Dielectric-thickness dependence of damage induced by electron-beam irradiation of MNOS gate pattern

We analyzed the electron-irradiation damage induced by electron-beam inspection of MNOS capacitors with various gate-dielectric thicknesses. Damage induced in a MNOS capacitor with SiON dielectric for high-performance CMOS devices was compared with that induced on a MOS capacitor with SiO2 dielectric. We found that there is no remarkable difference between the damage to MOS capacitors and that to MNOS capacitors. The induced damage strongly depends on the thickness of the gate dielectric. Damages were induced when a higher-energy electron-beam, whose electron range was larger than the thickness of the gate electrode, was irradiated. When the electron beam was irradiated to a MOS capacitor with gate-dielectric thickness of 10.0 nm the flat-band-voltage shifted due to the created traps. When the electron beam was scanned to a MOS or MNOS capacitor with gate-dielectric thickness of 4.0 nm, Vfb shifted by less than 6 mV. However, the leakage-current density increased to 10-7 A/cm2 at gate-electrode voltage of 3.0 V. On the other hand, when the electron beam was scanned on a MNOS capacitor with 2.5-nm-thick SiON dielectric, even the leakage current density was not increased. Accordingly, for damage-free inspection when gate-dielectric thickness is 4.0 nm or more, the electron-beam energy should be lower so that the electron range is smaller than the thickness of the gate electrode.