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Title: Investigation of the interaction of a laser pulse with a preformed Gaussian Sn plume for an extreme ultraviolet lithography source

Abstract

The interaction of a laser pulse with a Sn preplasma formed by a low energy prepulse was investigated for an extreme ultraviolet (EUV) lithography light source. A much lower ion kinetic energy and nearly the same conversion efficiency from laser to in-band (2% bandwidth) 13.5 nm EUV light were simultaneously observed as compared with those from the direct interaction with a solid surface. The reason comes from the interaction of the laser pulse with a smooth preplume induced by the prepulse. The density profile of the preplume was measured with time-resolved shadowgraphy and could be fitted with a Gaussian function. The energy of the ions located at the flux peak E{sub p} scales with the length of the preplume l{sub s} as E{sub p}{proportional_to}1/l{sub s}. Laser absorption in the low-density preplume and ion acceleration during plasma expansion are discussed. This result provides a general way to control particle energy from a laser plasma interaction.

Authors:
; ; ; ;  [1];  [2]
  1. Department of Mechanical and Aerospace Engineering, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0438 (United States)
  2. (United States)
Publication Date:
OSTI Identifier:
20982628
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 101; Journal Issue: 2; Other Information: DOI: 10.1063/1.2426883; (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; ABSORPTION; ACCELERATION; EXTREME ULTRAVIOLET RADIATION; GAUSS FUNCTION; KINETIC ENERGY; LASERS; LIGHT SOURCES; LIGHT TRANSMISSION; PLASMA; PLASMA DENSITY; PLASMA DIAGNOSTICS; PLASMA EXPANSION; PLUMES; PULSES; TIME RESOLUTION; TIN

Citation Formats

Tao, Y., Tillack, M. S., Harilal, S. S., Sequoia, K. L., Najmabadi, F., and Center for Energy Research, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0438. Investigation of the interaction of a laser pulse with a preformed Gaussian Sn plume for an extreme ultraviolet lithography source. United States: N. p., 2007. Web. doi:10.1063/1.2426883.
Tao, Y., Tillack, M. S., Harilal, S. S., Sequoia, K. L., Najmabadi, F., & Center for Energy Research, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0438. Investigation of the interaction of a laser pulse with a preformed Gaussian Sn plume for an extreme ultraviolet lithography source. United States. doi:10.1063/1.2426883.
Tao, Y., Tillack, M. S., Harilal, S. S., Sequoia, K. L., Najmabadi, F., and Center for Energy Research, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0438. Mon . "Investigation of the interaction of a laser pulse with a preformed Gaussian Sn plume for an extreme ultraviolet lithography source". United States. doi:10.1063/1.2426883.
@article{osti_20982628,
title = {Investigation of the interaction of a laser pulse with a preformed Gaussian Sn plume for an extreme ultraviolet lithography source},
author = {Tao, Y. and Tillack, M. S. and Harilal, S. S. and Sequoia, K. L. and Najmabadi, F. and Center for Energy Research, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0438},
abstractNote = {The interaction of a laser pulse with a Sn preplasma formed by a low energy prepulse was investigated for an extreme ultraviolet (EUV) lithography light source. A much lower ion kinetic energy and nearly the same conversion efficiency from laser to in-band (2% bandwidth) 13.5 nm EUV light were simultaneously observed as compared with those from the direct interaction with a solid surface. The reason comes from the interaction of the laser pulse with a smooth preplume induced by the prepulse. The density profile of the preplume was measured with time-resolved shadowgraphy and could be fitted with a Gaussian function. The energy of the ions located at the flux peak E{sub p} scales with the length of the preplume l{sub s} as E{sub p}{proportional_to}1/l{sub s}. Laser absorption in the low-density preplume and ion acceleration during plasma expansion are discussed. This result provides a general way to control particle energy from a laser plasma interaction.},
doi = {10.1063/1.2426883},
journal = {Journal of Applied Physics},
number = 2,
volume = 101,
place = {United States},
year = {Mon Jan 15 00:00:00 EST 2007},
month = {Mon Jan 15 00:00:00 EST 2007}
}
  • In this paper, experimental results are presented for the spatial and energy distributions of charge-discriminated Sn ions ejected from laser-produced plasmas. The plasmas were formed on solid, planar Sn targets, irradiated with a Nd:YAG laser. Ions were investigated using a calibrated electrostatic sector analyzer, scanning an energy-to-charge ratio range of 0.22 to 2.2 keV/e for emission angles between 20 and 80 degrees relative to target normal. Results were obtained for three laser power densities, in the region suitable for inducing significant extreme ultraviolet emission, of the order 1.5-8.1 x 10{sup 11} W/cm{sup 2}. The fully differentiated data were found tomore » be well characterized by Gaussian fits, which allowed trends in the emission profiles to be readily quantified. Ions of set energy and charge were observed to possess a preferential angle of emission, the superposition of which yields a physical basis for the total angular emission observed previously and in this work. The experimental results obtained have been related to physical processes within the plasma that influence the energy and angle of ejection of ions from laser produced plasmas.« less
  • The authors present evidence of the reduction of fast ion energy from laser-produced Sn plasma by introducing a low energy prepulse. The energy of Sn ions was reduced from more than 5 keV to less than 150 eV nearly without loss of the in-band conversion from laser to 13.5 nm extreme ultraviolet (EUV) emission as compared with that of a single pulse. The reason may come from the interaction of the main pulse with preplasma instead of the full density solid surface. This makes it possible to use the full density Sn target in the practical EUV lithography source.
  • An experimental study was made of a target consisting of the minimum mass of pure tin (Sn) necessary for the highest conversion to extreme ultraviolet (EUV) light while minimizing the generation of plasma debris. The minimum-mass target comprised a thin Sn layer coated on a plastic shell and was irradiated with a Nd:YAG laser pulse. The expansion behavior of neutral atoms and singly charged ions emanating from the Sn plasma were investigated by spatially resolved visible spectroscopy. A remarkable reduction of debris emission in the backward direction with respect to the incident laser beam was demonstrated with a decrease inmore » the thickness of the Sn layer. The optimal thickness of the Sn layer for a laser pulse of 9 ns at 7x10{sup 10} W/cm{sup 2} was found to be 40 nm, at which low-debris emission in the backward direction and a high conversion to 13.5 nm EUV radiation were simultaneously attained.« less
  • Out-of-band (OOB) radiation, in contrast to the in-band radiation at 13.5 nm in a 2% bandwidth, emitted from dense tin plasmas generated by a laser was investigated for application as an extreme ultraviolet lithography light source. It was found that the continuum spectrum, which overwhelms the atomic and ionic line emissions, is responsible for the intense OOB radiation. The spectral distribution of the continuum emission matches that of blackbody radiation with a temperature of about 10 eV. The OOB radiation can be considerably suppressed by employing a minimum-mass target and short-pulse laser irradiation. Spectroscopic observations were made to examine themore » spatiotemporal behavior of the plasma immediately after laser irradiation. Prominent line broadening due to the Stark effect in the high-density plasma was observed, from which the variation of the electron density was deduced. The electron density and temperature on the target surface were 10{sup 17}-10{sup 18} cm{sup -3} and a few eV's, respectively, in the first 200 ns after laser illumination. In addition, the expansion velocities of neutral and singly ionized tin atoms were deduced from time-of-flight transients in the spectral emission.« less
  • Laser-produced plasmas (LPP) from Sn targets are seriously considered to be the light source for extreme ultraviolet (EUV) next generation lithography, and optimization of such a source will lead to improved efficiency and reduced cost of ownership of the entire lithography system. We investigated the role of reheating a prepulsed plasma and its effect on EUV conversion efficiency (CE). A 6 ns, 1.06 {mu}m Nd:yttrium aluminum garnet laser was used to generate the initial plasma that was then reheated by a 40 ns, 10.6 {mu}m CO{sub 2} laser to generate enhanced EUV emission from a planar Sn target. The effectsmore » of prepulsed laser intensity and delay timings between the prepulsed and the pumping pulse were investigated to find the optimal pre-plasma conditions before the pumping pulse. The initial optimization of these parameters resulted in 25% increase in CE from the tin LPP. The cause of increased EUV emission was identified from EUV emission spectra and ion signal data.« less