Measurement and analysis of EUV photoresist related outgassing and contamination

Abstract

Photoresist outgassing and the related risk for optics contamination in extreme ultraviolet (EUV) exposure tools are concerns in the development of EUV lithography, especially towards the high volume manufacturing tools. The measurement however of how much and what species are outgassing/contaminating, is still very challenging. Various techniques are investigated worldwide, but there is still no consensus on which technique is most adequate. Moreover, since the outgassing/contamination qualification of photoresists needs dedicated tool set-up, it is likely that the testing configuration (with parameters such as exposure intensity, background vacuum quality, pumping speed, ...) can impact the measurement result. In this paper, we are comparing two candidates for outgassing/contamination measurement which are integrated in one experimental set-up : RGA (Residual Gas Analysis) and witness plate testing. RGA is based on in situ mass spectrometer measurements during photoresist EUV exposure and enables chemical identification of species that are outgassing, but has limited information on the probability of mirror contamination. Results are shown on how the measurement results can depend on the testing configuration. Witness plate testing is based on the evaluation of EUV exposed mirror samples that are placed in the vicinity of EUV outgassing photoresist. Results are shown on how the generated contamination can be affected by the tool configuration, and on how to measure/analyze the contamination. Finally, since both techniques are integrated in one test-set-up, measurement results will be compared and correlated, which should help in understanding the phenomena and lead to well defined measurement for photoresist qualification.