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We evaluated the characteristics of Sn debris generated by a CO 2 laser (10.6µm) produced plasma. Experiments were performed with bulk Sn-plate targets and Mo/Si multilayer mi rror samples were used for debris analysis. We observed very thin and uniform Sn layers of nano/sub-nano size debris particles. The layer deposition rate at 120mm from the plasma is, without magnetic field, about 30nm per million shots. The fundamental magnetic field effect has been confirmed experimentally. The fast Sn ion flux was measured with Faraday cups and the signal decreased by more than 3 orders of magnitude applying a magnetic field of 1T. The Sn deposition on the Mo/Si multilayer mirror decreased in this case by a factor of 4. The contribution of the remaining neutral Sn particles is under study in order to decrease the deposition rate. Keywords: Extreme Ultraviolet Lithogra phy, Laser Produced Plasma, CO 2 laser, Sn, Debris, magnetic field 1. INTRODUCTION The target material for EUVL plasma light sources is Sn due to its high conversion efficiency (CE). The Sn debris, however, has to be efficiently removed from the plasma regi on in order to guarantee the lifetime of the EUV collector mirror because otherwise deposition (evaporated material, molten droplets, slow ions), erosion (fast ions), and implantation (ultra fast ions) quickly degrade the collector mirror reflectivity. The critical issue is, however, Sn deposition; only about 1nm Sn deposited on the EUV collector mirror, i.e. only several atomic layers, reduces the mirror reflectivity by 10%, which is considered as the mirror lifetime specification. On the other hand, the acceptable multilayer erosion of the collector mirror depends on its multilayer number and can therefore be taken into account with sacrificial layers. Sn implantation, finally, occurs at higher kinetic ion energies than we observed. We previously reported Sn debris characteristics from Nd:YAG laser (1064nm) and CO |
