30 June 2012 Direct phase-shift measurement of thin and thick absorber EUV masks
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Proceedings Volume 8441, Photomask and Next-Generation Lithography Mask Technology XIX; 84411M (2012); doi: 10.1117/12.976817
Event: Photomask and NGL Mask Technology XIX, 2012, Yokohama, Japan
Abstract
The measurement and extraction method of phase-shift values for thin and thick absorber Extreme Ultra-Violet (EUV) masks has been studied by both of experiments and simulations. We fabricated 4 EUV masks with different absorber thicknesses. We first estimated the phase-shift values from the absorber thicknesses of each mask and the nandk values which were derived in advance by other experiments. This method is indirect and may contain plate-by-plate errors. In order to extract the phase-shift values directly, we developed a phase-shift measurement method based on scatterometry. We measured the reflectivity of the open and dark area of the 4 masks by using the EUV reflectometer at Lawrence Berkeley National Laboratory (LBNL). We also measured the diffracted light intensities of grating pattern. The phaseshift values were derived from these data assuming an interference of reflected and diffracted lights. We calibrated the method by including the shadowing effect of 6 degree incident angle, and adding the information on the measured mask patterns. The extraction results of phase-shift values by this method agreed well within the error bar. The absorber thickness having 180 degree phase-shift, which works as an embedded attenuated phase-shifting mask, could be somewhere between 66 nm and 76 nm. The measurement accuracy of this method depends on the phase-shift values. The error becomes the largest at 180 degree phase-shift, and the worst one in this experiment was much larger than the proposed phase-shift measurement accuracy of ± 2 degree [1]. Much effort will be required to achieve this target.
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Tetsunori Murachi, Hiroyoshi Tanabe, Seh-Jin Park, Eric Gullikson, Taichi Ogase, Tsukasa Abe, Naoya Hayashi, "Direct phase-shift measurement of thin and thick absorber EUV masks", Proc. SPIE 8441, Photomask and Next-Generation Lithography Mask Technology XIX, 84411M (30 June 2012); doi: 10.1117/12.976817; https://doi.org/10.1117/12.976817
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KEYWORDS
Reflectivity

Photomasks

Phase measurement

Extreme ultraviolet

Extreme ultraviolet lithography

Reflectometry

Phase shifts

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