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Abstract

A method and apparatus for measuring the width of a small object between a pair of opposed edges thereof e.g. the width of a line on a semiconductor wafer, having a light microscope, a video system for receiving an optical image from the microscope and for displaying the image on a display surface having a reference datum, and an optical system for transmitting the optical image from the light microscope to the video system. In order to measure the width of the line of the wafer, relative adjustment is carried out between the optical system and the object to a first measuring position in which the image is moved across the display surface until a predetermined intensity level of one of the edges of the line is brought to a predetermined position relative to the reference datum. Further relative adjustment is then carried out to a second measuring position in which a further predetermined intensity level of the other edge of the object is brought to a predetermined position relative to the reference datum. The extent of adjustment movement is then measured, so as to provide a value which corresponds with the width of the object to be measured between the opposed edges thereof. The reference datum will be positioned on a detecting surface at a position where substantially distortion-free images can be produced i.e. remote from the edges of the screen, and then the images are moved relative to this datum, so an accurate inspection can be carried out.

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First Claim