Micromechanical structure and a method of fabricating a micromechanical structure

• US 8,278,725 B2
• Filed: 11/09/2007
• Issued: 10/02/2012
• Est. Priority Date: 11/10/2006
• Status: Active Grant

• Current Assignee: Agency For Science Technology and Research
• Original Assignee: Agency For Science Technology and Research
• Inventors: Tripathy, Sudhiranjan, Sahmuganathan, Vicknesh s/o
• Primary Examiner(s): Mandala, Victor A
• Assistant Examiner(s): Ahmed, Selim
• Application Number:
  US12/514,304
• Publication Number:
  US 20100193781A1
• Time in Patent Office: 1,789 Days
• Field of Search: 257/47, 257/76, 257/77, 257/E29.094, 257/E29.082, 257/E29.089, 257/E21.09, 257/414, 257/E29.324, 438/479, 438/50, 438/52, 977/720, 977/723
• US Class Current: 257/414
• CPC Class Codes: B81C 1/00484 Processes for releasing structures not provided for in group B81C1/00476
• CPC Class Codes: B81C 2201/0109 Sacrificial layers not provided for in B81C2201/0107 - B81C2201/0108
• 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 2201/017 Methods for controlling internal stress of deposited layers not provided for in B81C2201/0164 - B81C2201/0169

Abstract

A micromechanical structure and a method of fabricating a micromechanical structure are provided. The micromechanical structure comprises a silicon (Si) based substrate; a micromechanical element formed directly on the substrate; and an undercut formed underneath a released portion of the micromechanical element; wherein the undercut is in the form of a recess formed in the Si based substrate.

Claims

1. A micromechanical structure comprising:

a silicon-on-insulator (SOI) substrate;

a micromechanical element comprising wide bandgap material formed directly on the substrate; and

an undercut formed underneath a released portion of the micromechanical element;

the undercut being in the form of a recess formed in an inherent Si overlayer of the SOI substrate;

wherein a thickness of the Si overlayer of the SOI substrate is chosen for controlling growth-induced stress in the micromechanical element, for in turn controlling a stress in the released portion of the micromechanical element; and

wherein the wide band gap material comprises one or more materials selected from a group consisting of ZnO, Zn(Mg)O, Zn(Cd)O, ZnS, GaN, AIN, AlGaN, InGaN, InN, polycrystalline diamond and nanocrystalline diamond.

2. The structure as claimed in claim 1, wherein the recess extends through substantially the thickness of the Si overlayer of the SOI substrate.

3. The structure as claimed in claim 1, wherein the thickness is in a range of about 10 nm to about 4 μ

m.

4. The structure as claimed in claim 1, wherein a crystalline orientation of the SOI substrate is chosen for controlling the growth-induced stress in the micromechanical element, for in turn controlling the stress in the released portion of the micromechanical element.

5. The structure as claimed in claim 4, wherein the crystalline orientation is (111).

6. The structure as claimed in claim 1, wherein the micromechanical element comprises a light emitting diode (LED) structure, and the undercut in the form of a recess formed in the Si overlayer of the SOI substrate is formed using a XeF₂ dry etch process.

7. The structure as claimed in claim 1, wherein the micromechanical element comprises one or more Field-effect transistor (FET) structures, and the undercut in the form of a recess formed in the Si overlayer of the SOI substrate is formed using a XeF₂ dry etch process.

8. A method of fabricating a micromechanical structure, the method comprising the steps of:

providing a silicon-on-insulator (SOI) substrate;

forming a micromechanical element comprising wide bandgap material directly on the substrate;

forming an undercut in the form of a recess underneath a released portion of the micromechanical element;

the recess being formed in an inherent Si overlayer of the SOI substrate;

wherein a thickness of the Si overlayer of the SOI substrate is chosen for controlling growth-induced stress in the micromechanical element, for in turn controlling a stress in the released portion of the micromechanical element; and

wherein the wide band gap material comprises one or more materials selected from a group consisting of ZnO, Zn(Mg)O, Zn(Cd)O, ZnS, GaN, AIN, AlGaN, InGaN, InN, polycrystalline diamond and nanocrystalline diamond.

9. The method as claimed in claim 8, wherein the recess extends through substantially the thickness of the Si overlayer of the SOI substrate.

10. The method as claimed in claim 8, wherein the thickness is in a range of about 10 nm to about 4 μ

m.

11. The method as claimed in claim 8, further comprising choosing a crystalline orientation of the SOI substrate for controlling the growth-induced stress in the micromechanical element, for in turn controlling the stress in the released portion of the micromechanical element.

12. The method as claimed in claim 11, wherein the crystalline orientation is (111).

13. The method as claimed in claim 8, wherein the micromechanical element is formed directly on the substrate using metalorganic chemical vapour deposition (MOCVD).

14. The method as claimed in claim 8, wherein the micromechanical element comprises a light emitting diode (LED) structure, and the undercut in the form of a recess formed in the Si overlayer of the SOI substrate is formed using a XeF₂ dry etch process.

15. The method as claimed in claim 8, wherein the micromechanical element comprises one or more Field-effect transistor (FET) structures, and the undercut in the form of a recess formed in the Si overlayer of the SOI substrate is formed using a XeF₂ dry etch process.