Exploring the electron density in plasma induced by EUV radiation: I. Experimental study in hydrogenстатья
Статья опубликована в высокорейтинговом журнале
Информация о цитировании статьи получена из
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Статья опубликована в журнале из списка Web of Science и/или Scopus
Дата последнего поиска статьи во внешних источниках: 26 августа 2016 г.
Аннотация: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
1014 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.