Model for negative bias temperature instability in p-MOSFETs with ultrathin oxynitride layers

The decrease of the threshold voltage of p-channel metal-oxide-semiconductor field effect transistors with ultrathin (2 nm) oxynitride layers is studied, during negative gate bias stress at high temperature (125 °C). It is shown that the degradation of the threshold voltage is more important when the nitrogen content at the Si/SiON interface increases. A degradation model is developped, based on the generation of Si3Si (Pb0) centers during the electrical stress. The model includes a gaussian distribution of dissociation energies of the Pb0 centers, a distribution that is related to the interfacial strain at the Si/SiON interface. The experimental data can be reproduced by the model, assuming that the strain at the Si/SiON interface increases with increasing nitrogen content.