X-ray production in the region approximately 13 nm from laser-produced
plasmas has been investigated as a source for projection x-ray lithog
raphy. The dependence of x-ray conversion efficiency on target materia
l, intensity, and pulse length has been studied by using a 0.53-mum la
ser with a maximum of 0.3 J. A conversion efficiency of 1% into a 0.3-
nm bandwidth has been demonstrated for Sn targets at intensities of ap
proximately 10(11) W/cm2 by using a 7.5-ns pulse. Intensity scaling su
ggests that laser spot size and two-dimensional expansion are importan
t for optimizing x-ray production at these low-irradiation intensities
.