29 September 2010 EUV mask stack optimization for enhanced imaging performance
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Abstract
EUVL requires the use of reflective optics including a reflective mask. The reticle blank contains a reflecting multilayer, tuned for 13.5nm, and an absorber which defines the dark areas. The EUV mask is a complex optical element with many more parameters than the CD uniformity of the patterned features that impact the final wafer CDU. Peak reflectivity, centroid wavelength and absorber stack height variations need to be tightly controlled for optimum performance. Furthermore the oblique incidence of light in combination with the small wavelength compared to the mask topography causes a number of effects which are unique to EUV, such as an H-V CD offset and an orientation dependent pattern placement error. These so-called shadowing effects can be corrected by means of OPC, but also need to be considered in the mask stack design. In this paper we will show that it is possible to improve the imaging performance significantly by reducing the sensitivity to mask making variations such as capping layer thickness and absorber stack height variations. The impact of absorber stack height variations on CD and proximity effects will be determined experimentally by changing the local absorber stack height using the novel e-beam based reticle repair tool MeRiT® HR 32 from Carl Zeiss in combination with exposures on ASML's alpha demo tool. The impact of absorber reflectivity will be shown experimentally and used to derive requirements for the reticle border around the image field, as well as possible correction techniques.
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Eelco van Setten, Eelco van Setten, Dorothe Oorschot, Dorothe Oorschot, Cheuk-Wah Man, Cheuk-Wah Man, Mircea Dusa, Mircea Dusa, Robert de Kruif, Robert de Kruif, Natalia Davydova, Natalia Davydova, Kees Feenstra, Kees Feenstra, Christian Wagner, Christian Wagner, Petra Spies, Petra Spies, Nils Wiese, Nils Wiese, Markus Waiblinger, Markus Waiblinger, } "EUV mask stack optimization for enhanced imaging performance", Proc. SPIE 7823, Photomask Technology 2010, 78231O (29 September 2010); doi: 10.1117/12.864247; https://doi.org/10.1117/12.864247
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