Plasma based radiation sources optimized to emit 13.5 nm Extreme UV radiation also produce a significant amount of light at longer wavelengths. This so called out-of-band (OoB) radiation is detrimental for the imaging capabilities of an EUV lithographic imaging system, particularly the deep ultraviolet (DUV) and ultraviolet (UV) parts of the light (λ=100-400 nm). To suppress these wavelengths while maintaining the high efficiency of the mirror for EUV light, several methods have been developed, including phase-shift gratings (PsG) and anti-reflection layers (SPE layer). PsG’s use the diffraction properties of a quarter-wavelength high multilayer grating to filter out the DUV/UV light, while the SPE layer works as an anti-reflection coating. Both methods have achieved a suppression factor of 10 - 30 around the target wavelength. To achieve a full band suppression effect, a new scheme based on surface pyramid structures was developed. An average suppression ofmore than 10 times can be achieved with a relative EUV efficiency of 89% (compared to standard multilayer (ML)) in theory. Different methods were discussed and their results are presented.

Date Published: 27 September 2013
PDF: 5 pages
Proc. SPIE 8848, Advances in X-Ray/EUV Optics and Components VIII, 88480N (27 September 2013); doi: 10.1117/12.2023889

Published in SPIE Proceedings Vol. 8848:
Advances in X-Ray/EUV Optics and Components VIII
Ali Khounsary; Shunji Goto; Christian Morawe, Editor(s)