Spectral irradiance of singly and doubly ionized zinc in low-intensity laser-plasma ultraviolet light sources

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.

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Generation of collimated far-ultraviolet (FUV) light using the laser-produced metal plasma

Ohnishi

Tamaki

Shiina

et al. 2023

Journal of Applied Physics

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Laser-produced plasma is a promising compact light source applicable in a broad range of wavelengths. We performed a spectroscopic analysis and plasma characterization of the laser-produced plasma of Al, Fe, Cu, and Inconel alloy (Ni/Cr/Fe) to explore their potential applications in the far-ultraviolet (FUV) region where these methods are yet widely exploited. The emission spectrum from each target exhibited a characteristic spectral profile over the wavelength range from 120 to 250 nm. These results were well reproduced by spectral simulations, providing detailed information on the plasma. We also developed a dedicated parabolic mirror that successfully collimated the plasma radiation into beam with an intensity enhanced by a factor of ∼35. Our study demonstrated the generation of collimated FUV radiation with an intensity of a 107 photons/pulse/1% bandwidth as a potent laboratory-size light source for various applications.

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Spectral irradiance of singly and doubly ionized zinc in low-intensity laser-plasma ultraviolet light sources

Cited by 5 publications

References 39 publications

Quantitative analysis of vacuum-ultraviolet radiation from nanosecond laser-zinc interaction

Quantitative analysis of vacuum-ultraviolet radiation from nanosecond laser-zinc interaction

Ultraviolet out-of-band radiation studies in laser tin plasma sources

Generation of collimated far-ultraviolet (FUV) light using the laser-produced metal plasma

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