Image sensors with vertically stacked photodiodes and vertical transfer gates
Image sensors may include multiple vertically stacked photodiodes interconnected using vertical deep trench transfer gates. A first n-epitaxial layer may be formed on a residual substrate; a first p-epitaxial layer may be formed on the first n-epitaxial layer; a second n-epitaxial layer may be formed on the first p-epitaxial layer; a second p-epitaxial layer may be formed on the second n-epitaxial layer; and so on. The n-epitaxial layers may serve as accumulation regions for the different epitaxial photodiodes. A separate color filter array is not needed. The vertical transfer gates may be a deep trench that is filled with doped conductive material, lined with gate dielectric liner, and surrounded by a p-doped region. Image sensors formed in this way may be used to support a rolling shutter configuration or a global shutter configuration and can either be front-side illuminated or backside illuminated.
1. An image sensor comprising:
a substrate;
a n-type epitaxial layer formed on the substrate;
a p-type epitaxial layer formed over the n-type epitaxial layer;
a deep n-well formed in the p-type layer over the n-type epitaxial layer;
a floating diffusion region; and
a charge transfer gate coupled between the deep n-well and the floating diffusion region.
2. The image sensor defined in claim 1 , wherein the substrate is a p-type residual substrate, wherein the deep n-well is formed over only a portion of the n-type epitaxial layer, and wherein the image sensor further comprises:
a shallow p-type implant region formed above the deep n-well;
deep trench isolation structures that laterally surround the n-type epitaxial layer; and
a p-type liner that surrounds the deep trench isolation structures.
3. The image sensor defined in claim 1 , wherein the substrate is a residual substrate.
4. The image sensor defined in claim 1 , wherein the substrate is a p-type substrate.
5. The image sensor defined in claim 1 , wherein the deep n-well is formed over only a portion of the n-type epitaxial layer.
6. The image sensor defined in claim 1 , further comprising:
a shallow p-type implant region formed above the deep n-well.
7. The image sensor defined in claim 1 , further comprising:
deep trench isolation structures that laterally surround the n-type epitaxial layer.
8. The image sensor defined in claim 7 , further comprising:
a liner that surrounds the deep trench isolation structures.
9. The image sensor defined in claim 8 , wherein the liner is a p-type liner.
10. An image sensor having a front surface and a back surface, the image sensor comprising:
a substrate with first and second opposing surfaces, the first surface of the substrate forming the back surface of the image sensor;
a n-type epitaxial layer adjacent to the substrate;
a p-type layer formed adjacent to the n-type epitaxial layer, wherein the p-type layer has first and second opposing surfaces, and wherein the second surface of the p-type layer forms the front surface of the image sensor;
an n-well formed in the p-type layer, wherein the n-well overlaps the n-type epitaxial layer;
a floating diffusion region formed at the second surface of the p-type layer; and
a charge transfer gate coupled between the n-well and the floating diffusion region, wherein the charge transfer gate is configured to transfer charge along the second surface of the p-type layer from the n-well to the floating diffusion region.
11. The image sensor defined in claim 10 , wherein the substrate is a p-type residual substrate, wherein the n-well overlaps only a portion of the n-type epitaxial layer, and wherein the image sensor further comprises:
a shallow p-type implant region formed between the n-well and the second surface of the p-type layer;
deep trench isolation structures that laterally surround the n-type epitaxial layer, wherein the deep trench isolation structures extend from the second surface of the p-type layer to the p-type residual substrate; and
a p-type liner that surrounds the deep trench isolation structures.
12. The image sensor defined in claim 10 , further comprising:
deep trench isolation structures that laterally surround the n-type epitaxial layer.
13. The image sensor defined in claim 12 , wherein the deep trench isolation structures extend from the second surface of the p-type layer to the p-type residual substrate.
14. The image sensor defined in claim 10 , further comprising:
a shallow p-type implant region formed between the n-well and the second surface of the p-type layer.
15. An image sensor comprising:
a substrate of a first type;
an epitaxial layer of a second type that is different than the first type formed on the substrate;
a layer of the first type formed over the epitaxial layer;
a region of the second type formed in the layer of the first type;
a floating diffusion region;
a charge transfer gate coupled between the region of the second type and the floating diffusion region;
deep trench isolation structures that laterally surround the epitaxial layer; and
a liner of the first type that surrounds the deep trench isolation structures.
16. The image sensor defined in claim 15 , wherein the substrate of the first type forms a back surface of the image sensor and the layer of the first type forms a front surface of the image sensor.
17. The image sensor defined in claim 16 , wherein the deep trench isolation structures extend from the front surface to the substrate of the first type.