12 June 2018 EUV mask with advanced hybrid black border suppressing EUV and DUV OOB light reflection
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Abstract
EUV lithography is expected to be the most promising technology for semiconductor device manufacturing of the 7nm node and beyond. The EUV mask is a key element in the lithographic scanner optical path. The image border is a pattern free dark area around the die on the photomask serving as transition area between the parts of the mask that is shielded from the exposure light by the Reticle Masking (REMA) blades and the die. When printing a die at dense spacing on an EUV scanner, the reflection from the image border overlaps edges of neighboring dies, affecting CD and contrast in this area. This is related to the fact that EUV absorber stack reflects 1-3% of actinic EUV light. To reduce this effect several types of image border with reduced EUV light reflectance (<0.05%) have been proposed; such an image border is referred to as a black border (BB). In particular, an etched multilayer type black border was developed; it was demonstrated that CD impact at the edge of a die is strongly reduced with this type of the black border. However, wafer printing result still showed some CD change in the die influenced by the black border reflection. It was proven that the CD change was caused by DUV Out Of Band (OOB) light which is emitted from the EUV light source. In our previous study, a new types of multilayer etched BB called ‘Hybrid Black Border’ (HBB) had been developed and showed a good potential for DUV light suppression. OOB light reflection on HBB is ~3x lower than that of normal BB. Imaging performance was also demonstrated on NXE:3300 scanner system for N10 imaging structures of 16nm dense lines and 20nm isolated spaces. These results were compared to the imaging results obtained for a mask with the normal BB and 3x improvement was achieved; less than 0.2 nm CD changes were observed in the corners of the die. However, OOB light reflectance suppression was still not enough in short wavelength. In this study, we focused on OOB light reflectance reduction in short wavelength, and we developed a new HBB called ‘Advanced HBB’. We measured the OOB light reflectance of Advanced HBB by synchrotron radiation facility at PTB (Physikalisch- Technische Bundesanstalt, Germany). These results were compared to the results obtained from previous HBB. Then Advanced HBB achieved over 50% OOB light reflectance improvement in average wavelength 100nm to 270nm. Imaging performance also simulated in the edges and corners of the die. The CD-drop is expected to be more improved for Advanced HBB than previous HBB. As a result, it is expected the implementation of the Advanced HBB will help to mitigate the effects of possible increases of OOB light in the future higher power EUV sources.
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Genta Watanabe, Norihito Fukugami, Toru Komizo, Yutaka Kodera, and Toshio Konishi "EUV mask with advanced hybrid black border suppressing EUV and DUV OOB light reflection", Proc. SPIE 10807, Photomask Japan 2018: XXV Symposium on Photomask and Next-Generation Lithography Mask Technology, 108070N (12 June 2018); doi: 10.1117/12.2501999; https://doi.org/10.1117/12.2501999
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