Back-side deep trench isolation structure for image sensor

Patent metadata

Field	Value
Publication number	US-11869761-B2
Application number	US-202017017854-A
Country	US
Kind code	B2
Filing date	Sep 11, 2020
Priority date	Apr 24, 2020
Publication date	Jan 9, 2024
Grant date	Jan 9, 2024

Abstract

The present disclosure relates to an image sensor having a photodiode surrounded by a back-side deep trench isolation (BDTI) structure, and an associated method of formation. In some embodiments, a plurality of pixel regions is disposed within an image sensing die and respectively comprises a photodiode configured to convert radiation into an electrical signal. The photodiode comprises a photodiode doping column with a first doping type surrounded by a photodiode doping layer with a second doping type that is different than the first doping type. A BDTI structure is disposed between adjacent pixel regions and extending from the back-side of the image sensing die to a position within the photodiode doping layer. The BDTI structure comprises a doped liner with the second doping type and a dielectric fill layer. The doped liner lines a sidewall surface of the dielectric fill layer.

First claim

What is claimed is:

1. A method of forming an image sensor, comprising:
forming a plurality of photodiodes for a plurality of pixel regions from a front-side of an image sensing die, wherein a photodiode is formed to have a photodiode doping column with a first doping type surrounded by a photodiode doping layer with a second doping type that is different than the first doping type;
forming a deep trench between adjacent pixel regions in the photodiode doping layer from a back-side of the image sensing die, wherein an upper portion of the photodiode doping layer exposed to the deep trench is converted to a defective layer during the forming of the deep trench;
performing a cyclic cleaning process of at least two different etchants alternatively to remove the defective layer;
forming a doped liner precursor with the second doping type lining a sidewall surface of the deep trench, the doped liner precursor having a thickness smaller than 10 nm and a doping concentration greater than 1×10 19 cm− 3 ;
forming a doped liner by performing an annealing process to facilitate dopant diffusion from the doped liner precursor to an adjoining portion of the photodiode doping layer; and
forming a dielectric fill layer filling an inner space of the deep trench to form a back-side deep trench isolation (BDTI) structure;
wherein the doped liner is formed with a surface dopant concentration greater than 1×10 20 cm− 3 and a depth of 20 nm at which the dopant concentration is reduced to around 10 15 cm− 3 .

2. The method of claim 1 , wherein performing the cyclic cleaning process comprises using solutions of hydrofluoric acid (HF) and ammonia and hydrogen peroxide mixtures (APM) alternatively for multiple cycles.

3. The method of claim 1 , wherein the cyclic cleaning process removes at least about 1˜20 nm of the upper portion of the photodiode doping layer.

4. The method of claim 1 , wherein the doped liner precursor is formed by an epitaxial deposition process under a temperature lower than 500° C.

5. The method of claim 1 , wherein the annealing process comprises multiple rounds of a dynamic surface anneal process.

6. The method of claim 1 , wherein the cyclic cleaning process reduces a bowing angle of a bowing tip at a top corner of the deep trench to be smaller than 15° from an upper sidewall to a vertical line perpendicular to a lateral plane of the photodiode doping layer.

7. The method of claim 4 , wherein the annealing process is a laser annealing process.

8. The method of claim 1 , wherein a bowing width and a bowing angle of the deep trench are reduced by the cyclic cleaning process.

9. The method of claim 1 , wherein the BDTI structure is formed through the photodiode doping layer.

10. The method of claim 1 , wherein the doped liner is formed to reach on a surface of a doped isolation well.

11. A method of forming an image sensor, comprising:
forming photodiodes for a plurality of pixel regions from a front-side of an image sensing die, wherein a photodiode is formed to have a photodiode doping column with a first doping type surrounded by a photodiode doping layer with a second doping type that is different than the first doping type;
forming a doped isolation well from the front-side of the image sensing die by implanting dopants into the photodiode doping layer through at least one implanting process;
forming a gate structure and a metallization stack on the front-side of the image sensing die, wherein the metallization stack comprises a plurality of metal interconnect layers arranged within one or more inter-level dielectric layers;
bonding the image sensing die to a logic die from the front-side of the image sensing die, wherein the logic die comprises logic devices;
forming a deep trench between adjacent pixel regions in a back-side of the image sensing die;
performing a cyclic cleaning process to remove an upper portion of the photodiode doping layer exposed to the deep trench;
forming a doped liner with the second doping type lining a sidewall surface of the deep trench; and
forming a dielectric fill layer filling an inner space of the deep trench to form a back-side deep trench isolation (BDTI) structure;
wherein the cyclic cleaning process reduces a bowing angle of a bowing tip at a top corner of the deep trench to be smaller than 15° from an upper sidewall to a vertical line perpendicular to a lateral plane of the photodiode doping layer.

12. The method of claim 11 , wherein performing the cyclic cleaning process comprises using solutions of hydrofluoric acid (HF) and ammonia and hydrogen peroxide mixtures (APM) alternatively for multiple cycles.

13. The method of claim 11 , further comprising:
forming a shallow trench isolation (STI) structure between the adjacent pixel regions from the front-side of the image sensing die to a position within the photodiode doping layer;
wherein the deep trench is formed to expose the STI structure.

14. The method of claim 11 , wherein the deep trench is formed to expose the doped isolation well.

15. A method of forming an image sensor, comprising:
preparing an image sensing die having a front-side and a back-side opposite to the front-side;
forming a plurality of pixel regions within the image sensing die and respectively comprising a photodiode including a photodiode doping column with a first doping type surrounded by a photodiode doping layer with a second doping type that is different than the first doping type; and
forming a deep trench between adjacent pixel regions in the photodiode doping layer from the back-side of the image sensing die, wherein an upper portion of the photodiode doping layer exposed to the deep trench is converted to a defective layer during the forming of the deep trench;
performing a cyclic cleaning process of at least two different etchants alternatively to remove the defective layer;
forming a doped liner precursor with the second doping type lining a sidewall surface of the deep trench, the doped liner precursor having a thickness smaller than 10 nm and a doping concentration greater than 1×10 19 cm− 3 ;
forming a doped liner by performing an annealing process to facilitate dopant diffusion from the doped liner precursor to an adjoining portion of the photodiode doping layer; and
forming a dielectric fill layer filling an inner space of the deep trench to form a back-side deep trench isolation (BDTI) structure;
wherein a bowing width and a bowing angle of the deep trench are reduced by the cyclic cleaning process.

16. The method of claim 15 ,
wherein the doped liner and the dielectric fill layer of the BDTI structure extend laterally along the back-side of the image sensing die; and
wherein a lateral portion of the doped liner is formed overlying the photodiode doping column.

17. The method of claim 15 , further comprising:
forming a doped isolation well with the second doping type between the adjacent pixel regions and extending from the front-side of the image sensing die to a position within the photodiode doping layer;
wherein the doped isolation well directly contacts the BDTI structure.

18. The method of claim 15 , further comprising:
forming a shallow trench isolation (STI) structure between the adjacent pixel regions from the front-side of the image sensing die to a position within the photodiode doping layer.

19. The method of claim 18 , wherein the BDTI structure extends through the STI structure.

20. The method of claim 15 , wherein the bowing width is of about 10 nm, and the bowing angle is in a r

Assignees

• Taiwan Semiconductor Mfg Co Ltd
• Taiwan Semiconductor Mfg Co Ltd

Inventors

• Cheng Yu-Hung
• Kuo Chun-Tsung
• Lu Jiech-Fun
• Tsai Min-Ying
• Hsu Chiao-Chun
• Li Ching I

Classifications

• H10P70/20

  Cleaning during device manufacture · CPC title

• H10P50/642

  Chemical etching · CPC title

• H10W10/17

  formed using trench refilling with dielectric materials, e.g. shallow trench isolations · CPC title

• H10W10/014

  using trench refilling with dielectric materials, e.g. shallow trench isolations · CPC title

• H10F39/811 Primary

  Interconnections · CPC title