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Fabrication of SiO2 Microcantilever Using Isotropic Etching With ICP

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4 Author(s)
Qi Chen ; Louisiana Tech. Univ., Ruston ; Ji Fang ; Ji, Hai-Feng ; Varahramyan, K.

This paper reports a new design and microfabrication process for high sensing guard-armed silicon dioxide (SiO2 ) microcantilever sensor, which can be widely used in chemical, environmental and biomedical applications. One sensor platform consists of two SiO2 cantilever beams as the sensing and reference elements, two connecting wings, and three guard arms. The guard arms prevent damage to the cantilever beam from collision. To efficiently release the SiO2 cantilevers from the silicon substrate, an isotropic etch method using inductively coupled plasma (ICP) was developed. The isotropic etching with ICP system provides an advantage in good profile control and high etching rate than wet isotropic etching or conventional RIE (reactive ion etching); however, it has not been gained many attentions. In this work, the effects of chamber pressure, plasma source power, substrate power, SF6 flow rate relating with Si etching rate, undercutting rate, and isotropic ratio were investigated and discussed. The optimum isotropic etching process achieved a 9.1 mum/min etch rate, 70% isotropic ratio, and 92% etching uniformity. The SiO2 cantilever sensor was fabricated and the cantilever beam was successfully released using a patterned photoresist layer as an etching mask. This plasma isotropic etching release processing can be also applied to release other SiO2 or metal suspended MEMS structures, such as bridges and membranes, with a fast etch rate and reasonable isotropic ratio.

Published in:

Sensors Journal, IEEE  (Volume:7 ,  Issue: 12 )