Metal grid in backside illumination image sensor chips and methods for forming the same

A method comprising:

• forming a plurality of image sensors on a front side of a semiconductor substrate, wherein the plurality of image sensors forms an array, and wherein the plurality of image sensors comprises a first and a second plurality of image sensors, wherein in each row and each column of the array, image sensors in the first and the second plurality of image sensors are allocated in an alternating layout;
• forming a dielectric layer over a backside of the semiconductor substrate;
• patterning the dielectric layer to form a first plurality of grid-filling regions, wherein the first plurality of grid-filling regions overlaps the first plurality of image sensors in the array, and wherein the second plurality of image sensors is not overlapped by remaining portions of the dielectric layer;
• forming a metal layer on top surfaces and sidewalls of the first plurality of grid-filling regions;
• etching the metal layer to remove horizontal portions of the metal layer, wherein vertical portions of the metal layer remain after the step of etching to form a metal grid;
• and
• filling a clear-colored dielectric material into remaining grid openings of the metal grid not occupied by the first plurality of grid-filling regions to form second plurality of grid-filling regions, wherein the clear-colored dielectric material further comprises a top layer covering the first plurality of grid-filling regions, the second plurality of grid-filling regions, and the metal grid.

A method comprising:

• forming a plurality of image sensors on a front side of a semiconductor substrate, wherein the plurality of image sensors forms an array;
• forming a dielectric layer over a backside of the semiconductor substrate;
• patterning the dielectric layer into a plurality of grid-filling regions, wherein the step of patterning comprises removing first portions of the dielectric layer that overlap first alternating ones of the plurality of image sensors in each row and each column of the array;
• forming a metal layer on top surfaces and sidewalls of the plurality of grid-filling regions;
• etching the metal layer to remove the metal layer on the top surface of each grid-filling region, wherein remaining portions of the metal layer forms a metal grid on sidewalls of the plurality of grid-filling regions, wherein the metal grid comprises a first plurality of metal features continuously extending through a plurality of rows of the array, and a second plurality of metal features continuously extending through a plurality of columns of the array, and wherein the first plurality of metal features and the second plurality of metal features cross each other;
• and
• filling a transparent material into grid openings of the metal grid;
• and
• forming a plurality of color filters over the metal grid and the transparent material.