Reduction in Susceptibility of MOS Devices to Radiation- and Electrically-Induced Defects.

摘要

The goal of this project was to identify fabrication techniques by which the susceptibility of Metal-Oxide-Semiconductor devices to theNegative- Bias-Temperature Instability (NBTI) and to radiation damage could be reduced. To that end, two techniques were attempted. In the first attempt, helium ions were implanted into the oxide layer of the devices in an attempt to frustrate the formation of defects via hydrogen depassivation. This attempt was not successful, perhaps because defects are not generated via hydrogen depassivation, or because the hydrogen does not come from the oxide bulk and hence cannot be easily blocked. The second attempt was to repair missing oxygen centers at the interface between the silicon substrate and the silicon dioxide insulating layer by annealing the devices in oxygen using rapid thermal processing techniques. This attempt was also not successful. However, there was insufficient time to optimize the parameters of the anneal, and we remain hopeful that future work may reveal that this method is, in fact, viable. Although we were unable to develop fabrication techniques to mitigate damage, we nevertheless were able to draw some important conclusions concerning the nature of defects induced by Negative Bias-Temperature Stress. In particular, we developed a model in which a positively charged defect exists in a shallow trapping site in the oxide very near the silicon substrate, and that the population of this positive charge is in dynamic equilibrium with the substrate, requiring both elevated temperature and inversion bias to exist. In addition, measurements of these defects on Metal-Oxide-Semiconductor Field Effect Transistors fabricated with HfSiON insulators were made. These measurements showed that positive charge may be channeled into shallow defects between the oxide and HfSiON layers, and removed from the device insulator by the voltage applied to the drain of the device.