ABSTRACT
An extreme ultraviolet multilayer mirror with an integrated spectral filter for the IR range is presented and experimentally evaluated. The system consists of an IR-transparent B4C/Si multilayer stack which is used both as EUV-reflective coating and as a phase shift layer of the resonant IR antireflective (AR) coating. The AR coating is optimized in our particular case to suppress CO2 laser radiation at a wavelength of 10.6 µm, and a suppression of more than two orders of magnitude is demonstrated. The method allows high suppression over a large angular acceptance range, relevant for application in lithography systems.
ABSTRACT
We have developed a multilayer mirror for extreme UV (EUV) radiation (13.5 nm), which has near-zero reflectance for IR line radiation (10.6 µm). The EUV reflecting multilayer is based on alternating B4C and Si layers. Substantial transparency of these materials with respect to the IR radiation allowed the integration of the multilayer coating in a resonant quarter-wave structure for 10.6 µm. Samples were manufactured using magnetron sputtering deposition technique and demonstrated suppression of the IR radiation by up to 3 orders of magnitude. The EUV peak reflectance amounts 45% at 13.5 nm, with a bandwidth at FWHM being 0.284 nm. Therefore such a mirror could replace conventional multilayer mirrors to suppress undesired spectral components in monochromatic imaging applications, including EUV photolithography.
ABSTRACT
The article presents the results of the detailed experimental study of fast conical discharge with Ar as a working gas. The discharge produces a compact transient plasma which emits extreme ultraviolet (EUV) radiation with wavelength 10.8 nm. The intensity of this spectral line is an order of magnitude larger than the rest of the radiation in EUV band. Space resolved EUV spectra allowed us to get the estimation of the effective size of the radiation source (less than 0.5 mm). Time resolved spectra (frame time 20 ns) show that a 10.8-nm spectral line is emitted during 50-60 ns. Charge exchange of Ar IX ions with excited atoms of Ar I in the result of interaction of hot compact plasma in the cumulation point of conical shockwave and cold working gas is considered as the main phenomenon, responsible for the emission of the detected radiation.
ABSTRACT
Targeting micrometer sized metal droplets with near-infrared sub-picosecond laser pulses generates intense stress-confined acoustic waves within the droplet. Spherical focusing amplifies their pressures. The rarefaction wave nucleates cavitation at the center of the droplet, which explosively expands with a repeatable fragmentation scenario resulting into high-speed jetting. We predict the number of jets as a function of the laser energy by coupling the cavitation bubble dynamics with Rayleigh-Taylor instabilities. This provides a path to control cavitation and droplet shaping of liquid metals in particular for their use as targets in extreme-UV light sources.
ABSTRACT
The deformation and fragmentation of liquid metal microdroplets by intense subpicosecond Ti:sapphire laser pulses is experimentally studied with stroboscopic shadow photography. The experiments are performed at a peak intensity of 10^{14}W/cm^{2} at the target's surface, which produces shock waves with pressures in the Mbar range. As a result of such a strong impact, the droplet is transformed into a complex-shaped hollow structure that undergoes asymmetrical expansion and eventually fragments. The hollow structure of the expanding target is explained by the effects of cavitation and spallation that follow the propagation of the laser-induced shock wave.
ABSTRACT
Discharge sources in tin vapor have recently been receiving increased attention as candidate extreme ultraviolet (EUV) light sources for application in semiconductor lithography, because of their favorable spectrum near 13.5 nm. In the ASML EUV laboratory, time-resolved pinhole imaging in the EUV and two-dimensional imaging in visible light have been applied for qualitative characterization of the evolution of a vacuum-arc tin vapor discharge. An EUV spectrometer has been used to find the dominant ionization stages of tin as a function of time during the plasma evolution of the discharge.
ABSTRACT
Partially collective Thomson scattering measurements have been performed on a triggered vacuum arc in tin vapor, which is a candidate source of extreme ultraviolet light for application in semiconductor lithography. In this paper, results on the electron densities and temperatures are presented for the prepinch phase of the discharge. Electron densities and temperatures increase from 1 x 10(23) m(-3) to 1 x 10(24) m(-3) and from 5 eV to over 30 eV, respectively, in about 100 ns. The results are confirmed by Stark broadening data.
ABSTRACT
Pinched discharge plasmas in tin vapor are candidates for application in future semiconductor lithography tools. This paper presents time-resolved measurements of Stark broadened linewidths in a pulsed tin discharge. Stark broadening parameters have been determined for four lines of the Sn III spectrum in the range from 522 to 538 nm, based on a cross-calibration to a Sn II line with a previously known Stark width. The influence of the electron temperature on the Stark widths is discussed. Results for the electron densities in the discharge are presented and compared to Thomson scattering results.
ABSTRACT
An experimental method is proposed for the creation of plasma optical waveguides at low electron densities. The method consists of creating a hollow neutral-hydrogen channel by means of fast local heating of a hydrogen volume by a needlelike electron beam, followed by laser ionization of the hydrogen to provide the plasma waveguide. Results of numerical simulations are presented which show that guiding with an axial electron density in the range of 10(17) cm-3 can be achieved with a matched spot size of 30 microm. Its application for laser wakefield acceleration of electrons is discussed. The method would enable guiding lengths up to 30 cm at maximal energies of accelerated electrons in the range 10-100 GeV.