An image sensor device includes a substrate, photosensitive pixels, an interconnect structure, a dielectric layer, and a light blocking element. The photosensitive pixels are in the substrate. The interconnect structure is over a first side of the substrate. The dielectric layer is over a second side of the substrate opposite the first side of the substrate. The light blocking element has a first portion extending over a top surface of the dielectric layer and a second portion extending in the dielectric layer. The second portion of the light blocking element laterally surrounds the photosensitive pixels.