The life-time of the collection optics of an LPP EUV source is computationally studied. The near-field (radiating layer, micrometer scale) and far-field (optics, meter scale) radiation and particle dynamics are investigated with a twodimensional/ axisymmetric coupled hydrodynamic-particle code, which is used together with an atomic physics code to predict the laser-plasma processes. The droplet target is found to have a conversion efficiency of 2.2%. The nonuniformity of the initial plasma expansion is detailed. In the far field study, the neutral and ion distributions are projected on a normal incidence mirror. Ions up to Sn⁴⁺ reach the mirror. Fast neutrals mostly deposit in the central region of the mirror, while ions erode the outer region. The simulated ion kinetic energies, which are in the range of a few keV volts match experimental values. The local time durations for a reflectivity drop from 70% to 60% are in the range of 2.5 to 4 hours. The extension of the life-time of the collection optics up to 30'000 hours requires either a 4 order of magnitude reduction of the ion flux or a 5-fold reduction of the ion kinetic energies. In order to fulfill the EUVL source requirement of continuous operation, an effective mitigation scheme for fast ions and neutrals is mandatory.

Date Published: 18 March 2009
PDF: 10 pages
Proc. SPIE 7271, Alternative Lithographic Technologies, 72712W (18 March 2009); doi: 10.1117/12.814150

Published in SPIE Proceedings Vol. 7271:
Alternative Lithographic Technologies
Frank M. Schellenberg; Bruno M. La Fontaine, Editor(s)