Direct-imaging and plane-projection instruments are mainstays for definitive calibration-quality measurements of small dimensions for industrial and clinical applications. Light-and electron-optical techniques span six orders of sizes, from millimeters through micrometers down to nanometers. A common assumption is that, above the resolution limit of a device, accurate measurements can be made based on the geometric optic relation of image size x_i to object size x_o: x_i = Mx₀, where M is the scalar magnification of the device. However, in measurements of lengths, widths or diameters, the relation fails long before the resolution limit of the device is approached. As a result, substantial systematic errors in dimensional measurements occur in industrial applications from particle sizing to photomask metrology. The causes of such difficulties and the techniques to overcome them are discussed in the context of work at the National Bureau of Standards (NBS) on the development of SEM and optical techniques for accurate measurements in the range 0.1 to 100 μm.

Date Published: 28 May 1980
PDF: 8 pages
Proc. SPIE 0220, Optics in Metrology and Quality Assurance, (28 May 1980); doi: 10.1117/12.958577

Published in SPIE Proceedings Vol. 0220:
Optics in Metrology and Quality Assurance
Harvey L. Kasdan, Editor(s)