IMAGE SENSOR AND METHOD OF MAKING

• US 20200135785A1
• Filed: 10/07/2019
• Published: 04/30/2020
• Est. Priority Date: 10/31/2018
• Status: Active Grant

• Current Assignee: Taiwan Semiconductor Manufacturing Company Limited
• Original Assignee: Taiwan Semiconductor Manufacturing Company Limited
• Inventors: CHEN, Po-Han, CHEN, Chen-Chun, CHANG, Fu-Cheng, LEE, Kuo-Cheng
• Granted Patent: US 11,676,980 B2
• Time in Patent Office: Days
• CPC Class Codes: H01L 27/14605 Structural or functional details relating to the position of the pixel elements, e.g. smaller pixel elements in the center of the imager compared to pixel elements at the periphery
• CPC Class Codes: H01L 27/1462 Coatings
• CPC Class Codes: H01L 27/14623 Optical shielding
• CPC Class Codes: H01L 27/1463 Pixel isolation structures
• CPC Class Codes: H01L 27/1464 Back illuminated imager structures
• CPC Class Codes: H01L 27/14685 Process for coatings or optical elements

Abstract

An image sensor includes a substrate and a first photodiode (PD) having a first size in the substrate. The image sensor further includes a second PD having a second size in the substrate, wherein the first size is different from the second size. The image sensor further includes a first buffer layer over the substrate. The image sensor further includes a shield layer over the first buffer, wherein the first buffer layer and the shield layer define a first recess aligned with the first PD and a second recess aligned with the second PD. The image sensor further includes a flicker reduction layer in the first recess, wherein the second recess is free of the flicker reduction layer.

Claims

1. An image sensor comprising:

a substrate;

a first photodiode (PD) having a first size in the substrate;

a second PD having a second size in the substrate, wherein the first size is different from the second size;

a first buffer layer over the substrate;

a shield layer over the first buffer, wherein the first buffer layer and the shield layer define a first recess aligned with the first PD and a second recess aligned with the second PD; and

a flicker reduction layer in the first recess, wherein the second recess is free of the flicker reduction layer.

2. The image sensor of claim 1, wherein the first size is less than the second size.

3. The image sensor of claim 1, wherein the flicker reduction layer extends along a top surface of the shield layer.

4. The image sensor of claim 1, further comprising a second buffer layer over the flicker reduction layer.

5. The image sensor of claim 4, wherein the second buffer layer fills the second recess.

6. The image sensor of claim 1, further comprising an anti-reflection coating between the first buffer layer and the substrate.

7. The image sensor of claim 1, wherein the flicker reduction layer comprises a dielectric material.

8. The image sensor of claim 7, wherein a thickness of the flicker reduction layer ranges from about 600 Å

to about 2,000 Å

.

9. The image sensor of claim 1, wherein the flicker reduction layer comprises a metallic material.

10. The image sensor of claim 9, wherein a thickness of the flicker reduction layer ranges from about 200 Å

to about 800 Å

.

11. An image sensor comprising:

a substrate;

a plurality of large photodiodes (LPDs) in the substrate;

a plurality of small photodiodes (SPDs) in the substrate;

a buffer layer over the substrate;

a shield layer over the buffer layer, wherein the shield layer and the buffer layer define a plurality of recesses, the plurality of recesses including a first set of recesses and a second set of recesses, each recess of the first set of recesses is aligned with a corresponding LPD of the plurality of LPDs, and each recess of the second set of recesses is aligned with a corresponding SPD of the plurality of SPDs; and

a flicker reduction layer in each recess of the second set of recesses, wherein each recess of the first set of recesses is free of the flicker reduction layer.

12. The image sensor of claim 11, wherein the flicker reduction layer comprises a dielectric material.

13. The image sensor of claim 11, wherein the flicker reduction layer comprises a metallic material.

14. The image sensor of claim 11, wherein the flicker reduction layer extends along a top surface of the shield layer.

15. The image sensor of claim 11, wherein LPDs of the plurality of LPDs and SPDs of the plurality of SPDs are in an alternating array in the substrate.

16. A method of making an image sensor, the method comprising:

depositing a buffer layer over a substrate, wherein the substrate comprises a first photodiode (PD) and a second PD;

depositing a shield layer over the buffer layer;

etching the buffer layer and the shield layer to define a first recess aligned with the first PD and a second recess aligned with the second PD;

depositing a flicker reduction layer in the first recess and in the second recess; and

etching the flicker reduction layer to remove the flicker reduction layer from the first recess.

17. The method of claim 16, wherein etching the flicker reduction layer comprises maintaining a portion of the flicker reduction layer on a top surface of the shield layer.

18. The method of claim 16, wherein etching the buffer layer comprises maintaining a portion of the buffer layer in the first recess.

19. The method of claim 16, wherein depositing the flicker reduction layer comprises depositing a dielectric material.

20. The method of claim 16, wherein depositing the flicker reduction layer comprises depositing a metallic material.