Properties of thin oxynitride gate dielectrics produced by thermal nitridation of silicon dioxide

Oxynitride films have been fabricated by annealing thermal SiO2films in dilute NH3. These films are homogeneous and have breakdown fields over 9 MV/cm. Unlike films prepared by nitridation of bare surfaces, the thickness of these films is determined by the starting oxide and is largely insensitive to the anneal time. The conversion of oxide to nitride increases with anneal time and temperature as shown by Auger and etch rate measurements. Oxidation at 1000°C in oxygen yields low growth rates comparable to those reported (1) for direct nitridation of silicon. After irradiation with a megarad of ionizing radiation flatband shifts of less than 0.3 volt for gate bias of 5 volts were measured. This shift is mainly due to mobile charge. Conversion of oxide to oxynitride films should make it possible to fabricate by ordinary processing reproducible submicron FETs with gate insulation thickness of 100 Å to 150 Å having acceptable breakdown voltages.