Surface voltage induced by electron trapping and interface charge buildup in silicon oxynitride thin films

Abstract

The energy shifts in the C(KLL) Auger peak and their dependence on the primary beam energy Ep during electron irradiation of silicon oxynitride thin films can be directly related to the variations in the surface voltage of the films. These variations are due to a net change in the total balance of charge in the oxide between the bulk electron trapping and the generation of positive charge at the SiO2/Si interface. By using an appropriate numerical formulation, the contribution of three trapping centers, with capture cross sections σ of 10−16, 10−17 and 10−18cm2, as well as the component associated to the positive charge, have been separated The nitridation of the samples has been carried out in NH3 and N2 atmospheres at 1200°C. Auger depth profiling of these samples have shown that no incorporation of nitrogen in the bulk exist in the N2-annealed samples. In this case, the theoretical curves for the surface voltage, generated by using Ep as a parameter, fit satisfactorily with the experimental ones when the contribution of the traps with σ ≈ 10−17 and 10−18 cm2 is included in the model. No generation of positive charge has been observed. In the ammonia-annealed samples, it is necessary to add the contribution of a faster trap (σ ≈ 10−16 cm2) to explain the dependence of the surface voltage variations with Ep. The observed difference by 30% between theoretical and experimental values for the saturation surface voltage is explained in terms of generation of positive charge at the interface, that is damaged by the high-energy electrons.