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/sub p/ and Q/sub 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/sub p/ and Q/sub n/. From the extracted quantities and centroids of Q/sub p/ and Q/sub n/ of negatively stressed oxides, it was found that Q/sub p/ and Q/sub n/ are generated near the oxide/substrate interface and Q/sub p/ is initially much larger than Q/sub n/. After the continuous stressing, Q/sub p/ saturates and moves closer to the interface, but Q/sub n/ keeps increasing and moves away from the interface, especially for those oxides after the post-poly anneal (PPA) treatment. Q/sub p/ is very unstable and easily neutralized, either by a small stress of opposite polarity or the same polarity. For the latter, Q/sub p/ is mainly dependent on the level of the final stressing field.