Charging effects of SiO₂ thin film on Si substrate irradiated by penetrating electron beam

In this work, the charging effect and induced conductivity of SiO₂ thin films on Si substrate irradiated by penetrating electron beam (e-beam) are investigated based on numerical calculation and experiment. The numerical model is performed by considering the electron scattering, trapping, drift, diffusion and recombination, and solved by the Monte Carlo and finite difference method. The results show that, under e-beam irradiation, due to emission of secondary electrons (SEs) from the surface, the net charge density is positive near the surface, but negative inside the film. The net charge density and resulting negative charging intensity decrease under e-beam irradiation because of high electron mobility. With e-beam irradiation, the free electrons drift and diffuse to the meter and thus the sample current increases. Meanwhile, the transmission current remains unchanged due to the weak charging intensity. With the increasing beam energy, the transmission current increases to the beam current. The sample current and the induced current gain reach the maximum at the beam energy of 15 keV. The sample current and the induced conductivity at the steady state increase linearly with beam current. The induced current gain increases with the rising positive bias voltage. The influence of film parameters on the charge effect is also analyzed.