Microstructures and single mask, single-crystal process for fabrication thereof

• US 6,051,866 A
• Filed: 08/11/1998
• Issued: 04/18/2000
• Est. Priority Date: 02/04/1993
• Status: Expired due to Term

• Current Assignee: Cornell Research Foundation Incorporated (Cornell University)
• Original Assignee: Cornell Research Foundation Incorporated (Cornell University)
• Inventors: Zhang, Z. Lisa, Shaw, Kevin A., MacDonald, Noel C.
• Primary Examiner(s): MINTEL, WILLIAM A
• Application Number:
  US09/132,254
• Time in Patent Office: 616 Days
• Field of Search: 438/52, 257/622, 257/417, 257/418, 257/420, 73/514.36, 73/514.37, 73/514.21, 73/514.22, 73/DIG. 1
• US Class Current: 257/417
• CPC Class Codes: B81C 1/00142 Bridges deformable micromirrors G02B26/0841
• CPC Class Codes: B81C 1/0015 Cantilevers switches using MEMS H01H1/0036; electrostatic relays using micromechanics H01H59/0009; microelectro-mechanical resonators H03H9/02244
• CPC Class Codes: B81C 1/00619 Forming high aspect ratio structures having deep steep walls
• CPC Class Codes: B81C 1/00626 Processes for achieving a desired geometry not provided for in groups B81C1/00563 - B81C1/00619
• CPC Class Codes: B81C 2201/0112 Bosch process
• CPC Class Codes: B81C 2201/0132 Dry etching, i.e. plasma etching, barrel etching, reactive ion etching [RIE], sputter etching or ion milling
• CPC Class Codes: B81C 2201/053 Depositing a protective layers
• CPC Class Codes: G01P 15/0802 Details
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 2015/0814 for translational movement of the mass, e.g. shuttle type
• CPC Class Codes: G01P 2015/0817 for pivoting movement of the mass, e.g. in-plane pendulum
• CPC Class Codes: G01P 2015/0828 the mass being of the paddle type being suspended at one of its longitudinal ends
• CPC Class Codes: Y10S 148/05 Etch and refill
• CPC Class Codes: Y10S 73/01 Vibration

Abstract

A single mask, low temperature reactive ion etching process for fabricating high aspect ratio, released single crystal microelectromechanical structures independently of crystal orientation.

Claims

1. A microelectromechanical structure fabricated in a single crystal substrate independently of crystal orientation by a low temperature, single mask process, comprising:

a single crystal wafer having a top surface;

trench means in the surface of said wafer defining a released beam and a support for said beam spaced from a surrounding substrate, said beam being movable with respect to said substrate;

an electrically insulating layer on said released beam, said support, and said substrate; and

an electrically conductive coating on said insulating layer on said released beam, support and substrate, said trench means electrically isolating the conductive coating on said beam from the conductive coating on said substrate.

2. The device of claim 1, further including means for producing a potential difference between said beam coating and said substrate coating for producing motion of said beam in the plane of said top surface.

3. The device of claim 1, wherein said support for said beam includes contact pad means and interconnect means including said electrically insulating layer and said conductive coating extending between said beam and said contact pad means, said contact pad and interconnect means being defined by said trench means.

4. The device of claim 3, wherein the electrically conductive coating on said interconnect means and on said contact pad means is electrically isolated from said substrate conductive coating by said trench means.

5. The device of claim 3, further including electrode means and corresponding electrode contact pad and electrode interconnect means in the top surface of said wafer, said electrode means having an electrically conductive coating and being spaced from and electrically isolated from said beam means by said trench means to provide capacitive coupling between said released beam and said electrode means.

6. The device of claim 3, wherein said released beam comprises an elongated, cantilevered arm connected at one end to said support.

7. The device of claim 6, wherein said released beam further comprises enlarged grid means carried by said arm.

8. The device of claim 7, further including means carried by said grid for increasing the mass thereof.

9. The device of claim 7, further including a membrane carried by said grid.

10. The device of claim 7, further including electrode means in said trench adjacent at least one edge of said grid and positioned to provide capacitive coupling between said grid and said electrode means to produce torsional motion of said grid about said cantilevered arm.

11. A micromechanical device, comprising:

a substrate having a top surface;

a trench extending into said substrate through said surface to form spaced walls and a floor in said substrate, said trench walls each having an undercut portion adjacent said floor;

a layer of conductive material on the surface of said substrate, on said walls, and on said floor, said undercut portions electrically isolating the layer of conductive material on said walls of said trench from the layer of conductive material on the floor of said trench.

12. The device claim 11, wherein said trench walls define a structure within a cavity in said substrate, a first of said spaced walls being located on said substrate and a second of said spaced walls being located on said structure, said trench floor extending between said walls and forming a floor for said cavity.

13. The device of claim 12, wherein at least a portion of said structure is released from said substrate and is movable with respect to said substrate.

14. The device of claim 13, wherein at least a portion of said structure is fixed to said substrate, said movable portion of said structure having a first end mounted on said fixed portion of said structure and a second end spaced from and movable with respect to said substrate.

15. The device of claim 12, wherein said structure includes a top surface, and further including a conductive material on at least a portion of said top surface and electrically connected to conductive material on said second spaced wall.

16. The device of claim 15, wherein conductive material on said surface of said substrate is electrically connected to conductive material on said first spaced wall, said undercut portions electrically isolating said conductive material on said first spaced wall from said conductive material on said second spaced wall.

17. The device of claim 15, wherein said first and second trench walls are substantially perpendicular to said substrate surface, said second wall forming sides of said structure.

18. The device of claim 17, wherein said trench surrounds said structure, said second wall being continuous and surrounding said structure to form an island spaced on all sides from said substrate.

19. The device of claim 17, wherein said trench extends substantially completely around said structure, said second wall being continuous to form a peninsula within said cavity.

20. The device of claim 17, wherein said undercut portions of said spaced walls extend laterally from trench sufficiently far to produce a discontinuity in said conductive material on said walls.

21. A microstructure, comprising:

a single crystal silicon substrate having a top surface and a trench extending into the substrate through said surface to form in the substrate at least a first vertical wall having a top edge at said surface and a base portion intersecting a horizontal floor;

an undercut cavity portion extending into said substrate along the intersection of said base portion and said floor to undercut the vertical wall;

an electrically insulating layer on said top surface and said vertical wall, and a metal layer on the insulating layers on said top surface, said vertical wall, and said horizontal floor, the metal layer on said vertical wall being electrically isolated from the metal layer on said floor by said undercut cavity portion.

22. The microstructure of claim 21, further including a second vertical wall spaced from said first wall and having a base portion intersecting said floor and a cavity portion extending into said substrate along the intersection of said base portion and said floor to undercut said second wall.

23. The microstructure of claim 22, further including an insulating layer on said second wall and a metal layer on the insulating layer, said undercut cavity in said second wall electrically isolating said second wall metal layer from the metal layers on said floor and on said first wall.