skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Extreme ultraviolet radiation emitted by helium microwave driven plasmas

Abstract

The extreme ultraviolet radiation emitted by helium microwave-driven (2.45 GHz) plasmas operating at low-pressure conditions was investigated. Novel data regarding emitted spectral lines of excited helium atoms and ions in the 20–33 nm wavelength range and their intensity behavior with variation of discharge operational conditions are presented. The intensity of all the spectral emissions was found to strongly increase with the microwave power delivered to the plasma. Furthermore, the intensity of the ionic spectral emissions decreases by nearly one order of magnitude as the pressure was raised from 0.2 to 0.5 mbar.

Authors:
; ; ;  [1]
  1. Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisboa (Portugal)
Publication Date:
OSTI Identifier:
22596663
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 119; Journal Issue: 24; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ATOMS; EMISSION; EXTREME ULTRAVIOLET RADIATION; GHZ RANGE 01-100; HELIUM; MICROWAVE RADIATION; PLASMA; WAVELENGTHS

Citation Formats

Espinho, S., Felizardo, E., Tatarova, E., E-mail: e.tatarova@tecnico.ulisboa.pt, and Alves, L. L. Extreme ultraviolet radiation emitted by helium microwave driven plasmas. United States: N. p., 2016. Web. doi:10.1063/1.4954850.
Espinho, S., Felizardo, E., Tatarova, E., E-mail: e.tatarova@tecnico.ulisboa.pt, & Alves, L. L. Extreme ultraviolet radiation emitted by helium microwave driven plasmas. United States. doi:10.1063/1.4954850.
Espinho, S., Felizardo, E., Tatarova, E., E-mail: e.tatarova@tecnico.ulisboa.pt, and Alves, L. L. 2016. "Extreme ultraviolet radiation emitted by helium microwave driven plasmas". United States. doi:10.1063/1.4954850.
@article{osti_22596663,
title = {Extreme ultraviolet radiation emitted by helium microwave driven plasmas},
author = {Espinho, S. and Felizardo, E. and Tatarova, E., E-mail: e.tatarova@tecnico.ulisboa.pt and Alves, L. L.},
abstractNote = {The extreme ultraviolet radiation emitted by helium microwave-driven (2.45 GHz) plasmas operating at low-pressure conditions was investigated. Novel data regarding emitted spectral lines of excited helium atoms and ions in the 20–33 nm wavelength range and their intensity behavior with variation of discharge operational conditions are presented. The intensity of all the spectral emissions was found to strongly increase with the microwave power delivered to the plasma. Furthermore, the intensity of the ionic spectral emissions decreases by nearly one order of magnitude as the pressure was raised from 0.2 to 0.5 mbar.},
doi = {10.1063/1.4954850},
journal = {Journal of Applied Physics},
number = 24,
volume = 119,
place = {United States},
year = 2016,
month = 6
}
  • A precise absolute intensity calibration of a flat-field space-resolved extreme ultraviolet (EUV) spectrometer working in wavelength range of 60-400 A is carried out using a new calibration technique based on radial profile measurement of the bremsstrahlung continuum in Large Helical Device. A peaked vertical profile of the EUV bremsstrahlung continuum has been successfully observed in high-density plasmas (n{sub e}{>=} 10{sup 14} cm{sup -3}) with hydrogen ice pellet injection. The absolute calibration can be done by comparing the EUV bremsstrahlung profile with the visible bremsstrahlung profile of which the absolute value has been already calibrated using a standard lamp. The line-integratedmore » profile of measured visible bremsstrahlung continuum is firstly converted into the local emissivity profile by considering a magnetic surface distortion due to the plasma pressure, and the local emissivity profile of EUV bremsstrahlung is secondly calculated by taking into account the electron temperature profile and free-free gaunt factor. The line-integrated profile of the EUV bremsstrahlung continuum is finally calculated from the local emissivity profile in order to compare with measured EUV bremsstrahlung profile. The absolute intensity calibration can be done by comparing measured and calculated EUV bremsstrahlung profiles. The calibration factor is thus obtained as a function of wavelength with excellent accuracy. It is also found in the profile analysis that the grating reflectivity of EUV emissions is constant along the direction perpendicular to the wavelength dispersion. Uncertainties on the calibration factor determined with the present method are discussed including charge-coupled device operation modes.« less
  • Properties of ion debris emitted from laser-produced mass-limited tin plasmas have been experimentally investigated for an application to extreme ultraviolet (EUV) lithography. Simple scaling laws to design the mass-limited target, which is a key technique to minimize contamination of the first EUV collection mirror, is discussed. The measured energy spectrum of the tin ions is consistent with a prediction by the isothermal expansion model. The average charge state of the tin ions is evaluated to be +5 at 180 mm away from the plasma, and higher-energy ions have higher charge state. It was found that not only EUV emission butmore » also ion energy spectra are sensitively affected by the target mass limitation.« less
  • The cause of the lower intensities of extreme-ultraviolet (EUV) He II lines emitted by coronal hole (CH) plasmas compared with quiet Sun (QS) plasmas has been the subject of many studies dating back over half a century. In this paper, we study the effect of small amounts of 'hot' electrons at coronal temperatures (T{sub e} = 1.4 x 10{sup 6} K) on the intensities of EUV He II lines, as well as on the intensities of EUV lines of C III, C IV, O III, and O IV emitted by 1.5 x 10{sup 4} K-1.5 x 10{sup 5} K (4.2more » <= log T{sub e} <= 5.2) plasmas in the QS. We show that although the influence of a fraction as small as 10{sup -4}-10{sup -3} of hot electrons on the intensities of the C and O lines is noticeable, the effect on the intensities of the He lines is much larger, to the extent that it could explain the excess brightness of He II lines emitted by QS regions relative to CH plasmas.« less
  • A self-consistent kinetic particle-in-cell model has been developed to describe a radiation driven plasma. Collisions between charged species and the neutral background are represented statistically by Monte Carlo collisions. The weakly ionized plasma is formed when extreme ultraviolet radiation coming from a pulsed discharge photoionizes a low pressure argon gas. The presence of a plasma close to optical components is potentially dangerous in case the ions that are accelerated in the plasma sheath gain enough energy to sputter the optics. The simulations predict the plasma parameters and notably the energy at which ions impact on the plasma boundaries. Finally, sputtermore » rates are estimated on the basis of two sputtering models.« less
  • Future generation lithography tools will use extreme ultraviolet radiation to enable the printing of sub-50 nanometer features on silicon wafers. The extreme ultraviolet radiation, coming from a pulsed discharge, photoionizes the low pressure background gas in the tool. A weakly ionized plasma is formed, which will be in contact with the optical components of the lithography device. In the plasma sheath region ions will be accelerated towards the surfaces of multilayer mirrors. A self-consistent kinetic particle-in-cell model has been applied to describe a radiation driven plasma. The simulations predict the plasma parameters and notably the energy at which ions impactmore » on the plasma boundaries. We have studied the influence of photoelectron emission from the mirror on the sheath dynamics and on the ion impact energy. Furthermore, the ion impact energy distribution has been convoluted with the formula of Yamamura and Tawara [At. Data Nucl. Data Tables 62, 149 (1996)] for the sputter yield to obtain the rate of physical sputtering. The model predicts that the sputter rate is dominated by the presence of doubly ionized argon ions.« less