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

Patent metadata

Field	Value
Publication number	US-10224364-B2
Application number	US-201715666086-A
Country	US
Kind code	B2
Filing date	Aug 1, 2017
Priority date	Jul 5, 2017
Publication date	Mar 5, 2019
Grant date	Mar 5, 2019

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.

First claim

What is claimed is:

1. An image sensor, comprising:
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;
a near infrared (NIR) quantum efficiency (QE) and modulation transfer function (MTF) enhancement structure, comprising:
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 sub-structure has a geometry corresponding to the NIR QE enhancement sub-structure, to ensure the incident light is still within the photodiode after redistribution.

2. The image sensor of claim 1 , wherein the MTF enhancement sub-structure comprises an optical reflective layer embedded in a first dielectric layer, wherein the optical reflective layer has the geometry corresponding to the NIR QE enhancement sub-structure, to ensure the incident light is reflected back into the photodiode after redistribution.

3. The image sensor of claim 2 , wherein the optical reflective layer comprises at least one of Au, Cu, Ti, Al, Pt, Ag, Ta, and Al/Cu.

4. The image sensor of claim 2 , wherein the first dielectric layer comprises organic dielectric materials and inorganic dielectric materials.

5. The image sensor of claim 1 , wherein each NIR QE enhancement element of the NIR QE enhancement sub-structure comprises a second dielectric material having a refractive index smaller than a refractive index of the semiconductor material.

6. The image sensor of claim 1 , wherein each NIR QE enhancement element of the NIR QE enhancement sub-structure comprises a shape of one of a parallelepiped, a polygon, a cylinder, an ellipsoids, a hemispheroid, and a hemisphere.

7. The image sensor of claim 1 , wherein the illuminated surface of the semiconductor material is one of a front side surface and a back side surface of the semiconductor material.

8. The image sensor of claim 1 , wherein each NIR QE enhancement element of the NIR QE enhancement sub-structure extends from the illuminated surface of the semiconductor material in the photodiode.

9. The image sensor of claim 1 , wherein each NIR QE enhancement element of the NIR QE enhancement sub-structure is disposed at least partially on the illuminated surface of the semiconductor material.

10. The image sensor of claim 1 , wherein an isolation region surrounds, at least partially, the photodiode, and isolates the photodiode electrically and optically.

11. The image sensor of claim 1 , further comprising a reset transistor electrically coupled to the floating diffusion to reset the charges received in the floating diffusion.

12. The image sensor of claim 1 , further comprising an amplifier transistor electrically coupled to the floating diffusion to amplify the charges received in the floating diffusion.

13. An imaging system, comprising:
a semiconductor material having an illuminated surface and a non-illuminated surface;
a plurality of photodiodes 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 photodiodes;
a plurality of isolation structures, wherein each of the plurality of isolation structures is disposed between two adjacent photodiodes of the plurality of photodiodes;
a plurality of transfer gates electrically coupled to the plurality of photodiodes to transfer the generated charges from the plurality of photodiodes to one or more floating diffusions;
A plurality of near infrared (NIR) quantum efficiency (QE) and modulation transfer function (MTF) enhancement structures, wherein each of 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 imaging system; 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 sub-structure has a geometry corresponding to the NIR QE enhancement sub-structure, to ensure the incident light is still within the photodiode after redistribution.

14. The imaging system of claim 13 , wherein the MTF enhancement sub-structure comprises an optical reflective layer embedded in a first dielectric layer, wherein the optical reflective layer has the geometry corresponding to the NIR QE enhancement sub-structure, to ensure the incident light is reflected back into the photodiode after redistribution.

15. The image sensor of claim 14 , wherein the optical reflective layer comprises at least one of Au, Cu, Ti, Al, Pt, Ag, Ta, and AlCu.

16. The image sensor of claim 14 , wherein the first dielectric layer comprises at least one of organic dielectric materials and inorganic dielectric materials.

17. The imaging system of claim 13 , further comprising a plurality of reset transistors, wherein each of the plurality of reset transistors electrically coupled to the one or more floating diffusions to reset the charges received in the one or more floating diffusions.

18. The imaging system of claim 13 , further comprising a plurality of amplifier transistors, wherein each of the plurality of amplifier transistors electrically coupled to the one or more floating diffusions to amplify the charges received in the one or more floating diffusions.

19. The imaging system of claim 13 , further comprising a control circuitry and a readout circuitry, wherein the control circuitry controls operation of the plurality of photodiodes, and the readout circuitry reads out image data from the plurality of photodiodes.

20. The image sensor of claim 13 , wherein each NIR QE enhancement element of the NIR QE enhancement sub-structure comprises a second dielectric material having a refractive index smaller than a refractive index of the semiconductor material.

21. The imaging system of claim 13 , wherein each NIR QE enhancement element of the NIR QE enhancement sub-structures comprises a shape of one of a parallelepiped, a polygon, a cylinder, an ellipsoids, a hemispheroid, and a hemisphere.

22. The imaging system of claim 13 , wher

Assignees

• Omnivision Tech Inc

Inventors

• Zhao Cheng
• Yang Cunyu
• Lu Chen-Wei
• Lin Zhiqiang

Classifications

• H04N25/77

  Pixel circuitry, e.g. memories, A/D converters, pixel amplifiers, shared circuits or shared components · CPC title

• H04N25/00

  Circuitry of solid-state image sensors [SSIS]; Control thereof · CPC title

• H01L27/14612

  Electricity · mapped topic

• H01L27/14649 Primary

  Electricity · mapped topic

• H01L27/14629

  Electricity · mapped topic