LASER PLASMA SOURCES FOR PROXIMITY PRINTING OR PROJECTION X-RAY-LITHOGRAPHY

In this article, we present a theoretical and experimental study of the x-ray emission produced by laser plasma sources in different spectral ranges appropriate for x-ray lithography either in proximity printing (XRL) or projection (XRPL) approaches. For XRPL application, experiments using 10 ns laser pulses show that the maximum conversion efficiency in the (80-250 eV) range is attained at I = 10(11) W cm-2 whereas for 25 ns pulses and I less-than-or-equal-to 6 X 10(11) W cm-2, it is still increasing with laser intensity. On the other hand, higher laser intensities are required to obtain a high conversion efficiency for XRL (0.9-1.4 keV). Efficient emission peaked at 1.1 keV can be achieved for I > 10(13) W cm-2 with copper targets and pulse duration shorter than 5 ns. For iron line emission (peak at 0.9 keV), the laser intensity can be lower (I = 5 X 10(12) W cm-2) and the pulse duration longer (tau(p) = 10 ns). Finally, we discuss the different approaches which may lead to the appropriate laser design.