks Under DC and AC Stressing

摘要

Ultrathin nMOSFET hafnium oxide (HfO2) gate stacks with TiN metal gate and poly-Si gate electrodes are compared to study the impact of the gate electrode on long term threshold instability reliability for both dc and ac stress conditions. The poly-Si/high-k interface exhibits more traps due to interfacial reaction than the TiN/high-K interface, resulting in significantly worse dc V{sub}(th) instability. However, the V{sub}(th) instability difference between these two stacks decreases and eventually diminishes as ac stress frequency increases, which suggests the top interface plays a minor role in charge trapping at high operating frequency. In addition, ac stress induced interface states (Nit) can be effectively recovered, resulting in negligible G{sub}m degradation.