Back side illuminated CMOS image sensor arrays

1. An image sensor including at least one pixel for collecting charge in its photodiode, comprising:

a substrate having a first surface on a front side and a second surface on a back side;

a photodiode formed in the substrate and having a light-receiving surface on the second surface; and

a first positively-charged layer disposed over the second surface and outside the substrate, the first positively-charged layer being configured to attract electrons in the substrate to accumulate at the second surface of the photodiode for suppressing dark current of the image sensor, wherein:

the photodiode comprises a p− region and a p region,

the p− region and the p region are configured to receive light and generate carriers in response to the received light, and

at least a portion of the second surface is a surface of the p− region.

2. The image sensor of claim 1 , wherein the first positively-charged layer is a silicon nitride layer.

3. The image sensor of claim 1 , further comprising a color filter on the first positively-charged layer.

4. The image sensor of claim 3 , further comprising one or more micro lenses disposed on the color filter.

5. The image sensor of claim 1 , further comprising an n-type doped pinning layer, at least a portion of the first surface being a surface of the pinning layer.

6. The image sensor of claim 1 , further comprising a p-type doped floating diffusion region formed on the first surface of the substrate, and an n-type doped region formed between the floating diffusion region and the photodiode.

7. The image sensor of claim 1 , wherein the first positively-charged layer is an anti-reflection layer.

8. The image sensor of claim 1 , further comprising an insulating layer disposed between the second surface and the first positively-charged layer.

9. The image sensor of claim 8 , wherein the insulating layer is made of silicon dioxide.

10. The image sensor of claim 1 , further comprising a second positively-charged layer disposed over the first surface of the substrate.

11. The image sensor of claim 10 , wherein the second positively-charged layer is a silicon nitride layer configured to attract electrons in the substrate to accumulate at the first surface, causing dark current suppression at the first surface.

12. A method of fabricating an image sensor, comprising:

introducing p-type dopants on a first surface of a silicon wafer to form one or more p-type regions;

introducing n-type dopants on the first surface of the silicon wafer to form an n+ potential pinning layer;

depositing a layer of silicon dioxide and one or more poly gates on the first surface of the silicon wafer;

flipping the silicon wafer;

thinning the silicon wafer to form a second surface opposite to the first surface;

depositing a first layer of silicon dioxide on the second surface;

depositing a first layer of silicon nitride on the first layer of silicon dioxide;

depositing a second layer of silicon dioxide on the n+ potential pinning layer; and

depositing a second layer of silicon nitride on the second layer of silicon dioxide, wherein the second surface is configured as a light-receiving surface of the image sensor.

13. The method of claim 12 , further comprising:

forming at least one of: a color filter layer, and a micro-lens, on the first layer of silicon nitride.

14. An image sensor including at least one pixel for collecting charge in its photodiode, comprising:

a substrate having a first surface and a second surface away from the first surface, the substrate comprising a photodiode configured to receive light via the second surface; and

a first positively-charged layer disposed over the second surface and outside the substrate, the first positively-charged layer being configured to attract electrons in the substrate to accumulate at the second surface, causing dark current suppression at the second surface, wherein:

the photodiode comprises a p− region and a p region,

the p− region and the p region are configured to receive light and generate carriers in response to the received light, and

at least a portion of the second surface is a surface of the p− region.

15. The image sensor of claim 14 , wherein the first positively-charged layer is a silicon nitride layer.

16. The image sensor of claim 14 , further comprising a second positively-charged layer disposed over the first surface of the substrate.

17. The image sensor of claim 16 , wherein the second positively-charged layer is a silicon nitride layer configured to attract electrons in the substrate to accumulate at the first surface, causing dark current suppression at the first surface.