Thin micromachined structures

• US 6,808,956 B2
• Filed: 12/27/2000
• Issued: 10/26/2004
• Est. Priority Date: 12/27/2000
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Ridley, Jeffrey Alan, Cabuz, Cleopatra
• Primary Examiner(s): Niebling, John F.
• Assistant Examiner(s): Simkovic, Viktor
• Application Number:
  US09/749,171
• Publication Number:
  US 20020081765A1
• Time in Patent Office: 1,399 Days
• Field of Search: 438/50, 438/51, 438/52, 438/53, 735/142.1, 735/142.2, 735/142.3, 735/143.6, 735/041.4, 735/041.5, 735/041.6, 738/626.32, 738/626.33, 738/626.34, 738/626.37, 738/626.38, 738/626.79
• US Class Current: 438/52
• CPC Class Codes: B81B 2201/0228 Inertial sensors
• CPC Class Codes: B81C 1/0015 Cantilevers switches using MEMS H01H1/0036; electrostatic relays using micromechanics H01H59/0009; microelectro-mechanical resonators H03H9/02244
• CPC Class Codes: B81C 2201/019 Bonding or gluing multiple substrate layers

Abstract

Methods for making thin silicon layers suspended over recesses in glass wafers or substrates are disclosed. The suspended silicon wafers can be thin and flat, and can be made using methods not requiring heavy doping or wet chemical etching of the silicon. Devices suitable for production using methods according to the invention include tuning forks, combs, beams, inertial devices, and gyroscopes. One embodiment of the present invention includes providing a thin silicon wafer, and a glass wafer or substrate. Recesses are formed in one surface of the glass wafer, and electrodes are formed in the recesses. The silicon wafer is then bonded to the glass wafer over the recesses. The silicon wafer is them etched to impart the desired suspended or silicon wafer structure. In another embodiment of the present invention, the silicon wafer has a patterned metal layer. The silicon wafer is bonded to the glass wafer, with the patterned metal layer positioned adjacent the recesses in the glass wafer. The silicon wafer is selectively etched down to the metal layer, which serves as an etch stop. The metalized layer can provide sharper feature definition at the silicon-metalization layer interface, and may also serve to seal gasses within the recessed cavities of the glass wafer during the silicon etching process. The metal layer can then be subsequently removed.

Claims

1. A method for making a thin silicon structure comprising the steps of:

providing a glass wafer or substrate;

providing a silicon wafer having a first substantially planar surface and a second substantially planar surface;

forming a recess in said glass wafer or silicon wafer first surface;

bonding said silicon wafer to said glass wafer such that at least part of said silicon wafer first surface bonds to said glass wafer and at least part of said silicon wafer first surface overhangs said recess;

after said bonding step, selectively removing a portion of said silicon wafer from said silicon wafer second surface through to said silicon wafer first surface such that a silicon structure is formed overhanging said recess;

providing a metal layer on the first substantially planar surface of the second wafer, such that the metal layer is patterned to approximately coincide with said recess;

stopping the selective removal step at or near said metal layer to form the silicon structure; and

removing said metal layer.

2. A method for making a thin silicon structure as in claim 1, further comprising forming at least one electrode on said glass wafer within said recess.

3. A method for making a thin silicon structure as in claim 2, wherein said electrode forming step includes forming a titanium-platinum electrode.

4. A method for making a thin silicon structure as in claim 2, wherein said electrode forming step includes forming a gold electrode.

5. A method for making a thin silicon structure as in claim 1, wherein said bonding step includes anodic bonding.

6. A method for making a thin silicon structure as in claim 1, wherein said selectively removing silicon step includes a DRIE process.

7. A method for making a thin silicon structure comprising the steps of:

providing a glass wafer or substrate;

providing a silicon wafer having a first substantially planar surface and a second substantially planar surface;

forming a recess in said glass wafer surface or said silicon wafer;

providing a patterned metal layer adjacent the silicon wafer, the patterned metal layer coinciding with said recess;

bonding said silicon wafer to said glass wafer such that at least part of said silicon wafer first surface bonds to said glass wafer and overhangs said recess;

selectively etching said silicon wafer above said recess from said second surface through to said first surface and stopping at or near said metal layer to form a silicon structure that at least partially overhangs said recess; and

removing said metal layer.

8. A method for making a thin silicon structure as in claim 7, further comprising forming at least one electrode on said glass wafer that is in alignment with at least part of said recess.

9. A method for making a thin silicon structure as in claim 7, wherein said bonding step includes anodic bonding.

10. A method for making a thin silicon structure as in claim 7, wherein said etching step includes a DRIE process.

11. A method for making a thin silicon structure as in claim 8, wherein said electrode forming step includes forming a titanium-platinum electrode.

12. A method for making a thin silicon structure as in claim 8, wherein said electrode forming step includes forming a gold electrode.

13. A method for making a thin silicon structure as in claim 8, wherein said electrode includes an electrode tab or ear extending nearer the unrecessed surface of the glass wafer or silicon wafer.

14. A method for making a thin structure, comprising:

providing a first wafer or substrate;

providing a second wafer having a first substantially planar surface and a second substantially planar surface;

forming a recess in said first wafer substrate;

bonding said second wafer to said first wafer such that at least part of said second wafer first surface bonds to said first wafer so that at least part of said second wafer first surface overhangs said recess;

after said bonding step, selectively removing a portion of said second wafer from said second wafer second surface through to said second wafer first surface such that a thin structure is formed overhanging said recess;

providing a patterned metal layer on the first substantially planar surface of the second wafer, such that the metal layer is patterned to coincide with said recess;

stopping the selective removal step at or near said metal layer to form the thin structure; and

removing said metal layer, and

wherein at least one portion of said second wafer is not connected to another portion of said second wafer.

15. A method for making a thin structure as in claim 14, wherein the first wafer or substrate is a glass wafer or substrate.

16. A method for making a thin structure as in claim 15, wherein the second wafer is a silicon wafer.

17. A method for making a thin structure as in claim 14, wherein the first wafer or substrate is a silicon wafer.

18. A method for making a thin structure as in claim 17, wherein the second wafer is a glass wafer or substrate.

19. A method for making a thin structure comprising the steps of:

providing a first substrate having a first substantially planar surface and a second substantially planar surface;

providing a second substrate having a first substantially planar surface and a second substantially planar surface;

forming a recess in said first substantially planar surface of said first substrate and/or said first substantially planar surface of said second substrate;

securing said first substrate to said second substrate such that said first substantially planar surface of said first substrate faces said first substantially planar surface of said second substrate;

after said securing step, selectively removing a portion of said first substrate from said second substantially planar surface of said first substrate such that a structure is formed overhanging said recess;

providing a metal layer on the first substantially planar surface of the second wafer, such that the metal layer is patterned to approximately coincide with said recess;

stopping the selective removal step at or near said metal layer to form the structure; and

removing said metal layer.

20. A method for making a thin structure comprising the steps of:

providing a first substrate having a first substantially planar surface and a second substantially planar surface;

providing a second substrate having a first substantially planar surface and a second substantially planar surface;

forming a recess in said first substantially planar surface of said first substrate and/or said first substantially planar surface of said second substrate;

securing said first substrate to said second substrate such that said first substantially planar surface of said first substrate faces said first substantially planar surface of said second substrate;

selectively removing a portion of said first substrate from said second substantially planar surface of said first substrate such that a thin structure is formed overhanging said recess, said thin structure being doped at a concentration of between zero and 1×

10¹⁸ atm/cm3,

providing a metal layer on the first substantially planar surface of the second wafer, such that the metal layer is patterned to approximately coincide with said recess;

stopping the selective removal step at or near said metal layer to form the thin structure; and

removing said metal layer; and

wherein at least one portion of said first substrate is not connected to another portion of said first substrate.

21. A method for making a thin structure, comprising:

providing a first substrate having a first substantially planar surface and a second substantially planar surface;

providing a second substrate having a first substantially planar surface and a second substantially planar surface;

forming a recess in said first substantially planar surface of said first substrate and/or said first substantially planar surface of said second substrate;

providing a metal layer on the first substantially planar surface of the second substrate adjacent said recess;

securing said second substrate to said first substrate such that said first substantially planar surface of said first substrate faces said first substantially planar surface of said second substrate;

selectively removing a portion of said second substrate from said second substrate second substantially planar surface through to said second substrate first substantially planar surface such that a thin structure is formed overhanging said recess;

stopping the selective removal step at or near said metal layer to form the thin structure; and

removing said metal layer.

22. A method for making a thin silicon structure comprising the steps of:

providing a glass wafer or substrate;

providing a silicon wafer having a first substantially planar surface and a second substantially planar surface;

forming a recess in said glass wafer or silicon wafer first surface;

bonding said silicon wafer to said glass wafer such that at least part of said silicon wafer first surface bonds to said glass wafer and at least part of said silicon wafer first surface overhangs said recess;

after said bonding step, selectively removing a portion of said silicon wafer from said silicon wafer second surface through to said silicon wafer first surface such that a silicon structure is formed overhanging said recess;

providing a etch stop layer on the first substantially planar surface of the second wafer, such that the etch stop layer is patterned to approximately coincide with said recess;

stopping the selective removal step at or near said etch stop layer to form the silicon structure; and

removing said etch stop layer.

23. A method for making a thin silicon structure as in claim 22, further comprising forming at least one electrode on said glass wafer within said recess.

24. A method for making a thin silicon structure as in claim 23, wherein said electrode forming step includes forming a titanium-platinum electrode.

25. A method for making a thin silicon structure as in claim 23, wherein said electrode forming step includes forming a gold electrode.

26. A method for making a thin silicon structure as in claim 22, wherein said bonding step includes anodic bonding.

27. A method for making a thin silicon structure as in claim 22, wherein said selectively removing silicon step includes a DRIE process.

28. A method for making a thin silicon structure comprising the steps of:

providing a glass wafer or substrate;

providing a silicon wafer having a first substantially planar surface and a second substantially planar surface;

forming a recess in said glass wafer surface or said silicon wafer;

providing a patterned etch stop layer adjacent the silicon wafer, the patterned etch stop layer coinciding with said recess;

bonding said silicon wafer to said glass wafer such that at least part of said silicon wafer first surface bonds to said glass wafer and overhangs said recess;

selectively etching said silicon wafer above said recess from said second surface through to said first surface and stopping at or near said etch stop layer to form a silicon structure that at least partially overhangs said recess; and

removing said etch stop layer.

29. A method for making a thin silicon structure as in claim 28, further comprising forming at least one electrode on said glass wafer that is in alignment with at least part of said recess.

30. A method for making a thin silicon structure as in claim 28, wherein said bonding step includes anodic bonding.

31. A method for making a thin silicon structure as in claim 28, wherein said etching step includes a DRIE process.

32. A method for making a thin silicon structure as in claim 29, wherein said electrode forming step includes forming a titanium-platinum electrode.

33. A method for making a thin silicon structure as in claim 29, wherein said electrode forming step includes forming a gold electrode.

34. A method for making a thin silicon structure as in claim 29, wherein said electrode includes an electrode tab or ear extending nearer the unrecessed surface of the glass wafer or silicon wafer.

35. A method for making a thin structure, comprising:

providing a first wafer or substrate;

providing a second wafer having a first substantially planar surface and a second substantially planar surface;

forming a recess in said first wafer substrate;

bonding said second wafer to said first wafer such that at least part of said second wafer first surface bonds to said first wafer so that at least part of said second wafer first surface overhangs said recess;

after said bonding step, selectively removing a portion of said second wafer from said second wafer second surface through to said second wafer first surface such that a thin structure is formed overhanging said recess;

providing a patterned etch stop layer on the first substantially planar surface of the second wafer, such that the etch stop layer is patterned to coincide with said recess;

stopping the selective removal step at or near said etch stop layer to form the thin structure; and

removing said etch stop layer; and

wherein at least one portion of said second wafer is not connected to another portion of said second wafer.

36. A method for making a thin structure as in claim 35, wherein the first wafer or substrate is a glass wafer or substrate.

37. A method for making a thin structure as in claim 36, wherein the second wafer is a silicon wafer.

38. A method for making a thin structure as in claim 35, wherein the first wafer or substrate is a silicon wafer.

39. A method for making a thin structure as in claim 38, wherein the second wafer is a glass wafer or substrate.

40. A method for making a thin structure comprising the steps of:

providing a first substrate having a first substantially planar surface and a second substantially planar surface;

providing a second substrate having a first substantially planar surface and a second substantially planar surface;

forming a recess in said first substantially planar surface of said first substrate and/or said first substantially planar surface of said second substrate;

securing said first substrate to said second substrate such that said first substantially planar surface of said first substrate faces said first substantially planar surface of said second substrate;

after said securing step, selectively removing a portion of said first substrate from said second substantially planar surface of said first substrate such that a structure is formed overhanging said recess;

providing a etch stop layer on the first substantially planar surface of the second wafer, such that the etch stop layer is patterned to approximately coincide with said recess;

stopping the selective removal step at or near said etch stop layer to form the structure; and

removing said etch stop layer.

41. A method for making a thin structure comprising the steps of:

providing a first substrate having a first substantially planar surface and a second substantially planar surface;

providing a second substrate having a first substantially planar surface and a second substantially planar surface;

forming a recess in said first substantially planar surface of said first substrate and/or said first substantially planar surface of said second substrate;

securing said first substrate to said second substrate such that said first substantially planar surface of said first substrate faces said first substantially planar surface of said second substrate;

selectively removing a portion of said first substrate from said second substantially planar surface of said first substrate such that a thin structure is formed overhanging said recess, said thin structure being doped at a concentration of between zero and 1×

10¹⁸ atm/cm3,

providing a etch stop layer on the first substantially planar surface of the second wafer, such that the etch stop layer is patterned to approximately coincide with said recess;

stopping the selective removal step at or near said etch stop layer to form the thin structure; and

removing said etch stop layer; and

wherein at least one portion of said first substrate is not connected to another portion of said first substrate.

42. A method for making a thin structure, comprising:

providing a first substrate having a first substantially planar surface and a second substantially planar surface;

providing a second substrate having a first substantially planar surface and a second substantially planar surface;

forming a recess in said first substantially planar surface of said first substrate and/or said first substantially planar surface of said second substrate;

providing a etch stop layer on the first substantially planar surface of the second substrate adjacent said recess;

securing said second substrate to said first substrate such that said first substantially planar surface of said first substrate faces said first substantially planar surface of said second substrate;

selectively removing a portion of said second substrate from said second substrate second substantially planar surface through to said second substrate first substantially planar surface such that a thin structure is formed overhanging said recess;

stopping the selective removal step at or near said etch stop layer to form the thin structure; and

removing said etch stop layer.