Image sensor having deep isolation regions

A method, comprising:

• forming an n-type semiconductor layer of a photodiode over a top surface of a substrate;
• forming a p well in the n-type semiconductor layer of the photodiode;
• forming a floating diffusion region in the n-type semiconductor layer of the photodiode and adjacent the p well, the floating diffusion region being configured to receive charges from the photodiode;
• forming an isolation structure extending through the p well and the n-type semiconductor layer of the photodiode;
• and
• forming a gate structure extending through the floating diffusion region without extending through the n-type semiconductor layer of the photodiode, wherein the gate structure is disposed between the p well and the floating diffusion region,
• wherein, in a top view, the gate structure surrounds the floating diffusion region.

A method, comprising:

• epitaxially growing an n-type semiconductor layer over a substrate;
• forming a p-type well in the n-type semiconductor layer, wherein the p-type well extends from a top surface of the n-type semiconductor layer into the n-type semiconductor layer;
• forming an n-type doped region in the n-type semiconductor layer and surrounded by the p-type well;
• forming a first trench extending through the n-type semiconductor layer and a second trench separating the n-type doped region and the p-type well;
• depositing a dielectric layer in the first trench and the second trench;
• and
• depositing a conductive layer over the dielectric layer and in the first trench and the second trench, thereby forming a first feature in the first trench and a second feature in the second trench,
• wherein, in a top view, the first feature surrounds the p-type well, and the second feature surrounds the n-type doped region.