A Comprehensive Review on Convex and Concave Corners in Silicon Bulk Micromachining based on Anisotropic Wet Chemical Etching

Pal, Prem and Sato, K (2015) A Comprehensive Review on Convex and Concave Corners in Silicon Bulk Micromachining based on Anisotropic Wet Chemical Etching. Micro and Nano Systems Letters, 3 (6). pp. 1-42. ISSN 2213-9621 (Submitted)

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Wet anisotropic etching based silicon micromachining is an important technique to fabricate freestanding (e.g. cantilever) and fixed (e.g. cavity) structures on different orientation silicon wafers for various applications in microelectromechanical systems (MEMS). {111} planes are the slowest etch rate plane in all kinds of anisotropic etchants and therefore, a prolonged etching always leads to the appearance of {111} facets at the sidewalls of the fabricated structures. In wet anisotropic etching, undercutting occurs at the extruded corners and the curved edges of the mask patterns on the wafer surface. The rate of undercutting depends upon the type of etchant and the shape of mask edges and corners. Furthermore, the undercutting takes place at the straight edges if they do not contain {111} planes. {100} and {110} silicon wafers are most widely used in MEMS as well as microelectronics fabrication. This paper reviews the fabrication techniques of convex corner on {100} and {110} silicon wafers using anisotropic wet chemical etching. Fabrication methods are classified mainly into two major categories: corner compensation method and two-steps etching technique . In corner compensation method, extra mask pattern is added at the corner. Due to extra geometry, etching is delayed at the convex corner and hence the technique relies on time delayed etching. The shape and size of the compensating design strongly depends on the type of etchant, etching depth and the orientation of wafer surface. In this paper, various kinds of compensating designs published so far are discussed. Two-step etching method is employed for the fabrication of perfect convex corners. Since the perfectly sharp convex corner is formed by the intersection of {111} planes, each step of etching defines one of the facets of convex corners. In this method, two different ways are employed to perform the etching process and therefore can be subdivided into two parts. In one case, lithography step is performed after the first step of etching, while in the second case, all lithography steps are carried out before the etching process, but local oxidation of silicon (LOCOS) process is done after the first step of etching. The pros and cons of all techniques are discussed.

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IITH Creators:
IITH CreatorsORCiD
Item Type: Article
Additional Information: Sincere thanks to Ms. Michiko Shindo (Secretory to Prof. K. Sato) for her assistance in obtaining permissions to reproduce some figures from published papers and Mr. Sajal Sagar Singh for his suggestions.
Uncontrolled Keywords: MEMS, Silicon anisotropic etching, Micromachining, Alkaline solution, TMAH, KOH, Convex and concave corners, Corner compensation,
Subjects: Physics
Divisions: Department of Physics
Depositing User: Library Staff
Date Deposited: 03 Jun 2015 07:07
Last Modified: 10 Nov 2017 05:53
URI: http://raiith.iith.ac.in/id/eprint/1547
Publisher URL: https://doi.org/10.1186/s40486-015-0012-4
OA policy: http://www.sherpa.ac.uk/romeo/issn/2213-9621/
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