Novel silicon bulk micromachining process for submillimeter rectangular waveguide fabrication

Ma, K.K., Drysdale, T.D., Blaikie, R.J. and Cumming, D.R.S. (2001) Novel silicon bulk micromachining process for submillimeter rectangular waveguide fabrication. Proceedings of the SPIE: The International Society for Optical Engineering, 4407, pp. 372-379. (doi: 10.1117/12.425324)

Abstract

Micromachining of ultra-high frequency waveguide structures requires etching with vertical sidewalls and flat bottoms simultaneously. The required geometries can be difficult to achieve using a single-step orientation dependent etching (ODE) process without incurring a severe mask-undercutting penalty. This may inhibit the production of isolated convex structures, such as the central pillars that are required to couple radiation into the waveguide. In this paper we will described a new technique for ODE of deep, vertical sidewall structures in (100) Si with reduced undercut etching. The process uses a two stage KOH/IPA etch with a mask pattern that is designed to compensate for the differing etch rates on the Si planes. To date we have achieved overall etch depths of 350 microns, with a lateral undercut of as little as 275 microns, compared with a 350 micron undercut for a single-stage etch. The sidewalls are at exactly 90 degrees to the surface of the (100) Si, and the bottoms of the trenches are smooth and flat. Using the process we have also been able to routinely fabricate isolated, square pillars as small as 50 X 50 square microns, and over 300 microns high. The process enables structures to be made that might previously only have been possible with high-density-plasma dry etch techniques. The new technique has clear advantages of low cost and high throughput.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Cumming, Professor David and Drysdale, Dr Timothy
• Authors: Ma, K.K., Drysdale, T.D., Blaikie, R.J., and Cumming, D.R.S.
• College/School: College of Science and Engineering > School of Engineering > Electronics and Nanoscale Engineering
• Journal Name: Proceedings of the SPIE: The International Society for Optical Engineering
• Publisher: SPIE - The International Society for Optical Engineering
• ISSN: 0277-786X
• Published Online: 23 April 2003