Browse Prior Art Database

Detection of Defects in Chips or Wafers by Use of Incoherent Imaging System

IP.com Disclosure Number: IPCOM000074270D
Original Publication Date: 1971-Apr-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 2 page(s) / 42K

Publishing Venue

IBM

Related People

Kobayashi, H: AUTHOR [+2]

Abstract

This is a method for detecting small defects in periodic patterns.

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Detection of Defects in Chips or Wafers by Use of Incoherent Imaging System

This is a method for detecting small defects in periodic patterns.

In Fig. A there is shown an object P1 which is illuminated by incoherent light source 5. The object P1 is a periodic pattern such as a mask or circuit chip. If the pattern is a circuit chip, the reflected light is then used as the input to an optical processor.

At the plane P2, a spatial filter H(f(x),f(y)) is set which has a high transmittance in the vicinity of the frequencies f(x) = m/2//delta x and f(y) = n/delta y, where m, n = 0, +/- 1, +/- 2, ... and where delta x and delta y are periods of x and y direction, respectively, in the object pattern. The output image 1 at Plane P3 obtained through lenses L1 and L2 gives an almost defect-free pattern. The image 1 is subtracted from the image 2 which is obtained unfiltered via lenses L1' and L2'.

The subtraction of incoherent images is performed by a grid coding process as shown in Fig. B. The two images 1 and 2 are present at a Ronchi ruling coding plate of sufficient spatial frequency to resolve specified errors. Mirrors 10, 11, 12 and 13 are arranged so as to add or superimpose the two input images 1 and 2 onto the front surface of vidicon tube 14. The optical axes of the two paths are separated by 1/2 period of the ruling to satisfy the grid coding condition. Image differences are highlighted by the appearance of the code plate locally on the composite image and areas...