Method and apparatus for using an alignment target with designed in offset

  • US 6,982,793 B1
  • Filed: 04/04/2002
  • Issued: 01/03/2006
  • Est. Priority Date: 04/04/2002
  • Status: Active Grant
First Claim
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1. A method of determining the alignment of a first element with respect to a second element, said method comprising:

  • providing an alignment target on said first element and said second element, the alignment target having a first overlay pattern, a second overlay pattern, and a third overlay pattern, each overlay pattern including a periodic pattern on said first element and a periodic pattern on said second element, said first overlay pattern having a first designed in offset between the periodic pattern on said first and second elements, said first designed in offset having a first magnitude, said third overlay pattern having a third designed in offset between the periodic pattern of said first and second elements, said third designed in offset having a magnitude that is different than said first magnitude;

    illuminating said first overlay pattern, said second overlay pattern, and said third overlay pattern on said alignment target with incident radiation that reacts with said alignment target;

    detecting the radiation that is diffracted from said first overlay pattern, said second overlay pattern, and said third overlay pattern; and

    calculating the difference between the diffracted radiation from said first overlay pattern and the diffracted radiation from said second overlay pattern to produce a first measured difference;

    calculating the difference between the diffracted radiation from said first overlay pattern and the diffracted radiation from said third overlay pattern to produce a second measured difference, and determining the approximate alignment error based on said first measured difference and said second measured difference.

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