Ultraviolet Out-Of-Band Radiation Studies In Laser Tin Plasma Sources
Abstract
Out-of-band long wavelength emission measurements from high power, high-repetition-rate extreme-ultra-violet lithography (EUVL) laser plasma sources are imperative to estimating heat deposition in EUV mirrors, and the impact of short wavelength light transported through the imaging system to the wafer surface. This paper reports a series of experiments conducted to measure the absolute spectral irradiances of laser-plasmas produced from planar tin targets over the wavelength region of 124 to 164 nm by 1.06 μm wavelength, 10 ns full-width-at-half-maximum Gaussian laser pulses. The use of spherical targets is relevant to the EUVL source scenario. Although plasmas produced from planar surfaces evolve differently, there is a close similarity to the evolution of current from 10.6 μm CO2 laser EUVL sources, which use a pre-pulse from a lower energy solid-state laser to melt and reform an initial spherical droplet into a thin planar disc target. The maximum of radiation conversion efficiency in the 124-164 nm wavelength band (1%/2πsr) occurs at the laser intensity of 1010 W cm-2. A developed collisional-radiative model reveals the strong experimental spectra that originate mainly from the 4d105p2-4d105s5p, 4d105p-4d105s resonance lines, and 4d95p-4d95s unresolved transition arrays from Sn III, Sn IV, and Sn V ions, respectively. The calculated conversion efficiencies using a 2D radiation-hydrodynamics model are in agreement with the measurements. The model predicts the out-of-band (100-400 nm) radiation conversion efficiencies generated by both 1.06 and 10.6 μm pulses. The 10.6 μm laser pulse produces a higher conversion efficiency (12%/2πsr) at the lower laser intensity of 109 W cm-2.
Publication Date
11-7-2017
Publication Title
Journal of Applied Physics
Volume
122
Issue
17
Document Type
Article
Personal Identifier
scopus
DOI Link
https://doi.org/10.1063/1.4986782
Copyright Status
Unknown
Socpus ID
85033362415 (Scopus)
Source API URL
https://api.elsevier.com/content/abstract/scopus_id/85033362415
STARS Citation
Parchamy, Homaira; Szilagyi, John; Masnavi, Majid; and Richardson, Martin, "Ultraviolet Out-Of-Band Radiation Studies In Laser Tin Plasma Sources" (2017). Scopus Export 2015-2019. 5075.
https://stars.library.ucf.edu/scopus2015/5075