Analysis of the threshold voltage turn-around effect in high-voltage n-MOSFETs due to hot-carrier stress

The turn-around effect of the threshold voltage shift during hot-carrier stress has been investigated. Such a phenomenon is explained by the interplay between interface states and oxide traps, i.e. by the compensation of the rapidly created oxide charges by the more slowly created interface states. To prove this idea, a refined extraction scheme for the defect distribution from charge-pumping measurements has been employed. The obtained results are in a good agreement with the findings of our physics-based model of hot-carrier degradation. This approach considers not only damage produced by channel electrons but also by secondary generated channel holes. Although the contribution of the holes to the total defect creation is smaller compared to that of electrons, their impact on the threshold voltage shift is comparable with the electronic contribution. The reason behind this trend is that hole-induced traps are shifted towards the source, thereby more severely affecting the device behavior.