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Apparatus and methods for determining overlay of structures having rotational or mirror symmetry

  • US RE45,245 E1
  • Filed: 05/01/2013
  • Issued: 11/18/2014
  • Est. Priority Date: 08/30/2000
  • Status: Expired due to Fees
First Claim
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1. A semiconductor target for determining a relative shift between two or more successive layers of a substrate, the target comprising:

  • a plurality of first structures formed in a first layer, and the first structures having a first center of symmetry (COS), the first structures being aperiodic; and

    a plurality of second structures formed in a second layer, and the second structures having a second COS, the second structures being aperiodic,wherein the difference between the first COS and the second COS corresponds to an overlay error between the first and second layer and wherein the first and second structures have a 180°

    rotational symmetry, without having a 90°

    rotational symmetry, with respect to the first and second COS, respectively.

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