Method of forming a CMOS image sensor

摘要

This invention provides a method of forming a CMOS image sensor. The image sensor is formed in a predetermined region of a semiconductor wafer covered with a P-type substrate. The wafer comprises at least one N-channel area for forming one NMOS transistor and a sensor area for forming a photo-diode sensor. At least one gate electrode in the N-channel area is formed first. A first ion-implantation is performed to form a lightly doped drain (LDD) layer in predetermined areas on the surface of the P-type substrate in the N-channel area next to the gate electrode. A second ion-implantation is performed to form a heavy doped drain (HDD) layer in another predetermined area on the surface of the substrate in the N-channel area next to the LDD. A third ion-implantation is performed to form a doped layer with phosphorus as the major dopant on the surface of the substrate in the sensor area. The dopant concentration of the HDD layer is heavier than that of the LDD layer, and the doped layer in the sensor area and the P-type substrate under the doped layer form a PN junction that functions as a photo-diode sensor.