Detection and mitigation of particle contaminants in MEMS devices

• US 8,598,891 B2
• Filed: 02/25/2013
• Issued: 12/03/2013
• Est. Priority Date: 10/20/2009
• Status: Active Grant

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Kumar, Vineet, Clark, William A., Geen, John A., Wolfe, Edward, Sherman, Steven
• Primary Examiner(s): Koval, Melissa
• Assistant Examiner(s): Baldridge, Benjamin M
• Application Number:
  US13/775,335
• Publication Number:
  US 20130168675A1
• Time in Patent Office: 281 Days
• Field of Search: 324/649
• US Class Current: 324/649
• CPC Class Codes: B81B 7/0029 Protection against environmental influences not provided for in groups B81B7/0012 - B81B7/0025
• CPC Class Codes: B81C 1/00333 Aspects relating to packaging of MEMS devices, not covered by groups B81C1/00269 - B81C1/00325
• CPC Class Codes: B81C 99/0045 End test of the packaged device
• CPC Class Codes: G01C 19/5776 Signal processing not specific to any of the devices covered by groups G01C19/5607 - G01C19/5719
• CPC Class Codes: H01L 22/14 for electrical parameters, e.g. resistance, deep-levels, CV, diffusions by electrical means

Abstract

Detecting and/or mitigating the presence of particle contaminants in a MEMS device involves converting benign areas in which particles might become trapped undetectably by electric fields during test to field-free regions by extending otherwise non-functional conductive shield and gate layers and placing the same electrical potential on the conductive shield and gate layers. Particle contaminants can then be moved into detection locations remote from the potential trap areas and having particle detection structures by providing some mechanical disturbance.

Claims

1. A MEMS device comprising:

a substrate supporting a set of MEMS device structures;

a conductive shield layer partially covering a surface of the substrate and leaving an uncovered potential trap region;

a conductive gate layer embedded within the substrate, the conductive gate layer having a first extended portion underlying the potential trap region; and

a controller coupled to the conductive shield layer and the conductive gate layer, the controller including circuitry to place the same electrical potential on both the conductive shield layer and the conductive gate layer such that the potential trap region becomes a substantially field-free region when the same electrical potential is placed on both the conductive shield layer and the conductive gate layer.

2. A MEMS device according to claim 1, further comprising a device cap bonded to the substrate and covering the device structures, wherein the conductive gate layer includes a second extended portion that extends beyond an outer perimeter of the device cap, and wherein the controller connects to the second extended portion to place the electrical potential on the conductive gate layer.

3. A MEMS device according to claim 1, wherein the controller circuitry connects the conductive gate layer to the potential of the conductive shield layer.

4. A MEMS device according to claim 1, wherein the conductive shield layer comprises polysilicon.

5. A MEMS device according to claim 1, wherein conductive gate layer is embedded in an oxide layer of the substrate.

6. A MEMS device according to claim 5, wherein the oxide layer supports the conductive shield layer.

7. A MEMS device according to claim 1, further comprising:

at least one particle detection structure remote from the potential trap region for detecting a particle contaminant moved from the potential trap region by a mechanical disturbance of the MEMS device.

8. A method of producing a MEMS device, the MEMS device including a substrate supporting a set of MEMS device structures, the method comprising:

forming a conductive gate layer embedded within the substrate, the conductive gate layer having a first extended portion underlying a potential trap region; and

forming a conductive shield layer partially covering a surface of the substrate and leaving the potential trap region uncovered, wherein the conductive shield layer and the conductive gate layer are configured such that the potential trap region becomes a substantially field-free region when the same electrical potential is placed on both the conductive shield layer and the conductive gate layer.

9. A method according to claim 8, further comprising:

bonding a device cap to the substrate and covering the device structures, wherein the conductive gate layer includes a second extended portion that extends beyond an outer perimeter of the device cap for placement of the electrical potential on the conductive gate layer.

10. A method according to claim 8, further comprising:

connecting the conductive gate layer to the potential of the conductive shield layer.

11. A method according to claim 8, wherein the conductive shield layer comprises polysilicon.

12. A method according to claim 8, wherein conductive gate layer is embedded in an oxide layer of the substrate.

13. A method according to claim 12, wherein the oxide layer supports the conductive shield layer.

14. A method according to claim 8, further comprising:

forming at least one particle detection structure remote from the potential trap region for detecting a particle contaminant moved from the potential trap region by a mechanical disturbance of the MEMS device.

15. A method of detecting particle contaminants in a MEMS device having a substrate supporting a set of MEMS device structures, a conductive shield layer partially covering a surface of the substrate and leaving an uncovered potential trap region, and a conductive gate layer embedded within the substrate and having a first extended portion underlying the potential trap region, the method comprising:

placing the same electrical potential on both the conductive shield layer and the conductive gate layer such that the potential trap region becomes a substantially field-free region; and

providing a mechanical disturbance to the MEMS device to move any particles from the potential trap region to at least one particle detection structure.

16. A method according to claim 15, wherein the MEMS device further comprises a device cap bonded to the substrate and covering the device structures such that the conductive gate layer includes a second extended portion that extends beyond an outer perimeter of the device cap, and wherein the method further comprises:

placing the electrical potential on the second extended portion of the conductive gate layer.

17. A method according to claim 15, wherein placing the same electrical potential on both the conductive shield layer and the conductive gate layer comprises:

connecting the conductive gate layer to the potential of the conductive shield layer.

18. A method according to claim 15, wherein the conductive shield layer comprises polysilicon.

19. A method according to claim 15, wherein conductive gate layer is embedded in an oxide layer of the substrate.

20. A method according to claim 19, wherein the oxide layer supports the conductive shield layer.