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  • Received: Nov. 12, 2019

    Accepted: Jan. 16, 2020

    Posted: Apr. 28, 2020

    Published Online: Apr. 29, 2020

    The Author Email: Junwu Wang (wjw1546112421@163.com)

    DOI: 10.3788/COL202018.051405

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    Junwu Wang, Xinbing Wang, Duluo Zuo, Vassily Zakharov. Laser-induced liquid tin discharge plasma and its EUV spectra[J]. Chinese Optics Letters, 2020, 18(5): 051405

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Chinese Optics Letters, Vol. 18, Issue 5, 051405 (2020)

Laser-induced liquid tin discharge plasma and its EUV spectra

Junwu Wang1,*, Xinbing Wang1, Duluo Zuo1, and Vassily Zakharov2

Author Affiliations

  • 1Wuhan National Research Center for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074, China
  • 2Keldysh Institute of Applied Mathematics, Russian Academy of Sciences, Moscow 125047, Russia

Abstract

Laser-induced discharge plasmas (LDPs) have the potential to be inspection and metrology sources in extreme ultraviolet (EUV) lithography. An LDP EUV source was developed to avoid tin electrode erosion in which a tin pool was used as a cathode. A CO2 pulse laser was focused on the liquid tin target surface, and then a breakdown occurred in a very short time. The voltage-current characteristics of the discharge oscillated, lasting for several microseconds, and an RLC fitting model was used to obtain the inductance and resistance. An intensified charge-coupled device (ICCD) camera was used to investigate the dynamics of LDP, which can explain the formation of a discharge channel. The EUV spectra of laser-induced liquid tin discharge plasma were detected by a grazing incident ultraviolet spectrometer, compared with a laser-produced tin droplet plasma EUV spectrum. To explain the EUV spectrum difference of laser-induced liquid tin discharge plasma and laser-produced tin droplet plasma, the collision radiation (CR) model combined with COWAN code was used to fit the experimental EUV spectrum, which can estimate the electron temperature and density of the plasma.

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