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Optical Engineering

Accuracy of diffraction-based overlay metrology using a single array target
Author(s): Yi-sha Ku; Hsiu-Lan Pang; Wei-Te Hsu; Deh-Ming Shyu
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Paper Abstract

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

Paper Details

Date Published: 1 December 2009
PDF: 7 pages
Opt. Eng. 48(12) 123601 doi: 10.1117/1.3275449
Published in: Optical Engineering Volume 48, Issue 12
Show Author Affiliations
Yi-sha Ku, Industrial Technology Research Institute (Taiwan)
Hsiu-Lan Pang, Industrial Technology Research Institute (Taiwan)
Wei-Te Hsu, Industrial Technology Research Institute (Taiwan)
Deh-Ming Shyu, Industrial Technology Research Institute (Taiwan)


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