Cantilevered multilevel LIGA devices and methods

• US 6,458,263 B1
• Filed: 09/29/2000
• Issued: 10/01/2002
• Est. Priority Date: 09/29/2000
• Status: Active Grant

• Current Assignee: National Technology & Engineering Solutions Of Sandia LLC (Honeywell International Inc.)
• Original Assignee: Sandia National Laboratories (Government of the United States of America)
• Inventors: Morales, Alfredo Martin, Domeier, Linda A.
• Primary Examiner(s): Phasge, Arun S.
• Application Number:
  US09/677,041
• Time in Patent Office: 732 Days
• Field of Search: 205/118, 205/125, 205/123, 430/325, 430/269
• US Class Current: 205/118
• CPC Class Codes: B81B 2203/0118 Cantilevers
• CPC Class Codes: B81C 1/00666 Treatments for controlling internal stress or strain in MEMS structures
• CPC Class Codes: B81C 2201/019 Bonding or gluing multiple substrate layers
• CPC Class Codes: B81C 2201/032 LIGA process
• CPC Class Codes: C25D 1/003 3D structures, e.g. superposed patterned layers
• CPC Class Codes: C25D 5/022 using masking means
• 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 7/0035 Multiple processes, e.g. applying a further resist layer on an already in a previously step, processed pattern or textured surface
• CPC Class Codes: H01L 21/76885 By forming conductive members before deposition of protective insulating material, e.g. pillars, studs

Abstract

In the formation of multilevel LIGA microstructures, a preformed sheet of photoresist material, such as polymethylmethacrylate (PMMA) is patterned by exposure through a mask to radiation, such as X-rays, and developed using a developer to remove the exposed photoresist material. A first microstructure is then formed by electroplating metal into the areas from which the photoresist has been removed. Additional levels of microstructure are added to the initial microstructure by covering the first microstructure with a conductive polymer, machining the conductive polymer layer to reveal the surface of the first microstructure, sealing the conductive polymer and surface of the first microstructure with a metal layer, and then forming the second level of structure on top of the first level structure. In such a manner, multiple layers of microstructure can be built up to allow complex cantilevered microstructures to be formed.

Claims

1. A method of forming a multi-layered LIGA microstructure on a plating base comprising the steps of:

(a) providing a first level microstructure having raised conductive portions;

(b) covering and surrounding the first level microstructure with a conductive polymer layer;

(c) machining the conductive polymer layer to a desired level so as to reveal the surface of the first level microstructure;

(d) coating the conductive polymer layer and the surface of the first level microstructure with a metal sealing layer;

(e) depositing a second polymer layer onto the metal sealing layer;

(f) exposing portions of the second polymer layer to a radiation source to provide a pattern of dissolvable portions in the second polymer layer;

(g) removing the dissolvable portions in the second polymer layer to provide accessible underlying areas of the metal sealing layer;

(h) removing the accessible underlying areas of the metal sealing layer to provide accessible underlying areas of the first microstructure and the conductive polymer layer;

(i) electroplating a second layer of metal onto the accessible underlying areas of the first microstructure and the conductive polymer layer;

(j) machining the electroplated metal to provide a substantially planar surface;

(k) removing the remainder of the second polymer layer; and

(l) removing the metal sealing layer and the conductive polymeric layer to provide a multi-layered microstructure.

2. The method of claim 1, wherein steps (e) through (k) are repeated resulting in a multi-layered LIGA microstructure having at least three layers.

3. The method of claim 1, wherein the first and second polymer layers comprise first and second adhesive layers bonded to first and second polymer sheets, respectively.

4. The method of claim 3, wherein the first and second polymer sheets are machined to a desired thickness.

5. The method of claim 3, wherein the first and second adhesive polymers are applied as first and second adhesive compositions that are each either cured or thickened prior to coverage by the first and second polymer sheets.

6. The method of claim 5, wherein the first and second adhesive compositions are comprised of polymethylmethacrylate.

7. The method of claim 3, wherein the first polymer sheet is comprised of polymethylmethacrylate.

8. The method of claim 3, wherein the second polymer sheet is comprised of polymethylmethacrylate.

9. The method of claim 3, wherein the first and second polymer sheets are solvent bonded to the respective first and second cured polymeric layers.

10. The method of claim 3, wherein the first and second polymer sheets are machined to a desired thickness.

11. The method of claim 3, wherein the radiation source is a synchrotron.

12. The method of claim 1, wherein the first layer microstructure comprises alignment means.

13. The method of claim 1, wherein the conductive polymer is comprised of polymethylmethacrylate containing conductive particles in the range of about 60% w/w to about 80% w/w.

14. The method of claim 13, wherein the conductive particles are silver particles and comprise 70% w/w of the conductive polymer.

15. The method of claim 1, wherein the metal layer comprises approximately 1,000 Å

of Ti.

16. The method of claim 1, further including (m) removing the microstructure from the base.

17. A method of forming a multi-layered LIGA microstructure on a plating base comprising the steps of:

(a) depositing a first polymer layer comprised of a first radiation-degradable polymer onto the plating base;

(b) exposing the first polymer layer in a pattern to a radiation source to provide a pattern of dissolvable portions in the first polymer layer;

(c) removing the pattern of dissolvable portions in the first polymer layer to reveal exposed areas of the plating base;

(d) electroplating a first layer of a metal onto the exposed areas of the plating base;

(e) machining the electroplated metal to provide a substantially planar surface;

(f) removing the remainder of the first polymer layer to provide a first level microstructure;

(g) covering and surrounding the first level microstructure with a conductive polymer layer;

(h) machining the conductive polymer layer to a desired level so as to reveal the surface of the first level microstructure and provide a substantially planar surface;

(i) coating the conductive polymer layer and the surface of the first level microstructure with a metal sealing layer;

(j) depositing a second polymer layer onto the metal sealing layer;

(k) exposing the second polymer layer in a pattern to a radiation source to provide a pattern of dissolvable portions in the second polymer layer;

(l) removing the dissolvable portions-in the second polymer layer to provide accessible underlying areas of the metal sealing layer;

(m) removing the accessible underlying areas of the metal sealing layer to provide accessible underlying areas of the first microstructure and the conductive polymer layer;

(n) electroplating a second layer of metal onto the accessible underlying areas of the first microstructure and the conductive polymer layer;

(o) machining the electroplated metal to provide a substantially planar surface;

(p) removing the remainder of the second polymer layer; and

(q) removing the metal sealing layer and the conductive polymeric layer to provide a multi-layered microstructure.

18. The method of claim 17, wherein steps (i) through (p) are repeated resulting in a multi-layered LIGA microstructure having at least three layers.

19. The method of claim 18, wherein the plating base is comprised of a tri-layered laminate.

20. The method of claim 19, wherein the tri-layered laminate is comprised of upper and lower titanium layers and a copper mid-layer.

21. The method of claim 19, wherein the upper and lower titanium layers and the copper mid-layer each have a thickness in the range of approximately about 1000 Å

to about 2000 Å

.

22. The method of claim 18, wherein the upper layer of the tri-layered laminate is removed from the exposed portions of the plating base in step (c).

23. The method of claim 17, further including (r) removing the microstructure from the base.

24. A method of forming a multi-layered LIGA microstructure on a plating base comprising the steps of:

(a) forming a first microstructure on the plating base;

(b) covering the first microstructure with a conductive polymer layer;

(c) machining the conductive polymer layer to expose the surface of the first microstructure;

(d) sealing the conductive polymer and the surface of the first microstructure with a metal layer; and

(e) forming a second microstructure on top of the first microstructure and the conductive polymer layer.