Patent ID: 7741666

Claim:
A complementary metal-oxide-semiconductor (“CMOS”) backside illuminated imaging sensor, comprising: a semiconductor layer having a P-type region; a frontside P + doped layer formed within the semiconductor layer; a backside P + doped layer formed within the semiconductor layer, wherein the backside P+ doped layer has a graded concentration of a first dopant extending from a back surface of the semiconductor layer to a first distance from the back surface of the semiconductor layer such that a first concentration of the first dopant at the back surface of the semiconductor layer is greater than a second concentration of the first dopant at the first distance from the back surface of the semiconductor layer; and an imaging pixel having a photodiode formed within the semiconductor layer, wherein the photodiode is an N − region formed within the P-type region of the semiconductor layer between the frontside P + doped layer and the backside P + layer.