Low temperature method for forming a microcavity on a substrate and article having same

• US 20040028849A1
• Filed: 04/16/2003
• Published: 02/12/2004
• Est. Priority Date: 04/18/2002
• Status: Active Grant

• Current Assignee: Board of Regents of the University of Michigan (University of Michigan)
• Original Assignee: Board of Regents of the University of Michigan (University of Michigan)
• Inventors: Stark, Brian H., Najafi, Khalil
• Granted Patent: US 7,029,829 B2
• Time in Patent Office: Days
• US Class Current: 428/34.1
• 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 2203/0136 Growing or depositing of a covering layer
• CPC Class Codes: B81C 2203/0145 Hermetically sealing an opening in the lid
• CPC Class Codes: Y10T 428/13 Hollow or container type article [e.g., tube, vase, etc.]

Abstract

A low temperature method for forming a microcavity on a substrate and article having same are provided which utilize electroplated films. The method is particularly useful to package microelectromechanical systems (MEMS) in vacuum on the wafer level and provide sealed feedthroughs to the outside world. The method may be performed in a batch process to substantially reduce cost and to form metal diaphragms. Furthermore, the method is performed at near room temperature, which provides more flexibility in the manufacturing process. The method enables substantial cost savings in the production of vacuum-sealed MEMS. Many feedthroughs can be incorporated into the package to transfer signals in and out of the package. One significant advantage of this method is that it does not require bonding of a second substrate, which reduces the system cost.

Claims

1. A low temperature method for forming a microcavity on a substrate, the method comprising:

forming a sacrificial spacer on a region of the substrate;

depositing a metal film to a desired thickness over the sacrificial spacer to encapsulate the sacrificial spacer;

forming at least one fluid passageway communicating the sacrificial spacer with the ambient; and

removing the sacrificial spacer through the at least one fluid passageway so that the metal film forms a metal diaphragm which defines a microcavity.

2. The method as claimed in claim 1 further comprising sealing the at least one fluid passageway to form a sealed microcavity.

3. The method as claimed in claim 1, wherein the sacrificial spacer is a photoresist and wherein the step of removing utilizes a photoresist etch.

4. The method as claimed in claim 1, wherein the metal is nickel.

5. The method as claimed in claim 1, wherein the step of depositing includes the step of electroplating the metal over the sacrificial spacer.

6. The method as claimed in claim 1, wherein the at least one fluid passageway includes at least one etch channel.

7. The method as claimed in claim 2, wherein the step of sealing is performed in vacuum so that the sealed microcavity is a sealed vacuum microcavity and wherein the desired thickness of the metal diaphragm is sufficient to sustain one atmosphere of differential pressure thereacross.

8. The method as claimed in claim 1, wherein the substrate is a wafer.

9. The method as claimed in claim 2, further comprising forming at least one fluid feedthrough in communication with the sealed microcavity.

10. The method as claimed in claim 1, wherein the desired thickness is greater than approximately 20 microns.

11. The method as claimed in claim 2, wherein the step of sealing includes the step of sputtering a layer of material to seal the microcavity.

12. The method as claimed in claim 2, wherein the step of sealing includes the step of collapsing the at least one fluid passageway.

13. The method as claimed in claim 2, wherein the step of sealing includes the step of plugging the at least one fluid passageway with solder.

14. The method as claimed in claim 1 wherein temperature does not exceed 250°

C. during the entire method.

15. An article of manufacture comprising:

a substrate;

a metal diaphragm which defines a sealed vacuum microcavity and which has a desired thickness; and

at least one microstructure formed on the substrate and located within the sealed vacuum microcavity.

16. The article as claimed in claim 15, wherein the substrate is a wafer.

17. The article as claimed in claim 15, wherein the at least one microstructure includes at least one MEMS device.

18. The article as claimed in claim 15 wherein the metal is nickel.

19. The article as claimed in claim 15 wherein the desired thickness of the metal diaphragm is sufficient to sustain one atmosphere of differential pressure thereacross.

20. The article as claim in claim 15 further comprising at least one feedthrough in communication with the at least one microstructure.

21. The article as claimed in claim 15 wherein the desired thickness is greater than approximately 20 microns.

22. The article as claimed in claim 15 wherein the metal diaphragm is electroplated.