High density image sensor

A CMOS image sensor, comprising:

• a vertical transfer gate extending vertically from a front-side to a first position within a p-type substrate;
• an n-type photodiode region disposed within the p-type substrate under the vertical transfer gate and extending laterally toward a first side of the vertical transfer gate;
• a p-type pixel device well arranged at the first side of the vertical transfer gate overlying the n-type photodiode region;
• a p-type isolation region including a lateral portion disposed under the along a top surface of the n-type photodiode region and a vertical portion connected to the lateral portion and vertically extending to the front-side of the p-type substrate along a sidewall of the vertical transfer gate, wherein the p-type isolation region has a doping concentration greater than that of the p-type pixel device well;
• and
• a deep trench isolation (DTI) structure surrounding the n-type photodiode region;
• wherein the DTI structure extends vertically from a back-side of the p-type substrate to the lateral portion of the p-type isolation region.

A method of forming an image sensor, comprising:

• forming a photodiode doped region within a substrate and a floating diffusion well from a front-side of the substrate;
• forming a doped isolation region including a lateral portion along a top surface of the photodiode doped region and a vertical portion connected to the lateral portion and extending upwardly to the front-side of the substrate,
• forming a vertical transfer gate between the floating diffusion well and the vertical portion of the doped isolation region;
• and
• forming a pixel device from the front-side of the substrate on one side of the vertical portion of the doped isolation region opposite to the vertical transfer gate, wherein the pixel device laterally overlaps with the photodiode doped region.