High density image sensor

A CMOS image sensor, comprising:

• a p-type substrate having a front-side and a back-side opposite to the front-side;
• an n-type photodiode region disposed within and in direct contact with the p-type substrate;
• a vertical transfer gate electrode extending vertically from the front-side of the p-type substrate to a first position within the p-type substrate and separated from the p-type substrate by a gate dielectric;
• a p-type lateral isolation region disposed on the n-type photodiode region;
• a p-type pixel device well disposed on the p-type lateral isolation region;
• a p-type vertical isolation region vertically extending from the front-side of the p-type substrate and reaching on the p-type lateral isolation region, wherein the p-type vertical 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 p-type lateral isolation region directly contacts and covers a top surface of the DTI structure.

A method of forming an image sensor, comprising:

• forming a shallow trench isolation (STI) structure at a peripheral of a pixel region from a front-side of a substrate;
• forming a photodiode doped region of a photodiode of the pixel region from the front-side of the substrate;
• forming a doped lateral isolation region and a doped vertical isolation region on the photodiode doped region, along the STI structure, and within the substrate, wherein the doped lateral isolation region and the doped vertical isolation region separate the photodiode doped region from the pixel region thereabove;
• forming a vertical transfer gate structure aside of the doped vertical isolation region and a floating diffusion well at one side of the vertical transfer gate structure opposite to the doped vertical isolation region;
• forming a pixel device on the front-side of the substrate on one side of the doped vertical isolation region opposite to the vertical transfer gate structure;
• and
• forming a deep trench isolation (DTI) structure of a dielectric fill layer from a back-side of the substrate extending into the substrate, surrounding the photodiode doped region, and reaching to a bottom surface of the doped lateral isolation region.