AVS 59th Annual International Symposium and Exhibition
    MEMS and NEMS Tuesday Sessions
       Session MN-TuP

Paper MN-TuP4
Low Damage Etching Process for Fabricating Micro Electro Mechanical Systems (MEMS) Devices using Neutral Beam

Tuesday, October 30, 2012, 6:00 pm, Room Central Hall

Session: MEMS and NEMS Poster Session
Presenter: K. Miwa, BEANS Laboratory, Japan
Authors: K. Miwa, BEANS Laboratory, Japan
Y. Nishimori, BEANS Laboratory, Japan
S. Ueki, BEANS Laboratory, Japan
M. Sugiyama, The University of Tokyo, Japan
T. Kubota, Tohoku University, Japan
S. Samukawa, Tohoku University, Japan
Correspondent: Click to Email
We have developed low damage etching process suitable for fabricating micro electromechanical systems (MEMS) devices based on silicon by using neutral beam. For cutting edge three-dimensional (3D) MEMS devices, high aspect ratio structures are indispensable. In addition, the surface of the silicon device is required to be smooth enough to achieve excellent properties as electromechanical or optical devices. However, conventional processes using reactive ion enhanced etching (RIE) of silicon are likely to have rough surfaces called scallops or ripples on sidewalls. Furthermore, conventional plasmas used for etching process cause damages on the etched surfaces by ion and electron fluxes (charges) or vacuum ultraviolet/ultraviolet (VUV/UV) light emission from etching plasmas. In turn, neutral beam etching technology is able to achieve ultra-low damage etching and to obtain atomically flat silicon surfaces. Therefore, by using neutral beam we have developed novel dry process to fabricate silicon MEMS devices of which surface is smooth enough and have damage-less surfaces. The neutral beam was produced from an inductively coupled plasma (ICP) of pure Cl2 gas in an etching tool. The ICP was generated by radio frequency (RF) wave (13.56 MHz) and the RF was time modulated at 10 kHz and the duty ratio was 50% (50μs ON/ 50μs OFF). Ions in the ICP were accelerated toward a carbon aperture and neutralized by colliding onto the aperture which was biased by applying 450 kHz alternating voltage. Two types of apertures are used for the experiment. The apertures have many small holes of its aspect ratio is approximately 10 and 20, respectively. We have found that the etched silicon trench profile by the neutral beam depend on bias voltage and aspect ratio (AR) of the aperture. In addition, mask material can change the trench shape.By optimizing these conditions to produce neutral beam, we have obtained silicon trenches which have perpendicular trench profile of its width is around 200 nm. No defects or damaged layer are seen in transmission electron microscope (TEM) observation of the trench sidewalls. The study was supported by new energy development organization (NEDO). Authors would like to thank to NEDO and project members in BEANS Laboratory.