Roughness of lithographic patterns is typically expressed as the absolute 3σ variation of resist lines by means of edge variation. However, full characterization of the roughness requires both its amplitude and frequency distribution. This necessity arises from the requirement to reduce different roughness frequencies for different lithographic levels. The International Technology Roadmap of Semiconductors (ITRS) has established a dedicated specification for low frequency roughness. To obtain full knowledge of the roughness behavior in the frequency domain, a power spectral density analysis technique is used. It is found that power spectral density has a unique profile for each process. Moreover, the major contribution to the roughness came from the low frequencies range. Besides this, an on-line metrological study on scanning electron microscopy resist roughness repeatability is executed to optimize the capturing image parameters and estimate eventual short- (daily) and long-term (yearly) contributions. In the end, 0.2-nm 3σ line width roughness stability value is found. To verify the validity of analysis and metrology, 32-nm extreme ultraviolet lithography exposures at different flare levels, 45-nm ArF immersion lithography through dose, and a rinse postlithography smoothing process are characterized with the aim to highlight the importance of low frequency roughness detection.