18 March 2009 High-accuracy EUV reflectometry at large optical components and oblique incidence
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Proceedings Volume 7271, Alternative Lithographic Technologies; 72713Y (2009); doi: 10.1117/12.813697
Event: SPIE Advanced Lithography, 2009, San Jose, California, United States
Abstract
The development of EUV lithography is critically based on the availability of suitable metrology equipment. To meet industry's requirements, the Physikalisch-Technische Bundesanstalt (PTB) operates an EUV reflectometry facility at the electron storage ring BESSY II. It is designed for at-wavelength metrology of full-sized EUVL optics with a maximum weight of 50 kg and a linear dimension of up to 1 m. With the development of EUV lithography tools, the requirements for lower measurement uncertainty are steadily increasing. For small test samples at near normal incidence, a total uncertainty of 0.10 % for peak reflectance is achieved with a reproducibility of 0.05 % and the uncertainty in the center wavelength of 2 pm is mainly given by the uncertainty for the reference wavelength of the Kr 3d5/2-5p resonance. For real optical elements like PO-box mirrors and collectors for EUV pulsed plasma sources it is also essential to measure at the exact location on the mirror because of gradients in the layer thickness and also to measure at the correct local angle of incidence (LAOI) which may deviate significantly from normal. Thus alignment becomes critical for achieving low measurement uncertainties. Here we present PTB's experience in measuring large EUV optical components.
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Christian Laubis, Frank Scholze, Christian Buchholz, Andreas Fischer, Steven Hesse, Annett Kampe, Jana Puls, Christian Stadelhoff, Gerhard Ulm, "High-accuracy EUV reflectometry at large optical components and oblique incidence", Proc. SPIE 7271, Alternative Lithographic Technologies, 72713Y (18 March 2009); doi: 10.1117/12.813697; https://doi.org/10.1117/12.813697
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KEYWORDS
Mirrors

Reflectivity

Sensors

Diodes

Extreme ultraviolet

Reflectometry

Extreme ultraviolet lithography

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