Paper PS1-ThA6
Research at CPMI Towards Making EUVL a Success

Thursday, October 18, 2007, 3:40 pm, Room 606

Center for Plasma Material Interactions (CPMI) at the University of Illinois is currently expanding efforts to solve critical problems for timely implementation of extreme ultraviolet lithography. The research at CPMI is focused on variety of different problems being currently faced in this technology. A commercial extreme ultraviolet light source (XTS 13-35) is investigated to characterize the debris ejecta. A fully calibrated ion diagnostic device (spherical sector ion energy analyzer) is developed, which is used for measuring the ion debris fluxes and their energies in absolute units. Ion debris is measured both from Xe as well as Sn EUV sources. Several mitigation schemes are investigated and tested for their effectiveness in the XTS 13-35 source. Recent work towards debris mitigation includes gas curtain, pulsed foil trap, plasma based mitigation, mixed fuel experiments. In the case of mixed fuel experiments, by adding 5% of H₂ in the main fuel (Xe), the ion energies and fluxes could be reduced by half of the original value. Using pulsed foil trap mitigation, 4 keV Xe⁺ ion flux could be reduced about 4 times whereas Xe²⁺ ion flux were dramatically reduced by a factor of about 90. Mirror samples are exposed to the EUV source and erosion due to harsh plasma debris is measured for variety of different EUV compatible materials (C, MLM, Si, Mo, Pd, Mo-Au, Au). For example, the measured erosion on EUV exposed multilayer mirror (MLM) sample is about 13 nm ± 2 nm. Comparison with theory predicts the major damage from high energy ions itself, but also indicates the role of neutral particles. To advance the debris diagnostic tool, the detector is further modified to account for neutral debris measurement. Ion and neutral debris measuring capabilities allowed us to perform life time testing. We have also studied the problems with Sn EUV sources and currently developing methods to clean Sn effectively from the mirror surface without actually harming the surface underneath. Reactive ion etching is found to be a viable solution and variety of different samples are tested and processed through the cleaning techniques. Encouraging results in this area has motivated us to do a full blown test in the EUV source and install an integrated cleaning system, which could run in a manufacturing environment.