An Introduction to MEMS
Prime Faraday Technology Watch – January 2002
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3.3.2 Dry Etching
Dry etching relies on vapour phase or plasma-based methods of etching using suitably
reactive gases or vapours usually at high temperatures. The most common form for MEMS is
reactive ion etching (RIE) which utilizes additional energy in the form of radio frequency
(RF) power to drive the chemical reaction. Energetic ions are accelerated towards the
material to be etched within a plasma phase supplying the additional energy needed for the
reaction; as a result the etching can occur at much lower temperatures (typically 150º - 250ºC,
sometimes room temperature) than those usually needed (above 1000ºC). RIE is not limited
by the crystal planes in the silicon, and as a result, deep trenches and pits, or arbitrary shapes
with vertical walls can be etched [4].
Deep Reactive Ion Etching (DRIE) is a much higher-aspect-ratio etching method that involves
an alternating process of high-density plasma etching (as in RIE) and protective polymer
deposition to achieve greater aspect ratios (Figure 20).
Figure 20. Deep Reactive Ion Etching (DRIE) [2,3].
Etch rates depend on time, concentration, temperature and material to be etched. To date
there are no universally accepted master equations to predict etch performance and behaviour.
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