Image sensor and method of manufacturing the same

A method, comprising:

• receiving a semiconductor substrate having a first side, a second side, and a pixel area;
• implanting dopants through the first side to form an n-doped region;
• implanting dopants through the first side to form a p-doped region above the n-doped region, wherein the n-doped region and the p-doped region form a PN junction in the pixel area;
• etching an opening in the first side in the pixel area;
• lining the opening with a gate dielectric;
• depositing a conductive material, wherein the conductive material fills the opening to form a transfer gate electrode, and the transfer gate electrode is confined to a depth that is at or above the PN junction;
• removing excess conductive material whereby the transfer gate electrode is confined at or below a surface of the semiconductor substrate;
• implanting a dopant into the semiconductor substrate using a first dopant implantation process to form a floating diffusion region laterally adjacent the transfer gate in the pixel area;
• forming a dielectric layer over the first side;
• forming vias through the dielectric layer, wherein the vias include a via that contacts the transfer gate electrode and a via that contacts the floating diffusion region;
• thinning the semiconductor substrate from the second side;
• and
• forming a microlens on the second side opposite the transfer gate.

A method, comprising:

• receiving a semiconductor substrate having a first side, a second side, and a pixel area;
• implanting dopants through the first side to form an n-doped region;
• implanting dopants through the first side to form a p-doped region above the n-doped region, wherein the n-doped region and the p-doped region form a PN junction in the pixel area;
• etching a trench in the first side in the pixel area, wherein the trench curves;
• lining the trench with a gate dielectric;
• depositing a conductive material, wherein the conductive material fills the trench to form a transfer gate electrode, wherein the transfer gate electrode curves without forming a closed loop so as to define a concavity;
• implanting dopants to form a floating diffusion region, wherein the floating diffusion region is at least partially within the concavity;
• forming a dielectric layer over the first side;
• forming vias through the dielectric layer, wherein the vias include a via that contacts the transfer gate electrode and a via that contacts the floating diffusion region;
• thinning the semiconductor substrate from the second side;
• and
• forming a microlens on the second side opposite the transfer gate.