METHODS FOR CMOS-MEMS INTEGRATED DEVICES WITH MULTIPLE SEALED CAVITIES MAINTAINED AT VARIOUS PRESSURES

• US 20120326248A1
• Filed: 06/27/2012
• Published: 12/27/2012
• Est. Priority Date: 06/27/2011
• Status: Active Grant

• Current Assignee: Invensense Incorporated (TDK Corporation)
• Original Assignee: Invensense Incorporated (TDK Corporation)
• Inventors: LIM, Martin, HUANG, Kegang, DANEMAN, Michael, TCHERTKOV, Igor
• Granted Patent: US 9,540,230 B2
• Time in Patent Office: Days
• US Class Current: 257/415
• CPC Class Codes: B81B 7/02 containing distinct electrical or optical devices of particular relevance for their function, e.g. microelectro-mechanical systems [MEMS] B81B7/04 takes precedence
• CPC Class Codes: B81C 1/0023 Packaging together an electronic processing unit die and a micromechanical structure die MEMS packages B81B7/0032; MEMS packaging processes B81C1/00261
• CPC Class Codes: B81C 1/00293 maintaining a controlled atmosphere with processes not provided for in B81C1/00285
• CPC Class Codes: B81C 2203/0145 Hermetically sealing an opening in the lid
• CPC Class Codes: B81C 2203/019 characterised by the material or arrangement of seals between parts

Abstract

A Microelectromechanical systems (MEMS) structure comprises a MEMS wafer. A MEMS wafer includes a handle wafer with cavities bonded to a device wafer through a dielectric layer disposed between the handle and device wafers. The MEMS wafer also includes a moveable portion of the device wafer suspended over a cavity in the handle wafer. Four methods are described to create two or more enclosures having multiple gas pressure or compositions on a single substrate including, each enclosure containing a moveable portion. The methods include: A. Forming a secondary sealed enclosure, B. Creating multiple ambient enclosures during wafer bonding, C. Creating and breaching an internal gas reservoir, and D. Forming and subsequently sealing a controlled leak/breach into the enclosure.

Claims

1. A Microelectromechanical Systems (MEMS) structure comprising:

a MEMS substrate comprising;

a handle substrate with cavities bonded to a device substrate through a dielectric layer disposed between the handle and device substrates;

a moveable portion of the device substrate suspended over a cavity in the handle substrate;

a capping layer attached to the device substrate and separated by an air gap from the moveable portion of the device substrate, wherein the capping layer includes first and second portions, wherein first portion has openings that are filled by the second portion, wherein the second portion is on top of the first portion, wherein the capping layer and the handle substrate comprise a first sealed enclosure; and

a second substrate bonded to the MEMS substrate, wherein a second sealed enclosure is formed between the MEMS substrate and the second substrate.

2. The MEMS structure of claim 1, wherein the second substrate comprises a CMOS substrate.

3. The MEMS structure of claim 2, wherein the first and second sealed enclosures are at different pressures.

4. The MEMS structure of claim 2, wherein the first and second sealed enclosures contain different gas compositions.

5. The MEMS structure of claim 2, wherein at least one of the first or second portions of the capping layer makes electrical contact to a portion of the device substrate disposed outside of the first sealed enclosure.

6. The MEMS structure of claim 5, wherein the portion of the device substrate making electrical contact to the capping layer makes electrical contact to a portion of the CMOS substrate.

7. A Microelectromechanical Systems (MEMS) structure comprising:

A MEMS substrate with cavities bonded to a second substrate, forming a plurality of sealed enclosures of two or more types, wherein each of the plurality of sealed enclosure is defined by the MEMS substrate, the second substrate, and a seal-ring material;

and where the seal-ring material of each of the sealed enclosure types have different reflow temperatures.

8. The MEMS structure of claim 7, wherein the second substrate comprises a CMOS substrate.

9. The MEMS structure of claim 8, wherein a first seal-ring material for sealing a first enclosure type is of lower reflow temperature than a second seal-ring material for sealing a second enclosure type.

10. The MEMS structure of claim 9, wherein the first seal-ring material seals a first pressure inside the first enclosure type and the second seal-ring material seals a second pressure different from the first pressure inside the second enclosure type.

11. The MEMS structure of claim 9, wherein the first seal-ring material seals a first gas composition inside the first enclosure type and the second seal-ring material seals a second composition different from the first gas composition inside the second enclosure type.

12. A Microelectromechanical Systems (MEMS) structure comprising:

A MEMS substrate with cavities bonded to a second substrate, forming a plurality of sealed enclosures of at least two types, wherein each of the plurality of sealed enclosures is defined by the MEMS substrate, the second substrate, and a seal-ring;

wherein a first enclosure type has a first seal ring type, and a second enclosure type has a second seal-ring type, wherein the second seal ring type further comprises a gap.

13. The MEMS structure of claim 12, wherein the second substrate comprises a CMOS substrate.

14. The MEMS structure of claim 13, wherein the first sealed enclosure is sealed with a sealant by the first seal ring at a first pressure, at a first temperature, and at a first force applied to the MEMS and CMOS substrates.

15. The MEMS structure of claim 14 wherein the sealant is solder.

16. The MEMS structure of claim 14, wherein the second sealed enclosure is sealed with the sealant by a second seal ring at a second pressure, at a second temperature, and at a second force applied to the MEMS and CMOS substrates.

17. The MEMS structure of claim 16, wherein the second temperature is at a predetermined value to reflow solder to seal the gap in the second seal ring to seal the second sealed enclosure.

18. A Microelectromechanical Systems (MEMS) structure comprising:

a MEMS substrate with cavities bonded to a second substrate, forming a plurality of sealed enclosures of at least two types, wherein each of the plurality of sealed enclosures is defined by the MEMS substrate, the second substrate, and a seal-ring material,

and where the first enclosure type further includes at least one of a gettering element to decrease cavity pressure in the first enclosure type and an outgassing element to increase cavity pressure in the first enclosure type.

19. The MEMS structure of claim 18, wherein the second substrate comprises a CMOS substrate.

20. A Microelectromechanical Systems (MEMS) structure comprising:

A MEMS substrate with cavities bonded to a second substrate, forming a plurality of sealed enclosures of at least two types, wherein each of the plurality of sealed enclosures is defined by the MEMS substrate, the second substrate, and a seal-ring material,

and wherein thickness of a first seal-ring material of a first enclosure type is greater than thickness of a second seal-ring material of a second enclosure type.

21. The MEMS structure of claim 20, wherein the second substrate comprises a CMOS substrate.

22. The MEMS structure of claim 21, wherein the first enclosure type is sealed by the first seal-ring material at a first pressure, at a first temperature and a first force applied to the MEMS and CMOS substrates.

23. The MEMS structure of claim 21, wherein the second enclosure is sealed by a second seal ring material at the second pressure, at a second temperature, and a second force applied to the MEMS and CMOS substrates.

24. The MEMS structure of claim 21 wherein the first and second seal-ring material is solder.

25. A Microelectromechanical Systems (MEMS) structure comprising:

a MEMS substrate comprising;

a handle substrate with cavities bonded to a device substrate through a dielectric layer disposed between the handle and device substrates;

a first sealed reservoir having a first gas composition and pressure formed between the handle and device substrates;

a second substrate bonded to the MEMS substrate via a seal-ring material, wherein one or more sealed enclosures are formed between the MEMS substrate, the second substrate, and the seal-ring material;

the one or more sealed enclosures having a second gas composition and pressure;

a first sealed enclosure separated from the first sealed reservoir by a first seal.

26. The MEMS structure of claim 25, wherein the second substrate comprises a CMOS substrate.

27. The MEMS structure of claim 26, wherein a first equilibrium gas composition and pressure is achieved by balancing the first reservoir gas composition and pressure with the first enclosure gas composition and pressure when the first seal is breached.

28. The MEMS structure of claim 26, further comprising a second sealed reservoir having a second gas composition and pressure and being separated from a second sealed enclosure by a second seal.

29. The MEMS structure of claim 28, wherein a second equilibrium gas composition and pressure is achieved by balancing the second reservoir gas composition and pressure with the second enclosure gas composition and pressure when the second seal is breached.

30. A Microelectromechanical Systems (MEMS) structure comprising:

a MEMS substrate comprising;

a handle substrate with cavities bonded to a device substrate through a dielectric layer disposed between the handle and device substrates;

a moveable portion of the device substrate suspended over a cavity in the handle substrate;

a second substrate bonded to the MEMS substrate, wherein a first sealed enclosure having a first seal-ring and having a first gas composition and pressure, and a second sealed enclosure having a second seal-ring are formed between the MEMS substrate and the second substrate;

a port opening connecting the second sealed enclosure to the external environment for establishing a pressure or gas composition different than that of the first sealed enclosure.

31. The MEMS structure of claim 30, wherein the second substrate comprises a CMOS substrate.

32. The MEMS structure of claim 31, wherein the port opening in the second sealed enclosure is sealed to maintain a pre-determined pressure and gas composition.

33. A Microelectromechanical Systems (MEMS) structure comprising:

a MEMS substrate comprising;

a handle substrate with cavities bonded to a device substrate through a dielectric layer disposed between the handle and device substrates;

a moveable portion of the device substrate suspended over a cavity in the handle substrate;

a second substrate bonded to the MEMS substrate, wherein at least one sealed enclosure comprising at least one cavity is formed between the MEMS substrate and the second substrate;

a port formed in the handle substrate and dielectric layer sufficiently proximate to the at least one sealed enclosure to enable a substantially high and finite gas flow resistance R_B between the port and the sealed enclosure.

34. The MEMS structure of claim 33, wherein the second substrate comprises a CMOS substrate.

35. A method for integrating a secondary sealed enclosure in addition to a main sealed enclosure of a Microelectromechanical Systems (MEMS) device having a silicon device layer, whereby the process creates a first cavity prior and a second cavity using substrate bonding, comprising:

forming a MEMS substrate, comprising

forming one or more cavities in a handle substrate;

bonding the handle substrate to a device substrate;

thinning the device substrate to a desired thickness;

forming stand-offs from the device substrate;

patterning and etching the silicon device layer to define one or more MEMS devices to be sealed in a separate enclosure;

applying a sacrificial spacer layer onto the substrate to plug openings in and form a film on top of the silicon device layer;

applying a first capping layer on top of the sacrificial spacer layer;

patterning and etching the first capping layer to stop on the underlying sacrificial layer thereby creating openings over the cavity to be sealed;

processing the substrate via an etchant to selectively remove portions of the sacrificial layer while preserving the first capping layer and the silicon device layer;

depositing a second capping layer to plug openings in the first capping layer and form a sealed enclosure;

patterning and etching both the first and second capping layers to the underlying sacrificial layer; and

bonding the MEMS substrate to a CMOS substrate such that stand-offs on the MEMS substrate are bonded to metal pads on the CMOS substrate.

36. The method of claim 35, further comprising removing the remaining sacrificial layer prior to bonding the MEMS substrate to the CMOS substrate.

37. The method of claim 35, wherein the openings in the device layer are sufficiently narrow to be plugged using a sacrificial spacer layer of no more than 10 μ

m thickness.

38. The method of claim 35, wherein the sacrificial spacer layer is an electrically insulating material.

39. The method of claim 38, wherein the electrically insulating material is silicon oxide.

40. The method of claim 35, wherein the sacrificial spacer layer is applied to a predetermined and sufficient thickness so as to plug openings in the silicon device layer.

41. The method of claim 35, wherein the second capping layer is deposited to a predetermined and sufficient thickness to seal the openings in the first capping layer over the cavity to create a sealed enclosure.

42. A method for integrating a secondary sealed enclosure in addition to a main sealed enclosure, wherein the main enclosure and the secondary enclosure have different pressures or gas compositions, comprising:

forming a Microelectromechanical Systems (MEMS) substrate, comprising

forming one or more cavities in a handle substrate;

bonding the handle substrate to a device substrate via a dielectric layer disposed between the handle substrate and the device substrate;

thinning the device substrate to a desired thickness;

forming stand-offs from the device substrate;

bonding the MEMS substrate to a CMOS substrate such that stand-offs on the MEMS substrate are bonded to metal pads on the CMOS substrate and at least one sealed enclosure is formed comprising at least one cavity in the handle substrate;

forming a port through the handle substrate and dielectric layer sufficiently proximate to the at least one sealed enclosure to enable a high but finite gas flow resistance between the port and the sealed enclosure;

bringing external pressure and gas composition to a predetermined value for a predetermined time to obtain, via a controlled gas leak through the flow resistance, a desired pressure and gas composition in the sealed enclosure to a predetermined level;

sealing off the port by depositing a sealing material.

43. The method of claim 42, wherein the port is vertical.

44. The method of claim 42, wherein the port is horizontal.

45. A method of integrating two sealed enclosures in a bond chamber comprising:

forming a Microelectromechanical Systems (MEMS) substrate;

bonding the MEMS substrate to a second substrate;

wherein a bond process controls the bond chamber ambient to seal the two sealed enclosures at different times of the bond process to provide different pressures in the two sealed enclosures.