Spectra from various target materials from a KrF-laser plasma
source have been investigated in the Extreme UV spectral range between
12 and 17nm using an off-Rowland grazing-incidence spectrograph. The
electron temperature Te and mean ionization stages Z have been measured to amount to Te = 80eV
and Z = 10–12, respectively. Additional calibration and
measurement of the spatial and temporal characteristics of the plasma
has been done using a combination of a multilayer mirror and XUV diode
or fiber image carrier system. The maximum yield at 13.5nm
(2.4–3 × 1015 phot/srnm) has been observed for
targets with atomic number Za = 32, 50, 73–75,
of which the radiative transitions have been identified as
3p–3d, 4d–4f and 4f–5d transitions respectively. The
corresponding maximum conversion efficiency at 13.5nm was 0.43% in a
1% bandwidth. An option for further optimization of the KrF laser
plasma source for application in EUV lithography is
discussed.