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1 December 2009 Accuracy of diffraction-based overlay metrology using a single array target
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We focus on the capability and theoretical limits of a model-based scatterometry method to determine overlay using a single two-dimensional array target. We use our modeling capability to design an optimized test target for scatterometer-based overlay measurements in a range of semiconductor films. We propose a methodology to measure the overlay using a single two-dimensional array target designed with intentional offsets, Δx and Δy, between the top and bottom grid arrays along the X and Y directions. This method allows extraction of the two-dimensional overlays from first diffraction order measurements through bi-azimuth angle analysis (0 and 90 deg with respect to the incidence plane), and includes a simple linear response algorithm. Two critical issues are taken into account: correlation of Δx and Δy and lithography process errors. We have simulated the diffraction signatures of a two-dimensional target with a pitch of 400 nm and linewidth of 100 nm, and optimized the overlay target design to maximize the measurement sensitivity and minimize the correlation of two axial measurements. We also investigate the influence of parameter variations on overlay measurement error
©(2009) Society of Photo-Optical Instrumentation Engineers (SPIE)
Yi-sha Ku, Hsiu-Lan Pang, Wei-Te Hsu, and Deh-Ming Shyu "Accuracy of diffraction-based overlay metrology using a single array target," Optical Engineering 48(12), 123601 (1 December 2009).
Published: 1 December 2009

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