Apparatus and method for forming optical black pixels with uniformly low dark current

• US 20080217712A1
• Filed: 03/07/2007
• Published: 09/11/2008
• Est. Priority Date: 03/07/2007
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: AltaSens, Inc. (JVC Kenwood Corporation)
• Inventors: Rossi, Giuseppe, Richardson, John, Lin, Henry, Patel, Gaurang, Kozlowski, Lester, Chow, Gregory
• Granted Patent: US 7,999,340 B2
• Time in Patent Office: Days
• US Class Current: 257/431
• CPC Class Codes: H01L 27/14603 Special geometry or disposition of pixel-elements, address-lines or gate-electrodes
• CPC Class Codes: H01L 27/14623 Optical shielding

Abstract

An apparatus and method for forming optical black pixels having uniformly low dark current. Optical Black opacity is increased without having to increase Ti/TiN layer thickness. A hybrid approach is utilized combining a Ti/TiN OB layer in conjunction with in-pixel metal stubs that further occlude the focal radius of each pixel'"'"'s incoming light beam. Additional metal layers can be used to increase the opacity into the infrared region.

Claims

1. An optical black pixel comprising:

a photodiode;

a metal layer overlaying the photodiode; and

a Ti/TiN layer overlaying the metal layer.

2. The optical black pixel of claim 1, wherein the metal layer comprises a metal stub formed in a top inter-level metal layer.

3. The optical black pixel of claim 2, wherein the metal stub is smaller than a full pixel area.

4. The optical black pixel of claim 3, wherein the pixel further comprises a microlens covering the pixel.

5. The optical black pixel of claim 3, wherein the Ti/TiN layer is approximately 1000 Å

thick.

6. The optical black pixel of claim 3, further comprising at least one additional metal stub at a different metal layer to increase opacity in the infrared region.

7. A method of increasing the opacity in an optical black pixel, the method comprising:

forming a metal stub in an inter-level metal, the metal stub covering an area of a photodiode in the pixel; and

forming a Ti/TiN layer above the metal stub.

8. An image sensor comprising an array of clear pixels, and a plurality of optical black pixels, the optical black pixels comprising:

a metal stub in an inter-level metal, the metal stub covering an area of a photodiode in the pixel; and

a Ti/TiN layer formed above the metal stub.

9. The image sensor of claim 8, wherein the Ti/TiN layer is approximately 1000 Å

thick.