Radiation-induced charge trapping in thin Al/sub 2/O/sub 3//SiO/sub x/N/sub y//Si(100) gate dielectric stacks

Abstract

We examine the total-dose radiation response of capacitors and transistors with stacked Al/sub 2/O/sub 3/ 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/sub 2/O/sub 3/ and SiO/sub x/N/sub y/ thickness. The thinnest dielectrics, of most interest to industry, are extremely hard to ionizing irradiation, exhibiting only /spl sim/50 mV of shift at a total dose of 10 Mrad(SiO/sub 2/) for the worst case bias condition. Oxygen anneals are found to improve the total dose radiation response by /spl sim/50% and induce a small amount of capacitance-voltage hysteresis. Al/sub 2/O/sub 3//SiO/sub x/N/sub y/ dielectrics which receive a /spl sim/1000/spl deg/C dopant activation anneal trap /spl sim/12% more of the initial charge than films annealed at 550/spl deg/C. Charge pumping measurements show that the interface trap density decreases with dose up to 500 krad(SiO/sub 2/). 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.