Evaluation of damage induced by electron-beam irradiation to metal-oxide semicondoctor gate pattern and method for damage-free inspection

摘要

We analyze the electron-irradiation damage induced in wafers by scanning electron microscope (SEM) inspection, which uses SEM images of voltage contrast formed by the charges on the pattern. The effects of electron-beam energy and charging on a metal-oxide semiconductor (MOS) capacitor are studied. We find that the higher energy electron beam, whose electron range is larger than the thickness of the gate electrode, creates traps at the interface between the silicon substrate and the gate dielectric. The flat-band voltage is shifted by the created traps. Although these traps are created by the transmission of the electron beam into the dielectric, they are not created only by charging on the gate electrode; neither is an oxide fixed charge created in the MOS capacitor. Accordingly, for damage-free inspection of MOS devices, the electron-beam energy should be low enough that the electron range is smaller than the thickness of the gate electrode. On the other hand, the flat-band voltage does not shift, owing to charging on the pattern surface during the electron irradiation. However, the gate dielectric is broken down by charging on the gate electrode at high voltage. Accordingly, for damage-free inspection, the charging voltage should be controlled so as not to break down the gate dielectric.