Multilayer high vertical aspect ratio thin film structures

• US 5,645,684 A
• Filed: 06/07/1995
• Issued: 07/08/1997
• Est. Priority Date: 03/07/1994
• Status: Expired due to Term

• Current Assignee: Regents of the University of California (University of California)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Keller, Christopher G.
• Primary Examiner(s): POWELL, WILLIAM A
• Application Number:
  US08/485,815
• Time in Patent Office: 762 Days
• Field of Search: 156/633.1, 156/636.1, 156/643.1, 156/645.1, 156/657.1, 156/659.11, 156/662.1, 216/2, 216/8, 216/17, 216/18, 216/20, 216/33, 216/38, 216/41, 216/52, 216/67, 437/228 P, 437/228 H, 437/927, 437/974, 257/247, 257/248, 148/33.2, 148/33.4, 148/33.5
• US Class Current: 148/33.2
• CPC Class Codes: A61K 9/0024 Solid, semi-solid or solidifying implants, which are implanted or injected in body tissue compositions for intravenous administration, normal injectable solutions or dispersions for, e.g. subcutaneous administration A61K9/0019; brain implants A61K9/0085; (coated) prostheses, catheters or stents A61L
• CPC Class Codes: A61K 9/0097 Micromachined devices; Microelectromechanical systems [MEMS]; Devices obtained by lithographic treatment of silicon; Devices comprising chips intradermal microneedle arrays A61K9/0021; MEMS in general B81B7/02
• CPC Class Codes: B01D 2323/24 Use of template or surface directing agents [SDA]
• CPC Class Codes: B01D 2325/04 Characteristic thickness
• CPC Class Codes: B01D 2325/26 Electrical properties
• CPC Class Codes: B01D 39/1692 Other shaped material, e.g. perforated or porous sheets
• CPC Class Codes: B01D 39/20 of inorganic material, e.g. asbestos paper, metallic filtering material of non-woven wires porous ceramic material C04B38/00 ; sintering metals C22C1/04; making porous sintered metal bodies B22F3/10, honeycomb filters B01D46/2418, materials used for filtering exhaust gases of an internal combustion engine F01N3/022, ceramic honeycomb structures C04B38/0006
• CPC Class Codes: B01D 67/0058 by selective elimination of components, e.g. by leaching
• CPC Class Codes: B01D 67/0069 by deposition from the liquid phase, e.g. electrochemical deposition B01D67/0046 takes precedence
• CPC Class Codes: B01D 67/0072 by deposition from the gaseous phase, e.g. sputtering, CVD, PVD
• CPC Class Codes: B01D 67/0083 Thermal after-treatment
• CPC Class Codes: B01D 69/02 characterised by their properties
• CPC Class Codes: B01D 69/12 Composite membranes; Ultra-thin membranes
• CPC Class Codes: B01D 71/0213 Silicon
• 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 2201/032 LIGA process
• CPC Class Codes: B81C 2203/0728 Pre-CMOS, i.e. forming the micromechanical structure before the CMOS circuit
• CPC Class Codes: B81C 99/0085 using moulds and master templates, e.g. for hot-embossing
• CPC Class Codes: C23C 16/01 on temporary substrates, e.g. substrates subsequently removed by etching
• 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

Abstract

This invention relates to the area of microelectromechanical systems in which electronic circuits and mechanical devices are integrated on the same silicon chip. The method taught herein allows the fabrication of thin film structures in excess of 150 microns in height using thin film deposition processes. Wafers may be employed as reusable molds for efficient production of such structures. Various material properties may be varied within the structures to produce electrical, mechanical or electromechanical devices.

Claims

1. A method of fabrication of a micromechanical element, comprising:

providing a mold having a depth;

coating said mold with a sacrificial thin film layer;

filling a first portion of said mold with a material having properties;

filling a second portion of said mold with a material having properties at least one of which is different from the material filling said first portion of said mold; and

etching said sacrificial thin film layer.

2. The method of claim 1 wherein said step of providing a mold includes providing a first substrate and anisotropically etching vertical trenches in said first substrate.

3. The method of claim 2 wherein said first substrate is a silicon substrate and said etching of vertical trenches includes coating said first substrate with a masking layer, patterning said masking layer to expose the silicon in the areas where trenches are to be etched, and etching said trenches using plasma etching.

4. The method of claim 3 wherein said step of providing a mold further includes smoothing walls of said trenches by growing thermal oxide on them and etching said thermal oxide away.

5. The method of claim 3 or 4 wherein said step of providing a mold further includes growing a layer of low temperature oxide (LTO) on said mold.

6. The method of claim 2 wherein after said step of coating the mold with a sacrificial layer, a second substrate is provided coated with a sacrificial layer patterned with anchoring holes, and said second substrate is bonded to said first substrate to provide a mold cavity.

7. The method of claim 6 wherein said bonding is anodic bonding or hydrophilic thermal bonding.

8. The method of claim 6 wherein at least one of said first substrate and said second substrate has at least one orifice for providing a mold cavity for a port.

9. The method of claim 1 wherein said step of coating said mold with a sacrificial thin film layer is carried out by chemical vapor deposition.

10. The method of claim 9 wherein said step of coating said mold with a sacrificial thin film layer includes growing a phosphosilicate glass layer.

11. The method of claim 10 wherein said step of coating said mold with a sacrificial thin film layer further includes growing a chemical vapor deposited oxide layer.

12. The method of claim 1 wherein said step of coating said mold with a sacrificial thin film layer includes growing a silicon layer by chemical vapor deposition and oxidizing said silicon layer.

13. The method of claim 1 wherein at least one of said steps of filling a first and a second portion of the mold is carried out by chemical vapor deposition.

14. The method of claim 13 wherein said chemical vapor deposition is chemical vapor deposition of silicon.

15. The method of claim 1 further including a step of reusing said mold.

16. The method of claim 1 wherein said material of said first portion and said material of said second portion have different electrical conductivity.

17. The method of claim 1 wherein said material of said first portion and said material of said second portion have different electronic energy band structure.

18. The method of claim 1 wherein said material of said first portion and said material of said second portion have different residual stress.

19. The method of claim 1 wherein said material of said first portion and said material of said second portion have different dopant concentrations.

20. The method of claim 1 wherein said material of said first portion is a reinforcement for said material of said second portion.

21. The method of claim 1 wherein at least one of said steps of filling a first and a second portion of the mold is carried out by plating.

22. The method of claim 1 further comprising after filling said second portion, filling a third portion of said mold with a material having properties at least one of which is different from the material filling said first portion of said mold, and at least one of which is different from the material filling said second portion of said mold.

23. The method of claim 22 wherein filling said first, second and third portions is carried out by thin film deposition, and no patterning is performed between the filling of the first, second and third portions and the mold has a variable wall-to-wall spacing whereby a micromechanical element with variable controlled material properties is formed.

24. A thin film structure, comprising:

a network of members shaped as ribs or tubes having a thickness and wherein an extent of said thin film structure in any direction is greater than about twice said thickness, a first portion of said structure being composed of a material having properties, and a second portion of said structure being composed of material having properties at least one of which is different from the material composing said first portion of said structure.

25. The structure of claim 24 having a lowest extent between about 5 microns and about 250 microns.

26. The structure of claim 24 or 25 wherein said thin film structure has a film thickness between about 5 microns and about 15 microns.

27. The structure of claim 24 wherein said members form substantially rigid portions connected by substantially flexible links.

28. The structure of claim 27 wherein said substantially rigid portions are networks of said members.

29. The structure of claim 28 wherein said networks are honeycomb-shaped.

30. The structure of claim 27 wherein said substantially rigid portions and said substantially flexible links form a machine.

31. The structure of claim 30 wherein said machine is powered by an actuator.

32. The structure of claim 31 wherein said actuator dilates as a result of ohmic heating.

33. The structure of claim 24 wherein said material of said first portion and said material of said second portion have different electrical conductivity.

34. The structure of claim 24 wherein said material of said first portion and said material of said second portion have different electronic energy band structure.

35. The structure of claim 24 wherein said material of said first portion and said material of said second portion have different residual stress.

36. The structure of claim 24 wherein said material of said first portion and said material of said second portion have different dopant concentration.

37. The structure of claim 24 wherein said material of said first portion is a reinforcement for said material of said second portion.

38. The structure of claim 24 wherein a third portion of said structure is composed of a material having properties at least one of which is different from the material of which said first portion of said structure is composed, and at least one of which is different from the material of which said second portion of said structure is composed.

39. A thin film structure, comprising:

a network of members shaped as ribs or tubes having a thickness and

a bimorph for lifting said network out of a mold and

wherein an extent of said thin film structure in any direction is greater than about twice said thickness.