Monitoring trapped charge generation for gate oxide under stress

Abstract

A measurement method to extract the respective quantities and centroids of positive and negative trapped charges, i.e., Q(p) and Q(n), generated by the negative current stress for gate oxides is proposed and demonstrated, The method is based on neutralization of Q(p) by a low positive current stress to differentiate the effects of Q(p) and Q(n). From the extracted quantities and centroids of Q(p) and Q(n) of negatively stressed oxides, it was found that Q(p) and Q(n) are generated near the oxide/substrate interface and Q(p) is initially much larger than Q(n). After the continuous stressing, Q(p) saturates and moves closer to the interface, but Q(n) keeps increasing and moves away from the interface, especially for those oxides after the post-poly anneal (PPA) treatment, Q(n) is very unstable and easily neutralized, either by a small stress of opposite polarity or the same polarity, For the latter, Q(n) is mainly dependent on the level of the final stressing field.