Back-illuminated CMOS image sensors

A method for fabricating a back-illuminated image sensor that includes a sensor layer disposed between an insulating layer and a circuit layer electrically connected to the sensor layer, wherein a frontside of the sensor layer is adjacent to the circuit layer and a backside of the sensor layer is adjacent to the insulating layer, the back-illuminated image sensor further including an imaging area comprising a plurality of photodetectors disposed in the frontside of the sensor layer, the method comprising:

• forming at least one shallow trench isolation (STI) region in the sensor layer, including thermal oxidation of the at least one STI region;
• forming an implanted sensor layer by implanting the sensor layer with an n-type dopant from the frontside and through the sensor layer to form an n-type well in the sensor layer adjacent to the backside of the sensor layer, wherein implanting the sensor layer with the n-type dopant occurs after the thermal oxidation of the at least one STI region to reduce thermal diffusion of dopants in the n-type well;
• and
• doping the implanted sensor layer with a p-type dopant to form the plurality of photodetectors doped with the p-type dopant in the frontside of the sensor layer.