Wet etching is a material removal process that uses liquid chemicals or etchants to remove
materials from a wafer. The specific patters are defined by masks on the wafer. Materials that are
not protected by the masks are etched away by liquid chemicals. These masks are deposited and
patterned on the wafers in a prior fabrication step using lithography.
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A wet etching process involves multiple chemical reactions that consume the original reactants
and produce new reactants. The wet etch process can be described by three basic steps. (1)
Diffusion of the liquid etchant to the structure that is to be removed. (2) The reaction between the
liquid etchant and the material being etched away. A reduction-oxidation (redox) reaction
usually occurs. This reaction entails the oxidation of the material then dissolving the oxidized
material. (3) Diffusion of the byproducts in the reaction from the reacted surface