Optical structure and method for manufacturing the same

An optical structure and methods of forming an optical structure are provided. In some embodiments, the optical structure includes a substrate having a frontside and a backside opposite the frontside, a plurality of image-sensing elements arranged within the substrate, and a deep trench isolation (DTI) structure disposed between adjacent image-sensing elements. The DTI structure extends from the backside of the substrate to a first depth within the substrate and laterally surrounds the plurality of image-sensing elements. The optical structure further includes a light transmission layer formed over the backside of the substrate. The light transmission layer includes a first side and a second side adjacent to the backside of the substrate. The optical structure further includes a buried grid structure in the light transmission layer, the buried grid structure extending from the first side of the light transmission layer to a second depth within the light transmission layer.