Variations in Radiation Response Due to Hydrogen: Mechanisms of Interface Trap Buildup and Annealing
Hughart, David Russell
Hydrogen produces variability in the radiation response of integrated circuits, whether incorporated in the oxide or present as a gas. The presence of molecular hydrogen can increase interface trap buildup and alter dose rate response. Defects with hydrogen incorporated in the oxide during processing can suppress interface trap buildup at elevated temperatures. This thesis explores the reactions of hydrogenous species at common oxide defects and the mechanisms that explain radiation-induced interface trap formation and annealing, focusing on the effects of temperature, molecular hydrogen concentration, and dose rate. Density functional theory (DFT) calculations identify defects likely to be present in common thermal oxides and provide energy barriers for reactions at those defects. Proton release mechanisms and defect interactions under a variety of conditions are identified that provide insight into enhanced degradation in the presence of molecular hydrogen, irradiation at elevated temperatures, and dose rate effects. These mechanisms are implemented in a numerical model that simulates interface trap buildup in a 1-D slice of oxide and silicon using the estimates for defect concentrations and energy barriers from the DFT calculations. The results provide insight into which reactions have a significant impact on interface trap density under a variety of conditions; the predictions are compared to experimental data. The results demonstrate how proton loss reactions can limit the supply of protons at the interface and suppress interface trap buildup at elevated temperature.