Micromechanical system fabrication method using (111) single crystalline silicon

• US 6,689,694 B1
• Filed: 11/17/2000
• Issued: 02/10/2004
• Est. Priority Date: 04/01/1998
• Status: Expired due to Term

• Current Assignee: Micromecha, Inc.
• Original Assignee: Dong-Ii Cho
• Inventors: Cho, Dong-Il, Park, Sangjun, Lee, Sangwoo
• Primary Examiner(s): Norton, Nadine G.
• Assistant Examiner(s): Anderson, Matthew A
• Application Number:
  US09/715,446
• Time in Patent Office: 1,180 Days
• Field of Search: 438/696, 438/694, 438/704, 438/705, 438/706, 438/748, 438/700, 438/701, 438/712, 438/739, 438/753, 216/2, 216/87
• US Class Current: 438/696
• CPC Class Codes: B81B 2203/0109 Bridges
• CPC Class Codes: B81B 2203/0118 Cantilevers
• CPC Class Codes: B81C 1/00801 Avoid alteration of functional structures by etching, e.g. using a passivation layer or an etch stop layer B81C1/00595, B81C1/00468 take precedence
• 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 2201/0133 Wet etching
• CPC Class Codes: B81C 2201/014 by depositing an etch stop layer, e.g. silicon nitride, silicon oxide, metal
• CPC Class Codes: C30B 29/06 Silicon
• CPC Class Codes: C30B 33/00 After-treatment of single crystals or homogeneous polycrystalline material with defined structure C30B31/00 takes precedence

Abstract

Disclosed is a micromechanical system fabrication method using (111) single crystalline silicon as a silicon substrate and employing a reactive ion etching process in order to pattern a microstructure that will be separated from the silicon substrate and a selective release-etching process utilizing an aqueous alkaline solution in order to separate the microstructure from the silicon substrate. According to the micromechanical system fabrication method of the present invention, the side surfaces of microstructures can be formed to be vertical by employing the RIE technique. Furthermore, the microstructures can be readily separated from the silicon substrate by employing the selective release-etching technique using slow etching {111} planes as the etch stop in an aqueous alkaline solution. In addition, etched depths can be adjusted during the RIE step, thereby adjusting the thickness of the microstructure and the spacing between the microstructure and the silicon substrate.

Claims

1. A method of forming a micromechanical system, the method comprising:

providing a (111) silicon substrate;

etching into the (111) silicon substrate to a depth to define a thickness of a silicon microstructure, wherein the etching forms walls;

covering at least a portion of the walls with an etch stop layer;

further etching through the etch stop layer and into the (111) silicon substrate using at least a portion of the etch stop layer to define a lateral extent of the further etching into the (111) silicon substrate; and

selective etching along at least one {100} plane or at least one {110} plane to separate the silicon microstructure from the (111) silicon substrate, the selective etching guided by one or more {111} planes, the selective etching proceeding between the silicon microstructure and the substrate to release the silicon microstructure.

2. The method of claim 1, wherein the selective etching terminates in part on a [{overscore (1)}11] or [1{overscore (11)}] face of the silicon substrate.

3. The method of claim 1, wherein the selective etching terminates in part on a [{overscore (1)}11] face of the silicon substrate.

4. The method of claim 1, wherein the selective etching terminates in part on a [1{overscore (11)}] face of the silicon substrate.

5. The method of claim 1, wherein a lower, released surface of the silicon microstructure is substantially parallel to a surface of the silicon substrate.

6. The method of claim 1, wherein the lower, released surface of the silicon microstructure is a [{overscore (111)}] face.

7. The method of claim 6, wherein the silicon microstructure is one beam of a comb drive structure.

8. The method of claim 1, wherein the selective etching includes an etch in an alkaline solution.

9. The method of claim 1, wherein the etch stop layer protects at least a portion of the silicon microstructure during the selective etching.

10. The method of claim 1, wherein the covering comprises overlaying a first layer over surfaces of the (111) silicon substrate exposed in the etching and overlaying a second layer over the first layer, and

wherein the further etching includes removing portions of the first and second layers to expose the (111) silicon substrate, wherein the further etching is performed through the opening created by the removing.

11. The method of claim 10, wherein the etching is part of a photolithography process and is a reactive ion etching process.

12. The method of claim 10, wherein the etch stop layer protects at least a portion of the silicon microstructure during the selective etching and the walls define opposing edges of the silicon microstructure.

13. The method of claim 10, wherein the first layer is silicon nitride and the second layer is silicon oxide.

14. The method of claim 13, wherein the removing includes a reactive ion etching process.

15. A method of forming a micromechanical system, the method comprising:

providing a (111) silicon substrate;

etching into the (111) silicon substrate to a depth to define a portion of a silicon microstructure, wherein the etching forms walls;

covering at least a portion of the walls with an etch stop layer;

anisotropic etching through the etch stop layer into the (111) silicon substrate using at least a portion of the etch stop layer to define a size of at least one opening in the etch stop layer created by the anisotropic etching; and

selective etching to separate a silicon microstructure from the (111) silicon substrate, the selective etching being guided by one or more etch-resistant {111} planes, the selective etching proceeding between the silicon microstructure and the (111) silicon substrate to release the silicon microstructure, the etch stop layer limiting the selective etching of at least a portion of the silicon microstructure during the selective etching.

16. The method of claim 15, wherein the selective etching includes an etch in an alkaline solution.

17. The method of claim 15, wherein the selective etching includes an etch in an alkaline solution.

18. The method of claim 15, wherein the walls define one or more edges of the silicon microstructure.

19. The method of claim 15, wherein the covering comprises overlaying a first layer over surfaces of the (111) silicon substrate exposed in the etching and overlaying a second layer over the first layer;

and

wherein the anisotropic etching includes removing portions of the first and second layers to expose the (111) silicon substrate, wherein the anisotropic etching is performed through the opening created by the removing.

20. The method of claim 19, wherein the first layer is silicon nitride and the second layer is silicon oxide.

21. The method of claim 15, wherein the etch stop layer protects at least a portion of the silicon microstructure during the selective etching.

22. The method of claim 21, wherein the removing includes a reactive ion etching process.

23. The method of claim 15, wherein the walls define opposing edges of the silicon microstructure.