Method of making released micromachined structures by directional etching

• US 6,086,774 A
• Filed: 12/18/1997
• Issued: 07/11/2000
• Est. Priority Date: 12/18/1997
• Status: Expired due to Fees

• Current Assignee: Japan Science And Technology Corpration, Board of Trustees of the Leland Stanford Junior University (Stanford Management Co.)
• Original Assignee: Japan Science And Technology Corpration, Board of Trustees of the Leland Stanford Junior University (Stanford Management Co.)
• Inventors: Ho, Francis, Yamamoto, Yoshihisa
• Primary Examiner(s): SERGENT, RABON A
• Application Number:
  US08/993,924
• Time in Patent Office: 936 Days
• Field of Search: 73/514.01, 73/514.36, 216/2, 216/11, 216/41, 216/63, 216/65, 216/66, 216/67, 216/94, 437/225
• US Class Current: 216/11
• CPC Class Codes: B81B 2201/0235 Accelerometers
• CPC Class Codes: B81B 2203/0118 Cantilevers
• CPC Class Codes: B81C 1/00531 Dry etching
• 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 2201/0143 Focussed beam, i.e. laser, ion or e-beam
• CPC Class Codes: G01P 15/0802 Details
• CPC Class Codes: G01P 15/0922 of the bending or flexing mode type
• CPC Class Codes: G01P 15/123 by piezo-resistive elements, e.g. semiconductor strain gauges
• CPC Class Codes: G01P 2015/0828 the mass being of the paddle type being suspended at one of its longitudinal ends
• CPC Class Codes: G01Q 70/16 Probe manufacture

Abstract

A method of making released structures by using at least two directional etching steps. Cantilevers, bridges and many other structures can be made with the present invention. In a preferred embodiment, two directional etching steps are performed at opposing angles nonnormal to the substrate surface such that the substrate is undercut and a structure is released. Alternatively, more than two directional etching steps may be performed at various angles. For example, the substrate may be rotated continuously during the directional etching process. A cantilever formed by the method of the present invention necessarily has a substantially triangular cross section. Directional etching processes that can be used include focused ion beam etching and ECR plasma etching. Some directional etching processes may require the use of a patterned etch resist layer. Other etching processes such as focused ion beam etching may use scanning techniques to select which regions are etched. A backside etch can be performed to remove remaining substrate material under the released micromachined structure. The method is particularly well suited for making released cantilevers.

Claims

1. A method of making a released micromachined structure, said method comprising the step of:

A) performing a plurality of directional etching steps on first regions of a substrate such that at least one second region adjacent to said first regions is released from said substrate by means of being undercut by said directional etching steps;

wherein at least one of said directional etching steps is performed at an angle nonnormal to the surface of said substrate.

2. The method of claim 1 further comprising the step of forming a patterned etch resist layer on said substrate which exposes said first regions of said substrate.

3. The method of claim 1 wherein said directional etching steps are performed by directional plasma etching.

4. The method of claim 1 wherein said directional etching steps are performed by a technique selected from the group consisting of focused ion beam etching and laser micromachining.

5. The method of claim 1 further comprising the step of a backside etch to remove remaining substrate material under said released micromachined structure.

6. The method of claim 1 wherein said released micromachined structure is selected from the group consisting of cantilevers and bridges.

7. The method of claim 1 wherein said released micromachined structure has a nonuniform width.

11. An accelerometer made according to the method of claim 1 wherein said accelerometer comprises a mass supported on the end of a flexible triangular cantilever.

8. A method of making are leased micromachined structure, said method comprising the step of:

A) performing a directional etching operation on first regions of a substrate such that at least one second region adjacent to said first regions is released from said substrate by means of being undercut by said directional etching operation;

wherein said directional etching operation is performed at an angle nonnormal to the surface of said substrate.

9. The method of claim 8 wherein said substrate is rotated in discrete steps during said directional etching operation.

10. The method of claim 8 wherein said substrate is rotated continuously during said directional etching operation.