Increased hole trapping in gate oxides as latent damage from plasma charging
With aggressive device scaling and the wide use of plasma-assisted processes, the device damage caused by process-induced charging is receiving growing attention, from both basic understanding and technological points of view. The paper presents results of hole-trapping studies in the thin gate oxide of plasma-damaged NMOS and PMOS transistors. In addition to neutral electron traps and passivated interface damage, which are commonly observed in plasma charging latent damage, we observed and identified hole traps, generated by plasma stress. Enhanced hole trapping in the gate oxide of plasma-damaged devices was studied using Fowler - Nordheim stress and substrate hot-hole injection applied to antenna test structures sensitive to process-induced charging. The number of hole traps increases with increasing antenna ratio, indicating that the mechanism of hole-trap generation is based on electrical stress and current flow, forced through the oxide due to charging under plasma etching or ion implantation conditions.