Correlation between mechanical stress and hydrogen-related effects on radiation-induced damage in MOS structures

Correlation between mechanical stress and hydrogen effects on radiation damage in polycide-gate MOS capacitors was investigated as a function of gate-oxide thickness. The compressive stress magnitude was altered by varying the silicide (TiSi2 or WSi2) thickness in the polycide-gate electrode, and hydrogen introduction into gate-SiO2 film was carried out by diffusion from plasma-deposited silicon-nitride passivation film (SiN-Cap). In a MOS capacitor without passivation film (No-Cap sample), it was found that compressive stress on gate-SiO2 reduces both positive charge build-up (ΔQot) and interface-trap generation (ΔDit). Radiation induced shift, ΔQot exhibits a smaller stress effect as compared with ΔDit. As gate-SiO2 thickness decreases, the stress effect on ΔQot increases, while this effect on ΔDit remains nearly constant. This compressive stress effect was inhibited by hydrogen diffusion, especially in ΔDit. In addition, both stress effects on ΔQot and ΔDit in SiN-Cap samples show a gate-oxide thickness dependence similar to that on ΔQot in No-Cap samples. The stress effect observed in No-Cap samples can be explained on the basis of the bond reformation process at the SiO2Si interface and near the electrodeSiO2 interface. In a SiN-Cap sample, hydrogen is highly distributed at the SiO2Si interface region and hydrogen-related interface-trap generation may occur at this interface region. As a result, only the stress effect near the gate-electrode was observed in SiN-Cap samples