Abstract: The current study status of line edge roughness (LER) is analyzed, which indicates LER itself has already been used to refer to many properties including line width uniformity, roughness of line edge and sidewall roughness. And the differ-ent meaning of LER is explained. A new definition of LER is brought forward, I.e, LER is the microcosmic roughness of the sidewall topography, which is caused by processing and the character of materials measured. At the same time, explain the definition relation with it from ITRS and also analysis this defi-nition rationality. According to the process which is mainly on the edge surface and dimension is in nanometer field, a mathe-matics model to calculate LER is shown in atomic dimension. In this model, the roughness from the material intrinsical char-acter is separated.

Key words: Atomic force microscope (AFM), Critical dimension, Intrinsical material roughness, Line edge roughness, Nano-measurement, Scanning electron microscopy (SEM)