Lifetime Measurements on Collector Optics from Xe and Sn Extreme Ultraviolet Sources

J. of Applied Physics, 102, 023301 (2007).

Srivastava, S. N., Thompson, K. C., Antonsen, E. L., Qiu, H., Spencer, J. B., Papke, D., Ruzic, D. N.

Next generation lithography to fabricate smaller and faster chips will use extreme ultraviolet (EUV) light sources with emission at 13.5  nm. A challenging problem in the development of this technology is the lifetime of collector optics. Mirror surfaces are subjected to harsh debris fluxes of plasma in the form of ions, neutrals, and other radiation, which can damage the surface and degrade reflectivity. This manuscript presents the measurement of debris ion fluxes and energies in absolute units from Xe and Sn EUV sources using a spherical sector ion energy analyzer. Experimentally measured erosion on Xe exposed samples is in good agreement with predicted erosion. This result allows prediction of erosion using measured ion fluxes in experiment. Collector optic lifetime is then calculated for Xe and Sn sources without debris mitigation. Lifetime is predicted as 6  h for Xe EUV sources and 34  h for Sn EUV sources. This result allows calculation of expected collector optic lifetimes, which can be an important tool in optimizing source operation for high volume manufacturing.