| 摘要 |
Spectra for diffraction based overlay (DBO) in orthogonal directions, i.e., along the X-axis and Y-axis, are acquired in parallel. A broadband light source produces unpolarized broadband light that is simultaneously incident on X-axis and Y-axis DBO targets. A polarization separator, such as a Wollaston prism or planar birefringent element, receives diffracted light from the X-axis and Y-axis DBO targets and separates the TE and TM polarization states of the diffracted light. A detector simultaneously detects the TE and TM polarization states of the diffracted light for both the X-axis DBO target and the Y-axis DBO target as a function of wavelength.
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