Generations of interface states in electrically stressed and high temperature annealed MOS devices

Polysilicon gate MOS transistors were stressed by Fowler-Nordheim tunneling injection. The stress generated interface states density as a function of the injected charge was measured both by the broadening of the C-V curve and by the charge pumping technique. Following the stress process, the devices which had polysilicon gate were treated at elevated temperatures to anneal the generated interface states. As expected the annealed devices had electrical characteristics similar to the fresh devices. However, repeated stress after the anneal show marked increase in interface state generation. The new interface states are of two types: one of the same nature and density as in the fresh device and one of faster generation rate with density which decreases with the increase of anneal temperature and the increase in anneal time. From Arenius plot an activation energy of 3.47±0.05 eV was obtained for the annealing process of the new type of interface states