Effects of electron-beam irradiation on the properties of CVD Si ₃N₄ films in MNOS structures

Abstract

The influence of energetic electron-beam irradiation on the trap properties of CVD Si3N4 films in MNOS structures has been investigated by means of charge-centroid and conduction measurements. Within the limit of our measurements, the results indicate that electron-beam radiation up to 6.6×10-5 C/cm2 does not affect the trap properties of the nitride, such as the density, capture cross section, and average capture distance, although the charging of these traps may be altered. Furthermore, the effects of radiation in the Si-SiO2 interface properties of MNOS structures have been examined by the C-V method. For an MNOS capacitor with relatively thick oxide, radiation was found to cause a significant increase in the density of surface states, the effective insulator charge, and the slow states. For an MNOS capacitor with very thin oxide, by contrast, the radiation causes a significant change only in the insulator charge - none in the surface states. Since the properties of the nitride have not been affected by the irradiation, the difference in effects must be due to the difference between the oxide films. An explanation based on a broken-bond model is consistent with the results.