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 (#x00394;Qot) and interface-trap generation (#x00394;Dit). Radiation induced shift, #x00394;Qot exhibits a smaller stress effect as compared witni #x00394;Dit. As gate-SiO2 thickness decreases, the stress effect on #x00394;Qot increases, while this effect on #x00394;Dit remains nearly constant. This compressive stress effect was inhibited by hydrogen diffusion, especially in #x00394;Dit. In addition, both stress effects on #x00394;Qot and #x00394;Dit in SiN-Cap samples show a gate-oxide Thickness dependence similar to that on #x00394;Qot 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 SiO2/Si interface and near the electrode/SiO2 interface. In a SiN-Cap sample, hydrogen is highly distributed at the SiO2/Si 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.