Effects of Plasma Spatial Profile on Conversion Efficiency of Laser Produced Plasma Sources for EUV Lithography

Extreme ultraviolet (EUV) lithography devices that use laser produced plasma (LPP), discharge produced plasma (DPP), and hybrid devices need to be optimized to achieve sufficient brightness with minimum debris generation to support the throughput requirements of High-Volume Manufacturing (HVM) lithography exposure tools with long lifetime. Source performance, debris mitigation, and reflector system are all critical to efficient EUV collection and component lifetime. Enhanced integrated models are continued to be developed using HEIGHTS computer package to simulate EUV emission at high power and debris generation and transport in multiple and colliding LPP. A new center for materials under extreme environments (CMUXE) is established to benchmark HEIGHTS models for various EUV related issues. The models being developed and enhanced include, for example, new ideas and parameters of multiple laser beams in different geometrical configurations and with different pre-pulses to maximize EUV production. Recent experimental and theoretical work show large influence of the hydrodynamic processes on EUV generation. The effect of plasma hydrodynamics evolution on the EUV radiation generation was analyzed for planar and spherical geometry of a tin target in LPP devices. The higher efficiency of planar target in comparison to the spherical geometry was explained with better hydrodynamic containment of the heated plasma. This is not the case if the plasma is slightly overheated. Recent experimental results of the conversion efficiency (CE) of LPP are in good agreement with HEIGHTS simulation.