Radiation-Induced Charge Trapping in Thin Al2O 3/SiOxNy/Si(100) Gate Dielectric Stacks
Abstract
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 Al 2O3 and SiOxNy 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. Al2O 3/SiOxNy 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.