Image sensor with backside passivation and metal layer

A frontside illuminated (“FSI”) image sensor, comprising:

• a P-type semiconductor layer;
• an imaging pixel having a photodiode disposed within the P-type semiconductor layer for absorbing photons having shorter wavelengths and longer wavelengths of visible light, wherein the photodiode is an N region formed within the P-type semiconductor layer, wherein the photons are incident upon a frontside of the FSI image sensor;
• a P+ implantation layer disposed within the P-type semiconductor layer between the N region of the photodiode and a back surface of the P-type semiconductor layer, wherein the back surface is opposite to the frontside upon which the photons are incident;
• and
• a metal layer disposed on the back surface of the P-type semiconductor layer, wherein a thickness of the P-type semiconductor layer is selected such that primarily the photons having the longer wavelengths are reflected by the metal layer back towards the N region while the photons having the shorter wavelengths are substantially absorbed prior to reaching the metal layer.