MEMS 3D fabrication

Three-dimensional silicon fabrication is demanded in optical lenses for collecting infrared radiation. We propose a method for the fabrication of shapes, which have depths varying in the x and y directions, vertical walls and smooth surfaces. A mask design with rectangular apertures was used in a two-stage etching process consisting of anisotropic etching to rough out the three-dimensional shape followed by isotropic etching to smooth the surface. The relationship between the etching depth and area and the aspect ratio (length-to-height ratio) of the rectangular apertures was determined experimentally. Based on this relationship, we describe a procedure for designing rectangular apertures. We fabricated a convex microlens with a diameter of 150 µm and a height of 4.3 µm surrounded by a vertical wall. The arithmetic mean surface roughness of the microlens was 100 nm.

Publications

1. Yusuke Takei, Takahiro Ohori, Tomoyuki Takahata, Tetsuo Kan, Eiji Iwase, Kiyoshi Matsumoto, and Isao Shimoyama, “Fabrication of Three Dimensional Silicon Slopes using Mask with Square Openings,” IEEJ Transactions on Sensors and Micromachines, vol. 130, no. 5, pp.182-187, 2010. [Paper (in Japanese)]
2. Tomoyuki Takahata, Eiji Iwase, Kiyoshi Matsumoto, Isao Shimoyama, “Three-Dimensional Silicon Fabrication using Microloading Effects with Rectangular Aperture Mask,” Journal of Micromechanics and Microengineering, vol. 20, no. 7, article no. 0750022, 2010. [Paper] (Highlights of 2010, IOP select)