Characterization of plasma charging damage in ultrathin gate oxides

Charging damage induced in oxides with thickness ranging from 8.7 to 2.5 nm is investigated. Results of charge-to-breakdown (Qbd) measurements performed on control devices indicate that the polarity dependence increases with decreasing oxide thickness at room temperature and elevated temperature (180 degrees C) conditions. As the oxide thickness is thinned down below 3 nm, the Qbd becomes very sensitive to the stressing current density and temperature. Experimental results show that severe antenna effect would occur during plasma ashing treatment in devices with gate oxides as thin as 2.6 nm. It is concluded that the negative plasma charging and high process temperature are the key factors responsible for the damage.