Topographical electrostatic protection grid for sensors

• US 6,326,227 B1
• Filed: 12/30/1998
• Issued: 12/04/2001
• Est. Priority Date: 12/30/1998
• Status: Expired due to Term

• Current Assignee: STMicroelectronics SA (STMicroelectronics NV)
• Original Assignee: STMicroelectronics Incorporated (STMicroelectronics NV)
• Inventors: Fang, Ming, Thomas, Danielle A.
• Primary Examiner(s): Picardat, Kevin M.
• Application Number:
  US09/223,707
• Time in Patent Office: 1,070 Days
• Field of Search: 438/48, 438/50, 438/51, 438/343, 438/346
• US Class Current: 438/48
• CPC Class Codes: G06V 40/1329 Protecting the fingerprint sensor against damage caused by the finger

Abstract

A structure and method for dissipating charges comprising an underlying dielectric layer disposed over capacitor plates of sensor circuitry a gap being formed conformally between adjacent plates and a topographic discharge grid over the underlying dielectric layer and wherein the topographic discharge grid fills at least a portion of the gap between the plates over the dielectric layer and diffuses electrostatic charges at the surface of the integrated circuit.

Claims

1. A method of forming an electrostatic discharge device comprising:

forming a composite insulating layer between and over a plurality of conductive plates, wherein a gap is formed between portions of the insulating layer over adjacent plates and wherein the insulating layer isolates the conductive plates and protects the conductive plates from damage; and

forming an electrostatic discharge region disposed, in the area over the conductive plates, only in the gap between portions of the insulating layer over adjacent plates.

2. The method of claim 1, wherein the electrostatic discharge region isa topographic discharge grid disposed on the insulating layer in gaps between portions of the insulating layer overlying adjacent conductive plates, the grid being connected to ground.

3. A method of forming an electrostatic discharge device comprising:

forming a conformal dielectric layer over a plurality of conductive plates with lower topographical regions between adjacent plates, the dielectric layer isolating and protecting the conductive plates from damage; and

forming a topographic discharge grid over the dielectric layer in at least a portion of the lower topographical regions between portions of the dielectric layer over one or more adjacent pairs of the conductive plates but not over the portions of the dielectric layer over one or more adjacent pairs of the conductive plates, wherein the topographic discharge grid dissipates an electrostatic charge in a manner that prevents the electrostatic charge from reaching the plurality of conductive plates.

4. The method of claim 3, wherein the thickness of the dielectric layer is between approximately 6,000 and 12,000 angstroms.

5. The method of claim 3, wherein the dielectric material comprises oxide.

6. The method of claim 3, wherein the dielectric material comprises a doped glass.

7. The method of claim 3, wherein the dielectric material comprises a first dielectric layer disposed under a second dielectric layer.

8. The method of claim 7, wherein the first and second dielectric layers comprise different compatible materials.

9. The method of claim 7, wherein the first dielectric layer comprises oxide.

10. The method of claim 7, wherein the first dielectric layer comprises doped glass.

11. The method of claim 7, wherein the second dielectric layer comprises nitride.

12. The method of claim 7, wherein the first and second dielectric layers have a thickness between approximately 3,000 and 6,000 angstroms.

13. The method of claim 3, wherein the topographic discharge grid has a sheet resistance low enough to adequately dissipate the electrostatic charge.

14. The method of claim 13, wherein the topographic discharge grid comprises aluminum.

15. The method of claim 13, wherein the topographic discharge grid has a thickness of between approximately 5,000 to 15,000 angstroms.

16. The method of claim 13, wherein the topographic discharge grid has a resistivity of approximately 0.04 ohms per square.

17. The method of claim 13, wherein the topographic discharge grid comprises titanium.

18. The method of claim 17, wherein the topographic discharge grid has a thickness of between approximately 500 to 1,000 angstroms.

19. The method of claim 17, wherein the topographic discharge grid has a resistivity of approximately 10 ohms per square.

20. The method of claim 17, wherein the topographic discharge grid comprises tungsten.

21. The method of claim 17, wherein the topographic discharge grid has a thickness of between approximately 4,000 to 8,000 angstroms.

22. The method of claim 21, wherein the topographic discharge grid has a resistivity of approximately 0.14 ohms per square.

23. The method of claim 3, further comprising:

forming a passivation layer disposed over at least a portion of the dielectric layer over the conductive plates and adjacent the topographic discharge grid, wherein an upper surface of the topographical discharge grid is substantially planar with an upper surface of the passivation layer.

24. The method of claim 23, further comprising:

forming the passivation layer prior to forming the topographic discharge grid.

25. The method of claim 24, wherein the passivation layer has an optimum thickness to prevent damage to the underlying conductive plates due to use and environment while also allowing the topographic discharge grid to be formed in the gap between adjacent plates with sufficient conductivity to dissipate an electrostatic discharge.

26. The method of claim 3, wherein the topographic discharge grid fills the lower topographical regions between portions of the dielectric layer over one or more adjacent pairs of the conductive plates.

27. The method of claim 3, wherein the topographic discharge grid fills the lower topographical regions between portions of the dielectric layer over one or more adjacent pairs of the conductive plates and any space between regions of the passivation layer overlying the dielectric layer.

28. The method of claim 24, wherein the passivation layer comprises silicon carbide.

29. The method of claim 24, wherein the passivation layer comprises silicon nitride.

30. The method of claim 24, wherein the passivation layer has a thickness of between approximately 2,000 and 3,000 angstroms.