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Small plasma-pinch devices operating at a gas mixture of Xe and He with a frequency of 5-10 kHz and pulsed energy of 1-100 J are very promising sources of EUV radiation for lithography. A key issue in design of EUV sources is erosion of the pinch facing material under the hot Xe plasma and electric currents. Material erosion limits the lifetime of device components and thereby reduces the economical feasibility of these devices. Selection of high-resistant materials is critically important for development of future commercial EUV sources.
Experiments are being carried out at plasma gun facilities in well-diagnosed and controlled conditions. The plasma gun is applied as a source of pulsed energetic Xe plasma capable of generating Xe plasma streams with a velocity 4 106 - 4 107 cm/s and duration of the plasma pulse 10-40 microseconds. Xenon plasma stream velocity of 4-10 106 is sufficient to obtain plasma temperture of 30-50 eV, i.e., typical for pinch EUV devices. The formation of plasma could makes possible to study erosion and surface damage induced by particles and radiation of Xe plasma at these temperatures.
Initial results of material testing by Xe plasma particles are presented. Samples of copper and tungsten, which are currently being used as electrode materials in pinch devices, were exposed to multiple irradiations by pulsed energetic Xe plasma. Material erosion and surface damages are analyzed. Future results will permit identification of the erosion mechanisms induced by Xe plasma particles, plasma radiation, and electric currents and their contributions to the net material erosion. The experimental data are being used for validation of numerical models developed in the HEIGHTS-EUV package for evaluation of material erosion in EUV sources.
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