Magnetic field ion mitigation for EUV light sources

Abstract

Fast ions from laser-produced EUV plasma are expected to significantly damage the collector mirror, which is located near the plasma in a EUV light source. Ion sputtering of the multilayer structure may be the main damage mechanism but layer boundary mixing and surface roughness increase are also observed from a Xe plasma exposure experiment. The magnetic field ion mitigation technology was evaluated in order to extend the collector mirror lifetime. A coil pair that produces a maximum static magnetic field of 0.6 T on the coil axis was used for magnetic confinement of ions. Liquid Xe jets of 10 to 30 micron mater in diameter were used as a plasma target. Spatial distributions and energy distributions of ions were measured with Faraday cups and time-of-flight measurements respectively. The effectiveness of the magnetic field ion mitigation was evaluated by measuring the erosion rate with a quartz crystal microbalance. A significant decrease of the Faraday cup signal was monitored by applying a magnetic field of 0.6 T. Though target size dependence on magnetic field effectiveness was observed, measured erosion rate was reduced to less than 10% by applying 0.6-T magnetic field in the case of 10-micron mater Xe jet and 300-mJ Nd:YAG laser irradiation.