A device includes a substrate, a deep-trench isolation structure, an oxide layer, a light blocking structure, and a metal-containing layer. The substrate includes a photosensitive region. The deep-trench isolation structure is embedded in the substrate and adjacent the photosensitive region. The oxide layer is over the photosensitive region of the substrate. The light blocking layer is over the deep-trench isolation structure and includes a top portion over the oxide layer and a bottom portion embedded in the oxide layer. The metal-containing layer is sandwiched between the bottom portion of the light blocking layer and the deep-trench isolation structure.