An Introduction to mems (Micro-electromechanical Systems)

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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 

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.