Acta Optica Sinica, Volume. 32, Issue 4, 430002(2012)
Extreme Ultraviolet and Visible Emission Spectroscopic Characterization of CO2 Laser Produced Tin Plasma for Lithography
The experiments of laser-produced tin plasma are carried out using a CO2 laser with the energy of 400 mJ of each pulse and the full width at half maximum (FWHM) of 75 ns. The temporal evolution of visible emission spectrum are measured using a spectrograph coupled with an intensified charge-coupled device (ICCD) in vacuum. The plasma electron temperature is inferred by the Bolzmann plot method from five singly ionized Sn emission lines, while electron density measurements are made using Stark broadening method by assuming the conditions of local thermodynamic equilibrium. Extreme ultraviolet (EUV) spectral measurement is made throughout the wavelength region of 6.5~16.8 nm using a grazing incidence flat-field grating spectrometer coupled with an X-ray CCD for the detection of time-integrated spectrum. The results show that optical emission spectrum is mainly the continuous spectrum at the early stage of plasma expansion (within the first 100 ns) and the continuous spectrum weakens gradually while the line spectrum becomes dominating. Electron temperature is measured in the range of 2.3~0.5 eV, and electron density is measured in the range of 7.6×1017~1.2×1016 cm-3, as the time delay is varied from 0.1 to 2.0 μs. Both the electron temperature and density decrease fast at early delay time and slowly decrease at later delay time. The extreme ultraviolet emission measurement of laser-produced-tin plasma shows that the peak of the EUV spectrum is located at 13.5 nm and the FWHM of the unresolved transition arrays is 1.1 nm.
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Wu Tao, Wang Xinbing, Tang Jian, Wang Shaoyi, Rao Zhiming, Yang Chenguang, Lu Hong. Extreme Ultraviolet and Visible Emission Spectroscopic Characterization of CO2 Laser Produced Tin Plasma for Lithography[J]. Acta Optica Sinica, 2012, 32(4): 430002
Category: Spectroscopy
Received: Sep. 29, 2011
Accepted: --
Published Online: Feb. 24, 2012
The Author Email: Tao Wu (wtlaser@126.com)