Lateral light shield in backside illuminated imaging sensors

A method of fabricating a backside illuminated image sensor, the method comprising:

• providing a semiconductor layer of the backside illuminated image sensor having a frontside surface and a backside surface, the semiconductor layer including a light sensing element and a periphery circuit region of the semiconductor layer containing a light emitting element and not containing the light sensing element, wherein the periphery circuit region is external to a sensor array region of the semiconductor layer;
• forming a trench that penetrates the backside surface of the semiconductor layer, the trench positioned to prevent light emitted by the light emitting element from reaching the light sensing element;
• and
• forming an anti-reflection coating along sidewalls of the trench and along a bottom of the trench, but not completely filling the trench with the anti-reflection coating.