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Metrology method and inspection apparatus, lithographic system and device manufacturing method

  • US 9,946,167 B2
  • Filed: 08/12/2015
  • Issued: 04/17/2018
  • Est. Priority Date: 11/12/2010
  • Status: Active Grant
First Claim
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1. A method comprising:

  • using a lithographic process to form a periodic structure on a substrate;

    a first measurement comprising detecting a first image of the periodic structure, while illuminating the structure with a first beam of radiation, the first image being formed using a first selected part of diffracted radiation;

    a second measurement comprising detecting a second image of the periodic structure, while illuminating the structure with a second beam of radiation, the second image being formed using a second selected part of the diffracted radiation which is symmetrically opposite to the first part, in a diffraction spectrum of the periodic structure;

    using a difference in intensity values derived from the detected first and second images together to determine a property of the periodic structure; and

    controlling a spatial light modulator to apply a varying non-binary optical attenuation over the first and second selected parts of the diffracted radiation prior to detecting the first and second images respectively.

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