Assessing the wavelength extensibility of optical patterned defect inspection
Bryan Barnes, Hui Zhou, Mark-Alexander Henn, Martin Sohn, Richard M. Silver
Qualitative comparisons have been made in the literature between the scattering off deep- subwavelength-sized defects and the scattering off spheres in free space to illustrate the challenges of optical defect inspection with decreasing patterning sizes. The intensity scattered by such a sphere (for diameters sized well below the wavelength) is proportional to its diameter to the sixth power, but also scales inversely to the fourth power of the wavelength. This paper addresses through simulation the potential advantages of applying shorter wavelengths for improved patterned defect inspection. Rigorous finite-difference time- domain 3-D electromagnetic modeling of the scattering from patterned defect layouts has been performed at five wavelengths which span the deep ultraviolet (193 nm), the vacuum ultraviolet (157 nm and 122 nm), and the extreme ultraviolet (47 nm and 13 nm). These patterned structures and defects are based upon publicly disclosed geometrical cross-sectional information from recent manufacturing processes, which then have been scaled down to an 8 nm Si linewidth. Simulations assume that these wavelengths have the same source intensity, noise sources, and optical configuration but do feature wavelength-dependent optical constants, thus yielding a more fundamental comparison of the potential gains from wavelength scaling. To make these results more practical, future work should include simulations with more process stacks and with more materials as well as the incorporation of available source strengths, known microscope configurations, and detector quantum efficiencies. In this study, a 47 nm wavelength yielded enhancements in the signal-to-noise by a factor of five compared to longer wavelengths and in the differential intensities by as much as three orders-of-magnitude compared to 13 nm, the actinic wavelength for EUV semiconductor manufacturing.
Proceedings of the SPIE
February 20-March 23, 2017
San Jose, CA, US
SPIE Advanced Lithography 2017: Metrology, Inspection, and Process Control for Microlithography
, Zhou, H.
, Henn, M.
, Sohn, M.
and Silver, R.
Assessing the wavelength extensibility of optical patterned defect inspection, Proceedings of the SPIE, San Jose, CA, US, [online], https://doi.org/10.1117/12.2262191, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=923116
(Accessed February 20, 2024)