Stability of thermally oxidized silicon junctions in wet atmospheres

The possibility of stabilization of silicon surfaces by oxidation has been studied, and the silicon/silicon-dioxide produced by high-temperature thermal oxidation has been examined in some detail. Field-effect measurements on such oxidized surfaces have indicated the absence of slow states. The oxidation process has been applied to silicon p-n junctions and their electrical properties have been studied under conditions of reverse bias in the presence of water vapour. It was found that: (a) The reverse current increased with time and saturated in a period of a few hours, the magnitude of the current increase being a function of relative humidity, applied voltage and oxide thickness. (b) The increase in current was generally accompanied by the growth of a channel or inversion layer on both sides of the junction. Carrier generation in the space-charge region of the induced channels rather than direct surface leakage accounted for the observed increase in current. (c) The channels could be removed and the initial characteristics of the junction restored by removing the reverse bias in the presence of the water vapour. The experimental results are discussed in terms of a tentative model which invokes ionization and migration of impurities on the outer surface of the oxide layer.