Important processes in modeling and optimization of EUV lithography sources

Laser produced plasma (LPP) sources for extreme ultraviolet (EUV) photons are currently based on using small liquid tin droplets as target that has advantages in generation of stable continuous targets at high repetition rate, larger photon collection angle, and reduced contamination and damage to optical mirror system from plasma debris and energetic particles. The ideal target is to generate a source of maximum EUV radiation output and collection in the 13.5 nm range with minimum atomic debris. Based on our predictions, the smallest efficient droplets are of diameters in the range of 20-30 μm. In this study we analyzed detail plasma evolution processes in LPP systems using small spherical tin targets to predict the optimum droplet size yielding maximum EUV output. We identified several important processes during laser-plasma interaction that can affect conditions for optimum EUV photons generation. The importance of accurate description of modeling these processes increases with the decrease in target size and its simulation domain.