Effects of ionizing radiation on thin-oxide (20–1500 Å) MOS capacitors

Abstract

Metal-oxide-semiconductor capacitors with SiO2 oxides ranging from 20 to 1500 Å thick were exposed to a 60Co γ radiation dose of 106 rad(Si). Both p- and n-type substrates and Al- and Au-metal electrodes were used. For devices with oxides less than 100 Å thick, little or no parallel shift, no increased distortion, and no increased dispersion as a result of irradiation were observed in the C-V characteristic, indicating negligible buildup of oxide charge and negligible change in the interface density upon irradiation. For oxides thicker than 100 Å, the oxide-charge buildup increased greatly with thickness in the p-type devices, whereas in the n-type devices the oxide-charge buildup was comparable to the thin-oxide value. Interpretation of the p-type Al-metal electrode devices for oxides thicker than 100 Å are consistent with 1018 cm−3 hole traps residing in the oxide. However, for oxides thinner than 100 Å, a larger value of oxide-charge buildup is predicted in these p-type Al-metal electrode devices than observed. Differences in oxide-charge buildup between p- and n-type Al-metal electrode thick-oxide devices can be understood qualitatively by metal-semiconductor work-function differences.