RIE process for fabricating submicron, silicon electromechanical structures

• US 5,198,390 A
• Filed: 01/16/1992
• Issued: 03/30/1993
• Est. Priority Date: 01/16/1992
• Status: Expired due to Term

• Current Assignee: Cornell Research Foundation Incorporated (Cornell University)
• Original Assignee: Cornell Research Foundation Incorporated (Cornell University)
• Inventors: MacDonald, Noel C., Zhang, Zuoying L.
• Primary Examiner(s): Hearn, Brian E.
• Assistant Examiner(s): Picardat, Kevin M.
• Application Number:
  US07/821,944
• Time in Patent Office: 439 Days
• Field of Search: 437/203, 437/225, 437/228, 148/DIG. 50, 148/DIG. 51
• US Class Current: 438/52
• 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 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: H01H 1/0036 Switches making use of microelectromechanical systems [MEMS] for electromagnetic relays H01H50/005; for electrostatic relays H01H59/0009
• CPC Class Codes: H01L 21/3065 Plasma etching; Reactive-ion etching
• CPC Class Codes: H01L 21/3081 characterised by their composition, e.g. multilayer masks, materials
• CPC Class Codes: Y10S 148/05 Etch and refill
• CPC Class Codes: Y10S 148/051 Etching

Abstract

A reactive ion etching process is used for the fabrication of submicron, single crystal silicon, movable mechanical structures and capacitive actuators. The reactive ion etching process gives excellent control of lateral dimensions while maintaining a large vertical depth in the formation of high aspect-ratio freely suspended single crystal silicon structures. The silicon etch process is independent of crystal orientation and produces controllable vertical profiles.

Claims

1. A reactive ion etching process for the fabrication of submicron, single crystal released structures, comprising:

forming a wafer from which a single crystal structure is to be fabricated;

forming an etch mask on a top surface of said wafer;

transferring to said etch mask by reactive ion etching in a CHF₃ plasma a pattern defining a structure to be formed in said wafer;

transferring said pattern by a Cl₂ /BCl₃ reactive ion etching from said etch mask to said wafer to form vertical walls defining trenches and steps in said pattern in said wafer;

selectively masking said vertical walls to define structures to be released in said wafer; and

releasing said selected structures in said wafer using an SF₆ /O₂ reactive ion etching process to completely undercut said selected structures.

2. The process of claim 1, further including, after transferring said pattern to said wafer:

forming an electrically insulating layer on all exposed surfaces of said wafer, including the vertical walls of said trenches and steps,

conformally depositing on said insulating layer a layer of aluminum; and

transferring an electrode pattern to said aluminum layer by reactive ion etching.

3. The process of claim 2, wherein the step of selectively masking said vertical walls includes removing selected portions of said insulating layer to expose the bottoms of said trenches in the regions of structures to be released.

4. A reactive ion etching process for fabricating a high aspect ratio, submicron, released, single crystal electromechanical structure independently of crystal orientation, comprising:

forming a patterned etch mask on a top surface of a single crystal substrate, the etch mask defining a structure of arbitrary shape to be formed in said substrate;

transferring the pattern of said etch mask by reactive ion etching to said substrate to form trenches defining the structure to be formed in the substrate, said etching step forming trenches having bottom walls and vertical side walls;

forming an electrically insulating layer on exposed surfaces of said substrates, including the vertical side walls of said trenches;

forming metal electrodes on selected portions of said vertical side walls; and

reactive ion etching the bottom walls of said trenches to undercut and to release said defined structure to thereby produce a movable, high aspect ratio released single crystal structure having vertical side walls.

5. The process of claim 4, wherein the step of forming metal electrodes includes:

depositing on said electrically insulating layer a conformal layer of metal;

producing an electrode pattern on said layer of metal; and

selectively removing said metal to produce metal electrodes on at least selected portions of said vertical side walls.

6. The process of claim 4, further including selectively removing said electrically insulating layer from said bottom walls of said trenches and thereafter reactive ion etching said bottom walls to undercut and release said defined structure.

7. The process of claim 6, wherein the step of reactive ion etching the bottom walls of said trenches includes etching said substrate material below said side wall insulating material to produce undercut cavities beneath said defined structure to form a cantilever structure.