28 July 2014 Achievements and challenges of EUV mask imaging
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Abstract
The impact of various mask parameters on CDU combined in a total mask budget is presented, for 22 nm lines, for reticles used for NXE:3300 qualification. Apart from the standard mask CD measurements, actinic spectrometry of multilayer is used to qualify reflectance uniformity over the image field; advanced 3D metrology is applied for absorber profile characterization including absorber height and side wall angle. The predicted mask impact on CDU is verified using actual exposure data collected on multiple NXE:3300 scanners. Mask 3D effects are addressed, manifesting themselves in best focus shifts for different structures exposed with off-axis illumination. Experimental NXE:3300 results for 16 nm dense lines and 20 nm (semi-)isolated spaces are shown: best focus range reaches 24 nm. A mitigation strategy by absorber height optimization is proposed based on experimental results of a special mask with varying absorber heights. Further development of a black image border for EUV mask is considered. The image border is a pattern free area surrounding image field preventing exposure the image field neighborhood on wafer. Normal EUV absorber is not suitable for this purpose as it has 1-3% EUV reflectance. A current solution is etching of ML down to substrate reducing EUV reflectance to <0.05%. A next step in the development of the black border is the reduction of DUV Out-of-Band reflectance (<1.5%) in order to cope with DUV light present in EUV scanners. Promising results achieved in this direction are shown.
© (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Natalia Davydova, Eelco van Setten, Robert de Kruif, Brid Connolly, Norihito Fukugami, Yutaka Kodera, Hiroaki Morimoto, Yo Sakata, Jun Kotani, Shinpei Kondo, Tomohiro Imoto, Haiko Rolff, Albrecht Ullrich, Ad Lammers, Guido Schiffelers, and Joep van Dijk "Achievements and challenges of EUV mask imaging", Proc. SPIE 9256, Photomask and Next-Generation Lithography Mask Technology XXI, 925602 (28 July 2014); doi: 10.1117/12.2072945; https://doi.org/10.1117/12.2072945
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