The present disclosure relates to an image sensor comprising a substrate. A photodetector is in the substrate. A trench is in the substrate and is defined by sidewalls and an upper surface of the substrate. A first isolation layer extends along the sidewalls and the upper surface of the substrate that define the trench. The first isolation layer comprises a first dielectric material. A second isolation layer is over the first isolation layer. The second isolation layer lines the first isolation layer. The second isolation layer comprises a second dielectric material. A third isolation layer is over the second isolation layer. The third isolation layer fills the trench and lines the second isolation layer. The third isolation layer comprises a third material. A ratio of a first thickness of the first isolation layer to a second thickness of the second isolation layer is about 0.17 to 0.38.