Charge trapping in metal gate/high-k n-mosfets during substrate injection

Charge trapping characteristics of MOCVD HfSi _xO _y (20% SiO ₂) gate stack of n-MOSFETs during substrate injection have been investigated. Positive constant voltage stress (CVS) and constant current stress (CCS) were applied at the gate of TJN/HfSi _xO _y/SiO ₂/p-Si n-MOSFETs having EOT of 2nm. Significant electron trapping is observed from the positive shift of threshold voltage (ΔV _t) after stress. Curve fitting of the threshold voltage shift data confirms power law dependence for Hf-silicate gate stacks. Electron trapping at bulk high-k oxide and interface trap generation were observed from charge pumping measurement for both cases. A turn-around effect is noticed for ΔV _t as the stress current and voltage increases under CCS and CVS. Dependence of spatial distribution of charge trapping at shallow traps on stress level in the high-k film, and redistribution of trapped charges during and after removal of stress are possibly responsible for the turn-around effect.