The role of nitrogen on charge-trapping-induced Vth instability in HfAlON high-κ gate dielectric with metal and poly-Si gate electrodes

Abstract

The impact of N on HfAlON dielectrics has been extensively studied in devices with TaN metal and poly-Si gate electrodes. A similar trend of the N effects was observed in both TaN and poly-Si devices in terms of equivalent oxide thickness, gate leakage current, threshold voltage (Vth), transconductance, and subthreshold swing. However, compared to the HfAlON with TaN metal gate, a severe Vth instability induced by charge trapping was generally observed in the poly-Si/HfAlON devices. In addition, the incorporation of N in the HfAlON films was found to play an opposite role in the Vth instability between the TaN and poly-Si devices: In the TaN metal gate devices, the charge-trapping-induced Vth instability in the HfAlON was slightly degraded by increasing the N concentration, whereas the Vth instability was remarkably improved by increasing the N concentration in the poly-Si gate devices. The degradation of the Vth instability observed in the TaN metal gate devices is believed to be due to the increase in preexisting bulk traps that is caused by incorporating N into the gate dielectric. The significant improvement on the Vth instability in the devices with poly-Si gate could be mainly attributed to the remarkable suppression of electron trapping at oxygen vacancies by adding N into the high-κ gate dielectric. © 2007 IEEE.