Method for forming a low leakage contact in a CMOS imager

• US 6,639,261 B2
• Filed: 12/08/1998
• Issued: 10/28/2003
• Est. Priority Date: 12/08/1998
• Status: Expired due to Term

• Current Assignee: Micron Technology, Inc.
• Original Assignee: Micron Technology, Inc.
• Inventors: Rhodes, Howard E.
• Primary Examiner(s): JACKSON JR, JEROME
• Application Number:
  US09/207,593
• Publication Number:
  US 20020011614A1
• Time in Patent Office: 1,785 Days
• Field of Search: 257/754, 257/755, 257/751, 257/767, 257/448, 257/459, 257/291
• US Class Current: 257/291
• CPC Class Codes: H01L 27/14609 Pixel-elements with integrated switching, control, storage or amplification elements scanning details of imagers (circuitry of solid-state image sensors H04N25/00); circuitry of imagers H04N25/70
• CPC Class Codes: H01L 27/14636 Interconnect structures
• CPC Class Codes: H01L 27/14643 Photodiode arrays; MOS imagers
• CPC Class Codes: H01L 27/14689 MOS based technologies
• CPC Class Codes: H04N 25/00 Circuitry of solid-state image sensors [SSIS]; Control thereof

Abstract

An imaging device formed as a CMOS semiconductor integrated circuit includes a doped polysilicon contact line between the floating diffusion region and the gate of a source follower output transistor. The doped polysilicon contact line in the CMOS imager decreases leakage from the diffusion region into the substrate which may occur with other techniques for interconnecting the diffusion region with the source follower transistor gate. Additionally, the CMOS imager having a doped polysilicon contact between the floating diffusion region and the source follower transistor gate allows the source follower transistor to be placed closer to the floating diffusion region, thereby allowing a greater photo detection region in the same sized imager circuit.

Claims

1. An imaging device comprising:

a substrate;

a photosensitive area within said substrate for accumulating photo-generated charge in said area;

a floating diffusion region in said substrate for receiving charge from said photosensitive area, said floating diffusion region being doped to a first conductivity type at a first concentration;

a readout circuit comprising at least an output transistor formed in said substrate;

an insulating layer formed over said substrate;

a doped polysilicon conductor formed in said insulating layer for connecting said floating diffusion region with a gate of said output transistor, said doped polysilicon conductor being doped to said first conductivity type; and

a contact region between said doped polysilicon conductor and said floating diffusion region, said contact region being in diffusible communication with said polysilicon conductor, and said contact region comprising dopants of said first conductivity type at said first concentration, and diffused dopants of said first conductivity type from said doped polysilicon conductor.

2. The imaging device according to claim 1 wherein the accumulation of charge in said photosensitive area is conducted by a photoconductor.

3. The imaging device according to claim 1, wherein the accumulation of charge in said photosensitive area is controlled by a photogate.

4. The imaging device according to claim 1, wherein said photosensitive area is a photodiode.

5. The imaging device according to claim 1, further comprising a charge transfer region between said photosensitive area and said floating diffusion region, said charge transfer region including a field effect transistor.

6. The imaging device according to claim 1, wherein said doped polysilicon conductor is a composite layered structure of doped polysilicon/refractory metal silicide.

7. The imaging device according to claim 1, wherein said doped polysilicon conductor is a composite layered doped polysilicon/barrier metal silicide/metal structure.

8. The imaging device according to claim 5, wherein the accumulation of charge in said photosensitive area is conducted by a photoconductor.

9. The imaging device according to claim 5, wherein the accumulation of charge in said photosensitive area is conducted by a photogate.

10. The imaging device according to claim 5, wherein said photosensitive area is a photodiode.

11. An imaging device comprising

a semiconductor integrated circuit substrate;

a photosensitive device formed on said substrate for accumulating photo-generated charge in an underlying region of said substrate;

a floating diffusion region in said substrate for receiving said photo-generated charge, said floating diffusion region being doped to a first conductivity type at a first dopant concentration, wherein said floating diffusion region comprises a second region of said first conductivity type at a second dopant concentration, said second dopant concentration being greater than said first dopant concentration;

a readout circuit comprising at least an output transistor formed in said substrate;

an insulating layer formed over said substrate; and

said floating diffusion region being connected to the output transistor by a doped polysilicon conductor formed at least partially within the insulating layer, the doped polysilicon conductor being doped to said first conductivity type, said doped polysilicon conductor being a composite layered doped polysilicon/barrier metal suicide/metal structure.

12. The imaging device according to claim 11, wherein said photosensitive device is a photogate.

13. The imaging device according to claim 11, wherein said photosensitive device is a photodiode.

14. The imaging device according to claim 11, wherein said photosensitive device is a photoconductor.

15. The imaging device according to claim 11 further comprising a contact region between said doped polysilicon conductor and said floating diffusion region, said contact region being doped to said first conductivity type and comprising dopants from said doped polysilicon conductor and dopants from said floating diffusion region.

16. The imaging device according to claim 11, wherein said substrate includes an n-type implant of arsenic or phosphorous into said substrate at a sheet concentration of about 1.0×

10¹² to about 3.0×

10¹³ ions/cm².

17. The imaging device according to claim 11, further comprising at least one charge transfer device for transferring charge from said photosensitive area to said floating diffusion region in accordance with a control signal applied to a control terminal.

18. The imaging device according to claim 11, wherein said doped polysilicon conductor is a composite layered structure of doped polysilicon/refractory metal suicide.

19. The imaging device according to claim 11, wherein said output transistor is formed adjacent to said floating diffusion region on said substrate.

20. The imaging device according to claim 11, further comprising a reset transistor for resetting said floating diffusion region to a predetermined voltage.

21. The imaging device according to claim 11, wherein said floating diffusion region is an n-doped region in a p-well.

22. The imaging device according to claim 12, wherein said photogate is formed of doped polysilicon.

23. The imaging device according to claim 13, further comprising a lightly doped n region beneath said photodiode.

24. An imaging device comprising:

a substrate;

a photosensitive area within said substrate for accumulating photo-generated charge in said area;

a floating diffusion region in said substrate for receiving charge from said photosensitive area, said floating diffusion region having a first conductivity type at a first concentration, wherein said floating diffusion region comprises a second region of said first conductivity type at a second concentration, said second concentration being greater than said first concentration;

a readout circuit comprising at least an output transistor formed in said substrate;

an insulating layer formed over said substrate;

a doped polysilicon conductor formed in said insulating layer for connecting said floating diffusion region with a gate of said output transistor, said doped polysilicon conductor having a first conductivity type at a third concentration, wherein said third concentration is greater than said first and second concentrations.