Cmos image sensor having enhanced near infrared quantum efficiency and modulation transfer function

Abstract

An image sensor comprises a semiconductor material having an illuminated surface and a non-illuminated surface; a photodiode formed in the semiconductor material extending from the illuminated surface to receive an incident light through the illuminated surface, wherein the received incident light generates charges in the photodiode; a transfer gate electrically coupled to the photodiode to transfer the generated charges from the photodiode in response to a transfer signal; a floating diffusion electrically coupled to the transfer gate to receive the transferred charges from the photodiode; and a near infrared (NIR) quantum efficiency (QE) and modulation transfer function(MTF) enhancement structure. The NIR QE and MTF enhancement structure comprises: a NIR QE enhancement sub-structure comprising at least one NIR QE enhancement elements within a photosensitive region of the photodiode, wherein the NIR QE enhancement sub-structure is configured to modify the incident light at the illuminated surface of the semiconductor material by at least one of diffraction, deflection and reflection, to redistribute the incident light within the photodiode to improve optical sensitivity, including NIR light sensitivity, of the image sensor; and a MTF enhancement sub-structure disposed on the non-illuminated surface of the semiconductor material, facing toward the NIR QE enhancement sub-structure, wherein the MTF enhancement structure has a geometry corresponding to the NIR QE enhancement sub-structure, to ensure the incident light is still within the photodiode after redistribution.