Multiple-level actuators and clamping devices

• US 20040067346A1
• Filed: 10/08/2003
• Published: 04/08/2004
• Est. Priority Date: 12/19/2000
• Status: Abandoned Application

• Current Assignee: Hercules Neves, Noel C. Macdonald, Scott G. Adams, Wolfgang M.J. Hofmann
• Original Assignee: Hercules Neves, Noel C. Macdonald, Scott G. Adams, Wolfgang M.J. Hofmann
• Inventors: Neves, Hercules, Hofmann, Wolfgang M. J., MacDonald, Noel C., Adams, Scott G.
• Application Number:
  US10/680,245
• Publication Number:
  US 20040067346A1
• Time in Patent Office: Days
• US Class Current: 428/195.1
• CPC Class Codes: B81B 2201/033 Comb drives
• CPC Class Codes: B81B 2203/0136 Comb structures
• 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 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 2201/0198 for making a masking layer
• CPC Class Codes: Y10T 428/13 Hollow or container type article [e.g., tube, vase, etc.]
• CPC Class Codes: Y10T 428/24273 including aperture
• CPC Class Codes: Y10T 428/24562 Interlaminar spaces
• CPC Class Codes: Y10T 428/24744 Longitudinal or transverse tubular cavity or cell
• CPC Class Codes: Y10T 428/24802 Discontinuous or differential coating, impregnation or bond [e.g., artwork, printing, retouched photograph, etc.]

Abstract

Improved fabrication processes for microelectromechanical structures, and unique structures fabricated by the improved processes are disclosed. In its simplest form, the fabrication process is a modification of the know SCREAM process, extended and used in such a way as to produce a combined vertical etch and release RIE process, which may be referred to as a “combination etch”.

Fabrication of a single-level micromechanical structure using the process of the present invention includes a novel dry etching process to shape and release suspended single crystal silicon elements, the process combining vertical silicon reactive ion etching (Si-RIE) and release etches to eliminate the need to deposit and pattern silicon dioxide mask layers on the sides of suspended structures and to reduce the mechanical stresses in suspended structures caused by deposited silicon dioxide films.

Claims

1. A combined vertical and release micromachining process, comprising the steps of:

forming a mask on a substrate;

substantially isotropically etching said substrate through said mask and slightly undercutting said mask;

conformally passivating said substrate to produce a passivation layer of selected thickness;

alternately etching and passivating said substrate to define a structure in said substrate;

controlling the timing of said etching and passivating steps to produce a structure having substantially vertical walls; and

thereafter altering the timing of said etching and passivating steps to deposit a passivation layer of increased thickness and to etch said substrate to completely undercut and to release said structure.

2. The process of claim 1, wherein said steps are repeated to produce a second released structure self-aligned below said first structure in said substrate.

3. The process of claim 1, wherein said steps form a first level structure, and further including the steps of:

vertically etching said substrate through said mask and through said first level structure to form a trench defining a second level structure;

applying an oxide layer to the sidewalls of said trench; and

anisotropically etching said trench below said sidewall oxide layer to release said second level structure.

4. The process of claim 3, wherein forming a mask includes defining said first level structure to have a first width, and wherein vertically etching said substrate through said first level structure defines said second level structure to have a second width greater than said first width by the thickness of said first level passivation layer.

5. The process of claim 4, further including electrically isolating selected segments of said first and second structures by thermal oxidation of said structures.

6. The process of claim 5, further forming an electrical contact point on said structures.

7. The process of claim 6, further including applying an electrically conductive layer to said structures.

8. The process of claim 4, further including removing selected portions of said structures by a focused ion beam.

9. The process of claim 4, further including removing a selected portion of said structures by fully oxidizing a selected thin segment of said structure and etching away said thin segment.

10. The process of claim 4, further including depositing a second mask on said structures, and thermally oxidizing a selected portion of said structure through said mask.

11. The process of claim 1, wherein said substrate is alternately etched and passivated to produce a high aspect ratio structure.

12. A microelectromechanical structure comprising:

a substrate having a cavity formed by etching through a single mask a two-level suspended structure in said substrate, the structure including;

a first level incorporating a first clamp stage suspended in said substrate and movable by a first set of actuators;

a second level incorporating a second clamp stage suspended in said substrate and movable independently of said first stage by a second set of actuators, said first and second levels being substantially identical and vertically self-aligned, said first and second sets of actuators being operable in opposite directions to shift one of said first and second clamp stages with respect to the other.