Resist roughness evaluation and frequency analysis: metrological challenges and potential solutions for extreme ultraviolet lithography

摘要

Roughness of lithographic patterns is typically expressed asnthe absolute 3σ variation of resist lines by means of edge variation. How-never, full characterization of the roughness requires both its amplitude andnfrequency distribution. This necessity arises from the requirement to re-nduce different roughness frequencies for different lithographic levels. ThenInternational Technology Roadmap of Semiconductors (ITRS) has estab-nlished a dedicated specification for low frequency roughness. To obtain fullnknowledge of the roughness behavior in the frequency domain, a powernspectral density analysis technique is used. It is found that power spectralndensity has a unique profile for each process. Moreover, the major con-ntribution to the roughness came from the low frequencies range. Besidesnthis, an on-line metrological study on scanning electron microscopy re-nsist roughness repeatability is executed to optimize the capturing imagenparameters and estimate eventual short- (daily) and long-term (yearly)ncontributions. In the end, 0.2-nm 3σ line width roughness stability valuenis found. To verify the validity of analysis and metrology, 32-nm extremenultraviolet lithography exposures at different flare levels, 45-nm ArF im-nmersion lithography through dose, and a rinse postlithography smoothingnprocess are characterized with the aim to highlight the importance of lownfrequency roughness detection