Measuring the Phase of EUV Photomasks

Stuart Sherwin; Isvar Cordova; Laura Waller; Andrew Neureuther; Patrick Naulleau

doi:10.1117/12.2538107

11 November 2019 Measuring the Phase of EUV Photomasks

Stuart Sherwin, Isvar Cordova, Laura Waller, Andrew Neureuther, Patrick Naulleau

Proceedings Volume 11147, International Conference on Extreme Ultraviolet Lithography 2019; 111471F (2019) https://doi.org/10.1117/12.2538107
Event: SPIE Photomask Technology + EUV Lithography, 2019, Monterey, California, United States

Abstract

We demonstrate complementary reflectometry and scatterometry methods to measure the phase and amplitude of a patterned EUV photomask at its operating wavelength (13.5nm) and angle range (2 − 10°). We carried out experimental measurements at ALS Reflectometry and Scattering Beamline 6.3.2 on an EUV photomask with a 40-bilayer MoSi multilayer mirror and 60nm TaN absorber. We took three types of measurements: reflectometry for blank multilayer, reflectometry for blank absorber-coated multilayer, and scatterometry for line- space gratings. We used the reflectometry data to fit the Fresnel reflectance amplitude by adjusting the thickness, atomic density, and interface roughness of multilayer and absorber layers. We then fit the scatterometry data using a thin-mask approximation. The advantage of reflectometry is the higher level of model fidelity (2 − 4% vs 6% − 15% error), whereas the advantage of scatterometry is its direct sensitivity to relative phase through spatial interference. Despite differences between the two approaches, both gave similar phase values, mutually-consistent to within π/51 RMS. We observe the phase to vary from 0.78μ at 2° to 0.88μ at 10°, suggesting that engineering phase effects to improve image contrast will need to consider phase values across a range of illumination angles rather than simply the chief ray.

Citation Download Citation

Stuart Sherwin, Isvar Cordova, Laura Waller, Andrew Neureuther, and Patrick Naulleau "Measuring the Phase of EUV Photomasks", Proc. SPIE 11147, International Conference on Extreme Ultraviolet Lithography 2019, 111471F (11 November 2019); https://doi.org/10.1117/12.2538107

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