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A new plasma induced damage mechanism on CMOS image sensor is analyzed. An increase of the mean pixel dark current is observed after the plasma etch of a cavity on the pixel area. The degradation increases non-linearly when the dielectric layers between the photodiode and the plasma become thinner. This can be explained by a photo generation phenomenon in the dielectric nitride layer, induced by the plasma UV, and assisted by the wafer surface charge. This mechanism leads to a positive fix charge creation on the pixel surface, which can next deplete the top P layer of the pinched photodiode. Process and pixel architecture optimization ways are finally proposed.