Optics contamination studies in support of high-throughput EUV lithography tools
Shannon B. Hill, Fardina Asikin, Lee J. Richter, Steven E. Grantham, Charles S. Tarrio, Thomas B. Lucatorto, Sergiy Yulin, Mark Schurmann, Viatcheslav Nesterenko, Torsten Feigl
We report on optics contamination rates induced by exposure to broad-bandwidth, high-intensity EUV radiation peaked near 8 nm in a new beamline at the NIST synchrotron. The peak intensity of 50 mW/mm2 allows extension of previous investigations of contamination by in-band 13.5 nm radiation at intensities an order of magnitude lower. We report non-linear pressure and intensity scaling of the contamination rates which is consistent with the earlier lower-intensity studies. The magnitude of the contamination rate per unit EUV dose, however, was found to be significantly lower for the lower wavelength exposures. We also report an apparent dose-dependent correlation between the thicknesses as measured by spectroscopic ellipsometry and x-ray photoelectron spectroscopy for the carbon deposits created using the higher doses available on the new beamline. It is proposed that this is due to different sensitivities of the metrologies to variations in the density of the deposited C induced by prolonged EUV irradiation.