Plasma-radiation-induced interface states in metal-nitride-oxide-silicon structure of charge-coupled device image sensor and their reduction using pulse-time-modulated plasma

We found that ultraviolet (UV) light from helium discharge plasma and a halogen lamp clearly induce SiO₂-Si interface states in a metal-silicon-nitride-oxide-silicon (MNOS) structure. A dark current originating in the interface states of charge-coupled-device (CCD) image sensors also increases by this UV irradiation. Pulse-time-modulated (TM) plasma suppresses the interface states, resulting in the CCD dark current, by decreasing the UV light. On the other hand, results of Capacitance-Voltage (CV) measurement did not show the difference between UV irradiation and no irradiation. This indicates that fixed charges in the SiO₂ cannot be generated by the UV lights. 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 the interface states.