Ridge structure for back side illuminated image sensor

An apparatus comprising an image sensor device that comprises:

• a substrate having a front surface and a back surface;
• a plurality of radiation-sensing regions formed in the substrate, each of the radiation-sensing regions being operable to sense radiation projected toward the radiation-sensing region through the back surface;
• and
• a plurality of anti-reflective features formed over the back surface of the substrate, each of the anti-reflective features being approximately aligned to one of the radiation-sensing regions, each of the anti-reflective features being separated from adjacent anti-reflective features by a material that has a lower refractive index than each of the anti-reflective features.

A method of fabricating an image sensor device, comprising:

• providing a substrate having a front surface and a back surface;
• forming a plurality of radiation-sensing regions in the substrate, each of the radiation-sensing regions being operable to sense radiation projected toward the radiation-sensing region through the back surface;
• forming an interconnect structure over the front surface of the substrate;
• thinning the substrate from the back surface;
• and
• forming a plurality of anti-reflective features over the back surface of the substrate, each of the anti-reflective features being approximately aligned to one of the radiation-sensing regions, the anti-reflective features being separated by a material that has a lower refractive index than each of the anti-reflective features.