Plasma cleaning of lithium off of collector optics material for use in extreme ultraviolet lithography applications

Grazing Incidence Mirrors for EUV Lithography

“…The overall reflectivity of EUV mirrors, especially of those in the collection module, is under continuous degradation due to erosion and contamination from within the EUV source, as Xe, Li and Sn are the conventional, currently used, EUV light fuel [Allain et al, 2008]. This is a matter of great concern because it directly affects the available power of the EUV source, and thus the final cost of production [Neumann et al, 2007], [Bakshi, 2006]. The collector mirrors are facing a continuous bombardment of debris emerging from EUV light sources, fast ions, neutrals, off-band radiation, droplets, and background impurities (i.e., H, C, N, O), as well as the heat load generated by the sources themselves, all of them inducing serious damage to the nearby collector mirrors.…”

Debris transport analysis at the intermediate focus of an extreme ultraviolet light source

“…Such efforts seek to extend the lifetime of the collector optics and reduce the cost of ownership of a tool. 7,8 Typical techniques include the use of collimated foil traps, buffer gas, magnetic field confinement, secondary plasmas of low mass gas species to reduce the coulomb acceleration caused by the rapid expulsion of electrons from the plasma, as well as increasing chamber pressure to increase gas scattering in the short distance between the plasma and the optics. [9][10][11] While considerable research has been performed in preventing energetic ions and neutrals, as well as condensable Sn plasma fuel from reaching the reflective mirrors, mitigation techniques at the IF have not been widely investigated.…”