Critical dimension (CD)
Beginner
The size of the smallest, most important shapes on a layer, such as the width of a gate.
Novice
The width of the key features on a layer, measured after lithography and after etch. Gate length is the classic CD because it sets a transistor’s speed and leakage.
Expert
Controlled through dose and focus in the scanner and through resist and etch bias, and measured on dedicated targets. CD and overlay are the two numbers each critical layer is held to.