Cmos image sensor having indented photodiode structure

A CMOS image sensor, comprising:

• a substrate with a first doping type;
• and
• a pixel array comprising a plurality of pixels, each of the pixels comprising a transfer gate disposed on a front-side of the substrate and a photo detecting column with a second doping type disposed within the substrate at one side of the transfer gate opposing to a floating diffusion region with the second doping type;
• wherein the photo detecting column and the substrate are in contact with each other at a junction interface and configured as a photodiode structure to convert radiation that enters the substrate into an electrical signal;
• and
• wherein the junction interface comprises recessed portions that are symmetrically distributed along an extended line of centers of the transfer gate and the floating diffusion region.

A method of forming an image sensor, comprising:

• preparing a substrate with a first doping type;
• forming a transfer gate over the substrate;
• forming a floating diffusion region within the substrate;
• forming a masking layer over the substrate, the masking layer having a circumference including recessed portions that are symmetrically distributed along an extended line of centers of the transfer gate and the floating diffusion region;
• and
• with the masking layer in place, performing a plurality of implantation processes to form a photo detecting column within the substrate at one side of the transfer gate opposing to the floating diffusion region;
• wherein the photo detecting column and the substrate are in contact with each other at a junction interface and configured as a photodiode structure to convert radiation that enters the substrate into an electrical signal.