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

摘要

We found that ultraviolet (UV) light from helium discharge plasma and a metal halide lamp clearly induce SiO{sub}2-Si interface states in a metal-silicon-nitride-oxide-silicon (MNOS) structure produced by charge-coupled-devices (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 the CCD dark current. Using optical filters, we revealed that 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 reduces more an increase in interface states for micro-lens formation processes using CF{sub}4 and O{sub}2 plasma etching than CW plasma.