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Optimizing Wavelengths for Optics-based Measurements of Advanced Electronics



Bryan Barnes


The semiconductor industry has just recently met the end of "Moore's Law", the cyclical reduction in transistor cost observed over several decades. New architectures, materials combinations, and limited dimensional scaling are anticipated over the next decade to realize smaller, energy-efficient, high-performance, and secure devices. These changes extend not only to the advanced gate stack but also to the metal interconnects in the back-end-of-line, or BEOL. Two simulation studies using wavelengths from the ultraviolet to the infrared yield the anticipated optical response from two metal line width extremes presented in recent literature. First, simulations of micrometer-scale Cu interconnects agree qualitatively with a published experimental image and support the use of long visible and infrared wavelengths. Second, tailoring the linear polarization axes and incident angles enables comparable or better sensitivities to line width changes using ultraviolet light relative to infrared illumination for nanoscale periodic Ru and Cu lines with air gaps. The optical response of Cu lines buried about 1 micrometer in SiO2 are compared, indicating that optical density is integral to utilizing deep ultraviolet wavelengths for characterizing such interconnects.
Proceedings Title
Modeling Aspects in Optical Metrology VIII
Conference Dates
June 21-25, 2021
Conference Location
Munich, DE
Conference Title
SPIE Optical Metrology: Modeling Aspects in Optical Metrology VIII


Optical scattering, metal interconnects, electromagnetic simulation, scatterfield microscopy, deep ultraviolet, normalized sensitivity


Barnes, B. (2021), Optimizing Wavelengths for Optics-based Measurements of Advanced Electronics, Modeling Aspects in Optical Metrology VIII, Munich, DE, [online],, (Accessed April 20, 2024)
Created September 15, 2021, Updated December 1, 2022