The present disclosure provides one embodiment of a method. The method includes providing a semiconductor substrate having a front side and a backside, wherein the front side of the semiconductor substrate includes a plurality of backside illuminated imaging sensors; bonding a carrier substrate to the semiconductor substrate from the front side; thinning the semiconductor substrate from the backside; performing an ion implantation to the semiconductor substrate from the backside; performing a laser annealing process to the semiconductor substrate from the backside; and thereafter, performing a polishing process to the semiconductor substrate from the backside.