Image sensor with metal grids and manufacturing method thereof

1. A method for manufacturing an image sensor, comprising:

providing a substrate structure, comprising:

a substrate having a first surface, wherein the substrate has a second surface facing the first surface and a third surface connecting the first surface and the second surface, an insulating layer is on the third surface, and the substrate structure further includes an interconnect structure under the second surface of the substrate and a bonding pad on the interconnection structure and separated from the third surface;

a plurality of pixels in the substrate;

isolation structures around each of the plurality of pixels; and

an anti-reflective coating on the first surface of the substrate;

forming a mask layer on the substrate structure, the mask layer having openings, wherein

a lateral size of an upper half of the openings is smaller than a lateral size of a lower half of the openings, and

the openings include first openings exposing a portion of the first surface of the substrate structure above the isolation structures;

depositing a metal grid material covering a surface of the mask layer and a bottom of the openings; and

stripping the mask layer for removing a portion of the metal grid material on the top surface of the mask layer, wherein a remaining portion of the metal grid material at the bottom of the openings forms metal grids, wherein:

the openings further include a second opening exposing a portion of the bonding pad and the insulating layer, and

a portion of the metal grid material on the bottom of the second opening is connected with the bonding pad.

2. The method according to claim 1 , further comprising:

providing an initial substrate structure, the initial substrate structure comprising:

an initial substrate having a first surface and a second surface;

the plurality of pixels in the initial substrate;

the isolation structures around each of the plurality of pixels;

an initial anti-reflective coating on the first surface of the initial substrate; and

the interconnect structure under the second surface of the initial substrate;

removing a portion of the initial substrate and the initial anti-reflective coating on the portion of the initial substrate exposing a portion of a surface of the interconnect structure and a side surface of a remaining portion of the initial substrate, wherein the remaining portion of the initial substrate is the substrate, the side surface of the remaining portion of the initial substrate is the third surface, and a remaining portion of the initial anti-reflective coating is the anti-reflective coating on the first surface of the substrate;

forming the insulating layer on the third surface;

forming through-holes extending in the interconnect structure to a metal layer located closest to the surface of the interconnect structure; and

forming the bonding pad by filling the through-holes with a metal material.

3. The method according to claim 1 , wherein:

the plurality of pixels includes photodiodes.

4. The method according to claim 1 , wherein the image sensor is a back-illuminated sensor.

5. The method according to claim 1 , wherein a size of the openings gradually increases from a top of the openings to a bottom of the openings.

6. The method according to claim 1 , wherein:

the metal grid material further covers a portion of side walls of the openings, and

stripping the mask layer further includes removing a portion of the metal grid material on side walls of the openings.

7. The method according to claim 1 , further comprising:

forming a color filter corresponding to each of the plurality of pixels in each area surrounded by metal grids.

8. The method according to claim 7 , further comprising:

forming a micro lens on the color filter.

9. The method according to claim 1 , wherein:

the metal grid material includes one or more of W, Al, Ti, TiN, Ta, and TaN.

10. The method according to claim 1 , wherein:

the metal grid material is deposited by a physical vapor deposition process.

11. The method according to claim 1 , wherein the anti-reflective coating includes:

a silicon oxide layer on the first surface of the substrate; and

a silicon nitride layer on the silicon oxide layer.