Advances in computer simulations of LPP sources for EUV lithography

Abstract

Photon sources for extreme ultraviolet Lithography (EUVL) are still challenging problem to achieve high volume manufacture in the semiconductor industry. Currently EUVL community narrowed the research and developments to two directions: discharge produced plasma (DPP) assisted with trigger lasers and dual-pulse laser produced plasma (LPP) with mass-limited targets. Such complicated systems require extensive optimization to enhance the conversion efficiency (CE) and components lifetime and detail source optimization requires significant experimental and costly efforts. We used our HEIGHTS simulation package to study and optimize LPP sources and to make realistic predictions as well as benchmarking of key experimental results. HEIGHTS package includes 3-D detail description of various integrated physical processes involved in LPP and DPP devices. The models are extensively tested and benchmarked separately in each physics phase of laser/target interaction as well as in the entire integrated system without any parameters adjustments or fittings. We simulated LPP sources in full 3-D geometry using 10-50 μm tin droplet targets, as single droplets as well as distributed fragmented microdroplets with equivalent mass. We studied mass dependence, laser parameters efficiency, atomic and ionic debris generation, and optimization of EUV radiation output. Our modeling and simulation included all phases of laser target evolution: from laser/droplet interaction, energy deposition, target vaporization and fragmentation, ionization, plasma hydrodynamic expansion, thermal and radiation energy redistribution, and EUV photons collection as well as detail mapping of photons source location and size. We also predicted potential damage to the optical collection system from plasma energetic debris and the requirements for mitigating systems to reduce debris fluence. The debris effect on mirror collection system is analyzed using our 3-D ITMC-DYN Monte Carlo package. Modeling results were benchmarked against our CMUXE experimental studies for the in-band photons production and for debris and ions generation.