Backside structure and methods for BSI image sensors

1. A method of manufacturing an image sensor, the method comprising:

providing a semiconductor substrate having a sensor array region and a periphery region and having a front side and an opposing back side surface;

forming a bottom anti-reflective coating (BARC) layer over the back side surface of the semiconductor substrate to a first thickness over the sensor array region and the periphery region;

forming a metal shield layer over the BARC layer;

selectively removing portions of the metal shield layer from over the sensor array region to form a metal shield grid over the sensor array region;

selectively removing portions of the BARC layer exposed by the selectively removing the metal shield layer, wherein a portion of the first thickness of the BARC layer is also removed and a remainder of the first thickness of the BARC layer remains during the selectively removing the portions of the metal shield layer;

forming a first dielectric layer within the metal shield grid over the sensor array region and over a remainder of the first thickness of the BARC layer over the periphery region; and

forming a second dielectric layer within the metal shield grid, the second dielectric layer having a different refractive index than the first dielectric layer.

2. The method of claim 1 , further comprising forming a third dielectric layer over the second dielectric layer within the metal shield grid over the sensor array region.

3. The method of claim 2 , wherein the third dielectric layer has a different refractive index than the second dielectric layer.

4. The method of claim 3 , further comprising forming a passivation layer over the third dielectric layer.

5. The method of claim 1 , wherein the first dielectric layer and the second dielectric layer fill a region within the metal shield grid.

6. The method of claim 1 , wherein the metal shield grid has a width that is between 5% and 70% of a pixel pitch of the image sensor.

7. The method of claim 1 , wherein the second dielectric layer has a first thickness along a sidewall of the metal shield grid that is less than 50% of a width from a first surface of the metal shield grid to a second surface of the metal shield grid, the first surface facing the second surface.

8. A method of manufacturing an image sensor, the method comprising:

forming a BARC layer and a grid layer over an array region of a substrate and a periphery region of the substrate;

forming an opening in the BARC layer and the grid layer, wherein the opening is confined to over the array region, wherein the opening extends fully through the grid layer and extends partially through the BARC layer;

forming a first dielectric layer lining the opening and extending over the periphery region; and

forming a second dielectric layer within the opening, the second dielectric layer having a different refractive index than the first dielectric layer.

9. The method of claim 8 , wherein the grid layer comprises a metal.

10. The method of claim 9 , wherein the metal comprises tungsten, aluminum, or copper.

11. The method of claim 8 , wherein the grid layer comprises titanium nitride, silicon nitride, tantalum oxide, hafnium oxide, or aluminum oxide.

12. The method of claim 8 , wherein the forming the opening forms a grid.

13. The method of claim 12 , wherein the grid has sidewalls aligned with photodiodes located within the substrate.

14. The method of claim 13 , wherein the grid has a width that is between about 5% and about 70% of a pixel pitch of the image sensor.

15. A method of manufacturing an image sensor, the method comprising:

manufacturing a sensor array and a periphery region on a semiconductor substrate;

depositing a BARC layer with a first thickness over the sensor array and the periphery region;

depositing a metal layer with a second thickness over the BARC layer and over both the sensor array and the periphery region;

forming a metal grid by removing portions of the metal layer over the sensor array to form one or more openings, each of the one or more openings having a depth larger than the second thickness, wherein the metal layer over the periphery region remains at the second thickness; and

lining the one or more openings with a first dielectric layer, wherein the first dielectric layer extends from the one or more openings to a point over the periphery region.

16. The method of claim 15 , wherein the first dielectric layer has a uniform thickness.

17. The method of claim 15 , wherein a uniformity of the first dielectric layer varies less than 7%.

18. The method of claim 15 , wherein the metal grid has a width of between about 5 μm and about 0.5 μm.

19. The method of claim 15 , wherein the first dielectric layer has a first thickness over the periphery region and a second thickness on sidewalls of the one or more openings, and wherein a ratio of the second thickness to the first thickness is greater than about 40%.

20. The method of claim 15 , wherein the one or more openings have vertical sidewalls.