High Dynamic Range, Backside-illuminated, Low Crosstalk Image Sensor with Walls Between Silicon Surface and First Layer Metal to Isolate Photodiodes

A backside-illuminated image sensor includes arrayed photodiodes separated by isolation structures, and interlayer dielectric between first layer of metal interconnect and substrate. The image sensor has barrier metal walls in the interlayer dielectric between isolation structures and first layer interconnect, the barrier metal walls aligned with the isolation structures and disposed between the isolation structures and first layer interconnect. The barrier metal wall deflects light passing through photodiodes of the sensor that would otherwise be reflected by interconnect into different photodiodes. The sensor is formed by providing a partially fabricated semiconductor substrate with photodiodes and source-drain regions formed; forming gate electrodes on a frontside surface of the semiconductor substrate, depositing an etch-stop layer over the gate electrodes; depositing interlayer dielectric on the etch-stop layer; forming trenches extending to the etch-stop layer through the interlayer dielectric, the trenches being between photodiodes; and filling trenches with metal to form barrier metal walls.