Critical Dimension

In the renormalization group analysis of phase transitions in physics, a critical dimension is the dimensionality of space at which the character of the phase transition changes. Below the lower critical dimension there is no phase transition. Above the upper critical dimension the critical exponents of the theory become the same as that in mean field theory.
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the width of a line or space that has been identified as critical to the device being fabricated operating properly. Critical dimensions are frequently measured on some or all wafers following any photolithography or etching process in which the dimensions are critical.