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Isotropy is uniformity in all orientations[1]. In microfabrication, it means that the process proceeds at the same rate regardless of direction. For instance, most chemical etches are isotropic: they will etch in all directions equally.

The opposite, anisotropy refers to a situation where the process proceeds more favorably in one direction over another. A highly anisotropic etch process (such as reactive ion etching will proceed highly vertically and have minimal undercut.

Isotropy Etch anisotropy.png Red: masking layer; yellow: layer to be removed
  1. A perfectly isotropic etch produces round sidewalls.
  2. A perfectly anisotropic etch produces vertical sidewalls.