Fabrication of SiO$_{2}$ Microcantilever Using Isotropic Etching With ICP

This paper reports a new design and microfabrication process for high sensing guard-armed silicon dioxide (SiO
₂
) microcantilever sensor, which can be widely used in chemical, environmental and biomedical applications. One sensor platform consists of two SiO
₂
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 SiO
₂
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, SF
₆
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 SiO
₂
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 SiO
₂
or metal suspended MEMS structures, such as bridges and membranes, with a fast etch rate and reasonable isotropic ratio.