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Title: Optimizing 13.5 nm laser-produced tin plasma emission as a function of laser wavelength

Abstract

Extreme ultraviolet lithography requires a light source at 13.5 nm to match the proposed multilayer optics reflectivity. The impact of wavelength and power density on the ion distribution and electron temperature in a laser-produced plasma is calculated for Nd:YAG and CO{sub 2} lasers. A steady-state figure of merit, calculated to optimize emission as a function of laser wavelength, shows an increase with a CO{sub 2} laser. The influence of reduced electron density in the CO{sub 2} laser-produced plasma is considered in a one-dimensional radiation transport model, where a more than twofold increase in conversion efficiency over that attainable with the Nd:YAG is predicted.

Authors:
; ; ; ;  [1]
  1. School of Physics, University College Dublin, Belfield, Dublin 4 (Ireland)
Publication Date:
OSTI Identifier:
20971895
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 90; Journal Issue: 18; Other Information: DOI: 10.1063/1.2735944; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; CARBON DIOXIDE LASERS; ELECTRON DENSITY; ELECTRON TEMPERATURE; EXTREME ULTRAVIOLET RADIATION; ION TEMPERATURE; LASER-PRODUCED PLASMA; LIGHT SOURCES; NEODYMIUM LASERS; ONE-DIMENSIONAL CALCULATIONS; OPTICS; OPTIMIZATION; PERFORMANCE; PLASMA DENSITY; PLASMA PRODUCTION; POWER DENSITY; RADIATION TRANSPORT; REFLECTIVITY; STEADY-STATE CONDITIONS; TIN; WAVELENGTHS

Citation Formats

White, J., Dunne, P., Hayden, P., O'Reilly, F., and O'Sullivan, G. Optimizing 13.5 nm laser-produced tin plasma emission as a function of laser wavelength. United States: N. p., 2007. Web. doi:10.1063/1.2735944.
White, J., Dunne, P., Hayden, P., O'Reilly, F., & O'Sullivan, G. Optimizing 13.5 nm laser-produced tin plasma emission as a function of laser wavelength. United States. doi:10.1063/1.2735944.
White, J., Dunne, P., Hayden, P., O'Reilly, F., and O'Sullivan, G. Mon . "Optimizing 13.5 nm laser-produced tin plasma emission as a function of laser wavelength". United States. doi:10.1063/1.2735944.
@article{osti_20971895,
title = {Optimizing 13.5 nm laser-produced tin plasma emission as a function of laser wavelength},
author = {White, J. and Dunne, P. and Hayden, P. and O'Reilly, F. and O'Sullivan, G.},
abstractNote = {Extreme ultraviolet lithography requires a light source at 13.5 nm to match the proposed multilayer optics reflectivity. The impact of wavelength and power density on the ion distribution and electron temperature in a laser-produced plasma is calculated for Nd:YAG and CO{sub 2} lasers. A steady-state figure of merit, calculated to optimize emission as a function of laser wavelength, shows an increase with a CO{sub 2} laser. The influence of reduced electron density in the CO{sub 2} laser-produced plasma is considered in a one-dimensional radiation transport model, where a more than twofold increase in conversion efficiency over that attainable with the Nd:YAG is predicted.},
doi = {10.1063/1.2735944},
journal = {Applied Physics Letters},
number = 18,
volume = 90,
place = {United States},
year = {Mon Apr 30 00:00:00 EDT 2007},
month = {Mon Apr 30 00:00:00 EDT 2007}
}
  • An examination of the influence of target composition and viewing angle on the extreme ultraviolet spectra of laser produced plasmas formed from tin and tin doped planar targets is reported. Spectra have been recorded in the 9-17 nm region from plasmas created by a 700 mJ, 15 ns full width at half maximum intensity, 1064 nm Nd:YAG laser pulse using an absolutely calibrated 0.25 m grazing incidence vacuum spectrograph. The influence of absorption by tin ions (Sn I-Sn X) in the plasma is clearly seen in the shape of the peak feature at 13.5 nm, while the density of tinmore » ions in the target is also seen to influence the level of radiation in the 9-17 nm region.« less
  • Extreme ultraviolet lithography semiconductor manufacturing requires a 13.5 nm light source. Laser-produced plasma emission from Sn V-Sn XIV ions is one proposed industry solution. The effect of laser pulse width and spatial profile on conversion efficiency is analyzed over a range of power densities using a two-dimensional radiative magnetohydrodynamic code and compared to experiment using a 1.064 {mu}m, neodymium:yttrium aluminium garnet laser on a planar tin target. The calculated and experimental conversion efficiencies and the effects of self-absorption in the plasma edge are compared. Best agreement between theory and experiment is found for an 8.0 ns Gaussian pulse.
  • The angular distribution of extreme ultraviolet emission at 13.5 nm within 2% bandwidth was characterized for laser irradiated, planar, Sn targets at prototypic conditions for a lithography system. We have found that two dimensional plasma expansion plays a key role in the distribution of in-band 13.5 nm emission under these conditions. The angular distribution was found to have two peaks at 45 deg. and 15 deg. This complex angular distribution arises from the shape of both the emitting plasma and the surrounding absorbing plasma. This research reveals that the detailed angular distribution can be important to the deduction of conversionmore » efficiency.« less
  • Extreme ultraviolet lithography schemes for the semiconductor industry are currently based on coupling radiation from a plasma source into a 2% bandwidth at 13.5 nm (91.8 eV). In this paper, we consider the case for a laser-produced plasma (LPP) and address the calculation of ionic level populations in the 4p{sup 6}4d{sup N}, 4p{sup 6}4d{sup N-1}4f{sup 1}, 4p{sup 5}4d{sup N+1}, and 4p{sup 6}4d{sup N-1}5p{sup 1} configurations in a range of tin ions (Sn{sup 6+} to Sn{sup 13+}) producing radiation in this bandwidth. The LPP is modeled using a one-dimensional hydrodynamics code, which uses a hydrogenic, average atom model, where the levelmore » populations are treated as l degenerate. Hartree-Fock calculations are used to remove the l degeneracy and an energy functional method to calculate the nl level populations involved in n=4-4 transitions as a function of distance from the target surface and time. Detailed data are presented for the tin ions that contribute to in-band emission.« less
  • Many next generation lithography schemes for the semiconductor industry are based on a 13.5 nm tin plasma light source, where hundreds of thousands of 4d-4f, 4p-4d, and 4d-5p transitions from Sn{sup 5+}-Sn{sup 13+} ions overlap to form an unresolved transition array. To aid computation, transition arrays are treated statistically, and Hartree-Fock results are used to calculate radiation transport in the optically thick regime with a one-dimensional Lagrangian plasma hydrodynamics code. Time-dependent spectra and conversion efficiencies of 2% in-band 13.5 nm emission to laser energy are predicted for a Nd:YAG (yttrium aluminum garnet) laser incident on a pure tin slab targetmore » as a function of laser power density and pulse duration at normal incidence. Calculated results showed a maximum conversion efficiency of 2.3% for a 10 ns pulse duration at 8.0x10{sup 10} W/cm{sup 2} and are compared to experimental data where available. Evidence for the need to include lateral expansion is presented.« less