Lithium hydride capillary discharge creates x-ray plasma at 13.5 nanometers

Lithium hydride capillary discharge creates x-ray plasma at 13.5 nanometers

In a proof-of-concept experiment, researchers led by William Silfvast of the University of Central Florida`s Center for Research and Education in Electro-optics and Lasers (Orlando, FL), collaborating with Jorge Rocca at Colorado State University (Fort Collins, CO), have generated a 13.5-nm plasma discharge from doubly ionized lithium (Li2+) using a lithium hydride (LiH) capillary. Such a source could be useful in extreme-ultraviolet (EUV) lithography imaging systems.

Capacitors bonded along the edge of a 7-cm-diameter circular conducting plate were connected to a 2 ¥ 6-mm LiH capillary mounted along the plate axis. When the plate was charged to 15 kV and discharged along the inner surface of the capillary, the LiH was ablated and heated to create a highly ionized plasma. Filtered, soft-x-ray pinhole photographs showed 75% of the energy radiated from a 0.6-mm-diameter spot; this corresponds to 4.5 mJ of energy emitted from a cylindrical volume of 2 mm3. Within the reflectance bandwidth of the molybdenum/silicon multilayer mirrors used for normal-incidence EUV optics, the system produced a flux per pulse comparable to a laser-produced plasma while generating negligible debris and operating at a wallplug efficiency of 1%, almost an order of magnitude better than with laser-produced plasma. However, limited capillary lifetime (25 to 50 shots) prevents use of this design in high-average-power applications without further modification.