Characterization of line edge roughness in resist patterns by using Fourier analysis and auto-correlation function

We have evaluated periodicity of line edge roughness (LER) in electron beam (EB), KrF, and ArF resists. A set of 512 edge-point coordinates was obtained for a scanning electron microscope (SEM) image of one edge by using an in-house image-processing program. The edge-point fluctuations were given and analyzed by Fourier transform and auto-correlation function. Fourier analysis has shown that (1) the spatial frequency (f) distribution of LER can be described with the 1/f-rule and (2) an additional component appears at around 100 nm in the results from several kinds of ArF resists. The auto-correlation-function method gives histograms of the basic period of LER. The results from this method are consistent with those from Fourier analysis and show that several ArF resist samples have a specific period distribution at around 240 nm. Results from both of these methods show that not only the resist materials but also the lithographic tools and processes affect the period distribution.