Adjustable solubility in sacrificial layers for microfabrication

• US 8,357,616 B2
• Filed: 04/14/2006
• Issued: 01/22/2013
• Est. Priority Date: 04/14/2005
• Status: Active Grant

• Current Assignee: President and Fellows of Harvard College (Harvard Corporation)
• Original Assignee: President and Fellows of Harvard College (Harvard Corporation)
• Inventors: Linder, Vincent, Gates, Byron, Whitesides, George M., Ryan, Declan, Amir-parviz, Babak
• Primary Examiner(s): Deo, Duy
• Application Number:
  US11/918,269
• Publication Number:
  US 20090236310A1
• Time in Patent Office: 2,475 Days
• Field of Search: None
• US Class Current: 438/745
• CPC Class Codes: B81C 1/00246 Monolithic integration, i.e. micromechanical structure and electronic processing unit are integrated on the same substrate
• CPC Class Codes: B81C 2201/0108 Sacrificial polymer, ashing of organics
• CPC Class Codes: B81C 2203/0735 Post-CMOS, i.e. forming the micromechanical structure after the CMOS circuit
• CPC Class Codes: B82Y 10/00 Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
• CPC Class Codes: B82Y 40/00 Manufacture or treatment of nanostructures
• CPC Class Codes: G03F 7/0002 Lithographic processes using patterning methods other than those involving the exposure to radiation, e.g. by stamping

Abstract

The present invention provides fabrication methods using sacrificial materials comprising polymers. In some embodiments, the polymer may be treated to alter its solubility with respect to at least one solvent (e.g., aqueous solution) used in the fabrication process. The preparation of the sacrificial materials is rapid and simple, and dissolution of the sacrificial material can be carried out in mild environments. Sacrificial materials of the present invention may be useful for surface micromachining, bulk micromachining, and other microfabrication processes in which a sacrificial layer is employed for producing a selected and corresponding physical structure.

Claims

1. A method for microfabrication or other small-scale fabrication process, comprising:

forming a sacrificial material comprising a polymer on a substrate, wherein the polymer is soluble in aqueous solution;

treating the sacrificial material with a bivalent ion such that the polymer becomes substantially insoluble in aqueous solution;

removing the bivalent ion from the sacrificial material such the polymer becomes soluble in aqueous solution; and

removing the sacrificial material.

2. A method as in claim 1, further comprising carrying out a fabrication process in aqueous solution while the polymer is substantially insoluble in aqueous solution.

3. A method as in claim 1, wherein the polymer is poly(acrylic acid), dextran, poly(methacrylic acid), poly(acrylamide), poly(ethylene imine), poly(vinyl alcohol), poly(ethylene oxide), chitosan, or sucrose.

4. A method as in claim 3, wherein the polymer is poly(acrylic acid), dextran, or poly(methacrylic acid).

5. A method as in claim 4, wherein the polymer is poly(acrylic acid).

6. A method as in claim 5, further comprising forming an adhesion layer on the substrate.

7. A method as in claim 6, wherein the adhesion layer comprises poly(acrylic acid).

8. A method as in claim 1, wherein the bivalent ion is Ca²⁺ or Cu²⁺.

9. A method as in claim 1, wherein the bivalent ion is Ca²⁺.

14. A method as in claim 1, wherein the solvent is an aqueous solvent, comprising:

treating the polymer to lower the solubility of the polymer with respect to the solvent by subjecting the polymer to a first ion exchange reaction;

carrying out the fabrication process, using the polymer as sacrificial material;

after fabrication, treating the polymer to increase the solubility of the polymer with respect to the solvent by subjecting the polymer to a second ion exchange reaction; and

removing the polymer at least in part by dissolving the polymer in the solvent.

15. A method as in claim 14, wherein the first ion exchange reaction comprises replacing at least some univalent ion in the polymer with bivalent ion, and the second ion exchange reaction comprises replacing at least some bivalent ion in the polymer with univalent ion.

16. A method as in claim 1, wherein the sacrificial material comprises a first portion and a second portion, the method comprising treating the first portion of the sacrificial material with the bivalent ion such that the first portion becomes substantially insoluble in aqueous solution and the second portion is not treated with the bivalent ion.

17. A method as in claim 16, further comprising removing the first portion of the sacrificial material.

18. A method as in claim 16, further comprising removing the second portion of the sacrificial material.

10. A method for microfabrication or other small-scale fabrication process, comprising:

forming a sacrificial material comprising poly(acrylic acid) on a substrate, wherein the poly(acrylic acid) is associated with a univalent ion and the sacrificial material is soluble in aqueous solution;

treating the sacrificial material with a bivalent ion, such that the poly(acrylic acid) becomes associated with the bivalent ion and the sacrificial material becomes substantially insoluble in aqueous solution;

carrying out a fabrication process, using the poly(acrylic acid) as sacrificial material; and

removing the bivalent ion from the poly(acrylic acid) such the sacrificial material becomes soluble in aqueous solution; and

removing the sacrificial material.

11. A method as in claim 10, wherein the univalent ion is Na⁺.

12. A method as in claim 10, wherein the bivalent ion is Ca²⁺ or Cu²⁺.

13. A method as in claim 12, wherein the bivalent ion is Ca²⁺.

19. A method for microfabrication or other small-scale fabrication process, comprising:

forming a sacrificial material comprising a polymer on a substrate, wherein the sacrificial material comprises a first portion and a second portion and wherein the polymer is soluble in aqueous solution;

treating the first portion of the sacrificial material with a bivalent ion such that the polymer becomes substantially insoluble in aqueous solution, without similarly treating the second portion;

removing the second portion of the sacrificial material;

,

removing the bivalent ion from the first portion of the sacrificial material; and

removing the first portion of the sacrificial material.

20. A method as in claim 19, wherein the polymer is poly(acrylic acid), dextran, poly(methacrylic acid), poly(acrylamide), poly(ethylene imine), poly(vinyl alcohol), poly(ethylene oxide), chitosan, or sucrose.

21. A method as in claim 20, wherein the polymer is poly(acrylic acid), dextran, or poly(methacrylic acid).

22. A method as in claim 20, wherein the polymer is poly(acrylic acid).

23. A method as in claim 19, wherein the substrate further comprises an adhesion layer.

24. A method as in claim 23, wherein the adhesion layer comprises poly(acrylic acid).

25. A method as in claim 19, wherein the bivalent ion is Ca²⁺ or Cu²⁺.

26. A method as in claim 19, wherein the bivalent ion is Ca²⁺.