Direct measurement of gate oxide damage from plasma nitridation process

Surface voltage (Vsurf) measurements using a non-contact mode measurement (NCMM) tool on bare thick oxide wafers have been widely used for the characterization of plasma charging damage in BEOL processes. In this paper, plasma damage to gate oxide in a plasma nitridation (PN) system has been systematically studied by an NCMM system on bare oxide wafers. The results demonstrate that conventional V_surf measurement on thick oxide bare wafers has the sensitivity to detect the positive charge induced by the PN process and to characterize the plasma uniformity, but this method might underestimate the damage to gate oxide. It is found that both D_it and Q_tot measurements on very thin oxide are more accurate methods to quantify the plasma damage. However, only D_it correlates well with device performance. The findings of this study provide a time saving and cost effective method for PN process optimization and process monitoring.