Lateral light shield in backside illuminated imaging sensors

A backside illuminated image sensor comprising:

• a semiconductor layer having a frontside surface and a backside surface, the semiconductor layer including:
• a light sensing element of a pixel array disposed in a sensor array region of the semiconductor layer, wherein the pixel array is positioned to receive external incoming light through the backside surface of the semiconductor layer;
• and
• a light emitting element disposed in a periphery circuit region of the semiconductor layer external to the sensor array region, wherein the periphery circuit region includes circuit elements that facilitate operation of the light sensing element;
• and
• a trench disposed in the semiconductor layer between the light sensing element and the light emitting element, the trench positioned to impede a light path between the light emitting element and the light sensing element, wherein the light path is internal to the backside illuminated image sensor;
• and
• an anti-reflection coating disposed in the trench and along sidewalls of the trench, wherein a first refractive index of the anti-reflection coating is less than a second refractive index of the semiconductor layer.