Deeply buried color filter array (cfa) by stacked grid structure

The present disclosure relates to a BSI image sensor having a color filter disposed between sidewalls of a metallic grid, and a method of formation. In some embodiments, the BSI image sensor has a pixel sensor located within a semiconductor substrate, and a layer of dielectric material overlying the pixel sensor. A metallic grid is separated from the semiconductor substrate by the layer of dielectric material, and a stacked grid is arranged over the metallic grid. The stacked grid abuts an opening that vertically extends from an upper surface of the stacked grid to a position that is laterally arranged between sidewalls of the metallic grid. A color filter can be arranged within the opening. By having the color filter vertically extend between sidewalls of the metallic grid, a distance between the color filter and the pixel sensor can be made small, thereby improving performance of the BSI image sensor.