Back side illuminated image sensor pixel with dielectric layer reflecting ring

An imaging system, comprising:

• a pixel array having a plurality of pixel cells disposed in semiconductor material, wherein each one of the plurality of pixel cells includes:
• a photodiode disposed in the semiconductor material proximate to a front side of the semiconductor material to accumulate image charge in response to light directed through a back side of the semiconductor material and through the photodiode;
• a metal layer reflector structure disposed in a dielectric layer proximate to the front side of the semiconductor material such that the light that is directed through the back side of the semiconductor material and through the photodiode is reflected from the metal layer reflector structure back through the photodiode;
• a contact etch stop layer disposed over the front side of the semiconductor material between the dielectric layer and the photodiode in the semiconductor material;
• and
• a contact reflecting ring structure disposed in the dielectric layer, wherein all of the contacting reflecting ring structure is disposed between the metal layer reflector structure and the contact etch stop layer, wherein the contact reflecting ring structure encloses a portion of a light guide in the dielectric layer between the metal layer reflector structure and the photodiode in the semiconductor material such that the light that is directed through the photodiode and reflected from the metal layer reflector structure back through the photodiode is confined to remain within an interior of the contact reflecting ring structure when passing through the dielectric layer between the photodiode and the metal layer reflector structure;
• control circuitry coupled to the pixel array to control operation of the pixel array;
• and
• readout circuitry coupled to the pixel array to readout image data from the plurality of pixel cells.