Composite bsi structure and method of manufacturing the same

Abstract

Various embodiments of the present application are directed towards image sensors including composite backside illuminated (CBSI) structures to enhance performance. In some embodiments, a first trench isolation structure extends into a backside of a substrate to a first depth and comprises a pair of first trench isolation segments. A photodetector is in the substrate, between and bordering the first trench isolation segments. A second trench isolation structure is between the first trench isolation segments and extends into the backside of the substrate to a second depth less than the first depth. The second trench isolation structure comprises a pair of second trench isolation segments. An absorption enhancement structure overlies the photodetector, between the second trench isolation segments, and is recessed into the backside of the semiconductor substrate. The absorption enhancement structure and the second trench isolation structure collectively define a CBSI structure.