The present disclosure provides an image sensor device and a method for manufacturing the image sensor device. An exemplary image sensor device includes a substrate having a front surface and a back surface; a plurality of sensor elements disposed at the front surface of the substrate, each of the plurality of sensor elements being operable to sense radiation projected towards the back surface of the substrate; a radiation-shielding feature disposed over the back surface of the substrate and horizontally disposed between each of the plurality of sensor elements; a dielectric feature disposed between the back surface of the substrate and the radiation-shielding feature; and a metal layer disposed along sidewalls of the dielectric feature.