Etching (microfabrication) - Figures of Merit

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
  1. A poorly selective etch removes the top layer, but also attacks the underlying material.
  2. A highly selective etch leaves the underlying material unharmed.
Isotropy Red: masking layer; yellow: layer to be removed
  1. A perfectly isotropic etch produces round sidewalls.
  2. A perfectly anisotropic etch produces vertical sidewalls.

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)

    “The figures of the past go cloaked.
    They walk in mist and rain and snow
    And go, go slowly, but they go.”
    —Wallace Stevens (1879–1955)

    “Give nobly to indigent merit, and do not refuse your charity even to those who have not merit but their misery.”
    —Philip Dormer Stanhope, 4th Earl Chesterfield (1694–1773)