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Line Width Measurements Below the Classic Resolving Power

IP.com Disclosure Number: IPCOM000037137D
Original Publication Date: 1989-Nov-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 2 page(s) / 53K

Publishing Venue

IBM

Related People

Wagner, D: AUTHOR

Abstract

For line width measurements, a conventional optical miscroscope measures the intensity profile by means of characteristic points, yielding measuring characteristics as shown in Fig. 1. The classic Rayleigh limit (wx = 0.61 x g/N.A., where g is the wavelength and N.A. is the numeric aperture) is the limit down to which measurements are expedient (for g = 0.633 mm and for N.A. = 0.6 T wx = 0.6 m). For much smaller line widths, another measuring process has to be found.

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Line Width Measurements Below the Classic Resolving Power

For line width measurements, a conventional optical miscroscope measures the intensity profile by means of characteristic points, yielding measuring characteristics as shown in Fig. 1. The classic Rayleigh limit (wx = 0.61 x g/N.A., where g is the wavelength and N.A. is the numeric aperture) is the limit down to which measurements are expedient (for g = 0.633 mm and for N.A. = 0.6 T wx =
0.6 m). For much smaller line widths, another measuring process has to be found.

Fig. 2 shows the laser scanner signal of amplitude objects, such as Cr lines, having a width ranging from 1.0 to 0.3 mm. The signals were recorded in the confocal mode by a 20x/0.3 objective. Their shape was identical down to a line width of 0.3 mm. This is surprising, since the classic Rayleigh resolving power is limited to 0.61 x g/N.A. = 1 mm. In practice, it has been found however that optical images contain information below the Rayleigh limit of 0.3 mm, which in a suitable form may be used for line width measurement. In contrast to classic measurements, the line width information is not derived from

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the profile width but from the signal amplitude. The signal amplitude and the line width are clearly interrelated only for amplitude objects, such as Cr masks.

For measurements that are independent of the reflection factor of the object, a second, much wider line acting as a reference line is required. This line should be sele...