×

Apparatus for inspecting defects in a periodic pattern

  • US 4,330,775 A
  • Filed: 03/14/1980
  • Issued: 05/18/1982
  • Est. Priority Date: 03/19/1979
  • Status: Expired due to Term
First Claim
Patent Images

1. An apparatus for inspecting defects in a periodic pattern comprising:

  • a light source for producing a coherent light directed to the periodic pattern to be inspected;

    a fourier transformer for Fourier-transforming a light including the information of the periodic pattern and defects; and

    filtering means positioned at the backward focal point of the Fourier transformer and having a light block areas for blocking mainly the periodic pattern information component of the light passed the Fourier transformer and a ring-like light transmission area allowing mainly the defects information component of the light to pass therethrough, the light block area including a first light block area of spot like shape which prevents a transmission of the zeroth order diffraction light transmitted through the Fourier transformer and a second light block area which is disposed around the first area and prevents a transmission of the first and higher order diffraction light transmitted through the Fourier transformer.

View all claims
  • 1 Assignment
Timeline View
Assignment View
    ×
    ×