Backside illuminated image sensors and method of making the same

A backside illuminated image sensor, comprising:

• a substrate having a first surface and a light receiving surface;
• a first isolation structure passing through the substrate, wherein the first isolation structure has a first depth and a bottom of the first isolation structure is exposed at the light receiving surface of the substrate;
• a sensor element in the first surface of the substrate;
• a color filter overlying the light receiving surface of the substrate;
• a second isolation structure in the substrate, wherein the second isolation structure has a second depth less than the first depth;
• and
• an implant region adjacent to at least a portion of sidewalls of each first isolation structure, wherein the portion of the sidewalls are located closer to the light receiving surface than the first surface of the substrate, wherein the second isolation structure is free of the implant region.

A backside illuminated image sensor, comprising:

• a substrate having a first surface and a light receiving surface;
• a first isolation structure extending from the first surface to the light receiving surface;
• a second isolation structure in the substrate, wherein the second isolation structure has a depth from the first surface less than a depth of the first isolation structure from the first surface;
• an implant region adjacent to at least a portion of sidewalls of each first isolation structure, wherein the portion of the sidewalls is located closer to the light receiving surface than the first surface, wherein the second isolation structure is free of the implant region;
• and
• an inter-layer dielectric layer over the first surface of the substrate.