Reduction of plasma-radiation-induced interface states for plasma processes of charge-coupled-device image sensors using pulse-time-modulated plasma

We found that ultraviolet (UV) light from helium discharge plasmas and a metal halide lamp clearly induce SiO₂-Si interface states in a metal-silicon-nitride-oxide-silicon (MNOS) structure produced by charge-coupled-device (CCD) wafer processes. A dark current originating in the interface states of CCD image sensors also increases by this UV irradiation. Decreasing the UV light causes pulse-time-modulated (TM) plasma to suppress the interface states, resulting in a CCD dark current. Using optical filters, we revealed that a photon energy of 3.90 eV (318 nm) to 4.96 eV (250 nm) causes an increase in interface states. Even in a practical CCD process, we also found that TM plasma is more effective in suppressing interface states for micro-lens formation processes using CF₄ and O₂ plasma etching than CW plasma.