A BSI image sensor includes a substrate including a front side and a back side opposite to the front side, a pixel sensor disposed in the substrate, and a color filter disposed over the pixel sensor. The pixel sensor includes a plurality of first micro structures disposed over the back side of the substrate. The color filter includes a plurality of second micro structures disposed over the back side of the substrate. Each of the first micro structures has a first height, and each of the second micro structures has a second height. The second height is less than the first height.