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Uniform Metal-Assisted Chemical Etching for Ultra-High-Aspect-Ratio Microstructures on Silicon | IEEE Journals & Magazine | IEEE Xplore

Uniform Metal-Assisted Chemical Etching for Ultra-High-Aspect-Ratio Microstructures on Silicon


Abstract:

Recently, uniform metal-assisted chemical etching (UMaCE) has been demonstrated as an effective wet etch method for fabrication of deep trenches and holes on silicon (Si)...Show More

Abstract:

Recently, uniform metal-assisted chemical etching (UMaCE) has been demonstrated as an effective wet etch method for fabrication of deep trenches and holes on silicon (Si). However, attempts to achieve higher aspect ratio by UMaCE was not successful because etching in random directions was observed. In this paper, the etching uniformity in UMaCE is systematically studied at different etching solution composition and catalyst configuration. The surface chemistry evolution of Si during etching is characterized by X-ray photoelectron spectroscopy, water contact angle, and electrical impedance spectroscopy. Based on the data, the reaction kinetics is analyzed, which shows that an electropolishing-type charge transport and a higher amount of oxide species on Si surface help mitigate the random etching behavior and effectively promote the aspect ratio of the etching with uniformity. Under the rationalized condition, uniform trenches with width of 2 μm and aspect ratio of 120:1 is successfully fabricated by UMaCE.
Published in: Journal of Microelectromechanical Systems ( Volume: 28, Issue: 1, February 2019)
Page(s): 143 - 153
Date of Publication: 05 December 2018

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I. Introduction

High-aspect-ratio (HAR) microstructures on single crystalline silicon (Si), such as deep trenches and holes, are among the core structures of microelectromechanical systems (MEMS) [1]. Dry etch and wet etch are the two major categories of fabrication methods for HAR structures on Si. A higher aspect ratio of these structures is beneficial for the performance of MEMS devices but brings challenges to available fabrication methods. For the dry etch methods, most research and development are based on cryogenic etch or Bosch etch [2]. Due to the difficulty in the mass transport of the ions in plasma, maximum aspect ratio by dry etch have typically been reported as around 30:1, although that of 98:1 [3] and 105:1 [4] has been demonstrated in few cases. Wet etch methods are able to fabricate HAR structures on Si due to the etching selectivity between different crystalline planes of Si. However, traditional wet etch methods, such as KOH etching or anodic etching, are limited to a few types of Si substrates [5] with compromised pattern-transfer fidelity in lateral dimensions [6].

References

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