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High Resolution Optical Surface Microtopography

IP.com Disclosure Number: IPCOM000052199D
Original Publication Date: 1981-May-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Wagner, D: AUTHOR

Abstract

The topography of a sample, such as a photolithographic mask, can be determined by a scanning laser beam in an autofocus arrangement, maintaining the laser focus on the sample by appropriate mechanical lens displacement. However, the probing of structures, such as mask openings, in the submicron range at a high depth-to-width ratio is difficult, as the focus Airy disk has dimensions comparable to those of objectives with great numerical apertures. Apart from this, the mechanical movement of the objective is cumbersome.

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High Resolution Optical Surface Microtopography

The topography of a sample, such as a photolithographic mask, can be determined by a scanning laser beam in an autofocus arrangement, maintaining the laser focus on the sample by appropriate mechanical lens displacement. However, the probing of structures, such as mask openings, in the submicron range at a high depth-to-width ratio is difficult, as the focus Airy disk has dimensions comparable to those of objectives with great numerical apertures. Apart from this, the mechanical movement of the objective is cumbersome.

To improve the resolution by reducing the diameter of the Airy disk, it is proposed to use a hollow cone of light for illuminating the sample surface; for this purpose, a central stop 8 is placed in the imaging system. For illumination, laser beam 14 is expanded by lenses 12, 13, transformed into a cylinder-like beam by a central blocking disk in beam splitter 8, and reflected by polarizing beam splitter 4 to a lambda/4 plate 5, a lens 6 and a mirror 7 oscillating about the focal plane of lens 6. The reflected beam, whose plane of polarization is rotated by 90 degrees as it passes lambda/4 plate 5 a second time, passes polarizing beam splitter 4 and lens 2 before reaching sample surface 1 arranged in the focal plane of lens 2. After having been reflected a second time at oscillating mirror 7, the light emerging from sample surface 1 reaches polarizing beam splitter 4 with the proper direction of polarization to be...