Ion energy distributions in highly transient EUV induced plasma in hydrogen

Abstract

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 (k ¼ 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 þ ; H þ 2 , and H þ 3. H þ 3 is the dominant ion as a result of the efficient conversion of H þ 2 to H þ 3 upon collision with background hydrogen molecules. The IEDFs of H þ 2 and H þ 3 appear similar, showing a broad distribution with a cutoff energy at approximately 8 eV. In contrast, the IEDF of H þ 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.

EUV-Induced Plasma: A Peculiar Phenomenon of a Modern Lithographic Technology

“…Experimentally, no etching was measured at a grounded sample in 3 Pa H 2 while using a photon fluence of 5 × 10 19 cm −2 [64]. This agrees with the experimental ion energy distributions that were measured in [59] (<8 eV) and the threshold of 10 eV. By increasing the bias voltage, and thereby the ion impact energy, yields between 0.1 C/ion and 1 C/ion were found.…”

“…to form H 3 + ions. Whereas, H 3 + has been recognized as the dominant ion in radiation-induced plasmas in H 2 background gas in outer-space, recent research has shown that this ion is also dominant under lithography scanner conditions on time scales longer than a few 100 ns after irradiation [59].…”

“…Ion species resolved ion energy distributions towards a grounded surface have been measured while using an ion mass spectrometer [59] (See Figure 10) [59]. Nevertheless, experimental data remains scarce and no data is available during, and shortly after, the EUV pulse, when the ion fluxes are expected to be large and ion energies to be high.…”

“…Increased pressures (i.e., up to 100 Pa) appear to have the same effect. Furthermore, the IEDF towards grounded or floating walls consists of large fractions of low energy (<10 eV) ions [59]. Therefore, the validity of the used ion sources as a proxy for EUV-induced plasmas strongly depends on the targeted experimental conditions.…”

Near-threshold sputter yields of ruthenium under argon and nitrogen ion bombardment

“…High temperature, dense plasmas in fusion reactors [1], diffuse plasmas induced by extreme ultraviolet radiation [2] and dense low pressure plasmas in laboratory ion sources and for electric propulsion [3]. Plasma facing materials (PFMs), such as divertors in fusion reactors are bombarded by hydrogen and deuterium ion species [4], ion lensing systems for electric propulsion technology deteriorate under xenon ion impingement and optics in next generation lithography applications face diffuse hydrogen and nitrogen plasmas [5,6].…”