The wavelength dependencies of the peak intensities calculated for LaN/B and multilayer mirrors using measured B and and CXRO optical constants are shown in Fig. 1. Here calculations were done for an ideal multilayer model as described in detail in 19. A significant difference between the CXRO database and measured optical constants is observed around the adsorption edge: the CXRO data shows a steep drop in reflectance for a wavelength below the edge, whereas the use of the measured data results in a more gradual drop in reflectance. Comparing reflectivity profiles of B- and -based multilayers calculated with measured optical constants, we observe a minor shift of the wavelength of maximum reflectance. For the maximum reflectivity can be achieved at while for LaN/B this maximum reflectance is found at . This difference can be explained by the 1s B binding energy chemical shift caused by formation of the boron-rich carbide. The most common structure of contains four icosahedrons and CBC chain as a unit cell,20–22 while pure crystalline or amorphous boron contains icosahedrons.23 Because of the large variety of possible bonds20 in , we cannot speak about a well-defined absorption edge position. The total effect of the presence of 20% of C in the boron matrix shifts the onset of photoabsorption of to higher energies with about 1 eV compared to amorphous and crystalline B.24 The origin of the B and -based multilayer EUV reflectivity drop at shorter wavelengths is the increase of B absorption. The shift of the absorption onset will lead to the shift of optimal wavelength. Our calculations yielded a difference in the optimal wavelengths of B and based multilayers of 0.02 nm or in eV, to be compared to the 1 eV shift found above. For estimation of the transmission of an EUV lithography system, we have calculated the integrated reflectivity of the convolution of a system consisting of 10 single-mirror normal incidence mirrors optimized for various wavelengths. In Fig. 2, we show the normalized integrated reflectivity calculated for and LaN/B using the measured optical constants in combination with the indication of measured Tb and Gd source spectral regions.12 All features of the single-mirror peak reflectivity spectra are more pronounced on the 10 mirror integral reflectivity spectra. Figure 2 shows clearly that the wavelength of maximum throughput is at a slightly different wavelength: for the LaN/B material combination, this is at while for it is at . These values are 0.02 and 0.01 nm higher compared to the optimal wavelength of a single B and -based mirror, respectively, because of the influence of the wavelength-dependent bandwidth on the integrated reflectivity.