We observed the spatial and temporal changes of the electron density (n
e) and the electron temperature (T
e) of hydrogen plasmas around a laser-produced Sn plasma EUV source. The plasma parameters were measured by the laser Thomson scattering (LTS) method. In the experiment, the Sn plasmas are produced in H2 gas at a pressure of 50–200 Pa and the hydrogen plasmas were induced by radiation from the Sn plasmas. The LTS measurements were performed at distances 30–90 mm away from the Sn plasmas. In all cases, the strong bremsstrahlung radiation of the Sn plasmas easily overwhelmed the weak LTS signals. To suppress noise due to the radiation, the solid angle of radiation from the Sn plasmas was restricted. The experimental results show that the n
e was in the order of 1017 m−3 and T
e was around 0.7 eV.
Plasma dynamics are governed by electron density (ne), electron temperature (Te), and radiative energy transfer as well as by macroscopic flows. However, plasma flow-velocity fields (vflow) inside laser-produced plasmas (LPPs) have rarely been measured, owing to their small sizes (< 1 mm) and short lifetimes (< 100 ns). Herein, we report, for the first time, two-dimensional (2D) vflow measurements of Sn-LPPs (“double-pulse” scheme with a CO2 laser) for extreme-ultraviolet (EUV) light sources for semiconductor lithography using the collective Thomson scattering technique, which is typically used to measure ne, Te, and averaged ionic charge (Z) of plasmas. Inside the EUV source, we observed plasma inflow speed exceeding 104 m/s magnitudes toward a plasma central axis from its peripheral regions. The time-resolved 2D profiles of ne, Te, Z, and vflow indicate that the plasma inflows maintain the EUV source at a temperature suitable (25 eV < Te < 40 eV) for EUV light emission at a high density (ne > 3 × 1024 m−3) and for a relatively long time (> 10 ns), resulting increment of total EUV light emission. These results indicate that controlling the plasma flow can improve EUV light output and that there is potential to increase the EUV output further.
Temporal evolutions of two-dimensional (2D) plasma profiles produced by Nd:YAG laser (
5.9
×
10
9
W
cm
−
2
,
8 ns FWHM) were investigated at 5–25 ns after the laser peak at 0.2–0.5 mm from the initial target surface by measuring the electron density (n
e), temperature (T
e), and drift velocity (V
d). The T
e profiles were nonuniform and showed a peak at 0.3 to 0.4 mm above the target surface. The high-temperature region of the plasma moved outward at the same speed as that of the expansion of the plasma, indicating the isothermal expansion ends immediately after the ablation pulse. The 2D profiles of V
d and pressure also show that the plasma expanded anisotropically.
Plasma temperature, density, and flow velocity are the critical physical properties of laser produced plasma (LPP) to reveal the ablation dynamics, energy transport, and hydrodynamic evolution. In the time window during and just after laser irradiation, experimental data are very scarce so that many theoretical models remain untested. Here we report a clear evolution history of LPP expansion dynamics within 0–14 ns after the laser peak and in a region very close to the target (0.13–0.6 mm). A table-top Nd: YAG laser (intensity 6 ×109 W/cm2, pulse 7 ns) was used to generate the LPP from a planar graphite target, whose width was arranged to be smaller than the laser spot diameter to produce a one-dimensional planar expansion plasma near the target. The electron density (ne), temperature (Te), and drift velocity (Vd) in the LPPs were measured using the ion feature of collective Thomson scattering, providing a space- and time-resolved 2D profile of the LPP. The experimental observations made it possible for the expansion dynamics to be compared directly with the LPP expansion models. The results suggest that during the laser pulse, the LPP is approximately isothermal and expands predominantly one-dimensionally in the target normal direction, in which the LPP drift velocity is found to increase linearly with distance. The linear extrapolation of the velocity indicates that the LPP has a considerable velocity at the initial target surface; this velocity is approximately the speed of sound derived from the observed Te. The experimental results were found to be in moderate agreement with the 1-D self-similar isothermal expansion model. The ratio of the internal to kinetic energy in the observed area was ~0.6, as predicted by the isothermal expansion model. The experimental findings were compared with the results of the 2-D hybrid code STAR, and good agreement was obtained.
A capacitively coupled Ar plasma was produced by the ultra-high frequency power source (450 MHz) and the plasma parameters were studied by laser Thomson scattering. It was found that a very high density plasma with a low electron temperature was realized; the electron density n e is around (1.1-1.5) × 10 18 m −3 and the electron temperature T e is around (1.7-2.1) eV. Radial profiles of n e and T e were obtained for different pressures and powers. In all the conditions explored, n e had a single-center-peak profile, while T e profiles were relatively flat along the electrode.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.