Multi-layer image sensor structure with dark current sensing photodiodes in black level calibration area surrounded by dual seal ring system and opaque cover with integrated trench isolation

Abstract

An image sensor includes a substrate having first and second surfaces opposite to each other, an image pixel area, and a black level calibration (BLC) area adjacent to the image pixel area. The BLC area includes a dark current sensing circuit including photo diodes disposed in the substrate, a first seal ring disposed over the second surface and surrounding the image pixel area in plan view, a second seal ring disposed over the second surface and surrounding the image pixel area in plan view such that the dark current sensing circuit is disposed between the first and second seal rings, an opaque cover disposed over the first surface and covering the dark current sensing circuit, the first and second seal rings, and one or more first trench isolation structures extending from the first surface to an inside the substrate and disposed between the first seal ring and the opaque cover.