Image sensor with metal grids and manufacturing method thereof

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.