The effect of gate metal and SiO₂ thickness on the generation of donor states at the Si-SiO₂ interface

Abstract

Two experimental observations are reported concerning the degradation of the Si-SiO2 interface during electron injection in metal-oxide-semiconductor structures. First, the generation of the interfacial positive charge during avalanche injection can be strongly inhibited by employing magnesium, instead of aluminum, as gate metal, or enhanced by employing gold. This correlates with the different work functions of the metals. Second, during negative bias high-field injection in Al-gate capacitors with thin oxides (≲100 Å), a threshold in gate voltage, of 7-8 V, is found for the generation of the positive charge. Both observations are consistent with a model which assumes that holes generated in the anode by hot electrons, via emission of surface plasmons, are injected into the SiO2 and are subsequently trapped at the Si-SiO2 interface. Other possible mechanisms are also discussed.