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Proceedings Paper

Measurement of initial absorption of fused silica at 193nm using laser induced deflection technique (LID)
Author(s): Dörte Schönfeld; Ursula Klett; Christian Mühlig; Stephan Thomas
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Paper Abstract

The ongoing development in microlithography towards further miniaturization of structures creates a strong demand for lens material with nearly ideal optical properties. Beside the highly demanding requirements on homogeneity and stress induced birefringence (SIB), low absorption is a key factor. Even a small absorption is associated with a temperature increase and results in thermally induced local variations of refractive index and SIB. This could affect the achievable resolution of the lithographic process. The total absorption of the material is composed of initial absorption and of absorption induced during irradiation. Thus, the optimization of both improves the lifetime of the material. In principal, it is possible to measure transmission and scattering with a suitable spectrometer assembly and calculate absorption from them. However, owing to the influence of sample surfaces and errors of measurement, these methods usually do not provide satisfactory results for highly light-transmissive fused silica. Therefore, it is most desirable to find a technique that is capable of directly measuring absorption coefficients in the range of (1...10)•10-4 cm-1 (base 10) directly. We report our first results for fused silica achieved with the LID technique. Besides a fused silica grade designed for 193 nm applications, grades with higher absorption at 193 nm were measured to test the LID technique. A special focus was set on the possibility of measuring initial absorption without the influence of degradation effects.

Paper Details

Date Published: 20 December 2007
PDF: 8 pages
Proc. SPIE 6720, Laser-Induced Damage in Optical Materials: 2007, 67201A (20 December 2007); doi: 10.1117/12.753081
Show Author Affiliations
Dörte Schönfeld, Heraeus Quarzglas GmbH and Co. KG (Germany)
Ursula Klett, Heraeus Quarzglas GmbH and Co. KG (Germany)
Christian Mühlig, Institut für Photonische Technologien e.V. (Germany)
Stephan Thomas, Heraeus Quarzglas GmbH and Co. KG (Germany)

Published in SPIE Proceedings Vol. 6720:
Laser-Induced Damage in Optical Materials: 2007
Gregory J. Exarhos; Arthur H. Guenther; Keith L. Lewis; Detlev Ristau; M. J. Soileau; Christopher J. Stolz, Editor(s)

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