Plasma irradiation damage to metal-insulator-semiconductor (MIS) devices can cause serious problems, such as an increase in the charge-pumping current and interface state density between SiO2 and Si during the dielectric film etching process using perfluorocarbon gas. The increase in a charge-pumping current was observed as a result of increasing the substrate rf bias for accelerating ions during plasma etching for thick dielectric film. The authors found that the current increase was caused by combination of E′ centers and Pb centers. That is, the generated electrons (E′ center) in the dielectric film surface by ion bombardment are trapped at the Si dangling bonds of the SiO2/Si interface (Pb centers). These Pb centers are generated by the penetration of UV photons. Control of both UV photons and ion bombardment is therefore crucial to eliminate damage at the SiO2/Si interface in MIS devices.