Invention Grant
- Patent Title: Method of measuring a structure, inspection apparatus, lithographic system and device manufacturing method
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Application No.: US15967861Application Date: 2018-05-01
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Publication No.: US10481506B2Publication Date: 2019-11-19
- Inventor: Murat Bozkurt , Maurits Van Der Schaar , Patrick Warnaar , Martin Jacobus Johan Jak , Mohammadreza Hajiahmadi , Grzegorz Grzela , Lukasz Jerzy Macht
- Applicant: ASML Netherlands B.V.
- Applicant Address: NL Veldhoven
- Assignee: ASML Netherlands B.V.
- Current Assignee: ASML Netherlands B.V.
- Current Assignee Address: NL Veldhoven
- Agency: Sterne, Kessler, Goldstein & Fox P.L.L.C.
- Priority: EP17169918 20170508; EP17202806 20171121
- Main IPC: G03F7/20
- IPC: G03F7/20 ; G01N21/47 ; G01N21/956 ; G01N21/95

Abstract:
An overlay metrology target (600, 900, 1000) contains a plurality of overlay gratings (932-935) formed by lithography. First diffraction signals (740(1)) are obtained from the target, and first asymmetry values (As) for the target structures are derived. Second diffraction signals (740(2)) are obtained from the target, and second asymmetry values (As′) are derived. The first and second diffraction signals are obtained using different capture conditions and/or different designs of target structures and/or bias values. The first asymmetry signals and the second asymmetry signals are used to solve equations and obtain a measurement of overlay error. The calculation of overlay error makes no assumption whether asymmetry in a given target structure results from overlay in the first direction, in a second direction or in both directions. With a suitable bias scheme the method allows overlay and other asymmetry-related properties to be measured accurately, even in the presence of two-dimensional overlay structure.
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