Modeling of radiative properties of Sn plasmas for extreme-ultraviolet source

Abstract

Atomic processes in Sn plasmas are investigated for application to extreme-ultraviolet (EUV) light sources used in microlithography. We develop a full collisional radiative (CR) model of Sn plasmas based on calculated atomic data using Hebrew University Lawrence Livermore Atomic Code (HULLAC). Resonance and satellite lines from singly and multiply excited states of Sn ions, which contribute significantly to the EUV emission, are identified and included in the model through a systematic investigation of their effect on the emission spectra. The wavelengths of the 4d−4f+4p−4d transitions of Sn5+ to Sn13+ are investigated, because of their importance for determining the conversion efficiency of the EUV source, in conjunction with the effect of configuration interaction in the calculation of atomic structure. Calculated emission spectra are compared with those of charge exchange spectroscopy and of laser produced plasma EUV sources. The comparison is also carried out for the opacity of a radiatively heated Sn sample. A reasonable agreement is obtained between calculated and experimental EUV emission spectra observed under the typical condition of EUV sources with the ion density and ionization temperature of the plasma around 1018 cm−3 and 20 eV, respectively, by applying a wavelength correction to the resonance and satellite lines. Finally, the spectral emissivity and opacity of Sn plasmas are calculated as a function of electron temperature and ion density. The results are useful for radiation hydrodynamics simulations for the optimization of EUV sources.

Effects of the dynamics of droplet-based laser-produced plasma on angular extreme ultraviolet emission profile

“…The lower emission at angles close to the laser axis is instead due to the lower production of EUV, which is the opposite of what happens with the larger droplets, caused by the lower density in the EDR. 10 The CE for the latter case with an irradiance of 5 Â 10 10 W/cm 2 was 2.5%, which is approximately double the CE calculated for the base case at 2 Â 10 11 W/cm 2 . The increase in CE for the lower irradiance is due to the reduction in overheating of the plasma on the one hand, 12 and to the lower absorption of EUV around the EDR on the other hand.…”

“…The latter observation is justified by considering that the in-band emissivity increases with the density. 10 The overall conversion efficiency (CE) increases by using 50 lm droplets from 1.3% to 1.4%. However, depending on where the EUV radiation is extracted, the local gain in using larger droplets is larger than 1 at angles from the laser axis of less than around 90 , and it is smaller than 1 at larger angles.…”

Investigation of the ionization balance of bismuth-to-tin plasmas for the extreme ultraviolet light source based on a computer-generated collisional radiative model

“…1 The emission from Sn plasmas at the wavelength of 13.5 nm, at which a high reflectivity is attained by Mo/Si multilayer optics, originates from the 4d n 4d n1 4f + 4p 6 4d n 4p 5 4d n1 unresolved transition array (UTA) of near 10 times ionized Sn. [2][3][4] The wavelength of the UTA emission from a near Pd-like ion of heavy elements decreases according to the quasi-Moseley's law to λ = 3.97 nm using Bi. 5 The emission at λ = 6.x nm from Gd and Tb 6 is considered a candidate source for future microlithography.…”

Influence of laser pulse duration on extreme ultraviolet and ion emission features from tin plasmas

“…Extreme ultraviolet (EUV) radiation from a laser produced tin plasma has been studied extensively in recent years for its potential application as a light source for semiconductor lithography. [1][2][3][4][5][6][7][8][9] A high-brightness and debris free source emitting at 13.5 nm radiation with 2% bandwidth (in-band) is necessary for this purpose. The selection of EUV source at 13.5 nm is due to the availability of Si-Mo multilayer (ML) mirrors which reflect $70% of radiation at normal incidence with the bandwidth of 2% centered at 13.5 nm.…”