Monitoring trapped charge generation for gate oxide under stress [MOS capacitors]

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 and 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_p is very unstable and easily neutralized, either by a small stress of opposite polarity or the same polarity. For the latter, Q_p is mainly dependent on the level of the final stressing field