Quantitative and comparative characterizations of plasma process-induced damage in advanced metal-oxide-semiconductor devices

Two plasma process-induced damage mechanisms are investigated in detail: charging damage by plasma conduction current through two different gate dielectrics (SiO2 and HfAlOx/SiO2 (high-k)) in metal-oxide semiconductor (MOS) devices and ion-bombardment damage in Si surfaces. The charging damage was identified as the changes in tunnelling currents and the decrease in the reliability lifetime. The behaviours were found to depend on the dielectric thickness as well as dielectric materials (SiO2 and high-k). For p-ch MOS transistors, the threshold voltage of devices with high-k exposed to Ar-based plasma shifted towards the positive direction, while with SiO2, towards the negative direction. This may be attributed to the difference in the trap site generation process and trapping phenomenon. With regard to the ion-bombardment damage, the changes in optical structures (surface layer thicknesses, dielectric function and mechanical strain within the interfacial damaged layers) by direct current and electron cyclotron resonance plasma exposures were investigated by spectroscopic ellipsometry and photoreflectance spectroscopy. The plasma-induced stressing current and the defect density were estimated to quantify the damage. The experimental findings provide key implications that a plasma-induced damage is one of the limiting factors for future-scaled device designs.