Abstract
Plasma charging induced damage on gate dielectrics of MOS devices is an important issue in terms of shrinking dimension, plasma non-uniformity and effects on high-k gate dielectrics. A comprehensive study of plasma charging effects on the electrical properties of MOS devices was investigated in this thesis. Scaling effect of gate oxide thickness shows that the electrical property degradation induced by plasma charging damage may be slight as gate oxide thickness scales down into direct tunneling regime. For high-frequency application, the 1/f noise was found to be a promising index for assessing plasma charging damage. Extra exposure to plasma ambient can greatly reduce the plasma charging induced damage, which can be attributed to photo-annealing. For reinforcing the robustness of gate dielectrics, gate oxynitride formed by two-step nitridation was demonstrated to have better electrical reliability as compared to the conventional one-step nitridation, especially accompanied by amorphous silicon gate electrode. This improvement could be attributed to the relaxation of interfacial strain by amorphous silicon gate electrode and the suppression of hydrogen effects by gate oxynitride using two-step nitridation. For alternative gate dielectric in the future application, plasma-charging damage on Si3N4 and Ta2O5 gate dielectrics with high dielectric constant was also investigated. In the stacked gate dielectrics, such as Ta2O5/oxynitride and Ta2O5/Si3N4, the mixed effect of the buffer layer (oxynitride or Si3N4) and Ta2O5 film works well in low electrical field region. Yet it doesn’t show any significant reduction in plasma charging induced electrical degradation and eventually limits the thickness scaling. For MOS devices with Si3N4 gate dielectric, the leakier characteristic and shorter time to breakdown reveal its inferior reliability. For MOS devices with Ta2O5 gate dielectric, the trap-assisted current mechanism makes a thicker physical thickness of Ta2O5 film more susceptible to plasma charging induced damage.