Abstract
During the past decade, high-accuracy soft x-ray radiometry has increasingly gained in importance. In particular, its routine availability is a prerequisite for the development of extreme UV lithography (EUVL). The PTB has been providing EUV calibration services for many years at a dedicated radiometry beamline at the electron storage ring BESSY I and from the year 2000 at the new PTB synchrotron radiation laboratory at BESSY II. Reflectometry, especially the measurement of the reflectance of Mo/Si multilayer mirrors for EUVL, is a major activity at the beamline. As the performance of the third-generation storage ring BESSY II is better than that of BESSY I, the measurement uncertainties could be significantly reduced. Efforts were made to accurately determine the wavelength scale for the monochromator and to suppress diffusely scattered light. For the spectral reflectance of a mirror in the EUV spectral region, a relative uncertainty of u = 0.14% is achieved. A new reflectometer will enable PTB to characterize EUVL optics up to 550 mm in diameter and 50 kg in mass. Detector calibration is based on a primary detector standard, a cryogenic electrical substitution radiometer. Photodiodes with a nearly constant spectral responsitivity in the soft x-ray range are calibrated as transfer detector standards with a relative uncertainty of u = 0.26% by direct comparison to the radiometer.