We investigated the electron density profile corresponding to the dominant extreme ultraviolet (EUV) emission from a laser-produced Sn plasma using a combination of a green and an UV interferometer. A comparison between experimental results and a one-dimensional radiation hydrodynamic simulation shows reasonable agreement, and the discrepancy could be attributed to three-dimensional plasma expansion. It was found that, due to opacity effects, most of the EUV light comes from an under-dense plasma region.
Properties of extreme ultraviolet (EUV) emission from laser-produced Sn and SnO2 plasmas were investigated. EUV emission images were taken with a monochromatic imager for 13.5nm with 4% bandwidth. It was found that the EUV emitting plasma is not formed symmetrically with respect to the target surface normal but extends toward laser incident axis. This result is consistent with the angular distribution of EUV emission peaked toward the direction nearly perpendicular to the laser axis. The asymmetric plasma can be attributed to the interaction of a long laser pulse with expanding plasma along the path of laser incidence.
The interaction of a laser pulse with a Sn preplasma formed by a low energy prepulse was investigated for an extreme ultraviolet (EUV) lithography light source. A much lower ion kinetic energy and nearly the same conversion efficiency from laser to in-band (2% bandwidth) 13.5nm EUV light were simultaneously observed as compared with those from the direct interaction with a solid surface. The reason comes from the interaction of the laser pulse with a smooth preplume induced by the prepulse. The density profile of the preplume was measured with time-resolved shadowgraphy and could be fitted with a Gaussian function. The energy of the ions located at the flux peak Ep scales with the length of the preplume ls as Ep∝1∕ls. Laser absorption in the low-density preplume and ion acceleration during plasma expansion are discussed. This result provides a general way to control particle energy from a laser plasma interaction.
Summary form only given. The ion energy and charge state spectrum far away from a laser produced plasma source is investigated with an electrostatic ion analyzer (EIA) probe. The effects of the wavelength of the pump laser are observed by using both a Nd:YAG laser with 1 mum wavelength, and a CO 2 laser with 10.6mum wavelength to irradiate a planar Sn target. For both pump lasers, the additional laser parameters are set to achieve a high conversion efficiency of laser energy to extreme ultraviolet (EUV) X-rays in a 2% bandwidth centered about 13.5 nm, which is a figure of merit for the EUV lithography application. The laser irradiance to achieve this conversion efficiency is approximately 10 12 W/cm 2 for the Nd:YAG laser, and 10 11 W/cm 2 for the CO 2 laser. It was observed that the CO 2 laser generates ions at higher charge states far away from the laser plasma interaction compared to the Nd:YAG laser, even though the CO 2 laser is operated at a lower irradiance. In addition to the measurement of the ion spectrum at two laser wavelengths, the details of the custom built EIA probe are discussed, including the method used to calibrate the response of the probe to Sn ions with energies from approximately 1 to 10 keV.
Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation Y. Shimada, H. Nishimura, M. Nakai, K. Hashimoto, M. Yamaura, Y. Tao, K. Shigemori, T. Okuno, K. Nishihara, T. Kawamura, A. Sunahara, T. Nishikawa, A. Sasaki, K. Nagai, T. Norimatsu, S. Fujioka, S. Uchida, N. Miyanaga, Y. Izawa, C. Yamanaka; Characterization of extreme ultraviolet emission from laser-produced spherical tin plasma generated with multiple laser beams. Appl. Phys. Lett. 31 January 2005; 86 (5): 051501. https://doi.org/10.1063/1.1856697 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioApplied Physics Letters Search Advanced Search |Citation Search
A temporally resolved monochromatic extreme ultraviolet (EUV) imager has been developed for use in EUV radiation source research. The imager consists of a Schwarzschild microscope, with near-normal-incident Mo/Si multilayer mirrors adjusted for 13.5 nm and 4% bandwidth, and an x-ray streak camera (XSC). The spatial resolution of the microscope was limited by the image detector’s resolution to 3.5 μm for the CCD camera and 15 μm for the XSC, respectively, for a field of view of 1.2 mm. With the high photon collection efficiency, clear streak images could be obtained on a single-shot basis with laser pulse energy as low as 50 mJ at an intensity of 1×1010 W/cm2. Expansion behavior of the EUV emission region was successfully observed for laser-produced Sn plasmas.
We investigate the extreme-ultraviolet (EUV) emission from targets that contain tin as an impurity and the advantages of using these targets for ion debris mitigation by use of a magnetic field. The EUV spectral features were characterized by a transmission grating spectrograph. The in-band EUV emission energy was measured with a calorimeter of absolute calibration. The ion flux coming from the plume was measured with a Faraday cup. Our studies indicate that 0.5% Sn density is necessary to obtain a conversion efficiency very close to that of full-density Sn. The use of Sn-doped low-Z targets provides a narrower unresolved transition array and facilitates better control of energetic ions in the presence of a moderate magnetic field of 0.64 T.
An in situ approach to the formation of cavities in liquid Sn droplets for the purpose of increasing ion density from Sn plasma produced by a CO2 laser is investigated. Two-dimensional hydrodynamic simulations, treating the laser as a pulsed pressure source, are compared both spatially and temporally to experimental shadowgraphs for verification of cavity formation. It is shown that a 15 ns pulse from a 1.064 μm laser with intensity of 2 × 1010 W/cm2 creates a cavity approximately 300 μm wide and 100 μm deep in approximately 1.4 μs. The presence of the cavity enhances the conversion of laser energy to 13.5 nm radiation from the plasma.
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