Radiation-induced charge trapping in thin Al2O3/SiOxNy/Si(100) gate dielectric stacks

We examine the total-dose radiation response of capacitors and transistors with stacked Al₂O₃ on oxynitride gate dielectrics with Al and poly-Si gates after irradiation with 10 keV X-rays. The midgap voltage shift increases monotonically with dose and depends strongly on both Al₂O₃ and SiO_xN_y thickness. The thinnest dielectrics, of most interest to industry, are extremely hard to ionizing irradiation, exhibiting only ∼50 mV of shift at a total dose of 10 Mrad(SiO₂) for the worst case bias condition. Oxygen anneals are found to improve the total dose radiation response by ∼50% and induce a small amount of capacitance-voltage hysteresis. Al₂O₃/SiO_xN_y dielectrics which receive a ∼1000°C dopant activation anneal trap ∼12% more of the initial charge than films annealed at 550°C. Charge pumping measurements show that the interface trap density decreases with dose up to 500 krad(SiO₂). This surprising result is discussed with respect to hydrogen effects in alternative dielectric materials, and may be the result of radiation-induced hydrogen passivation of some of the near-interfacial defects in these gate dielectrics.