Image sensor

Patent metadata

Field	Value
Publication number	US-10903259-B2
Application number	US-201916451918-A
Country	US
Kind code	B2
Filing date	Jun 25, 2019
Priority date	Jul 9, 2018
Publication date	Jan 26, 2021
Grant date	Jan 26, 2021

Abstract

A multispectral image sensor includes a semiconductor layer and a number of pixels formed inside and on top of the semiconductor layer. Each pixel includes an active photosensitive area formed in a portion of the semiconductor layer laterally delimited by peripheral insulating walls. The pixels include a first pixel of a first type and a second pixel of a second type. The portion of semiconductor layer of the first pixel has a first lateral dimension selected to define a lateral cavity resonating at a first wavelength and the portion of semiconductor layer of the second pixel has a second lateral dimension different from the first lateral dimension. The second lateral dimension is selected to define a lateral cavity resonating at a second wavelength different from the first wavelength.

First claim

What is claimed is:

1. A multispectral image sensor comprising:
a semiconductor layer; and
a plurality of pixels formed inside and on top of the semiconductor layer, each pixel comprising an active photosensitive area formed in a portion of the semiconductor layer laterally delimited by peripheral insulating walls, the plurality of pixels comprising a first pixel of a first type and a second pixel of a second type, wherein the first pixel has a first lateral dimension delimited by the corresponding peripheral insulating walls of the first pixel along a lateral direction parallel to a major surface of the semiconductor layer and selected to define a first laterally resonating optical cavity resonating along the lateral direction at a first wavelength and wherein the second pixel has a second lateral dimension delimited by the corresponding peripheral insulating walls of the second pixel along the lateral direction, the second lateral dimension being different from the first lateral dimension, the second lateral dimension being selected to define a second laterally resonating optical cavity resonating along the lateral direction at a second wavelength different from the first wavelength.

2. The sensor of claim 1 , wherein the first and second pixels each comprise a diffractive structure arranged on a rear surface of the portion of semiconductor layer of the pixels.

3. The sensor of claim 2 , wherein the diffractive structure is formed by a cavity formed in the portion of semiconductor layer of each pixel, the cavity being filled with a material having a refraction index smaller than that of a material of the semiconductor layer.

4. The sensor of claim 2 , wherein the sensor is configured to be back-side illuminated.

5. The sensor of claim 2 , further comprising an insulating region adjacent a front surface of the semiconductor layer, the insulating region having metal layers having metallizations of interconnection of the pixels.

6. The sensor of claim 1 , wherein the peripheral insulating walls are formed of a metal wall sandwiched between two walls made of an insulating material.

7. The sensor of claim 1 , wherein the sensor has more than two different types of pixels formed inside and on top of portions of the semiconductor layer, each different type of pixel having different lateral dimensions selected to define lateral cavities resonating at different wavelengths.

8. The sensor of claim 7 , wherein the sensor has at least four different types of pixels.

9. The sensor of claim 1 , wherein the portions of the semiconductor layer of the pixels of the first and second types have substantially the same thickness.

10. The sensor of claim 9 , wherein the first and second pixels each comprise a diffractive structure arranged on a rear surface of the portion of semiconductor layer of the pixel.

11. A method of forming an image sensor, the method comprising:
etching a trench structure in a semiconductor substrate to separate a first portion of the semiconductor substrate from a second portion of the semiconductor substrate, the first and second portions having different lateral dimensions;
filling the trench structure, wherein the first portion defines a first laterally resonating optical cavity that is laterally defined by first peripheral walls of the trench structure and the second portion defines a second laterally resonating optical cavity that is laterally defined by second peripheral walls of the trench structure;
after filling the trench structure, forming a first diffractive structure at a back side surface of the first portion of the semiconductor substrate and a second diffractive structure at a backside surface of the second portion of the semiconductor substrate; and
forming a microlens layer over the back side surface of the first portion of the semiconductor substrate and the back side surface of the second portion of the semiconductor substrate.

12. The method of claim 11 , wherein the first portion of the semiconductor substrate comprises a first active photosensitive area forming a first pixel of the image sensor and wherein the second portion of the semiconductor substrate comprises a second active photosensitive area forming a second pixel of the image sensor, the first pixel being configured to sense a different wavelength of light than the second pixel.

13. The method of claim 11 , wherein filling the trench structure comprises filling the trench structure with an insulating material to form the first and the second peripheral walls.

14. The method of claim 11 , wherein filling the trench structure comprises lining sidewalls of the trench structure with an insulating material to form the first and the second peripheral walls and filling the trench structure with a metal material.

15. The method of claim 11 , wherein the first and second portions are etched at a back side surface of the semiconductor substrate, the method further comprising forming a plurality of interconnection regions over a front side surface of the semiconductor substrate.

16. The method of claim 11 , wherein the first and second portions of the semiconductor substrate have the same thickness.

17. A multispectral sensor comprising:
a semiconductor substrate having a front side and a back side;
a plurality of interconnect layers at the front side of the semiconductor substrate;
a microlens layer at the back side of the semiconductor substrate; and
a plurality of photosensitive areas within the semiconductor substrate between the interconnect layers and the microlens layer, each of the photosensitive areas having a laterally resonating optical cavity with a lateral dimension along a lateral direction parallel to the front side of the semiconductor substrate, the laterally resonating optical cavity having a resonance wavelength associated with a color of light to be detected, wherein the multispectral sensor has photosensitive areas having at least four different lateral dimensions so that the multispectral sensor is capable of detecting at least four different colors of light.

18. The sensor of claim 17 , wherein the photosensitive areas are separated from one another by peripheral insulating walls formed of a metal wall sandwiched between two walls made of an insulating material.

19. The sensor of claim 17 , wherein the front side and backside of the semiconductor substrate are coated with an insulating material having a refraction index smaller than that of semiconductor material of the photosensitive areas.

20. The sensor of claim 17 , wherein each of the photosensitive areas has the same thickness.

Assignees

• St Microelectronics Crolles 2 Sas

Inventors

• Rideau Denis
• Crocherie Axel

Classifications

• H10F39/8063

  Microlenses · CPC title

• H10F39/811

  Interconnections · CPC title

• H10F39/802 Primary

  Geometry or disposition of elements in pixels, e.g. address-lines or gate electrodes · CPC title

• H10F39/199

  Back-illuminated image sensors · CPC title

• H10F39/024

  of coatings or optical elements · CPC title