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Enabling Quantitative Optical Imaging for In-die-capable Critical Dimension Targets



Bryan M. Barnes, Mark Alexander Henn, Martin Y. Sohn, Hui Zhou, Richard M. Silver


Dimensional scaling trends will eventually bring the semiconductor critical dimensions (CDs) down to only a few atoms in width. New optical techniques are required to address intra-die variability for these CDs using sufficiently small in-die metrology targets. Recently, Qin et al. [Light Sci Appl, 5, e16038 (2016)] demonstrated quantitative model-based measurements of finite sets of lines with features as small as 16 nm using 450 nm wavelength light. This paper uses simulation studies, augmented with experiments at 193 nm wavelength, to further minimize the patterned area of the 2 um x 6 um targets from that work with minimal increases in parametric uncertainty. A finite element method based solver for time-harmonic Maxwell’s equations yields three-dimensional simulations of the electromagnetic scattering as functions of reduced line lengths, fewer number of lines, fewer focal positions, smaller critical dimensions, and shorter illumination wavelength. Optimal metrology targets are shown to be as short as 4 wavelengths, feature as few as eight lines, and appear extensible to sub-10 nm CDs. Target areas, even when including buffers to minimize scattering effects with neighboring devices, can be as seven times smaller in area than anticipated scatterometry targets found in the literature. This new methodology is demonstrated to be a promising alternative for optical model-based in-die CD metrology.
Proceedings Title
Proceedings of the SPIE
Conference Dates
February 22-25, 2016
Conference Location
San Jose, CA
Conference Title
Metrology, Inspection, and Process Control for Microlithography XXX


optical metrology, electromagnetic simulation, normalized sensitivities, parametric uncertainties, phase sensitive measurements, through-focus three-dimensional field


Barnes, B. , , M. , Sohn, M. , Zhou, H. and Silver, R. (2016), Enabling Quantitative Optical Imaging for In-die-capable Critical Dimension Targets, Proceedings of the SPIE, San Jose, CA, [online], (Accessed April 16, 2024)
Created April 4, 2016, Updated June 2, 2021