Near ultraviolet photocell

Patent metadata

Field	Value
Publication number	US-10748951-B2
Application number	US-201916534056-A
Country	US
Kind code	B2
Filing date	Aug 7, 2019
Priority date	Nov 30, 2017
Publication date	Aug 18, 2020
Grant date	Aug 18, 2020

Abstract

In an embodiment, an image sensor includes a semiconductor substrate, an epitaxial layer disposed over the semiconductor substrate, a first heavily doped region disposed in the epitaxial layer, and a shallow trench isolation region disposed in the epitaxial layer and surrounding the first heavily doped region. The semiconductor substrate and the epitaxial layer are of a first doping type and the semiconductor substrate is coupled to a reference potential node. The first heavily doped region is of a second doping type opposite to the first doping type. The epitaxial layer, the first heavily doped region, and the shallow trench isolation region are part of a p-n junction photodiode configured to operate in the near ultraviolet region.

First claim

What is claimed is:

1. An image sensor comprising:
a p-type epitaxial layer;
an anti-reflection layer, wherein an electrical length of a thickness of the anti-reflection layer approximately corresponds to a quarter wavelength of near ultraviolet;
a shallow trench isolation (STI) region disposed in the p-type epitaxial layer; and
a plurality of n-type active regions disposed in the p-type epitaxial layer and surrounded by the STI region, each n-type active region having a first major surface facing the p-type epitaxial layer and an opposing second major surface facing the anti-reflection layer, the p-type epitaxial layer and each n-type active region of the plurality of n-type active regions are a part of a respective p-n junction photodiode, wherein each of the plurality of n-type active regions extend continuously between edges of the surrounding STI region.

2. The image sensor of claim 1 , wherein a depth of the STI region disposed in the p-type epitaxial layer is greater than a depth of each n-type active region disposed in the p-type epitaxial layer.

3. The image sensor of claim 2 , wherein the depth of each n-type active region disposed in the p-type epitaxial layer is in accordance with an operation of the image sensor in a near ultraviolet region.

4. The image sensor of claim 1 , further comprising a plurality of p-type well regions disposed in the p-type epitaxial layer and surrounded by the STI region, each p-type well region of the plurality of p-type well regions, corresponding n-type active region, and the p-type epitaxial layer area part of the respective p-n junction photodiode.

5. The image sensor of claim 4 , further comprising a plurality of intrinsic p-type semiconductor regions positioned between an n-type active region of the plurality of n-type active regions and a p-type well region of the plurality of p-type well regions, wherein each combination of the n-type active region, the p-type well region, and the intrinsic p-type semiconductor region are a part of a p-i-n junction photodiode.

6. The image sensor of claim 1 , further comprising a p-well guard ring disposed in the p-type epitaxial layer and surrounding the STI region, the p-well guard ring comprising a negative-channel metal-oxide semiconductor (NMOS) transistor.

7. The image sensor of claim 6 , further comprising an n-well guard ring disposed in the p-type epitaxial layer and surrounding the p-well guard ring, the n-well guard ring comprising a positive-channel metal-oxide semiconductor (PMOS) transistor.

8. An image sensor comprising:
a p-type epitaxial layer;
a shallow trench isolation (STI) region disposed in the p-type epitaxial layer;
a plurality of n-well regions disposed in the p-type epitaxial layer and surrounded by the STI region, wherein each n-well region of the plurality of n-well regions and the p-type epitaxial layer are a part of a corresponding p-n junction photodiode;
a plurality of n-type active regions, each n-type active region disposed in a corresponding n-well region; and
an anti-reflection layer formed over the STI region and the plurality of n-type active regions, wherein an electrical length of a thickness of the anti-reflection layer approximately corresponds to a quarter wavelength of near ultraviolet.

9. The image sensor of claim 8 , further comprising an operational amplifier and a feedback capacitor.

10. The image sensor of claim 8 , further comprising a p-well guard ring disposed in the p-type epitaxial layer and surrounding the STI region, the p-well guard ring comprising a negative-channel metal-oxide semiconductor (NMOS) transistor.

11. The image sensor of claim 10 , wherein the p-well guard ring forms a ground strap surrounding a plurality of p-n junction photodiodes formed by the n-well regions and the p-type epitaxial layer.

12. The image sensor of claim 10 , further comprising an n-well guard ring disposed in the p-type epitaxial layer and surrounding the p-well guard ring, the n-well guard ring comprising a positive-channel metal-oxide semiconductor (PMOS) transistor.

13. The image sensor of claim 8 , wherein a first surface of each of the plurality of n-type active regions faces the anti-reflection layer, and a second surface of each of the plurality of n-type active regions opposite the first surface faces a respective n-well region of the plurality of n-well regions.

14. The image sensor of claim 8 , wherein a doping concentration of the plurality of n-type active regions is higher than a doping concentration of the plurality of n-well regions.

15. A method of operating an image sensor, the method comprising:
providing a photodiode comprising:
a p-type epitaxial layer,
an anti-reflection layer, wherein an electrical length of a thickness of the anti-reflection layer approximately corresponds to a quarter wavelength of near ultraviolet,
a shallow trench isolation (STI) region disposed in the p-type epitaxial layer, and
a plurality of n-type active regions disposed in the p-type epitaxial layer and surrounded by the STI region, wherein each of the plurality of n-type active regions extend continuously between edges of the surrounding STI region;

applying bias to set the photodiode under reverse bias;
exposing the photodiode to a photon having a wavelength in a near ultraviolet range;
generating an electron-hole pair in the photodiode;
transferring an electron or a hole of the electron-hole pair to a connector node; and
converting the charge of the electron or the hole collected at the connector node to a read voltage.

16. The method of claim 15 , further comprising applying a reference voltage to a p-well guard ring surrounding the photodiode.

17. The method of claim 16 , further comprising applying a supply voltage to an n-well guard ring surrounding the p-well guard ring.

18. The method of claim 15 , wherein a depth of each n-type active region disposed in the p-type epitaxial layer is in accordance with an operation of the image sensor in a near ultraviolet region.

19. The method of claim 15 , wherein the photodiode further comprises a plurality of p-type well regions disposed in the p-type epitaxial layer and surrounded by the STI region, each p-type well region, corresponding n-type active region, and the p-type epitaxial layer area part of a respective p-n junction photodiode.

20. The method of claim 15 , wherein the photodiode further comprises a plurality of intrinsic p-type semiconductor regions positioned between an n-type active region and a p-type well region, each combination of the n-type active region, the p-type well region, and the intrinsic p-type semiconductor region area part of a p-i-n junction photodiode.

Assignees

• Stmicroelectronics (Research & Development) Ltd

Inventors

• Raynor Jeffrey M

Classifications

• H04N25/76

  Addressed sensors, e.g. MOS or CMOS sensors · CPC title

• H10F77/306

  for devices having potential barriers · CPC title

• H10F77/14

  Shape of semiconductor bodies; Shapes, relative sizes or dispositions of semiconductor regions within semiconductor bodies · CPC title

• H10F39/8033

  Photosensitive area · CPC title

• H10F39/806

  Optical elements or arrangements associated with the image sensors · CPC title