We present a recently patented apparatus which consists of an extreme ultraviolet radiation source writing invisible
patterns on thin tags of alkali halides. The tags patterned using this method are almost impossible to counterfeit, and
offer a much better protection against fakes than available anti-counterfeiting techniques. We will discuss if this novel
technology is ready for industrial production of anti-counterfeiting tags.
Within a National Project on nanotechnologies, at the ENEA Research Centre in Frascati a micro-exposure tool for
projection lithography at 14.4 nm has been developed. The laser-plasma soft X-ray source is equipped with a patented
debris mitigation system developed in the frame of a European Integrated Project, in order to preserve the collecting
optics. A 90-nm-resolution patterning has been achieved on resist by this laboratory-scale tool based on a Schwarzschildtype
projection optics.
Within a National Project on nanotechnologies, a Micro-Exposure Tool (MET) for projection lithography at 14.4 nm,
based on a laser-produced plasma source, is being developed at the Frascati ENEA Center. The choice of this "exotic"
wavelength is due to the higher efficiency of a Debris Mitigation System (DMS) working in the interval of
approximately 14 nm < λ < 15 nm. It has to be noted that Mo/Si multilayer mirrors (MLM) can still have a high
reflectivity also at these wavelengths.
The solid-tape-target laser-generated plasma is driven by a XeCl excimer laser, with an optimized intensity of about
3•1010 W/cm2, generating an extreme ultraviolet (EUV) source with a diameter of about 0.2 mm. Clearly, this kind of
source emits a lot of debris (both atomic and particulate types) and the 7-cm-far collector mirror must be protected
against them.
The paper is mostly devoted to the accurate and systematic study of these debris and to their reduction. The results of
mitigation efficiency obtained with a DMS prototype are very encouraging and lead to the design and patenting of its
improved version.
We present the design elements and the preliminary experimental results of an Extreme-UltraViolet (EUV) exposure tool driven by the high-output-energy excimer laser-facility Hercules, which is aimed at printing a sub-100-nm-pattern on a photoresist in a single-shot irradiation.
D. Alesini, S. Bertolucci, M. Biagini, R. Boni, M. Boscolo, M. Castellano, A. Clozza, G. Di Pirro, A. Drago, A. Esposito, M. Ferrario, V. Fusco, A. Gallo, A. Ghigo, S. Guiducci, M. Incurvati, C. Ligi, F. Marcellini, M. Migliorati, A. Mostacci, L. Palumbo, L. Pellegrino, M. Preger, R. Ricci, C. Sanelli, M. Serio, F. Sgamma, B. Spataro, A. Stecchi, A. Stella, F. Tazzioli, C. Vaccarezza, M. Vescovi, C. Vicario, F. Alessandria, A. Bacci, I. Boscolo, F. Broggi, S. Cialdi, C. De Martinis, D. Giove, C. Maroli, V. Petrillo, M. Romè, L. Serafini, D. Levi, G. Medici, M. Mattioli, P. Musumeci, L. Catani, E. Chiadroni, D. Moricciani, F. Ciocci, G. Dattoli, A. Doria, F. Flora, G. Gallerano, L. Giannessi, E. Giovenale, G. Messina, L. Mezi, P. Ottaviani, L. Picardi, M. Quattromini, A. Renieri, C. Ronsivalle, A. Cianchi, C. Schaerf, J. Rosenzweig
SPARC and SPARX are two different initiatives toward an X-ray FEL SASE source at LNF. SPARC is a high gain FEL
project devoted to provide a source of visible and VUV radiation while exploiting SASE mechanism. An advanced
Photo-Injector system, emittance self-compensating RF-gun plus a 150 MeV Linac, will inject a high quality e-beam into
the undulator to generate high brilliance FEL radiation in the visible region at the fundamental wavelength, (530 nm).
The production of flat top drive laser beams, high peak current bunches, and an emittance compensation scheme will be
investigated together with the generation of higher harmonic radiation in the VUV region. SPARX is the direct evolution
of such a high gain SASE FEL towards the 13.5 and 1.5 nm operating wavelengths, at 2.5 GeV. The first phase of the
SPARX project, fiinded by Government Agencies, will be focused on R&D activity on critical components and
techniques for future X-ray facilities as described in this paper.
The results of a numerical simulation of a conventional and a modified Schwarzschild objective are illustrated in relation with their use as imaging systems in an extreme ultraviolet lithography setup. It is demonstrated that the degradation of the resolution on the wafer due to the unavoidable tilt of the mask to the axis can fairly be vanished by a counter tilt of the wafer. In particular, it has been analysed the Schwarzschild objective setup under implementation at the ENEA Frascati Center within the context of the Italian FIRB project for EUV lithography.
The XeCl excimer laser Hercules at ENEA Frascati, thanks to its peculiar features, is a unique laser-facility for many irradiation experiments. Among these applications, most machine-time is devoted to drive a laser-plasma source. This laser-plasma source is used for high-resolution atomic spectroscopy, in vivo contact microscopy of biological samples, induced DNA damage, micro-radiography, generation of sub-micron luminescent pattern on Lithium Fluoride films for miniaturized active optical devices.
Recently, we equipped the Hercules-driven laser plasma source with a novel Debris Mitigation System to drastically reduce the amount of hot debris emitted by the solid target (potentially dangerous for optics, filters and detectors put near the plasma). Here we will discuss the challenging attempt of stopping debris emitted by our solid-target laser plasma, in order to achieve a clean and efficient EUV source.
A new imaging detector for EUV or soft-X-ray radiation based on optically stimulated luminescence (OSL) of lithium fluoride (LiF) films or crystals is presented. The first micro-radiography images of biological samples and of meshes obtained on LiF using a laser-plasma source or an X-ray laser are shown, and (up to now) a resolution better than one micron is demonstrated. The dependence of the coloration density vs the deposited X-ray dose is considered and the advantages of this new diagnostic technique for both coherent and non-coherent EUV sources, compared with CCDs detectors, photographic films and photoresists are discussed. This new detector is extremely suitable for laser plasmas and for X-ray lasers sources.
The recent progress in the development of the tabletop soft x-ray lasers pumped by capillary discharges has opened the possibility of the widespread use of these coherent sources for applications. In this paper, we present the latest results achieved in our laboratory concerning the optimization of a 46.9nm capillary discharge pumped soft x-ray laser and the imaging of the laser beam on Lithium Fluoride (LiF, films), which appears to be a new promising x-ray detector. The use of LiF allows a high spatial resolution (smaller than 1μm) on large areas, high-contrast imaging and simple manipulation. The laser, which is pumped by 18-20kA, 150-180ns long current pulses at a repetition rate of 0.1Hz, is produced in 3.2mm diameter up to 45cm length alumina capillary tubes filled with Ar at the initial gas pressure of 300-600mTorr. At the capillary lengths examined, the laser is operating in the saturation regime giving an output energy of about 300μJ per pulse and high coherence degree.
The effect of the transverse-direction electrical fields on the stability and dynamics of a capillary discharge Z-pinch, at conditions for which soft x-ray lasing in Ne-like Ar has been demonstrated, is studied. It is shown that the transverse electrical fields of the sliding surface discharge provide the instability-free compression and heating of the plasma. The stable and homogeneous heating and compression allows achievement of the appropriate conditions for the soft x-ray lasing in Ne-like Ar. Numerical calculations using the MHD model of the discharge yield new predictions for dynamics and stability of the plasma collapse in the presence of the transverse electrical fields and explain details of experimental observations without artificial adjustments.
The life time of the first multilayer mirror (the condenser) in optical systems for projection Extreme Ultra-Violet (EUV) lithography based on Laser Produced Plasmas (LPP) is limited both by the debris bombardment and by the EUV radiation photoablation. These problems can be dramatically reduced by using krypton as debris stopper, exploiting its high atomic weight (21 times the helium value) and its high transparency in the EUV region only between 60 and 90 eV. We demonstrate both theoretically and experimentally that by filling the laser-target interaction chamber with krypton at low pressure (a few mbar) it is possible to stop efficiently the small debris (having a size smaller than 1 micron, including ions, neutrals and clusters) while keeping a reasonable transmission of the EUV radiation in the 60-90 eV range. In particular, this is experimentally demonstrated for a solid target LPP based on a tantalum or copper tape target and pumped by a large energy (4 J - 120 ns) XeCl excimer laser. The poor transmission of krypton, out of the above mentioned spectral window, significantly reduces the exposition of the condenser mirror to useless radiation. This new technique for stopping the debris has recently been patented by our group. As far as the larger size debris is regarded, a dramatic reduction of their flux has been obtained by decreasing the laser intensity on the target, still keeping a laser to EUV energy conversion as high as 0.7 percent/eV/sr at 70 eV, from a Ta target, together with a shot to shot EUV pulse energy stability better than 1 percent.
We report on a fast soft x-ray source consisting in a high temperature small diameter plasma column produced by electric discharge in a ceramic capillary. This source was developed to produce pulses of few hundred nanosecond duration for EUV lithography, x-ray microscopy applications and also with the aim of developing a soft x-ray amplifier. We obtained experimental results concerning the intensity and spectral analysis of the emitted x radiation pumped by a 30-40 kA, 100-200 ns, electric discharge at 1 Torr pressure in Ar gas. We refer also on the spectra obtained using CO2, as plasma medium, after the optimization of the discharge setup and electrical parameters.
We propose to enhance the gain of Ne-like ion capillary lasers by the utilization of two discharge pulses. A first pulse working in the pinch regime mode is designed to create the cold-plasma column with the required ionization degree, followed by a second fast high-voltage pulse to do the effective collision excitation. The second pulse, which heats the electrons to a kinetic temperature Te greater than Tecold in times shorter than the ionization time, increases the laser gain. In the two stage pumping scheme, both the amplitude of each of the pulses and the delay between them can be adjusted for independent control of the ionization degree and excitation rate. Numerical estimations performed for the low-Z-ion (Na+1, . . ., Ar+8) lasers with the double pulse pumping predict enhancement in gain by a factor of approximately 10. In addition, the extension of two-stage electrical pumping to the high-Z-ion collision and recombination laser schemes is discussed. Description of the experimental set-up constructed for such experiments and some related measurement data are also presented.
An analytical technique based on a generalization of the Stappaerts method is proposed for discharge electrode designing. It allows one to consider asymmetry elements, such as current return bars, or to approach new laser geometries, e.g., the double-head laser.
In this paper we intend to present some recent result obtained in our laboratory on excimer laser development and applications. Even if the activity has been initiated as long as 15 years ago after 1986, following the European Eurolaser Initiative, the programs were strengthened and enlarged to accommodate more ambitious goals, according to the increased attention to this field. Actually the activity includes the following: (1) development of source, (2) computer models, 3) special devices, and (4) applications. The description of our activity is presented according to the above mentioned order, with special attention to the most recent results.
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