Abstract
We report a comprehensive study of the emission from Gd and Tb laser-produced plasmas in the 6.5-6.7-nm wavelength region for a broad range of laser-irradiation parameters using a single λ=1030 nm laser with tunable pulse duration in the 120-ps-to-4-ns range. The results are of interest for beyond-extreme-ultraviolet (BEUV) lithography of integrated circuits. BEUV emission spectra are measured as a function of laser-pulse duration, emission angle, and spatial location within the plasma. Images of the BEUV-emitting plasma region at the BEUV wavelength are obtained as a function of irradiation parameters. The emission spectrum is observed to broaden and to shift to a longer wavelength as the duration of the driver laser pulses is shortened from nanoseconds to hundreds of picoseconds. Transient self-consistent hydrodynamic and atomic physics simulations show that the picosecond irradiation creates significantly hotter plasmas in which the dominant emission originates from more highly ionized species. Gd-plasma emission driven by nanosecond laser pulses spectrally best matches the responsivity of the energy monitors used, centered near λ=6.74 nm. Spatially resolved spectra of the Gd plasma are acquired for different laser-pulse durations. The conversion efficiency (CE) of Gd/Tb plasma into a 0.6% bandwidth in a 2π solid angle is determined by integrating angularly resolved measurements obtained using an array of calibrated energy monitors. Similar maximum CEs of about 0.47% for both the Gd and Tb plasmas are obtained. The source size is measured to approximately match the spot size of the laser on target, in agreement with simulations.
Original language | English |
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Article number | 034009 |
Journal | Physical Review Applied |
Volume | 6 |
Issue number | 3 |
DOIs | |
State | Published - Sep 15 2016 |
Funding
This work was supported by NSF PFI: AIR, Award No.NSF IIP-1343456, and Cymer LLC. M.B. acknowledges the support of Oak Ridge National Laboratory/DOE. This manuscript has been authored by UT-Battelle, LLC under Contract No.DE-AC05-00OR22725 with the U.S. Department of Energy. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan. We are thankful to Michael Purvis for helpful discussions and comments.