Alexander P. Shevelko

Focusing crystal von Hamos spectrometer for x-ray spectroscopy and x-ray fluorescence applications

The use of bent crystals with high integrated reflectivity in focusing crystal spectrometers (Johann and von Hamos schemes) is considered. It is shown that in a von Hamos scheme mosaic focusing takes place. Thus a mosaic crystal simultaneously provides high spectral resolution and high efficiency. Expressions for the mosaic focusing are obtained. Focusing mica and graphite crystal von Hamos spectrometers (radius of crystal curvature is 20 mm) are investigated: spectral and spatial resolution and absolute efficiency are measured in a spectral range of 2 - 2.6 angstroms using laser-produced plasma and iron isotope x-ray sources. The mica crystal spectrometer showed high spatial (up to 10 micrometers ) and spectral ((lambda) /(delta) (lambda) approximately 1000) resolution, whereas the graphite spectrometer showed very high efficiency (30 - 70 times higher than the mica crystal) and moderate spectral resolution ((lambda) /(delta) (lambda) approximately 500 - 750). In the latter case mosaic focusing is observed: spectral resolution is 10 - 15 times higher than spectral resolution determined by the mosaic spread of the crystal ((lambda) /(delta) (lambda) approximately 50). The results allow one to estimate a maximum efficiency for focusing crystal spectrometers. Prospects for using the von Hamos spectrometers for x-ray spectroscopy and x-ray fluorescence are considered.

A high-power, low-contamination laser plasma source for Extreme UV lithography

Experimental results are reported on the development of a low-contamination laser-plasma source for extreme ultra-violet lithography (EUVL). The results concern the intensity in the 12.5 to 15.5 nm wavelength range and the pollution of EUV optics by plasma debris.

Issues of laser plasma sources for soft x-ray projection lithography

Abstract Results of optimization of an excimer laser-induced plasma x-ray source for projection lithography in the range λ = 13–15 nm are reported. A conversion efficiency of >0.7% in 2% BW has been achieved with high-Z target materials. Two methods of reducing contamination of optical elements by target debris have been tested: usage of a thin target layer (for Ta 1 μm was found to be optimal) and of a heavy buffer gas. The effect of the use of Ta-tape target and Kr buffer gas has been measured by determining the reflectivity of a Mo-Si multilayer sample after 10 5 shots.

Intense XUV source of radiation within the 4- to 45-nm spectral range based on capillary discharge plasmas

A compact device, based on fast capillary discharge plasmas, is an intense EUV and soft x-ray source of radiation. Th plasma is created by a discharge of low-inductance capacitors through a gas-filled ceramic capillary. Parameters of the discharge are: maximum current of 25 kA at applied voltage 40 kV, a pulse duration of 20-30 ns at FWHM, and a rise time of 1.5 ns. The soft x-ray and EUV emission of multiply charged ions is investigated using a compact 1 meter grazing incidence spectrometer-monochromator with a constant angle of deviation. The use of various gases allows the observation of XUV spectra in a wide spectral range (4- 45 nm). A Xe-filled capillary discharge shows intense radiation near 13.5 nm - the region of interest for EUV lithography applications. A reflectometer is used for testing grazing incidence gratings.

Developments of a high-power, low-contamination laser plasma source for EUV projection lithography

Results on laser plasma EUV characteristics for various target materials and irradiation conditions are presented. Spectra of high-Z elements in the 12.5-15.4 nm range from plasmas generated with a high-power KrF laser at 2 X 1012 W/cm2 were measured. The highest conversion efficiency (CE) of 0.85% in 2% BW was found for Re near 13.6 nm, corresponding to a maximal EUV power of 550 mW in 2% BW at 50 Hz. The use of two successive laser pulses, investigated with 2.5 ns pulses of 0.53 micrometers radiation at (0.5-1) X 1013, resulted in an increase of the CE by a factor of 1.8-2.3 for the second pulse at specific delay values (6 and 12 ns for W). The total CE gain amounted to 1.4-2. The first demonstration of an alternative concept of a laser plasma raget for EUVL was performed, based on the usage of a centrufugal force for elimination of particluates. The principle of the approach is generation of laser plasmas at the edge of a fastly-rotating disc. The effect of re- direction of particulates was observed in experiments with a (phi) 50 mm Ta disc at 36.000 rpm at laser power densitites between 109 and 1011 W/cm2.

Structure and intensity of x-ray radiation in a laser plasma-wall interaction

Intense soft x-ray radiation is observed when a high temperature laser produced plasma collides with a solid surface (wall). The laser plasma is produced by Nd:YAG laser radiation (0.53 micrometers ; 200 mJ; 3 ns; 5x1012 w/cm2 focused onto a Mg target. The wall is placed in the path of the plasma expansion. Two experimental techniques are used. 1) One-dimensional x-ray images of the plasma-wall gap formed by a slit are observed using an absolutely calibrated CCD linear array. 2) X-ray spectra of [H]- and [He]-like Mg ions are recorded using a crystal focusing x-ray von Hamos spectrometer. At a measured electron temperature of Te equals 195 eV, emission of [He]-like ions Mg XI gives the main contribution to the observed x-ray intensity. The spatial structure and the intensity of the radiation are studied at various laser plasma-wall distances (r0 equals 0.3 - 3.0 mm). Intense radiation near the wall is caused by an electron density jump in a shockwave formed in front of the wall. At small wall distances r0<<v(tau) (v is the expansion velocity, tau is the laser pulse duration) the radiation is caused by excitation processes, and at distances r0<0.3 mm the near wall intensity exceeds the emission from the laser plasma itself. At distances r0

Laser plasma source of polarized monochromatic beams in the XUV around multilayer mirrors

GTR

X-ray and EUV spectral instruments for plasma source characterization

GTRv(tau) the radiation causes recombination processes. These results are important for developing collision and recombination schemes for x-ray lasers in colliding plasmas.

Formation of quasi-monochromatic soft x-ray radiation from laser-produced plasmas

Using soft x-ray multilayer mirrors (MMs) and a laser-plasma broadband radiation source, we have implemented a pulsed 0.5-Hz-repetition-rate source of polarized quasimonochromatic radiation in the XUV. The x-ray optical setup comprises a focusing MM at near-normal incidence, a plane polarizing MM at 41 degrees off axis, and a plane multilayer analyzer which can be rotated by 90 degrees with respect to the polarizer. A stigmatic broadband spectrometer comprising a grazing incidence toroidal mirror and a large-aperture (5 cm2) transmission grating (TG) has proved to be useful in spectroscopic characterization of plane multilayer mirrors and the laser-plasma source. The second (reference) x-ray optical channel comprises a focusing MM and serves to monitor the energy of individual pulses. The focusing MMs image the laser-plasma source onto the sodium-salicylate-covered surfaces of flexible 0.7-cm-long light guides 13 mm in diameter coupled through light-guide disks to photomultipliers outside the vacuum tank. The visible and VUV radiation outside the resonance reflection peak is rejected by free-standing Al filters placed before the detectors. The dimension of the x-ray source was measured at 100 microns (width at base) using a CCD array covered with sodium salicylate. The polarizance of the plane MM was measured at 98.2% while the peak theoretical value for this Mo-Si multilayer structure (2d equals 240 angstrom, N equals 25, lambdao equals 171.4 angstrom, 41 degrees off axis) is 98.75%. The polarized source yields of the order of 5 (DOT) 108 photons per pulse in the resonance reflection band of the MMs.

Laser plasma XUV sources: a role for excimer lasers?

A set of spectral analytic instruments has been developed for absolute intensity measurements in a spectral range of 1 - 600 Å: (1) several modifications of grazing incidence spectrographs; (2) EUV monochromator- spectrometer with a constant angle of deviation; (3) focusing crystal von Hamos spectrometer using cylindrical mica and pyrolytic graphite crystals and a CCD linear array as a detector. These instruments are useful for plasma diagnostics, x-ray and EUV spectroscopy of laser-generated plasmas and capillary discharge plasmas, x-ray and EUV reflectometry, radiometry and x-ray fluorescence application.