Detection of trap activation by ionizing radiation in SiO2 by spatially localized cathodoluminescence spectroscopy

Abstract

Microcathodoluminescence (CLS) spectroscopy is used to probe the effect of ionizing radiation on defects inside Al gate oxide structures. Micron-scale Al–SiO2–Si capacitors exposed to 10 keV x-ray irradiation exhibit spatially localized CLS emissions characteristic of multiple deep level traps, including positively charged oxygen-deficient centers and nonbridging oxygen hole centers (NBOHC). Irradiation produces both increases and decreases in their relative emission intensities, depending on spatial location within the oxide. These changes result in a gradient of E′ versus NBOHC defect densities across the oxide thickness between Al and Si interfaces. These results demonstrate that x-ray irradiation-induced deep level traps can be monitored spatially in metal-oxide-semiconductor gate structures, that x-ray irradiation produces separate increases or decreases in E′ versus NBOHC defect densities, and that these changes vary with position within the oxides.