Method for sealing and backside releasing of microelectromechanical systems

• US 20070281381A1
• Filed: 05/30/2007
• Published: 12/06/2007
• Est. Priority Date: 05/31/2006
• Status: Active Grant

• Current Assignee: Georgia Tech Research Corporation (University System of Georgia)
• Original Assignee: Georgia Tech Research Corporation (University System of Georgia)
• Inventors: Ayazi, Farrokh
• Granted Patent: US 7,767,484 B2
• Time in Patent Office: Days
• US Class Current: 438/52
• CPC Class Codes: B81B 2207/015 the micromechanical device and the control or processing electronics being integrated on the same substrate
• CPC Class Codes: B81C 1/00285 using materials for controlling the level of pressure, contaminants or moisture inside of the package, e.g. getters
• CPC Class Codes: B81C 1/00476 removing a sacrificial layer B81C1/00912 takes precedence

Abstract

Disclosed are methods for fabricating encapsulated microelectromechanical systems (MEMS) devices. A MEMS device fabricated on a CMOS wafer is encapsulated using an etch resistant thin film layer prior to the release of the MEMS device. Once CMOS processing is completed, the wafer is etched to release the MEMS device. If the MEMS is fabricated on a silicon-on-insulator (SOI) wafer, the buried oxide of the SOI wafer acts as an etch stop for the etching. A sacrificial layer(s) is accessed and removed from the back side of the wafer, while the front side of the wafer is protected by a masking layer. The MEMS device is released without having any detrimental effects on CMOS components. If desired, the wafer can be mounted on another substrate to provide hermetic or semi-hermetic sealing of the device.

Claims

1. A method for encapsulating and integrating nano- and micro-electromechanical systems (MEMS) comprising:

fabricating a MEMS device in a substrate;

covering the MEMS device with an etch resistant mask layer;

etching the substrate beneath the MEMS device from the backside of the substrate; and

releasing the MEMS device from the substrate.

2. The method recited in claim 1 further comprising:

fabricating a transistor-based circuit in the substrate adjacent to the MEMS device.

3. The method recited in claim 1 further comprising:

fabricating a CMOS circuit in the substrate adjacent to the MEMS device.

4. The method recited in claim 1 further comprising:

attaching the substrate to another substrate to form an enclosed sealed cavity in which the MEMS device is disposed.

5. The method recited in claim 1 wherein releasing the MEMS device from the substrate comprises removing a silicon dioxide sacrificial layer in a hydrofluoric acid.

6. The method recited in claim 1 wherein the microelectromechanical systems (MEMS) device comprises a resonator.

7. The method recited in claim 4 further comprising:

disposing a getter film in the enclosed cavity.

9. The method recited in claim 6 further comprising:

fabricating a transistor-based circuit in the device layer.

19. The method recited in Claim 1 further comprising:

disposing a getter film in the enclosed cavity.

8. A method for encapsulating and integrating nano- and micro-electromechanical systems (MEMS) comprising:

providing a semiconductor-on-insulator substrate comprising a handle layer, a device layer, and an insulating layer disposed between the handle and device layers;

fabricating a microelectromechanical systems (MEMS) device in the device layer;

covering the MEMS devices with an etch resistant mask layer;

etching the handle layer beneath the MEMS device using the insulating layer as an etch stop; and

releasing the MEMS device from the device layer.

10. The method recited in claim 8 further comprising:

fabricating a CMOS circuit in the device layer.

11. The method recited in claim 8 further comprising:

attaching the handle layer to another substrate, which forms an enclosed sealed cavity in which the MEMS device is disposed.

12. The method recited in claim 8 wherein the device layer of the substrate is a semiconductor selected from a group including single crystalline silicon, poly-crystalline silicon, silicon carbide, diamond, gallium nitride and gallium arsenide.

13. The method recited in claim 8 wherein releasing the MEMS device from the substrate comprises removing a silicon dioxide sacrificial layer in a hydrofluoric acid.

14. The method recited in claim 8 wherein the microelectromechanical systems (MEMS) device comprises a resonator.

15. The method recited in claim 8 wherein the etch resistant layer comprises a low-pressure chemical vapor deposited (LPCVD) hydrofluoric acid resistant layer.

16. The method recited in claim 8 wherein the etch resistant layer comprises a silicon nitride layer.

17. The method recited in claim 8 wherein the etch resistant layer comprises a polysilicon layer.

18. The method recited in claim 8 wherein the semiconductor-on-insulator substrate comprises a silicon-on-silicon dioxide substrate.

20. A method for encapsulating and integrating nano and microelectromechanical systems (MEMS) comprising:

providing a semiconductor-on-insulator substrate comprising a handle layer, a device layer, and an insulating layer disposed between the handle and device layers;

fabricating a transistor-based circuit in the device layer;

fabricating a microelectromechanical systems (MEMS) device in the handle layer; and

releasing the MEMS device from the handle layer.

21. The method recited in claim 20 further comprising:

fabricating a CMOS circuit in the device layer.

22. The method recited in claim 20 wherein the device layer of the substrate is a semiconductor selected from a group including single crystalline silicon, poly-crystalline silicon, silicon carbide, diamond, gallium nitride and gallium arsenide.

23. The method recited in claim 20 wherein releasing the MEMS device from the substrate comprises removing a silicon dioxide sacrificial layer in a hydrofluoric acid.

24. The method recited in claim 21 wherein the microelectromechanical systems (MEMS) device comprises a resonator.

25. The method recited in claim 22 further comprising:

attaching the handle layer to another substrate, which forms an enclosed sealed cavity in which the MEMS device is disposed.

26. The method recited in claim 25 further comprising:

disposing a getter film in the enclosed cavity.