Fabrication of metallic microstructures by micromolding nanoparticles

• US 6,472,459 B2
• Filed: 01/16/2001
• Issued: 10/29/2002
• Est. Priority Date: 06/02/1999
• Status: Expired due to Term

• Current Assignee: National Technology & Engineering Solutions Of Sandia LLC (Honeywell International Inc.)
• Original Assignee: Sandia Corporation (Martin Marietta Corporation)
• Inventors: Winter, Michael R., Allan, Shawn M., Skala, Dawn M., Domeier, Linda A., Morales, Alfredo M.
• Primary Examiner(s): Cain, Edward J.
• Application Number:
  US09/764,615
• Publication Number:
  US 20010038803A1
• Time in Patent Office: 651 Days
• Field of Search: 244/39, 244/40, 244/41, 419/38, 419/39, 419/42
• US Class Current: 524/439
• CPC Class Codes: B22F 1/054 Nanosized particles
• CPC Class Codes: B22F 1/056 Submicron particles having a size above 100 nm up to 300 nm
• CPC Class Codes: B22F 2003/1046 with separating means for articles to be sintered
• CPC Class Codes: B22F 3/1275 by coating a model and eliminating the model before consolidation
• CPC Class Codes: B28B 1/14 by simple casting, the material being neither forcibly fed nor positively compacted for molten material B28B1/54
• CPC Class Codes: B28B 7/342 which are at least partially destroyed, e.g. broken, molten, before demoulding; Moulding surfaces or spaces shaped by, or in, the ground, or sand or soil, whether bound or not; Cores consisting at least mainly of sand or soil, whether bound or not
• 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 30/00 Nanotechnology for materials or surface science, e.g. nanocomposites
• CPC Class Codes: B82Y 40/00 Manufacture or treatment of nanostructures
• CPC Class Codes: C04B 35/111 Fine ceramics
• CPC Class Codes: C04B 35/2658 Other ferrites containing manganese or zinc, e.g. Mn-Zn ferrites
• CPC Class Codes: C04B 35/622 Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
• CPC Class Codes: G03F 7/00 Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor using photoresist structures for special production processes, see the relevant places, e.g. B44C, H01L, e.g. H01L21/00, H05K
• CPC Class Codes: G03F 7/0002 Lithographic processes using patterning methods other than those involving the exposure to radiation, e.g. by stamping
• CPC Class Codes: Y10S 977/777 Metallic powder or flake
• CPC Class Codes: Y10S 977/887 Nanoimprint lithography, i.e. nanostamp
• CPC Class Codes: Y10S 977/888 Shaping or removal of materials, e.g. etching
• CPC Class Codes: Y10S 977/893 Deposition in pores, molding, with subsequent removal of mold

Abstract

A method is provided for fabricating metallic microstructures, i.e., microcomponents of micron or submicron dimensions. A molding composition is prepared containing an optional binder and nanometer size (1 to 1000 nm in diameter) metallic particles. A mold, such as a lithographically patterned mold, preferably a LIGA or a negative photoresist mold, is filled with the molding composition and compressed. The resulting microstructures are then removed from the mold and the resulting metallic microstructures so provided are then sintered.

Claims

1. A method for preparing a metallic microstructure, comprising:

(a) providing, as a mold, a substrate having a pattern on its surface, said pattern comprised of elevated segments and corresponding voids therebetween;

(b) applying a molding composition to the substrate surface and pressing the composition into the voids of the surface pattern to provide a green microstructure in said voids, said molding composition comprising metallic nanoparticles and an optional binder;

(c) removing the green microstructure from the voids; and

(d) sintering the green microstructure.

2. The method of claim 1, wherein the molding composition further comprises a fluxing agent.

3. The method of claim 1, further including, prior to step (b), treating the substrate surface.

4. The method of claim 3, wherein the surface treatment comprises deposition of a low adhesion coating comprised of a material-releasing agent.

5. The method of claim 4, wherein the material-releasing agent is tungsten.

6. The method of claim 3, wherein the surface treatment comprises deposition of a metal or alloy layer, which is subsequently incorporated into the green microstructure in step (b).

7. The method of claim 6, wherein the metal or alloy layer is comprised of a metallic material selected from the group consisting of stainless steel, aluminum, nickel, iron, titanium, copper, gold, silver, tungsten, and mixtures thereof.

8. The method of claim 1, wherein step (c) comprises chemically releasing the green microstructures.

9. The method of claim 1, wherein step (c) comprises charring the mold and thereafter peeling the charred mold away from the green microstructure.

10. The method of claim 8, wherein prior to step (d) any organic material contained within the green microstructure is removed and the green microstructure is covered to reduce warping.

11. The method of claim 9, wherein prior to step (d) any organic material contained within the green microstructure is removed and the green microstructure is covered to reduce warping.

12. The method of claim 10, wherein the organic material is removed by heating the green microstructure at a temperature in the range of about 300°

to 700°

C.

13. The method of claim 10, wherein step (d) is conducted at a temperature in the range of about 300°

C. to 1400°

C.

14. The method of claim 11, wherein step (d) is conducted at a temperature in the range of about 300°

C. to 1400°

C.

15. The method of claim 1, wherein the metallic nanoparticles are in the range of approximately 1 to 1000 nanometers in diameter.

16. The method of claim 15, wherein the metallic nanoparticles are in the range of approximately 1 to 500 nanometers in diameter.

17. The method of claim 16, wherein the metallic nanoparticles are in the range of approximately 1 to 100 nanometers in diameter.

18. The method of claim 1, wherein the metallic nanoparticles are comprised of a metallic material selected from the group consisting of stainless steel, aluminum, nickel, iron, titanium, copper, gold, silver, tungsten, and mixtures thereof.

19. The method of claim 1, wherein the mold used in part (a) is a lithographically patterned mold and the voids of the surface pattern are less than about 100 microns in diameter, so that the resulting green microstructure is less than about 100 microns in diameter.

20. The method of claim 1, wherein the mold is a plastic replicate made by hot embossing, injection molding or casting using a LIGA prepared stamp.

21. The method of claim 1, wherein the mold is comprised of a negative photoresist.

22. The method of claim 1, wherein the binder is present.

23. The method of claim 1, wherein the metallic nanoparticles represent approximately 5 wt. % to approximately 100 wt. % of the molding composition.

24. The method of claim 2, wherein the fluxing agent comprises an acid or strong base.

25. The method of claims 24, wherein the acid or strong base is selected from the groups consisting of, carboxylic acids, amines and phenols.

26. The method of claim 24, wherein the fluxing agent comprises a mixture of an anhydride and a member of the group consisting of water, alcohols and polyols.

27. The method of claim 25, wherein the fluxing agent comprises an alcohol or a polyol.

28. The method of claim 27, wherein the alcohol or polyol is selected from the group consisting of methanol, ethanol, propanol, butanol, isobutanol, isopropanol, butyl carbitol, ethylene glycol, glycerol, mesoerythritol. adonitol and sorbitol.

29. The method of claim 2, wherein the fluxing agent represents approximately 5 wt. % to 30 wt. % of the molding composition.

30. The method of claim 1, wherein the elevated segments are comprised of a photoresist material.

31. The method of claim 30, wherein the photoresist material is poly(methyl methacrylate).

32. The method of claim 20, wherein the plastic material is poly(methyl methacrylate).

33. The method of claim 1, wherein the substrate is comprised of metallized silicon.

34. The method of claim 1, wherein step (b) is repeated prior to step (c).

35. The method of claim 34, wherein step (b) further comprises planarizing the substrate surface to remove excess molding composition after the composition is pressed into the voids.

36. The method of claim 35, wherein step (b) is repeated at least three times.

37. The method of claim 36, wherein in each repetition of step (b) the molding composition is pressed into the voids with greater pressure than used in the previous pressing.

38. The method of claim 37, wherein the substrate is comprised of poly(methyl methacrylate).

39. The method of claim 38, wherein the pressure used in step (b) ranges from about 5,000 psi to about 10,000 psi.

40. The method of claim 21, wherein the mold is comprised of SU8-25.

41. The method of claim 40, wherein the pressure used in step (b) ranges from about 20,000 psi to about 40,000 psi.

43. A metallic microstructure prepared by the process of claim 1.

42. A method for preparing a metallic microstructure, comprising:

(a) providing a lithographically patterned mold comprising a substrate having a pattern on its surface, said pattern comprised of elevated segments and corresponding voids therebetween, said voids having a diameter of less than about 100 microns in diameter;

(b) applying a molding composition to the substrate surface and pressing the composition into the voids of the surface pattern, said molding composition comprising a paste of;

(i) metallic nanoparticles having a diameter in the range of approximately 1 nm to 1000 nm;

(ii) an optional binder; and

(iii) a fluxing agent comprised of a member of the group consisting of acids, strong bases and mixtures of an anhydride and a member of the group consisting of water, alcohols and polyols; and

(c) repeating step (b) with increasing pressure to form a green microstructure;

(d) removing the green microstructure from the voids; and

(e) sintering the green microstructure to form a metallic microstructure.

44. A metallic microstructure prepared by the process of claim 42.