Electrochemical Charging of Thermal SiO2 Films by Injected Electron Currents

When electron currents flow in thermal SiO2 films which have been exposed to water, a buildup of negative charge occurs in the oxide. This paper describes a series of experiments designed to characterize this charging effect. It is found that if water is diffused into a SiO2 film, water related centers are formed which act like electron traps with capture cross section of approximately 1.5 × 10−17 cm2. Experiments are described which show that when one of these centers captures an electron, atomic hydrogen is released which diffuses away and escapes or reacts and a stable negative charge is left behind. Electrochemical charging effects of this type have not previously been considered, although they may play a very important role in some semiconductor device failure effects.