Direct Observation of Trap Charge in SiO2 by Electron Holography and Differential Phase Contrast (DPC)

It is known that trap charge in SiO2 plays a significant role in semiconductor device characteristics and reliability. By electron holography and differential phase contrast (DPC), trap charge in SiO2 was observed and its charge density calculated. It was discovered that high-energy positive ions of a focused ion beam (FIB) during TEM sample preparation can lead to a positive trap charge in the wide open SiO2 region, but not to the narrow gate oxide region. By reducing the energy of the ion beam in FIB sample preparation, the trap charge in SiO2 was minimized. Based on this observation, it is hypothesized that high-energy ion beam bombardment with secondary ion scattering in SiO2 may create an O vacancy, which leads to a positively charged Si dangling bond in the bulk of the SiO2 material.