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Jpn. J. Appl. Phys. 47 (2008) pp. 4898-4905  |Previous Article| |Next Article|  |Table of Contents|
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Evaluating the Optical Index of Ta and Ta-Based Absorbers for an Extreme Ultraviolet Mask Using Extreme Ultraviolet Reflectometry

Morio Hosoya, Noriyuki Sakaya, Osamu Nozawa, Yuki Shiota, Kazuo Hamamoto, Osamu Nagarekawa, Shoji Shimojima, Tsutomu Shoki, Takeo Watanabe1, and Hiroo Kinoshita1

R&D Center, HOYA Corp., 3-3-1 Musashino, Akishima, Tokyo 196-8510, Japan
1Laboratory of Advanced Science and Technology for Industry, University of Hyogo, 3-1-2 Kouto, Kamigori, Ako, Hyogo 678-1205, Japan

(Received December 21, 2007; accepted March 11, 2008; published online June 20, 2008)

We developed an accurate method for determining the optical index of Ta and Ta-based absorber layers with added nitrogen, oxygen, and boron for an extreme ultraviolet (EUV) mask using EUV reflectometry. The optical index at EUV wavelengths was derived from the density and atomic concentration of the composite materials. The atomic concentrations of Ta and Ta-based absorbers were determined using X-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectrometry (RBS) analysis methods when no inconsistency occurred between the results of the XPS and RBS analyses. The volume densities of the Ta and Ta-based absorbers were determined using RBS and EUV reflectivity measurements with the grazing angle (EUVRG) or reflectivity (EUVR) when no inconsistency was observed between results. Deriving the volume density was necessary to establish the layer structure and layer thickness, and the surface oxidation layer was especially important for determining the correct volume density. The layer structure and thickness were derived using a pattern-fitting method for the XRR spectrum. The extinction coefficients of Ta and Ta-based absorbers stacked using conventional sputtering were lower than the extinction coefficient of an ideal Ta crystal.

KEYWORDS: EUV, lithography, absorber, optical index, reflectometer, XRR
URL: http://jjap.ipap.jp/link?JJAP/47/4898/
DOI: 10.1143/JJAP.47.4898


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