A semiconductor structure for back side illumination (BSI) pixel sensors is provided. Photodiodes are arranged within a semiconductor substrate. A metal grid overlies the semiconductor substrate and is made up of metal grid segments that surround outer perimeters of the photodiodes, respectively, such that first openings within the metal grid overlie the photodiodes, respectively. A low-n grid is made up of low-n grid segments that surround the respective outer perimeters of the photodiodes, respectively, such that second openings within the low-n grid overlie the photodiodes, respectively. Color filters are arranged in the first and second openings of the photodiodes and have a refractive index greater than a refractive index of the low-n grid. A substrate isolation grid extends into the semiconductor substrate and is made up of isolation grid segments that surround outer perimeters of the photodiodes, respectively. A method for manufacturing the BSI pixel sensors is also provided.