Thomson Scattering Diagnostics of High Pressure Plasmas and Plasma Disturbances by Lasers

Tomita, Kentaro; Hassaballa, Safwat; Uchino, Kenji

doi:10.1541/ieejfms.130.1099

Cited by 11 publications

(12 citation statements)

References 3 publications

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“…The sufficient reproducibility of the spectra was also confirmed. Regarding the plasma heating by the probe laser, the relative temperature increase (Δ T e / T e ) was discussed in a previous paper 18 based on a model considering the absorption by the inverse bremsstrahlung and of the heat transport to the volume surrounding the laser beam during the laser pulse 19 , 20 . As a result, Δ T e / T e was estimated to be less than 3% for the cases reported here.…”

Section: Resultsmentioning

confidence: 99%

Time-resolved two-dimensional profiles of electron density and temperature of laser-produced tin plasmas for extreme-ultraviolet lithography light sources

Tomita

Sato

Tsukiyama

et al. 2017

Sci Rep

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Time-resolved two-dimensional (2D) profiles of electron density (n e ) and electron temperature (T e ) of extreme ultraviolet (EUV) lithography light source plasmas were obtained from the ion components of collective Thomson scattering (CTS) spectra. The highest EUV conversion efficiency (CE) of 4% from double pulse lasers irradiating a Sn droplet was obtained by changing their delay time. The 2D-CTS results clarified that for the highest CE condition, a hollow-like density profile was formed, i.e., the high density region existed not on the central axis but in a part with a certain radius. The 2D profile of the inband EUV emissivity (η EUV ) was theoretically calculated using the CTS results and atomic model (Hullac code), which reproduced a directly measured EUV image reasonably well. The CTS results strongly indicated the necessity of optimizing 2D plasma profiles to improve the CE in the future.Extreme-ultraviolet lithography is a promising technology for high-volume manufacturing of next-generation semiconductor devices [1][2][3] . A carbon dioxide (CO 2 ) drive laser and a tin droplet target are used as an efficient extreme-ultraviolet (EUV) light source 4,5 . One of the primary challenges involves the improvement of the conversion efficiency (CE) from laser energy to in-band EUV energy at a wavelength of λ = 13.5 nm (2% full-bandwidth) 5,6 . Debris reduction is also a crucial problem for commercial usage 7 . Therefore, mass-limited targets, such as small tin droplets with a diameter on the order of 20 μm, have been introduced 8 . However, it is desirable to have a large EUV plasma volume within the etendue limits to achieve a large EUV emission 9 . A double-pulse irradiation scheme is proposed, where a pre-pulse laser expands a small tin droplet, and the main laser irradiates when it reaches a size of approximately 300 μm in diameter 7,8 . A CE of approximately 4% was confirmed using this approach 5 .A strong correlation has recently been shown between the laser absorption and the CE by changing the delay time between the pre-and main-pulse lasers 10 . However, the reported CE was approximately 2% at the highest. The EUV emissivity strongly depends on plasma parameters, such as electron density (n e ), electron temperature (T e ), and average ion charge state (Z) [11][12][13] . Hence, we developed a collective Thomson scattering (CTS) system to measure these parameters [14][15][16] . In our previous study, it was confirmed that adequate n e and T e were achieved in the EUV light source plasmas, but this did not provide optimum plasma conditions for high CE 17 .This paper determined for the first time that it is important to generate a plasma with an optimal two-dimensional (2D) structure to achieve a large EUV conversion efficiency by adding theoretical analysis to

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Section: Resultsmentioning

confidence: 99%

Time-resolved two-dimensional profiles of electron density and temperature of laser-produced tin plasmas for extreme-ultraviolet lithography light sources

Tomita

Sato

Tsukiyama

et al. 2017

Sci Rep

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“…If the heating model shown in Ref. [21] is used, the plasma heating under our experimental conditions can be estimated to be < 0.2 eV. To confirm this experimentally, we compared the measured electron temperatures obtained when a measurement laser energy E L = 90 mJ was used with those when E L was halved (45 mJ).…”

Section: Resultsmentioning

confidence: 53%

“…Therefore, it is necessary to investigate the presence of plasma heating by the probing laser [20]. [21] is used, the plasma heating under our experimental conditions can be estimated to be < 0.2 eV. [21].…”

Section: Resultsmentioning

confidence: 99%

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Measurements of Electron Density and Electron Temperature of Arc Discharge Plasmas Containing Metallic Vapors Using Laser Thomson Scattering

Tomita

Yoshitake

Uchino

et al. 2014

Electrical Engineering Japan

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Laser Thomson scattering (LTS) was applied to arc discharges generated in the atmosphere to measure electron density (n e ) and electron temperature (T e ). The electrode gap was 0.8 mm, and the electrode diameter was 1 mm. The applied voltage was 6 kV, the peak current was 600 A, and the decay time of the voltage and current was 25 μs. The spatiotemporal evolution of n e and T e was measured 10, 30, and 50 μs after discharge initiation. At these times, the obtained values of n e and T e were estimated to be in the ranges of (0.8 to 2.0) × 10 23 m −3 and 1.0 to 2.2 eV, respectively. These values were consistent with those evaluated using Saha's thermodynamic equation at 1 atm. It was also found that the decay of the arc discharge produced using the tungsten-copper electrodes was much faster than that produced using the tungsten electrodes. C⃝ 2014 Wiley Periodicals, Inc. Electr Eng Jpn, 188(4): 1-8, 2014; Published online in Wiley Online Library (wileyonlinelibrary.com).

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“…The heating effect by the probe was minimized and verified to be negligible. 20) The measured temporally and spatially resolved profiles of the electron density n e , electron temperature T e , and drift velocity V z are presented as functions of time and Z at = Y 0 as contour plots in Figs. 3(a)-3(c), respectively.…”

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confidence: 99%

Time-resolved two-dimensional measurements of the electron density, electron temperature, and drift velocity of laser-produced carbon plasmas using the ion feature of collective laser Thomson scattering

Pan¹,

Tomita²,

Uchino³

et al. 2021

Appl. Phys. Express

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Temporal evolutions of two-dimensional (2D) plasma profiles produced by Nd:YAG laser ( 5.9 × 10 9 W cm − 2 , 8 ns FWHM) were investigated at 5–25 ns after the laser peak at 0.2–0.5 mm from the initial target surface by measuring the electron density (n e), temperature (T e), and drift velocity (V d). The T e profiles were nonuniform and showed a peak at 0.3 to 0.4 mm above the target surface. The high-temperature region of the plasma moved outward at the same speed as that of the expansion of the plasma, indicating the isothermal expansion ends immediately after the ablation pulse. The 2D profiles of V d and pressure also show that the plasma expanded anisotropically.

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Thomson Scattering Diagnostics of High Pressure Plasmas and Plasma Disturbances by Lasers

Cited by 11 publications

References 3 publications

Time-resolved two-dimensional profiles of electron density and temperature of laser-produced tin plasmas for extreme-ultraviolet lithography light sources

Time-resolved two-dimensional profiles of electron density and temperature of laser-produced tin plasmas for extreme-ultraviolet lithography light sources

Measurements of Electron Density and Electron Temperature of Arc Discharge Plasmas Containing Metallic Vapors Using Laser Thomson Scattering

Time-resolved two-dimensional measurements of the electron density, electron temperature, and drift velocity of laser-produced carbon plasmas using the ion feature of collective laser Thomson scattering

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