- Patent Title: Method and apparatus for measuring asymmetry of a microstructure, position measuring method, position measuring apparatus, lithographic apparatus and device manufacturing method
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Application No.: US14421434Application Date: 2013-07-17
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Publication No.: US09778025B2Publication Date: 2017-10-03
- Inventor: Simon Gijsbert Josephus Mathijssen , Erik Willem Bogaart , Patricius Aloysius Jacobus Tinnemans , Arie Jeffrey Den Boef
- 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: Pillsbury Winthrop Shaw Pittman LLP
- International Application: PCT/EP2013/065069 WO 20130717
- International Announcement: WO2014/026819 WO 20140220
- Main IPC: G01B11/00
- IPC: G01B11/00 ; G03B27/32 ; G03B27/54 ; G03B27/74 ; G01B11/14 ; G03F7/20 ; G03F9/00 ; G01B9/02 ; G01B11/27

Abstract:
A lithographic apparatus includes an alignment sensor including a self-referencing interferometer for reading the position of an alignment target comprising a periodic structure. An illumination optical system for focusing radiation into a spot on said structure. An asymmetry detection optical system receives a share of positive and negative orders of radiation diffracted by the periodic structure, and forms first and second images of said spot on first and second detectors respectively, wherein said negative order radiation is used to form the first image and said positive order radiation is used to form the second image. A processor for processing together signals from said first and second detectors representing intensities of said positive and negative orders to produce a measurement of asymmetry in the periodic structure. The asymmetry measurement can be used to improve accuracy of the position read by the alignment sensor.
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