Ion energy distributions in highly transient EUV induced plasma in hydrogen.

This work reports on the measurements of ion flux composition and ion energy distribution functions (IEDFs) at surfaces in contact with hydrogen plasmas induced by extreme ultraviolet (EUV) radiation. This special type of plasma is gaining interest from industries because of its appearance in extreme ultraviolet lithography tools, where it affects exposed surfaces. The studied plasma is induced in 5 Pa hydrogen gas by irradiating the gas with short (30 ns) pulses of EUV radiation ( λ = 10–20 nm). Due to the low duty cycle (10^–4), the plasma is highly transient. The composition and IEDF are measured using an energy resolved ion mass spectrometer. The total ion flux consists of H + , H 2 + , and H 3 + . H 3 + is the dominant ion as a result of the efficient conversion of H 2 + to H 3 + upon collision with background hydrogen molecules. The IEDFs of H 2 + and H 3 + appear similar, showing a broad distribution with a cut-off energy at approximately 8 eV. In contrast, the IEDF of H⁺ shows an energetic tail up to 18 eV. Most probably, the ions in this tail gain their energy during their creation process by photoionization and dissociative electron impact ionization. [ABSTRACT FROM AUTHOR]