Optical isolation of optically black pixels in image sensors

• US 9,232,162 B2
• Filed: 08/16/2012
• Issued: 01/05/2016
• Est. Priority Date: 11/08/2011
• Status: Active Grant

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Inventors: Lenchenkov, Victor, McGrath, Robert Daniel
• Primary Examiner(s): Dagnew, Mekonnen
• Application Number:
  US13/587,210
• Publication Number:
  US 20130113968A1
• Time in Patent Office: 1,237 Days
• Field of Search: 348/243, 348/302, 257/447
• US Class Current: 1/1
• 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: H04N 25/63 applied to dark current

Abstract

Optical isolation is provided for optically black pixels in image sensors. Image sensors, such as backside illumination (BSI) image sensors, may have an active pixel array and an array having optically black pixels. Isolation structures such as a metal wall may be formed in a dielectric stack between an active pixel array and optically black pixels. Patterned shallow trench isolation regions or polysilicon regions may be formed in a substrate between an active pixel array and optically black pixels. An absorption region such as a germanium-doped absorption region may be formed in a substrate between an active pixel array and optically black pixels. Optical isolation and absorption regions may be formed in a ring surrounding an active pixel array.

Claims

1. A backside illumination image sensor, comprising:

an active pixel region having a first plurality of pixels;

an optically black pixel region having a second plurality of pixels covered by an opaque layer;

a metal barrier between the active pixel region and the optically black pixel region, wherein the metal barrier extends vertically through a plurality of dielectric layers and metal interconnect layers.

2. The backside illumination image sensor of claim 1, further comprising at least one isolation structure in a silicon substrate between the active pixel region and the optically black pixel region.

3. The backside illumination image sensor of claim 2, wherein the at least one isolation structure comprises a plurality of isolation structures formed from shallow trench isolation.

4. The backside illumination image sensor of claim 2, wherein the at least one isolation structure comprises a plurality of isolation structures formed from polysilicon.

5. The backside illumination image sensor of claim 2, wherein the at least one isolation structure comprises a plurality of isolation structures at a front side of the silicon substrate adjacent to the plurality of dielectric layers and metal interconnect layers.

6. The backside illumination image sensor of claim 5, wherein the at least one isolation structure further comprises a plurality of isolation structures at a back side of the silicon substrate.

7. The backside illumination image sensor of claim 2, wherein the at least one isolation structure comprises a plurality of isolation structures each having a width of in a range of 50-200 nm and wherein the plurality of isolation regions are separated by a spacing in a range of 50-200 nm.

8. The backside illumination image sensor of claim 2, wherein the least one isolation structure comprises germanium-doped silicon.

9. A backside illumination image sensor, comprising:

an active pixel array;

an optically black pixel array;

a buffer region between the active pixel array and the optically black pixel array, wherein the buffer region comprises at least one optical isolation structure in a substrate and a metal wall that extends vertically through a plurality of dielectric layers and metal interconnect layers.

10. The backside illumination image sensor of claim 9, wherein the metal wall extends between the at least one optical isolation structure and the active pixel array.

11. The backside illumination image sensor of claim 10, wherein the metal barrier is formed across at least four metal interconnect layers.

12. The backside illumination image sensor of claim 11, wherein the at least one optical isolation structure comprises germanium-doped silicon.

13. The backside illumination image sensor of claim 11, wherein the at least one optical isolation structure comprises a plurality of shallow trench isolation structures.

14. The backside illumination image sensor of claim 11, wherein a shielding structure covers the optically black pixel array and the at least one optical isolation structure.

15. The backside illumination image sensor of claim 11, wherein the optical black pixel array surrounds the active pixel array and wherein the metal wall forms a guard ring around the active pixel array.

16. A system, comprising:

a central processing unit;

memory;

input-output circuitry; and

an imaging device, wherein the imaging device comprises;

an active pixel array in a substrate;

optically black pixels in the substrate;

a buffer region between the active pixel array and the optically black pixels, wherein the buffer region comprises a metal barrier, and the metal barrier extends vertically through a plurality of dielectric layers and metal interconnect layers.

17. The system defined in claim 16, wherein the buffer region further comprises a plurality of isolation regions in the substrate between the metal wall and the optically black pixels.

18. The system defined in claim 16, wherein the buffer region further comprises at least one optical isolation region formed of germanium-doped silicon.

19. The system defined in claim 18, wherein the germanium-doped silicon comprises four percent or more germanium.

20. The system defined in claim 16, wherein the imaging device comprises a backside illumination image sensor.