Figures of Merit
If the etch is intended to make a cavity in a material, the depth of the cavity may be controlled approximately using the etching time and the known etch rate. More often, though, etching must entirely remove the top layer of a multilayer structure, without damaging the underlying or masking layers. The etching system's ability to do this depends on the ratio of etch rates in the two materials (selectivity).
Some etches undercut the masking layer and form cavities with sloping sidewalls. The distance of undercutting is called bias. Etchants with large bias are called isotropic, because they erode the substrate equally in all directions. Modern processes greatly prefer anisotropic etches, because they produce sharp, well-controlled features.
| Selectivity | Yellow: layer to be removed; blue: layer to remain
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| Isotropy | Red: masking layer; yellow: layer to be removed
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Read more about this topic: Etching (microfabrication)
Famous quotes containing the words figures of, figures and/or merit:
“But that wasn’t fancy enough for Lord Byron, oh dear me no, he had to invent a lot of figures of speech and then interpolate them,
With the result that whenever you mention Old Testament soldiers to
people they say Oh yes, they’re the ones that a lot of wolves dressed up in gold and purple ate them.”
—Ogden Nash (1902–1971)
“But that wasn’t fancy enough for Lord Byron, oh dear me no, he had to invent a lot of figures of speech and then interpolate them,
With the result that whenever you mention Old Testament soldiers to
people they say Oh yes, they’re the ones that a lot of wolves dressed up in gold and purple ate them.”
—Ogden Nash (1902–1971)
“The silence that accepts merit as the most natural thing in the world is the highest applause.”
—Ralph Waldo Emerson (1803–1882)