Patent ID: 8748315

Claim:
A method of forming a back-side illuminated CMOS image sensor (BSI CSI), comprising: providing a semiconductor substrate having a front-side and a back-side; forming a plurality of photodetectors within the front-side of the semiconductor substrate; and implanting the back-side of the semiconductor substrate to form an implantation region separated from the plurality of photodetectors, which continually extends below the plurality of photodetectors along a lateral plane parallel to the back-side of the semiconductor substrate, wherein the implantation region has a non-uniform doping concentration along the lateral plane and along a vertical plane perpendicular to the lateral plane; and etching the back-side of the semiconductor substrate after forming the implantation region to reduce the thickness of the semiconductor substrate between the plurality of photodetectors and the back-side of the semiconductor substrate using an etchant that has an etching rate that is a function of doping concentration.