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Optical Measuring Method

IP.com Disclosure Number: IPCOM000089994D
Original Publication Date: 1969-Jan-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 3 page(s) / 46K

Publishing Venue

IBM

Related People

Kosanke, K: AUTHOR [+3]

Abstract

This method of optically measuring distances is well suited to measuring the spaces between individual elements on a mask or semiconductor wafer. For each measuring process the accurate determination of the reference points, the distance of which is to be measured, is of the greatest importance to the accuracy of the result. The determination of such reference points is particularly intricate in the case of accurate measurements on objects having irregular and no accurately defined border surfaces or border lines. These difficulties are particularly pronounced when measuring, under a microscope, carrier-mounted objects.

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Optical Measuring Method

This method of optically measuring distances is well suited to measuring the spaces between individual elements on a mask or semiconductor wafer. For each measuring process the accurate determination of the reference points, the distance of which is to be measured, is of the greatest importance to the accuracy of the result. The determination of such reference points is particularly intricate in the case of accurate measurements on objects having irregular and no accurately defined border surfaces or border lines. These difficulties are particularly pronounced when measuring, under a microscope, carrier-mounted objects.

Drawing 1 shows circle 1 with a partially blurred circumference and a point-shaped area 2 in order to illustrate the difficulties occurring when accurately measuring the distance between two objects. The distance between circle 1 and area 2 cannot be accurately determined, since the part of the circle 1 facing area 2 does not include an obvious reference point. This difficulty is avoided to some degree by the reference point on the circumference of circle 1 being defined not only on the basis of the information contained in the immediate proximity of this point but also by virtue of the information represented by circle 1 as a whole. This problem can be solved, for example, by methods relating to holographic transformation, in which the total structure, i.e., information, of an object contributes to the generation of each point recorded.

In this method for measuring the distances between two or several objects on a mask or a semiconductor wafer, a holographic filter is produced through the interference of the beams modulated through a diaphragm comprising, for example, two adjacent holes and through a standard sample, i.e., a standard mask. When this filter is transferred to a measuring plane by a beam modulated by the sample to be measured, the holes of the diaphragm are imaged onto this measuring plane. There standard sample, i.e., a standard mask. When this filter is transferred...