Curvature-Modulated Si Spherical Cap-Like Structure Fabricated by Multistep Ring Edge Etching

Area of Science:

• Materials Science
• Microfabrication
• Nanotechnology

Background:

• Fabricating three-dimensional (3D) microstructures with curved surfaces presents significant challenges in microelectromechanical systems (MEMS).
• Existing methods often face limitations due to crystallographic properties or lack precise control over curvature.
• There is a need for advanced techniques to produce complex 3D silicon structures for various microdevice applications.

Purpose of the Study:

• To present a novel wet-etching method for fabricating approximately spherical microstructures with controlled curved sidewalls.
• To demonstrate the precise modulation of spherical curvature using a multistep ring-edge etching process.
• To extend the capabilities of silicon wet etching for creating advanced 3D MEMS structures.

Main Methods:

• A multistep ring-edge etching technology involving concentric mask reduction and mesa shaping was employed.
• Surfactant-added Tetramethylammonium hydroxide (TMAH) wet etching was utilized, overcoming crystallographic constraints.
• Precise control over inclination angles was achieved by adjusting mask design and etching time.

Main Results:

• Successfully fabricated approximately spherical silicon microstructures with defined curved sidewalls.
• Demonstrated the ability to precisely modulate spherical curvature through controlled reduction of concentric masks.
• Validated the wet-etching method's effectiveness in achieving desired inclination angles and etching durations.

Conclusions:

• The developed wet-etching technique offers a versatile approach for fabricating advanced 3D MEMS curved-surface structures.
• The method allows for precise control over spherical curvature, enabling the production of microstructures for applications like microlenses and resonators.
• This research expands the scope of silicon wet etching for creating complex micro- and nanostructures.