Optics contamination studies in support of high-throughput EUV lithography tools S. B. Hill * a , N. S. Faradzhev a , L. J. Richter a , S. Grantham a , C. Tarrio a and T. B. Lucatorto a S. Yulin c , M. Schürmann c , V. Nesterenko c , T. Feigl c a National Institute of Standards and Technology, Gaithersburg, MD 20899 USA c Fraunhofer Institute for Applied Optics and Precision Engineering IOF, Jena, Germany ABSTRACT 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/mm 2 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 XPS 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. Keywords: Extreme ultraviolet lithography (EUVL); multilayer optics; optics lifetime; optics contamination; ellipsometry; carbon deposition; photochemistry 1. INTRODUCTION Carbon contamination of the multilayer mirror (MLM) optics used in extreme-ultraviolet (EUV) lithography is caused by the photon-induced cracking of adsorbed organic contaminants present in the ambient vacuum of the tool and originating from outgassing of the resist. The National Institute of Standards and Technology (NIST) and the Fraunhofer Institute for Applied Optics and Precision Engineering IOF have ongoing programs to measure and better understand the carbon contamination processes as a way of providing information that would be helpful to gauge the risks associated with different contaminants and improve the design of mitigation schemes. As EUV lithography moves closer to production, the EUV intensity will increase as will the amount of light outside the (13.5 ± 2 %) nm band. To better understand how the problem of optics contamination will be affected by these changes, we have used a new beamline constructed at the Synchrotron Ultraviolet Radiation Facility (SURF III) at NIST to investigate a regime of higher intensity and lower wavelengths than our previous studies. We have investigated the pressure and intensity scaling of the contamination rates under these new conditions. Since accurate characterization of optics contamination is also essential, we have also studied the correlation between the two widely used metrologies of x-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry (SE) which has revealed an apparent dose-dependent discrepancy between XPS and SE thickness measurements of C deposits created by the higher doses available on the new beamline. 2. EXPERIMENTAL PROCEDURES Multilayer samples with Ru or TiO 2 capping layers were exposed to EUV light in the presence of admitted gases in two different end stations on beamlines 1b and 8 of the NIST synchrotron. The partial pressures were measured with a Bayard-Alpert ionization gauge with an absolute uncertainty of 20 % and are reported below without correction for the different sensitivity factors for each gas. Prior to use, gasses are subjected to multiple freeze-pump-thaw cycles to remove primarily water and air impurities. The purity of the gases and cleanliness of the base vacuum are determined * shannon.hill@nist.gov ; phone (301) 975-4283; fax (301) 926-2746