The present disclosure relates to a semiconductor device including a semiconductor substrate. A grid structure extends from a first side of the semiconductor substrate to within the semiconductor substrate. An image sensing element is disposed within the semiconductor substrate and is laterally surrounded by the grid structure. A plurality of protrusions are arranged along the first side of the semiconductor substrate. The plurality of protrusions are disposed over the image sensing element and are laterally surrounded by the grid structure. The plurality of protrusions are substantially identical to one another and have a characteristic dimension. An inner surface of the grid structure facing the image sensing element is spaced apart from a point of one of the plurality of protrusions by a predetermined reflective length that is based on the characteristic dimension of the plurality of protrusions.