Method for release of surface micromachined structures in an epitaxial reactor

• US 6,939,809 B2
• Filed: 12/30/2002
• Issued: 09/06/2005
• Est. Priority Date: 12/30/2002
• Status: Active Grant

• Current Assignee: Robert Bosch GmbH
• Original Assignee: Robert Bosch GmbH
• Inventors: Partridge, Aaron, Lutz, Markus
• Primary Examiner(s): Pham, Long
• Assistant Examiner(s): RAO, SHRINIVAS H
• Application Number:
  US10/334,186
• Publication Number:
  US 20040124481A1
• Time in Patent Office: 981 Days
• Field of Search: 438/706, 438/711, 438/720, 438/722, 216/2, 735/04
• US Class Current: 438/706
• CPC Class Codes: B81C 1/00476 removing a sacrificial layer B81C1/00912 takes precedence

Abstract

A method for releasing from underlying substrate material micromachined structures or devices without application of chemically aggressive substances or excessive forces. The method starts with the step of providing a partially formed device, comprising a substrate layer, a sacrificial layer deposited on the substrate, and a function layer deposited on the sacrificial layer and possibly exposed portions of the substrate layer and then etched to define micromechanical structures or devices therein. The etching process exposes the sacrificial layer underlying the removed function layer material. Next there are the steps of cleaning residues from the surface of the device, and then directing high-temperature hydrogen gas over the exposed surfaces of the sacrificial layer to convert the silicon dioxide to a gas, which is carried away from the device by the hydrogen gas. The release process is complete when all of the silicon dioxide sacrificial layer material underlying the micromachined structures or devices is removed.

Claims

1. A method for manufacturing at least one micromechanical element, comprising:

providing a substrate layer, a sacrificial layer, and a function layer, the sacrificial layer overlaying at least a first portion of the substrate layer, the function layer overlaying at least a second portion of the sacrificial layer;

etching the function layer to expose at least a portion of the sacrificial layer, the etching forming an outline of the at least one micromechanical element; and

removing at least a third portion of the sacrificial layer between the at least one micromechanical element and the substrate layer by exposing the third portion of the sacrificial layer to heated gaseous hydrogen.

2. The method as recited in claim 1, wherein at least the removing operation is performed in an epitaxy reactor environment.

3. The method as recited in claim 1, further comprising, before the removing operation, cleaning at least one surface of at least one of the substrate layer, the sacrificial layer, and the function layer.

4. The method as recited in claim 1, wherein at least one of the substrate layer and the function layer include a silicon bearing compound.

5. The method as recited in claim 1, wherein the sacrificial layer includes an oxide bearing compound.

6. The method as recited in claim 5, wherein the removing operation further includes reacting between the gaseous hydrogen and the oxide bearing compound to form at least one of water, silicon monoxide, and silane.

7. The method as recited in claim 1, wherein the function layer includes a material including at least one of silicon, silicon/germanium, and silicon carbide.

8. The method as recited in claim 1, wherein the function layer is chemically resistant to heated gaseous hydrogen.

9. The method as recited in claim 1, wherein the gaseous hydrogen is heated to a temperature of between about 600°

C. and about 1,400°

C.

10. The method as recited in claim 9, wherein the gaseous hydrogen is heated to a temperature of between about 800°

C. and about 1,200°

C.

11. The method as recited in claim 1, wherein the removing operation is performed at a pressure below about 10 torr.

12. The method as recited in claim 1, wherein a germanium bearing compound is added to the gaseous hydrogen.

13. The method as recited in claim 1, wherein a silicon bearing compound is added to the gaseous hydrogen.

14. The method as recited in claim 1, wherein the providing operation further includes providing an SOI wafer, a top silicon layer of the SOI wafer being the function layer, an insulator layer of the SOI wafer being the sacrificial layer.

15. The method as recited in claim 1, wherein the providing operation further includes:

providing a bottom silicon layer, the bottom silicon layer being the substrate layer;

depositing an oxide layer including an oxide bearing compound on the bottom silicon layer, the oxide layer being the sacrificial layer; and

depositing a top silicon layer on the oxide layer, the top silicon layer being the function layer.

16. The method as recited in claim 15, wherein the top silicon layer is deposited in at least one of an epitiaxial reactor, a low pressure chemical vapor deposition process, and a sputtering process.

17. The method as recited in claim 15, further comprising, before depositing the top silicon layer, patterning the oxide layer to form at least one hole, the at least one hole exposing a fourth portion of the bottom silicon layer.

18. The method as recited in claim 1, wherein the function layer overlays a fourth portion of the substrate layer.

19. The method as recited in claim 1, further comprising at least one of:

depositing a further sacrificial layer; and

depositing a further function layer.

20. The method as recited in claim 19, wherein the at least one of the depositing of the further sacrificial layer and the depositing of the further function layer is performed before the removing operation.

21. The method as recited in claim 19, wherein the at least one of the depositing of the further sacrificial layer and the depositing of the further function layer is performed in an epitaxy reactor environment.

22. The method as recited in claim 1, further comprising exposing the sacrificial layer to hydrochloric acid.

23. The method as recited in claim 22, wherein the hydrochloric acid removes a silicon residue from the at least one micromechanical element.

24. The method as recited in claim 1, further comprising:

before the removing operation, cleaning at least one surface of at least one of the substrate layer, the sacrificial layer, and the function layer;

wherein at least the removing operation is performed in an epitaxy reactor environment;

wherein at least one of the substrate layer and the function layer includes a silicon bearing compound;

wherein the sacrificial layer includes an oxide bearing compound.

25. The method as recited in claim 24, wherein the removing operation further includes reacting between the gaseous hydrogen and the oxide bearing compound to form at least one of water, silicon monoxide, and silane.

26. The method as recited in claim 1, wherein:

the function layer includes a material including at least one of silicon, silicon/germanium, and silicon carbide,

the function layer is chemically resistant to heated gaseous hydrogen, and

the gaseous hydrogen is heated to a temperature of between about 600°

C. and about 1,400°

C.

27. The method as recited in claim 1, wherein:

the function layer includes a material including at least one of silicon, silicon/germanium, and silicon carbide,

the function layer is chemically resistant to heated gaseous hydrogen, and

the gaseous hydrogen is heated to a temperature of between about 800°

C. and about 1,200°

C.

28. The method as recited in claim 1, wherein:

the removing operation is performed at a pressure below about 10 torr,

one of a germanium bearing compound and a silicon bearing compound is added to the gaseous hydrogen, and

the providing operation further includes providing an SOI wafer, a top silicon layer of the SOI wafer being the function layer, an insulator layer of the SOI wafer being the sacrificial layer.

29. The method as recited in claim 24, wherein the providing operation further includes:

providing a bottom silicon layer, the bottom silicon layer being the substrate layer;

depositing an oxide layer including an oxide bearing compound on the bottom silicon layer, the oxide layer being the sacrificial layer; and

depositing a top silicon layer on the oxide layer, the top silicon layer being the function layer.

30. The method as recited in claim 29, wherein the top silicon layer is deposited in at least one of an epitiaxial reactor, a low pressure chemical vapor deposition process, and a sputtering process.

31. The method as recited in claim 29, further comprising:

before depositing the top silicon layer, patterning the oxide layer to form at least one hole, the at least one hole exposing a fourth portion of the bottom silicon layer.

32. The method as recited in claim 24, wherein the function layer overlays a fourth portion of the substrate layer.

33. The method as recited in claim 24, further comprising at least one of:

depositing a further sacrificial layer; and

depositing a further function layer.

34. The method as recited in claim 33, wherein the depositing is performed before the removing operation.

35. The method as recited in claim 33, wherein the depositing is performed in an epitaxy reactor environment.

36. The method as recited in claim 24, comprising exposing the sacrificial layer to hydrochloric acid, which removes a silicon residue from the at least one micromechanical element.