Radiation damage in SiO2/Si induced by low-energy electrons via plasmon excitation

Abstract

We have found definite evidence which proves that radiation damage in SiO2/Si induced by low-energy electrons is caused by plasmon excitation in SiO2. The SiO2/Si sample was irradiated by accelerated thermoelectrons, and the flat-band voltage shift, ΔVFB, of the sample was measured by the C-V method. The effective charge generation yield, Rf, in SiO2/Si was evaluated from the ΔVFB and the electron dose. The effective positive charges were measured in p-type SiO2/Si, and the effective negative charges were measured in n-type SiO2/Si. This is because interface states behave like positive charges in p-type SiO2/Si and negative charges in n-type SiO2/Si. The Rf in p-type SiO2/Si oscillated as a function of the incident electron energy of 5–150 eV with several clear peaks. These peaks correspond to the quantum energy of a bulk plasmon or a surface plasmon. Both plasmons decay into electron-hole pairs. The holes that escape from recombination with the electrons are trapped at the SiO2/Si interface and cause effective positive charges. The Rf was maximum when the SiO2 thickness was 20 nm, independent of the incident electron energy. This is because the plasmon region extends to about 20 nm in SiO2, and the hole-trapping efficiency is expected to be maximum at a SiO2 thickness of 20 nm.