EXTREME-ULTRAVIOLET SPECTROSCOPY OF A LASER-PLASMA SOURCE FOR LITHOGRAPHY

Spectra from various target materials from a KrF-laser plasma source h ave been investigated in the Extreme UV spectral range between 12 and 17 nm using an off-Rowland grazing-incidence spectrograph. The electro n temperature T-e and mean ionization stages Z have been measured to a mount to T-e = 80eV and Z = 10-12, respectively. Additional calibratio n and measurement of the spatial and temporal characteristics of the p lasma 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 x 10(15) phot/sr nm) has been observed for targets with atomic numb er Z(a) = 32, 50, 73-75, of which the radiative transitions have been identified as 3p-3d, 4d-4f and 4f-5d transitions respectively. The cor responding maximum conversion efficiency at 13.5nm was 0.43% in a 1% b andwidth. An option for further optimization of the KrF laser plasma s ource for application in EUV lithography is discussed.