Dielectric-thickness dependence of damage induced by electron-beam irradiation on metal nitride oxide semiconductor gate pattern

Abstract

We analyzed the electron-irradiation damage induced by electron-beam inspection of metal nitride oxide semiconductor (MNOS) capacitors with various gate-dielectric thicknesses. Damage induced in an MNOS capacitor with a SiON dielectric for high-performance CMOS devices was compared to that induced on a metal oxide semiconductor (MOS) capacitor. We found that there is no remarkable difference between the damage to MOS capacitors and that to metal nitride oxide semiconductor MNOS capacitors. Damage was induced when a high-energy electron beam, whose electron range was larger than the thickness of the gate electrode, was irradiated. The induced damage strongly depends on the thickness of the gate dielectric. When the beam was irradiated onto a capacitor with a gate-dielectric thickness of 10.0 nm the flatband voltage shifted. When the beam was scanned onto a capacitor with a gate-dielectric thickness of 4.0 nm, the flatband voltage shifted minimally. However, the leakage-current density increased to 10−7 A/cm2 at a gate voltage of 3.0 V. On the other hand, when the beam was scanned onto an MNOS capacitor with 2.5-nm-thick dielectric, not even the leakage current was increased. Accordingly, for damage-free inspection when a gate-dielectric thickness is 4.0 nm or more, the beam energy needs to be lower so that the electron range is shorter than the thickness of the gate electrode.