Backside structure and methods for BSI image sensors

A method for forming an image sensor comprising:

• providing a semiconductor substrate having a sensor array region and a periphery region and having a front side surface and an opposing back side surface;
• forming a bottom anti-reflective coating (BARC) over the back side surface of the semiconductor substrate to a first thickness, over the sensor array region and the periphery region;
• forming a first dielectric layer over the BARC;
• forming a metal shield over the first dielectric layer;
• selectively removing the metal shield from over the sensor array region;
• selectively removing the first dielectric layer from over the sensor array region, wherein a portion of the first thickness of the BARC is also removed and a remainder of the first thickness of the BARC remains, during the selectively removing the first dielectric layer;
• forming a second dielectric layer over the remainder of the first thickness of the BARC and over the metal shield over the periphery region;
• and
• forming a passivation layer over the second dielectric layer.