The near infrared (0.8−2.6µm) absorption spectrum of a dense sodium vapor and possible mechanisms of the spectrum formation

We investigated the effect of the excitation wavelength on the density evolution of laser-produced tin plasmas, both experimentally and numerically. For producing plasmas, Sn targets were excited with either 10.6 lm CO 2 laser or 1.06 lm Nd:yttrium aluminum garnet laser; both are considered to be potential excitation lasers for extreme ultraviolet lithography laser-produced plasma light sources. The electron density of the plasma during the isothermal expansion regime was estimated using an interferometric technique. The Stark broadening of isolated singly-ionized emission was employed for deducing the density during the plasma adiabatic expansion regime. Our results indicate that the excitation source wavelength determines the initial density of the plasma, as well the plume expansion dynamics. Numerical simulation using HEIGHTS simulation package agrees well with the experimentally measured density profile. V

Section: Modeling Resultssupporting

confidence: 50%

The effect of excitation wavelength on dynamics of laser-produced tin plasma

Harilal¹,

Sizyuk²,

Hassanein³

et al. 2011

“…It is also important to take into account the re-absorption of laser radiation in the evolving plasma after the reflection from the liquid target surface. For accurate modeling of the above-described processes, we used available data of the experimental optical properties for laser reflection from liquid tin; 16,17 then, since one of the main features of the collision-induced absorption is a quadratic dependence of the absorption coefficient on the density with a weak dependence on the temperature, 18 laser photons absorption in vapor was simulated with this approach and the inverse bremsstrahlung absorption was used for simulation of laser photons interaction with plasma. In our Monte Carlo modeling of laser photons absorption, reflection, and re-absorption in liquid/vapor/plasma as well as photon transport in plasma interplays with surface vaporization process.…”

Section: Introductionmentioning

confidence: 99%

Optimization of extreme ultraviolet photons emission and collection in mass-limited laser produced plasmas for lithography application

Sizyuk

Hassanein

2012

The progress in development of commercial system for next generation EUV lithography requires, among other factors, significant improvement in EUV photon sources such as discharge produced plasma (DPP) and laser produced plasma (LPP) devices. There are still many uncertainties in determining the optimum device since there are many parameters for the suitable and efficient energy source and target configuration and size. Complex devices with trigger lasers in DPP or with pre-pulsing in LPP provide wide area for optimization in regards to conversion efficiency (CE) and components lifetime. We considered in our analysis a promising LPP source configuration using 10-30 lm tin droplet targets, and predicted conditions for the most efficient EUV radiation output and collection as well as calculating photons source location and size. We optimized several parameters of dual-beam lasers and their relationship to target size. We used our HEIGHTS comprehensive and integrated full 3D simulation package to study and optimize LPP processes with various target sizes to maximize the CE of the system. V

“…Calculations of the tin target reflectivity give k target ¼ 0:84 for the Nd:YAG laser with k ¼ 1.064-lm, and k target ¼ 0:92 for the CO 2 laser with k ¼ 10.64-lm wavelength, based on the Sn optical data taken from the Ref. 23. The second and third media are a vapor/plasma mixture and a surrounding, welldeveloped plasma, which require special modeling of laser photon propagation.…”

Section: Mathematical and Physical Modelsmentioning

confidence: 99%

Recycling of laser and plasma radiation energy for enhancement of extreme ultraviolet sources for nanolithography

Sizyuk

Hassanein

et al. 2018

We have developed comprehensive integrated models for detailed simulation of laser-produced plasma (LPP) and laser/target interaction, with potential recycling of the escaping laser and out-ofband plasma radiation. Recycling, i.e., returning the escaping laser and plasma radiation to the extreme ultraviolet (EUV) generation region using retroreflective mirrors, has the potential of increasing the EUV conversion efficiency (CE) by up to 60% according to our simulations. This would result in significantly reduced power consumption and/or increased EUV output. Based on our recently developed models, our High Energy Interaction with General Heterogeneous Target Systems (HEIGHTS) computer simulation package was upgraded for LPP devices to include various radiation recycling regimes and to estimate the potential CE enhancement. The upgraded HEIGHTS was used to study recycling of both laser and plasma-generated radiation and to predict possible gains in conversion efficiency compared to no-recycling LPP devices when using droplets of tin target. We considered three versions of the LPP system including a single CO 2 laser, a single Nd:YAG laser, and a dual-pulse device combining both laser systems. The gains in generating EUV energy were predicted and compared for these systems. Overall, laser and radiation energy recycling showed the potential for significant enhancement in source efficiency of up to 60% for the dual-pulse system. Significantly higher CE gains might be possible with optimization of the pre-pulse and main pulse parameters and source size.