Reduction of plasma-induced damage in SiO₂ films during pulse-time-modulated plasma irradiation

Use of a pulse-time-modulated (TM) plasma is an effective way to reduce vacuum ultra-violet (VUV) radiation damage in SiO2 films because such a plasma can reduce the quantity of high-energy electrons while maintaining the electron density during the off time of the TM plasma. To understand the effects of VUV radiation, we measured the VUV-induced current in SiO2 films using a simple on-wafer monitoring technique. We found that the plasma-induced-current in the SiO2 films strongly depended on the VUV photon energy. Under the same conditions, the density of E′ centers in SiO2 films also depended on the photon energy. That is, the plasma-induced currents in the SiO2 films detected by on-wafer monitoring corresponded to the density of E′ centers (dangling bonds) in the films. By using a TM plasma, the plasma-induced current and the E′ center density in SiO2 films can be reduced during the plasma-off time. Consequently, use of a TM plasma can eliminate VUV radiation damage. These results also confirm that our developed on-wafer monitor can predict plasma-induced damage.