Plasmas induced by EUV radiation are unique since they are created without the need of any discharge. Moreover, it is essential to characterize these plasmas to understand and predict their long term impact on highly delicate optics in EUV lithography tools. In this paper we study plasmas induced by 13.5 nm EUV radiation in hydrogen gas. The electron density is measured temporally resolved using a non-invasive technique known as microwave cavity resonance spectroscopy. The influence of the EUV pulse energy and gas pressure on the temporal evolution of the electron density has been explored over a parameter range relevant for industry. Our experimental results show that the maximum electron density is in the order of 10 14 m −3 and depends linearly on the EUV pulse energy. Furthermore, the maximum electron density depends quadratically on the pressure; the linear term is caused by photoionization and the quadratic term by subsequent electron impact ionization. The decay of the plasma is governed by ambipolar diffusion and, hence, becomes slower at elevated pressures. Similarities and differences of the same processes in argon are highlighted in this paper.

VL - 49 IS - 14 U1 -FP

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U5 - 015abf036e8dc9e4923f2701aacf2c00 ER - TY - JOUR T1 - Exploring the electron density in plasma induced by EUV radiation: II. Numerical studies in argon and hydrogen JF - Journal of Physics D: Applied Physics Y1 - 2016 A1 - Astakhov, D. I. A1 - W. J. Goedheer A1 - Lee, C. J. A1 - Ivanov, V. V. A1 - Krivtsun, V. M. A1 - Koshelev, K. N. A1 - Lopaev, D. V. A1 - van der Horst, R. M. A1 - Beckers, J. A1 - Osorio, E. A. A1 - F. Bijkerk AB -We used numerical modeling to study the evolution of EUV-induced plasmas in argon and hydrogen. The results of simulations were compared to the electron densities measured by microwave cavity resonance spectroscopy. It was found that the measured electron densities can be used to derive the integral amount of plasma in the cavity. However, in some regimes, the impact of the setup geometry, EUV spectrum, and EUV induced secondary emission should be taken into account. The influence of these parameters on the generated plasma and the measured electron density is discussed.

VL - 49 UR - http://arxiv.org/abs/1603.08130 IS - 29 U1 -FP

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U5 - 8d71644a9a722605f42d8c7f3cab1cfb ER -