9 September 2013 Direct phase-shift measurement of an EUV mask with gradient absorber thickness
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Abstract
We directly extracted the phase-shift values of an EUV mask by measuring the reflectance of the mask. The mask had gradient absorber thickness along vertical direction. We measured the reflectance of the open multilayer areas and the absorber areas by using an EUV reflectometer at various absorber thicknesses. We also measured the diffracted 0th order light intensities of grating patterns having several sizes of lines or holes. The phase-shift values were derived from these data assuming a flat mask interference model of the diffracted lights. This model was corrected by including the scattering amplitude from the pattern edges. We recalculated the phase-shift values which was free from the mask topological effect. The extracted phase-shift value was close to 180 degrees at 67 nm and 71 nm absorber thicknesses. The phase measurement error around 180 degree phase shift was 5 degrees (3σ).
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Hiroyoshi Tanabe, Tetsunori Murachi, Seh-Jin Park, Eric M. Gullikson, Tsukasa Abe, Naoya Hayashi, "Direct phase-shift measurement of an EUV mask with gradient absorber thickness", Proc. SPIE 8880, Photomask Technology 2013, 88801D (9 September 2013); doi: 10.1117/12.2031135; https://doi.org/10.1117/12.2031135
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