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Kinoform Filters for Defect Inspection

IP.com Disclosure Number: IPCOM000074071D
Original Publication Date: 1971-Mar-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Hirsch, PM: AUTHOR [+3]

Abstract

The problem of doing rapid and accurate correlation measurements for defect identification in chips, substrates, read heads, and other small components is complicated by the complexity of the scene being examined. A typical defect in a substrate will be a thin bridge of solder shorting out a circuit. Such a bridge will represent less than 1% of the information content of the total substrate. Thus a matched filter giving a correlation measurement accurate within +/- 1% will probably not give a definitive indication of the defect.

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Kinoform Filters for Defect Inspection

The problem of doing rapid and accurate correlation measurements for defect identification in chips, substrates, read heads, and other small components is complicated by the complexity of the scene being examined. A typical defect in a substrate will be a thin bridge of solder shorting out a circuit. Such a bridge will represent less than 1% of the information content of the total substrate. Thus a matched filter giving a correlation measurement accurate within +/- 1% will probably not give a definitive indication of the defect.

A second problem involved when kinoform or other computermade filters are used is the complexity of the scene which must be encoded in the impulse response of the filter. For the example of the substrate given above, it is not unreasonable to require 10/6/ resolution elements to be encoded. Such an encoding requires considerable computer time and hence cost.

These problems can be alleviated by placing a high-pass kinoform filter apparatus between the scene and the kinoform matched filter.

As shown, the object to be inspected is assumed to be a substrate; e.g., for SLT modules. The object is illuminated with monochromatic, but incoherent, light. A high-pass kinoform filter apparatus observes the substrate. This apparatus consists of a beam splitter, kinoforms in which the positive and the negative parts of the high-pass impulse response are encoded, two vidicons, and a video subtraction unit. The outp...