Radiation Effects in MOS Capacitors with Very Thin Oxides at 80°K

Radiation induced flatband voltage shifts are measured at 80°K in MOS capacitors with oxides 6.0-50 nm thick. Previous studies have found that for relatively thick oxides (greater than 20 nm) the flatband voltage changes with radiation dose as the square of the oxide thickness suggesting that the holes created by the ionizing radiation in the oxide are uniformly created and trapped. For the thinner oxides examined in the present work, significantly smaller shifts than predicted by the oxide thickness squared dependence were observed indicating that many of the generated holes are escaping the thin oxide. Physical mechanisms to explain this effect, of which recombination of trapped holes by carrier tunneling appears the most important, are discussed.