High-Accuracy EUV Metrology of PTB Using Synchrotron Radiation F. Scholze, B. Beckhoff, G. Brandt, R. Fliegauf, A. Gottwald, R. Klein, B. Meyer, U. Schwarz, R. Thornagel, J. Tümmler, K. Vogel, J. Weser, and G. Ulm Physikalisch-Technische Bundesanstalt, Abbestraße 2-12, 10587 Berlin, Germany ABSTRACT The development of EUV lithography, has made high-accuracy at-wavelength metrology necessary. Radiometry using synchrotron radiation has been performed by the German national metrology institute, the Physikalisch-Technische Bundesanstalt (PTB), for almost 20 years. Recently, PTB has set up four new beamlines for EUV metrology at the electron storage ring BESSY II. At a bending magnet, a monochromator for soft X-ray radiometry is routinely used for reflectometry and detector characterisation. A reflectometer designed for mirrors up to 550 mm in diameter and 50 kg in mass will be operational in January 2002. Detector characterisation is based on a primary detector standard, a cryogenic electrical substitution radiometer. Measuring tools for EUV source characterisation are calibrated on this basis. Detector testing at irradiation levels comparable to the anticipated conditions in EUV tools is feasible at a plane grating monochromator, installed at an undulator optimised for EUV radiation. A test beamline for EUV optics alignment and system metrology has been installed, using undispersed undulator radiation. Bending magnet radiation is available at a station for irradiation testing. A focusing mirror collects a radiant power of about 10 mW within the multilayer bandwidth and a 1 mm² focal spot. Keywords: reflectometry, detector calibration, metrology, irradiation testing 1 INTRODUCTION Extreme UV lithography (EUVL) is presently the most promising candidate for the Next Generation Lithography. At present, there is a competition between the DUV (deep UV) and EUV systems for future application at the 70 nm and 50 nm technology nodes 1 .This competition will be decided mostly by economic and technological factors such as risk, time and cost of development, and ownership. It is therefore likely that DUV technology will be used up to its ultimate limits and EUV will take over at a feature sizes smaller than expected at the outset. This increases the technological efforts for, e.g., the α-tool which is being built at ASML 2 . One of the enabling technologies for EUVL is the multilayer coating process. Here, coatings with reflective properties approaching the theoretical limits are meanwhile produced, and reflectometry with the PTB reflectometer 3 at the PTB soft X-ray radiometry beamline 4 at BESSY I was successfully used within the European EUCLIDES project 5 to experimentally verify even small improvements in the mirror performance. For the requirements of the EUCLIDES project, the relative uncertainty in the region of the main maximum of the multilayer reflectance curve was reduced to u=0.25% 6 at the PTB laboratory at BESSY II 7 . Metrology for a variety of further items must, however, be available to characterize a complete EUVL system. Present designs of a complete EUVL system include ten normal incidence reflections 8 . A loss of only 1% of reflectance at each mirror would thus decrease the throughput by 10%. Instrumentation for irradiation testing of mirrors will therefore be needed. Additionally, the present designs of projection optics include large mirrors 8 which cannot be handled in any of the existing reflectometers. Furthermore, methods and tools must be developed for qualification and alignment of the complex EUV optical systems, i.e. instrumentation for system metrology is needed. Much development is also still needed for the production of EUV light sources. Here, first steps were made quite recently towards the development of characterization tools whose calibration is traceable to the SI system of units 9,10 . In this paper we report on the different PTB beamlines for EUV metrology. Correspondence: Frank Scholze, frank.scholze@ptb.de, tel.++49 30 6392 5094, fax ++49 30 6392 5082