Trench isolation for micromechanical devices

• US 6,239,473 B1
• Filed: 01/14/1999
• Issued: 05/29/2001
• Est. Priority Date: 01/15/1998
• Status: Expired due to Term

• Current Assignee: Cornell Research Foundation Incorporated (Cornell University), Kionix Incorporated (ROHM Co., Ltd.)
• Original Assignee: Cornell Research Foundation Incorporated (Cornell University), Kionix Incorporated (ROHM Co., Ltd.)
• Inventors: Webb, Russell Y., Reed, Bryan W., Shaw, Kevin A., MacDonald, Noel C., Adams, Scott G., Davis, Timothy J.
• Primary Examiner(s): Jackson, Jr., Jerome
• Application Number:
  US09/231,082
• Time in Patent Office: 866 Days
• Field of Search: 257/254, 257/417, 257/419
• US Class Current: 257/419
• CPC Class Codes: B81B 2203/0118 Cantilevers
• CPC Class Codes: B81B 2203/033 Trenches
• CPC Class Codes: B81C 1/00142 Bridges deformable micromirrors G02B26/0841
• CPC Class Codes: B81C 1/00698 Electrical characteristics, e.g. by doping materials
• CPC Class Codes: H01L 21/76224 using trench refilling with dielectric materials trench filling with polycristalline silicon H01L21/763; together with vertical isolation, e.g. trench refilling in a SOI substrate H01L21/76264

Abstract

An isolation process which enhances the performance of silicon micromechanical devices incorporates dielectric isolation segments within the silicon microstructure, which is otherwise composed of an interconnected grid of cantilevered beams. A metal layer on top of the beams provides interconnects and also allows contact to the silicon beams, electrically activating the device for motion or transduction. Multiple conduction paths are incorporated through a metal patterning step prior to structure definition. The invention improves manufacturability of previous processes by performing all lithographic patterning steps on flat topographies, and removing complicated metal sputtering steps required of most high aspect ratio processes. With little modification, the invention can be implemented with integrated circuit fabrication sequences for fully integrated devices.

Claims

1. A micromechanical structure comprising:

a substrate containing a cavity;

a beam suspended within said cavity, and

a transverse isolation segment integral with said beam, wherein the outermost surfaces of said isolation segment extend beyond the sides of said beam in the transverse direction and beyond the bottom of said beam in the vertical direction.

2. The device of claim 1, wherein said isolation segment is located in said beam to provide electrical discontinuity between immediately adjacent beam sections while maintaining mechanical integrity of said beam.

3. The device of claim 2, wherein said isolation segment is composed of silicon dioxide.

4. The device of claim 1, wherein said isolation segment consists of a trench filled with silicon dioxide in said beam, said trench extending through the entire thickness of said beam.

5. The device of claim 4, wherein said trench has a re-entrant profile.

6. The device of claim 4, wherein the width of said trench measured along the longitudinal axis of said beam is less than 5 microns.

7. The device of claim 1, wherein said beam has a width less than 5 microns and a height greater then 10 microns.

8. The device of claim 1, wherein said isolation segment is composed of chemical vapor deposited silicon dioxide.

9. The device of claim 1 further comprising:

an electrically conductive layer on top of said beam and on top of said transverse isolation segment, said layer being insulated from said beam by an intervening electrically insulating layer; and

an electrical connection between said electrically conductive layer and said beam.

10. The device of claim 9, further comprising an electronic device fabricated in the same substrate as said beam and an electrical connection between said electronic device and said beam said beam being electrically insulated from said electronic device by said integral isolation segment in said beam.

11. A multi-level interconnect for a micromechanical device comprising:

a first electrical conduction path provided by bulk material comprising a micromechanical device;

isolation segments breaking said first conduction path into a plurality of independent electrical conduction paths;

a second electrical conduction path comprising an electrically conductive layer insulated from said bulk material;

selective interconnections between said first and second electrical conduction paths; and

a cross-over between said first and second electrical conduction paths wherein said paths intersect without making electrical connection therebetween.

12. A released micromechanical beam cantilevered from a mesa and electrically insulated from said mesa by an isolation segment, transverse to and integral with said beam, extending beyond the sides and bottom of said beam.

13. A micromechanical device comprising:

released beams cantilevered above a substrate from mesas affixed to said substrate, each of said beams comprising a conductive core, an insulating layer on top of said core, and a conductive layer on top of said insulating layer;

an isolation segment integral to and extending beyond the sides and bottom of at least one of said released beams to provide electrical isolation between adjacent segments of said beam conductive core;

wherein said isolation segment is located in close proximity to a junction between said at least one released beam and the mesa from which said beam extends so as to minimize a parasitic circuit element formed by the length of said conductive layer on said insulating layer over said conductive core in the region where said conductive core is in electrical contact with said mesa.

14. The device of claim 13, wherein said isolation segment is transverse to and integral with said beam.