TDDB lifetime enhancement of high-k MOSFETs damaged by plasma processing — Conflicting results in plasma charging damage evaluation

Plasma-charging damage (PCD) to high-k MOSFETs was evaluated by various parameters such as random telegraph noise (RTN), threshold voltage shift (ΔV_th), and TDDB lifetimes. A new evidence of an enhancement of TDDB lifetime under constant-voltage stress (t_CVS) was found for plasma-damaged high-k MOSFETs - a certain amount of PCD results in conflicting data between t_CVS and other parameters (RTN, ΔV_th, and constant-current TDDB lifetime). The observed feature was ascribed to a characteristic defect generation mechanism in the high-k where trapped charges played important roles in the t_CVS test. This finding is another evidence of TDDB conflicting data previously pointed out for SiO₂ films with pre-stressed damage, PCD, and mechanical strain. One should properly employ a test method for evaluating PCD to high-k MOSFETs.