Effect of power on interface and electrical properties of SiO2 films produced by plasma-enhanced chemical-vapor deposition

Abstract

The effect of power on the electrical and interface properties of silicon dioxide films produced by direct plasma-enhanced chemical-vapor deposition, using nitrous oxide and silane with high helium dilution, has been investigated. Auger depth profiling measurements indicate that while the bulk of the films have no measurable impurities, the interface region contains about 1.6×1015 atoms/cm2 of nitrogen. In contrast to thermal oxides, there is no thick interface layer with a large intrinsic compressive stress. The interface-state densities of the films obtained from capacitance-voltage measurements on metal-oxide-semiconductor diodes increase with increasing plasma power, but these can be removed to some extent by high-temperature annealing at temperatures in the range 800–950 °C. The flatband voltage is relatively insensitive to plasma power. Thermal oxide samples have been subjected to the plasma processes and these also show evidence of plasma damage. A thin layer produced at the interface by a separate plasma oxynitridation process is shown to be incapable of protecting the Si/SiO2 interface from the plasma damage produced by subsequent high-power plasma deposition processes. The nature of the interface states is discussed.