A method of fabricating self-aligned grids in a BSI image sensor is provided. The method includes depositing a first dielectric layer over a back surface of a substrate that has a plurality of photodiodes formed therein, forming a grid of trenches, and filling in the trenches with dielectric material to create a trench isolation grid. Here, a trench passes through the first dielectric layer and extends into the substrate. The method further includes etching back dielectric material in the trenches to a level that is below an upper surface of the first dielectric layer to form recesses overlaying the trench isolation grid, and filling in the recesses with metallic material to create a metallic grid that is aligned with the trench isolation grid.