Atypical secondary electron emission yield curves of very thin SiO2 layers: Experiments and modeling

Abstract

The secondary electron emission phenomenon often refers to the emission of electrons as a result of the interaction of impinging energetic electrons with the surface of a material. Although it is fairly well described for metals, with a typical shape of the total electron emission yield (TEEY) first increasing to reach a maximum and then decreasing along with the energy increase in the primary electrons, there is still a lack of data and detailed analysis for dielectrics, in particular thin layers. The present work proposes a new insight into the electron emission phenomenon from very thin dielectric layers. It reports on the TEEY from very thin SiO2 layers, less than 100 nm. It is found that a departure from the typical shape of the TEEY curve occurs for primary electrons with energy of around 1 keV. The TEEY curve presents a dip, a local minimum that might be as deep as below 1. This atypical shape depends substantially on the layer thickness. The measured TEEY is compared to an electron emission 1D-model in which we consider the combined effect of the space-charge electric field induced by trapped charges in the dielectric layer and of the processes of field-dependent conductivity and radiation-induced conductivity on the fate of secondary electrons. Those mechanisms govern the charge transport in the dielectric and, consequently, the electron emission. The effects of the SiO2 layer thickness, an incidence angle of the primary electrons, and an applied external electric field on the TEEY curves are reported.