Angular distribution of ions and extreme ultraviolet emission in laser-produced tin droplet plasma

Cai, Hong; Wang, Xinbing; Duan, Lian; Liu, Hui; Chen, Ziqi; Zuo, Duluo; Lu, Peixiang

doi:10.1063/1.4921532

Cited by 13 publications

(9 citation statements)

References 33 publications

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“…As energy is invariably lost through other processes such as ionization and plasma kinetics, we conclude that a finite anisotropy conveniently causes a preferred emission of light into the backwards half sphere as also indicated, e.g., in Ref. [51].…”

Section: Model Fit and Discussionsupporting

confidence: 81%

“…The literature on Nd:YAG-driven tin plasma mostly deals with the emission from planar solid targets [31][32][33][34][35][36][37][38][39][40][41][42], tin-coated spherical targets [29,[43][44][45][46][47], or liquid-droplet targets out of tin alloys [48]. The literature covering the emission properties of laser-produced plasma (LPP) from high-purity tin microdroplets, the industrial targets of choice, remains scarce [49][50][51].…”

Section: Introductionmentioning

confidence: 99%

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Efficient Generation of Extreme Ultraviolet Light From Nd :YAG-Driven Microdroplet-Tin Plasma

et al. 2019

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We experimentally investigate the emission of EUV light from a mass-limited laser-produced plasma over a wide parameter range by varying the diameter of the targeted tin microdroplets and the pulse duration and energy of the 1-μm-wavelength Nd:YAG drive laser. Combining spectroscopic data with absolute measurements of the emission into the 2% bandwidth around 13.5 nm relevant for nanolithographic applications, the plasma's efficiency in radiating EUV light is quantified. All observed dependencies of this radiative efficiency on the experimental parameters are successfully captured in a geometrical model featuring the plasma absorption length as the primary parameter. It is found that laser intensity is the pertinent parameter setting the plasma temperature and the tin-ion charge-state distribution when varying laser pulse energy and duration over almost 2 orders of magnitude. These insights enabled us to obtain a record-high 3.2% conversion efficiency of laser light into 13.5-nm radiation and to identify paths towards obtaining even higher efficiencies with 1-μm solid-state lasers that may rival those of current state-of-the-art CO 2-laser-driven sources.

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Section: Model Fit and Discussionsupporting

confidence: 81%

Section: Introductionmentioning

confidence: 99%

Efficient Generation of Extreme Ultraviolet Light From Nd :YAG-Driven Microdroplet-Tin Plasma

et al. 2019

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“…3(g)) is very similar for both drive lasers and is consistent with previous studies where a 1µm laser was used to drive the LPP from a droplet target [32,41,55]. The similarities in the angular distributions is in line with a previous study by Chen et al [63] where only minor changes in emission anisotropy were found between 1-and 10-µm-driven droplet plasmas. Similarly to Sec.…”

Section: Euv Generation Using 1-and 2-µm Laser Lightsupporting

confidence: 90%

Characterization of angularly resolved EUV emission from 2-$μ$m-wavelength laser-driven Sn plasmas using preformed liquid disk targets

Schupp,

Behnke,

Bouza

et al. 2021

Preprint

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The emission properties of tin plasmas, produced by the irradiation of preformed liquid tin targets by severalns-long 2-µm-wavelength laser pulses, are studied in the extreme ultraviolet (EUV) regime. In a two-pulse scheme, a pre-pulse laser is first used to deform tin microdroplets into thin, extended disks before the main (2 µm) pulse creates the EUV-emitting plasma. Irradiating 30-to 300-µm-diameter targets with 2-µm laser pulses, we find that the efficiency in creating EUV light around 13.5 nm follows the fraction of laser light that overlaps with the target. Next, the effects of a change in 2-µm drive laser intensity (0.6-1.8 × 10 11 W/cm 2 ) and pulse duration (3.7-7.4 ns) are studied. It is found that the angular dependence of the emission of light within a 2% bandwidth around 13.5 nm and within the backward 2π hemisphere around the incoming laser beam is almost independent of intensity and duration of the 2-µm drive laser. With increasing target diameter, the emission in this 2% bandwidth becomes increasingly anisotropic, with a greater fraction of light being emitted into the hemisphere of the incoming laser beam. For direct comparison, a similar set of experiments is performed with a 1-µm-wavelength drive laser. Emission spectra, recorded in a 5.5-25.5 nm wavelength range, show significant self-absorption of light around 13.5 nm in the 1-µm case, while in the 2-µm case only an opacity-related broadening of the spectral feature at 13.5 nm is observed. This work demonstrates the enhanced capabilities and performance of 2-µm-driven plasmas produced from disk targets when compared to 1-µmdriven plasmas, providing strong motivation for the use of 2-µm lasers as drive lasers in future high-power sources of EUV light.

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“…24 Given the importance of SP as an indicator for source performance, its scaling with relevant source parameters such as tin-droplet size, laser pulse duration, and laser beam spot size needs to be quantified and understood. The existing literature on Nd:YAG-laser-driven plasma from high-purity tin microdroplets, [30][31][32] the industrial targets of choice, mainly focuses on the integrated amount of produced in-band emission rather than on the spectral properties of the plasma despite the importance of SP.…”

mentioning

confidence: 99%

Radiation transport and scaling of optical depth in Nd:YAG laser-produced microdroplet-tin plasma

Schupp

Torretti

Meijer

et al. 2019

Applied Physics Letters

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Experimental scaling relations of the optical depth are presented for the emission spectra of a tin-droplet-based, 1-lm-laser-produced plasma source of extreme-ultraviolet (EUV) light. The observed changes in the complex spectral emission of the plasma over a wide range of droplet diameters (16-65 lm) and laser pulse durations (5-25 ns) are accurately captured in a scaling relation featuring the optical depth of the plasma as a single, pertinent parameter. The scans were performed at a constant laser intensity of 1.4 Â 10 11 W/cm 2 , which maximizes the emission in a 2% bandwidth around 13.5 nm relative to the total spectral energy, the bandwidth relevant for industrial EUV lithography. Using a one-dimensional radiation transport model, the relative optical depth of the plasma is found to linearly increase with the droplet size with a slope that increases with the laser pulse duration. For small droplets and short laser pulses, the fraction of light emitted in the 2% bandwidth around 13.5 nm relative to the total spectral energy is shown to reach high values of more than 14%, which may enable conversion efficiencies of Nd:YAG laser light into-industrially-useful EUV radiation rivaling those of current state-of-the-art CO 2 -laser-driven sources.

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Angular distribution of ions and extreme ultraviolet emission in laser-produced tin droplet plasma

Cited by 13 publications

References 33 publications

Efficient Generation of Extreme Ultraviolet Light From Nd :YAG-Driven Microdroplet-Tin Plasma

Efficient Generation of Extreme Ultraviolet Light From Nd :YAG-Driven Microdroplet-Tin Plasma

Characterization of angularly resolved EUV emission from 2-$μ$m-wavelength laser-driven Sn plasmas using preformed liquid disk targets

Radiation transport and scaling of optical depth in Nd:YAG laser-produced microdroplet-tin plasma

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