Development of Visualization System of Neutral Particles Generated from Laser-Produced Plasma for an EUV Light Source

In the development of extreme ultraviolet (EUV) sources for practical optical lithography systems, one of the most important subjects is debris mitigation. In, particularly mitigation of fast neutral atoms is very difficult compared with other particles such as ions and droplets. Thus, in our study, we developed a visualization system for neutral atoms emitted from laser-produced plasma (LPP) based EUV source using a laser induced fluorescence (LIF) method and investigated neutral debris behaviors in order to obtain the guideline for the optimization of debris shields. In the present measurement system, neutral atoms with a kinetic energy of less than 200 eV could be detected at a pump fluence of about 4 102 J/cm2 using a solid tin target. The interaction between the fast ions and substrate was also observed by the LIF system