A backside illuminated CMOS image sensor comprises a photo active region formed over a substrate using a front side ion implantation process and an extended photo active region formed adjacent to the photo active region, wherein the extended photo active region is formed by using a backside ion implantation process. The backside illuminated CMOS image sensor may further comprise a laser annealed layer on the backside of the substrate. The extended photo active region helps to increase the number of photons converted into electrons so as to improve quantum efficiency.