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Proceedings Paper

Use of diffractive lenses in lithographic projection lenses
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Paper Abstract

Projection lenses for high resolution lithography have high NA and work at small wavelengths. In the wavelength regime of VUV (e.g. 193nm), there is a very limited number of optical glasses available, namely fused silica and calcium fluoride. The latter is very expensive and used only sparely, leading to limited possibilities for chromatic correction. In addition to catadioptric approaches, another way to deal with chromatic aberrations is the use of diffractive optical elements (DOEs). They have negative dispersion coupled with positive power and they do not contribute to the Petzval sum. Moreover, it is easy to integrate an aspherical functionality into the structure of the DOE. Usually a DOE is placed close to the aperture stop to correct axial color. The stop of a lithographic projection lens often is located at the largest diameter, causing some serious fabrication difficulties for the DOE. For this reason a class of lenses with intermediate image is of interest. Here, the accessible conjugate of the aperture stop enhances the possibilities to arrange the stop and the DOE. This allows a convenient tradeoff between fabrication challenges and aberration correcting properties. We present different lens designs that take advantage of the named properties of DOEs at high numerical aperture.

Paper Details

Date Published: 19 July 2006
PDF: 9 pages
Proc. SPIE 6342, International Optical Design Conference 2006, 63421S (19 July 2006); doi: 10.1117/12.692314
Show Author Affiliations
H.-J. Rostalski, Carl Zeiss SMT AG (Germany)
A. Epple, Carl Zeiss SMT AG (Germany)
H. Feldmann, Carl Zeiss SMT AG (Germany)

Published in SPIE Proceedings Vol. 6342:
International Optical Design Conference 2006
G. Groot Gregory; Joseph M. Howard; R. John Koshel, Editor(s)

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