Initial and radiation-induced charge distribution in silicon oxynitride MIS structures

Silicon oxynitride films deposited on a HF-etched Si surface show a large fixed positive charge in the dielectric (2-3 × 10^-2cm^-2). This charge is shown by etch-back experiments to be located near the silicon-oxynitride interface. Negative charge is injected into the oxynitride film if a negative bias larger than 2.8 × 10⁵V/cm is applied during irradiation. For saturation doses (about 1-2 Mrad of absorbed radiation), the magnitude of the injected charge can become as large or larger than the original positive charge in the oxynitride. The injected negative charge, is shown to be located at the silicon-oxynitride interface by etch-back experiments. The injection of negative charge under the above conditions appears to be an electronic phenomenon. An ionic mechanism appears unlikely because re-irradiation at room temperature without application of a bias restores the original flat-band condition of the MIS capacitor.