30 October 2007 Performance of actinic EUVL mask imaging using a zoneplate microscope
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Abstract
The SEMATECH Berkeley Actinic Inspection Tool (AIT) is a dual-mode, scanning and imaging extreme-ultraviolet (EUV) microscope designed for pre-commercial EUV mask research. Dramatic improvements in image quality have been made by the replacement of several critical optical elements, and the introduction of scanning illumination to im-prove uniformity and contrast. We report high quality actinic EUV mask imaging with resolutions as low as 100-nm half-pitch, (20-nm, 5× wafer equivalent size), and an assessment of the imaging performance based on several metrics. Modulation transfer function (MTF) measurements show high contrast imaging for features sizes close to the diffraction-limit. An investigation of the illumination coherence shows that AIT imaging is much more coherent than previously anticipated, with σ below 0.2. Flare measurements with several line-widths show a flare contribution on the order of 2-3% relative intensity in dark regions above the 1.3% absorber reflectivity on the test mask used for these experiments. Astigmatism coupled with focal plane tilt are the dominant aberrations we have observed. The AIT routinely records 250-350 high-quality images in numerous through-focus series per 8-hour shift. Typical exposure times range from 0.5 seconds during alignment, to approximately 20 seconds for high-resolution images.
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Kenneth A. Goldberg, Patrick P Naulleau, Anton Barty, Senajith B. Rekawa, Charles D. Kemp, Robert F Gunion, Farhad Salmassi, Eric M. Gullikson, Erik H. Anderson, Hak-Seung Han, "Performance of actinic EUVL mask imaging using a zoneplate microscope", Proc. SPIE 6730, Photomask Technology 2007, 67305E (30 October 2007); doi: 10.1117/12.746756; https://doi.org/10.1117/12.746756
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