WO1995024261B1 - Microfabricated particle filter - Google Patents

Abstract

A thin film filter portion (20) comprises a plurality of members (22) and (24) interconnected by bridges (26), forming walls of a plurality of port slits (28). The width (W) of slits (28) corresponds to diameter of the largest spherical particles that can pass through the slits (28) while the length (L) of slits (28) is the shortest path through the slits (28). The dimension of the slit width (W) can be precisely controlled and as small as about 50 angstroms. The filter portions (20) can withstand high temperatures and harsh solvents.

Description

4. The method of claim 3, wherein said step of providing a first thin film structure includes the substeps of providing a wafer, growing a second sacrificial layer on said wafer, growing said first structural layer on said second sacrificial layer, and patterning said first structural layer; and the method further comprises a step of etching said second sacrificial layer after said second thin film structure is formed whereby the wafer may be reused.

5. A filter produced by the method of claim 3.

6. The filter of claim 1 further including at least one reinforcing rib.

7. The filter of claim 6, wherein said rib has a height of between about 0.01 mm and about 0.25 mm.

8. The filter of claim 1, wherein said width is at most about 3000 angstroms.

9. The filter of claim 8, wherein said width is at most about 2000 angstroms.

10. The filter of claim 9, wherein said width is at most about 1000 angstroms.

11. The filter of claim 8, 9 or 10 wherein said width is substantially uniform.

12. The filter of claim 1 wherein said thin film structures include silicon.

13. The filter of claim 12 wherein walls of said pores are doped with boron.

/WENDED SHEET(ARTICLE 19) AMENDED CLAIMS

[received by the International Bureau on 7 June 1995 (07.06.95); original claims 1 and 3 amended; new claims 6-52 added; remaining claims unchanged (8 pages)]

1. A filter, comprising: a first thin film structure having openings therethrough; and a second thin film structure having openings therethrough, said second thin film structure positioned relative to said first thin film structure such that said openings of said first thin film structure are partially blocked by said second thin film structure and said openings of said second thin film structure are partially blocked by said first thin film structure to produce pores of a substantially uniform predetermined width, said pores being spaces between said first thin film structure and said second thin film structure.

2. The filter of claim 1, wherein said pores have a length in the range of about 1 micron to about 10000 microns.

3. A method for fabricating a filter, the method comprising: providing a first thin film structure having openings therethrough; forming a first sacrificial layer over at least part of said first thin film structure; forming a second thin film structure over said first thin film structure and said first sacrificial layer, said first sacrificial layer and said second thin film structure blocking said openings of said first thin film structure, and said second thin film structure having openings therethrough, said openings exposing a portion of said first sacrificial layer; and etching said first sacrificial layer. 14. The filter of claim 13 wherein said pores have a length between about 1000 angstroms and about 5000 angstroms.

15. The filter of claim 2 wherein said length is in the range of about 2 microns to about 4 microns.

16. The filter of claim 1 wherein said pores are straight-through pores.

17. The filter of claim 1 wherein said pores have ends, said ends not being in line of sight of each other.

18. The filter of claim 1 wherein said second structure formes a rivet-like shape underneath said first structure.

19. The filter of claim 1 wherein said pores have a length between about 500 angstroms and about 5000 angstroms.

20. The filter of claim 1 further comprising at least one additional thin film structure having pores, and a polymer matrix holding said thin-film structures.

21. The filter of claim 1 wherein said first and second thin film structures are conductive and are not in electrical contact.

22. The filter of claim 21 wherein at least one of said first and second thin film structures includes a metal film. 23. The filter of claim 22 having metal films on opposite sides.

24. The filter of claim 1 wherein said thin film structures have hydrophobic surfaces.

25. The filter of claim 24 wherein said width is less than about 3000 angstroms.

26. The filter of claim 1 wherein said thin film structures have surfaces with monoclonal antibodies bonded thereto.

27. The filter of claim 1 wherein said thin film structures have surfaces with a chemical coating covalently bonded thereto.

28. The filter of claim 27 wherein said chemical coating can effectively crystallize below a freezing point to stop flow through said pores.

29. The filter of claim 27 wherein said chemical coating is highly polarizable chain molecules.

30. The method of claim 3 wherein said step of providing a first thin film structure includes forming a reinforcing rib in a trench on a substrate.

31. The method of claim 30 wherein said first thin film structure is grown by chemical vapor deposition.

32. The method of claim 3 wherein said first sacrificial layer is formed by a chemical reaction at an exposed surface of said first thin film structure. 33. The method of claim 32 wherein said first thin film structure includes silicon and said chemical reaction is an oxidation.

34. The method of claim 32 wherein before said step of forming said first sacrificial layer, a portion of an initially exposed surface of said first thin film structure is covered with an anchor layer.

35. The method of claim 34 wherein said first and second thin film structures are conductive and said anchor layer is insulating.

36. The method of claim 35 wherein said first and second thin film structures include silicon and said chemical reaction is an oxidation.

37. The method of claim 36 wherein said anchor layer includes a material from the group consisting of alumina and silicon nitride.

38. The method of claim 3 wherein said second thin film structure is grown by chemical vapor deposition.

39. The method of claim 38 wherein said step of forming said second thin film structure includes etching back said second thin film structure without patterning.

40. The method of claim 39 wherein said first thin film structure is a sidewall structure.

41. The method of claim 39 further including: after forming said second thin film structure and before etching said first sacrificial layer, doping an exposed surface of said first and second thin film structure with boron; and after etching said first sacrificial layer, partially etching an undoped portion of said first and second thin film structures; and wherein said first and second thin film structures include silicon.

42. The method of claim 3 wherein said step of forming said second thin film structure includes patterning openings over unetched portions of said first thin film structure.

43. The method of claim 3 wherein said step of forming said first sacrificial layer includes etching anchoring holes in said first sacrificial layer to expose said first thin film structure.

44. The method of claim 43 further including, after forming said first sacrificial layer and before forming said second thin film layer, partially etching through said first thin film structure where it is exposed by said anchoring holes.

45. The method of claim 43 further including, after forming said first sacrificial layer and before forming said second thin film layer, etching through said first thin film structure where it is exposed by said anchoring holes and partly etching underneath said first thin film structure where it is exposed by said anchoring holes to provide a space for a rivet-like shape of said second thin film structure. 46. The method of claim 3 further including: etching trenches to form filter islands; applying and curing a polymer matrix; and patterning entrance holes in said polymer matrix.

47. The method of claim 3 further including: after etching said first sacrificial layer, growing a thin film on walls of pores of said filter.

48. The method of claim 47 further including: etching said thin film.

49. A method for fabricating a filter with short pore length, comprising: forming a. first structural layer over a sacrificial top layer of a substrate; forming a pore sacrificial layer whose thickness defines a width of said pores; forming a second structural layer covering vertical sidewalls of a sidewall support sacrificial layer, a thickness of said second structural layer defining a length of said pores; anisotropically etching said second structural layer to remove its horizontal portions; forming an entrance hole sacrificial layer covering a bottom portion of said second structural layer and leaving exposed a top portion of said second structural layer; forming a third structural layer; etching entrance holes in said third structural layer; and etching all sacrificial layers filling said pores and underlying said filter. 50. The method of claim 49 wherein said pore sacrificial layer is formed after etching exit holes in said first structural layer and forming said sidewall support sacrificial layer.

51. A method for operating a molecular crystallization valve, comprising: providing a filter having pores coated with a straight chain molecular coating capable of effectively crystallizing below a specific freezing point; and controlling a temperature of said coating.

52. A method for operating a molecular polarization valve, comprising: providing a filter having pores coated with highly polarizable chain molecules; and controlling an electric field across said pores.