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Optical metrology tool having improved contrast

  • US 20030133102A1
  • Filed: 05/28/2002
  • Published: 07/17/2003
  • Est. Priority Date: 01/16/2002
  • Status: Active Grant
First Claim
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1. A method for evaluating a sample with a optical wafer metrology tool employing an incoherent light source, illumination optics that collect a portion of the light from the source and illuminate the sample at a small-spot, the illumination interacting with and reflecting from the sample, collection optics that collect at least a fraction of the reflected illumination, a detection system generating output signals in response to the collected illumination and a processor for recording and analyzing the output signals, said method comprising:

  • limiting the angular range of the illumination striking the sample to an illumination numerical aperture, NAI;

    limiting the angular variation of the fraction of the reflected radiation collected by the collection optics to a collection numerical aperture, NAC;

    constraining the above described angular limitations to configurations where NAC>

    NAI, whereby the relative numerical aperture NAR

    NAI/NAC assumes a value less than 1.

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