Extreme ultraviolet (EUV) is strongly absorbed in any material and can be transmitted only through very thin foils. The
material surface after irradiation can remain unchanged or becomes modified in some way depending on radiation
fluence and material properties. In some materials the surface changes may arise due to fast melting or boiling followed
by solidification. In other cases photochemical or photothermal ablation can occur. It requires relatively high radiation
fluence of the order of tens mJ/cm2. A laser-plasma EUV source based on a gas puff target equipped with a proper optic
can deliver such conditions. In this work EUV radiation coming from xenon or krypton plasma was focused using an
ellipsoidal grazing incidence collector. Different kind of material samples were irradiated in the focal plane or at some
distance behind the focal plane. This way different intensities were applied for irradiation of the samples. Irradiation was
performed with 10 Hz repetition rate and different time duration varying from 1s to 2 min. Surface morphology after
irradiation was investigated using a scanning electron microscope. In a case of some materials EUV intensity in the focal
plane was sufficient for ablation. In other cases material ablation was not possible but surface structure was modified.
Forms of the structures for a certain material depend both on EUV fluence in a single shot and the number of shots.
Laser plasma source in WAT, Poland, is used as the source of EUV radiation for lithography and illumination
of biological samples. The source has to be equipped with a complementary condensor with the goal of having
a higher peak intensity than using current systems and moreover with the ability to illuminate larger areas
homogeneously. The work concentrates on the analysis and design process of the optics based on the known
source parameters, namely typical spectra, angular and intensity distributions and other constraints. Further,
the question of illuminating the samples via multi shot approach by shifting the sample is discussed and estimates
on the optimal sample shift in between two shots are explained.
In this paper some results of investigations concerning interaction of EUV radiation with inorganic and organic materials
were presented. Samples of different materials were irradiated with a 10 Hz laser - plasma EUV source based on a gas
puff target. The source was equipped with grazing incidence and multilayer collecting mirrors. The grazing incidence
collector was used in experiments concerning surface modification and micromachining of different materials. The
micromachining experiments were performed for different polymers that were irradiated through a fine metal grid as a
contact mask. For fluoropolymers, EUV radiation with fluence of 10 mJ/cm2 was enough for efficient photo-etching. The
photo-etching speed was maximal for polytetrafluoroethylene (PTFE) reaching 30nm per shot. It was shown that using
such a method microstructures with high aspect ratio could be produced. Experiments connected with surface
modification were performed either with organic or inorganic materials. Different kinds of surface structures were
obtained depending on irradiated materials and irradiation parameters. The Mo/Si collector together with argon plasma
was used for obtaining a quasi-monochromatic radiation for EUV microscopy and some metrological applications.
Results on micro- and nanoprocessing of organic polymers with extreme ultraviolet (EUV) radiation from a compact
laser plasma EUV source based on a gas puff target are presented in the paper. Processing of polymers is connected with
non-thermal ablation under the influence of energetic EUV photons. The process can be useful for practical applications
as it makes possible to produce structures with sub-micron spatial resolution that is not possible using the thermal
ablation. The new technology will be used for production of photonic microstructures and for modification of polymer
surfaces for biomedical applications.
Laser plasmas generated in result of interaction of intense laser pulses with matter are efficient sources of XUV radiation in the energy range from about 50 eV to 500 eV. The results of experiments on micro- and nanoprocessing of organic polymers using a laser plasma XUV source based on a laser-irradiated gas puff target are presented and discussed.
Results on micro- and nanoprocessing of organic polymers using X-rays and extreme ultraviolet (EUV) generated from
laser-plasma radiation sources are presented in the paper. The sources used in the studies are based on the gas puff target
approach developed at the Institute of Optoelectronics, Warsaw. Processing of polymers is connected with non-thermal
ablation under the influence of energetic photons of X-ray and EUV radiation. The process can be useful for practical
applications as it makes possible to produce structures with sub-micron spatial resolution that is not possible using the
thermal ablation. The new technology will be used for production of photonic microstructures and for modification of
polymer surfaces for biomedical applications.
The paper presents a measuring system of extreme ultraviolet radiation pulses (13.5 nm). The system is used for
monitoring a gas-puff laser-plasma source constructed at the Institute of Optoelectronics. The radiation source and the
system are used in metrology of EUV optics. The system consists of a detection head and a system of optical filters,
which are housing in a special construction. Additional element of the measuring system is a special processing unit.
The measuring system was used during investigations of the plasma-laser optimization. The results were comparable
with the ones from a spectrograph and an Emon energy meter.
The results of the spectral and spatial measurements of a laser-produced (LPP) plasma source of extreme ultraviolet (EUV) for 13.5 nm are presented. The double stream Xe/He gas puff target in the source was utilizing. The source was equipped with a Nd: YAG laser system (E = 0.55 J, t = 3.9 ns, f = 10 Hz, M2 = 2.5) and was dedicated to EUV metrology purposes. An advantage of this approach of the laser-plasma source is a debris free EUV emission. For the spectral research a transmission grating spectrograph (TGS) and a grazing incidence spectrograph (GIS) were utilized. For spatial measurements a pinhole camera was employed. The influence on EUV emission of the laser focal spot position in relation to the gas puff target and the time delays between opening valves and the laser pulse were investigated.
Organic polymers (PMMA, PTFE, PET, and PI) are considered as the important materials in microengineering, especially for biological and medical applications. Micromachining of such materials is possible with the use of different techniques that involve electromagnetic radiation or charged particle beams. Another possibility of high aspect ratio micromachining of PTFE is direct photo-etching using synchrotron radiation. X-ray and ultraviolet radiation from other sources, for micromachining of materials by direct photo-etching can be also applied.
In this paper we present the results of investigation of a wide band soft X-ray source and its application for direct photo-etching of organic polymers. X-ray radiation in the wavelength range from about 3 nm to 20 nm was produced as a result of irradiation of a double-stream gas puff target with laser pulses of energy 0.8 J and time duration of about 3 ns. The spectra, plasma size and absolute energies of soft X-ray pulses for different gas puff targets were
measured. Photo-etching process of polymers irradiated with the use of the soft X-ray radiation was analyzed and investigated. Samples of organic polymers were placed inside a vacuum chamber of the x-ray source, close to the gas puff target at the distance of about 2 cm from plasmas created by focused laser pulses. A fine metal grid placed in front of the samples was used as a mask to form structures by x-ray ablation. The results of photo-etching process for several
minutes exposition with l0Hz repetition rate were presented. High ablation efficiency was obtained with the use of the gas puff target containing xenon surrounded by helium.
A new high-density gas puff target for experiments on laser-driven X-ray lasers is presented. The target is based on a double-stream gas puff target approach, which makes possible to form an elongated gas sheet with steep density gradient and high density of gas in the interaction region. In the paper the valve system to produce the gas puff targets and the results of the target characterization measurements performed using X-ray backlighting technique are presented.
In the paper a newly developed compact and debris-free laser plasma soft X-ray source is presented. The source is based on the double-stream gas puff target approach. The targets are formed by pulsed injection of high-Z gas (xenon, krypton or argon) into a hollow stream of low-Z gas (helium or hydrogen) using the valve system composed of two electromagnetic valves and equipped with the double-nozzle setup. The outer stream of gas confines the inner stream improving the gas puff target characteristics (higher density of high-Z gas at longer distance from the nozzle output). It causes efficient absorption of laser energy in a plasma and strong soft X-ray production. Additionally, the use of the double-stream gas puff target approach makes possible to avoid degradation of the nozzle by the laser plasma. Spectral characteristics of soft X-ray emission from the source are presented. Applications in X-ray pulsed radiography, microprocessing of polymers by direct soft X-ray photo-etching, and EUV technologies are discussed.
The results of experiments on micromachining of organic polymers by direct photo-etching using a compact laser plasma soft X-ray source based on a gas puff target are presented. Soft X-ray radiation in the wavelength range from 2 to 15 nm was produced as a result of irradiation of a double-stream gas puff target with 0.8 J/3 ns laser pulses from a Nd:YAG laser. The soft X-ray pulses with energy of about 100-200 mJ in a single pulse were used to irradiate samples from organic polymers to form microstructures. The obtained results show that direct photo-etching using the laser plasma soft X-ray source could be useful for micromachining of organic polymers. Strong enhancement of the photo-etching process was observed for the samples heated up to 140oC.
For conventional wavelength (UV-vis-IR) lasers delivering radiation energy to the surface of materials, ablation thresholds, ablation (etch) rates, and the quality of ablated structures often differ dramatically between short (typically nanosecond) and ultrashort (typically femtosecond) pulses. Various short-wavelength (<100 nm) lasers emitting pulses with durations ranging from ~10 fs to ~1 ns have recently been put into routine operation. This makes it possible to investigate how ablation characteristics depend on pulse duration in the XUV spectral region. Four sources of intense short-wavelength radiation available in the authors' laboratories, including XUV and soft x-ray lasers, are used for the ablation experiments. Based on the results of the experiments, the etch rates for three different pulse durations are compared using the XUV-ABLATOR code to compensate for the wavelength difference. Comparing the values of etch rates calculated for nanosecond pulses with those measured for shorter pulses, we can study the influence of pulse duration on XUV ablation efficiency. The results of the experiments also show that the ablation rate increases while the wavelength decreases from the XUV spectral region toward x-rays, mainly due to increase of attenuation lengths at short wavelengths.
A pulse-train Nd:YAG laser system consisting of repetitively Q-switched Nd:YAG oscillator with Cr4+:YAG saturable absorber, double pass Nd:YAG amplifier and stimulated Brillouin scattering (SBS) pulse compressor has been demonstrated. Number and energy of the laser pulses were controlled by adjusting width and amplitude of the flash lamp pumping pulses. Efficient SBS compression of Nd:YAG laser pulses was obtained using single-cell compressor.
Experiments on direct photo-etching of organic polymers induced by high-intensity nanosecond pulses of soft X-ray radiation from a laser plasma X-ray source based on a gas puff target are presented. X-rays in the wavelength range from about 1 nm to 8 nm were produced by irradiation of the xenon/helium double-stream gas puff target with laser pulses from the Prague Asterix Laser System (PALS). The resulting X-ray pulses were used to irradiate samples from organic polymers and form microstructures. The results show relatively high efficiency of X-ray direct photo-etching that could be useful for micromachining of organic polymers.
For conventional wavelength (UV-Vis-IR) lasers delivering radiation energy to the surface of materials, ablation thresholds, ablation (etch) rates, and the quality of ablated structures often differ dramatically between short (typically nanosecond) and ultrashort (typically femtosecond) pulses. Various short-wavelength (l < 100 nm) lasers emitting pulses with durations ranging from ~ 10 fs to ~ 1 ns have recently been put into a routine operation. This makes it possible to investigate how the ablation characteristics depend on the pulse duration in the XUV spectral region. 1.2-ns pulses of 46.9-nm radiation delivered from a capillary-discharge Ne-like Ar laser (Colorado State University, Fort Collins), focused by a spherical Sc/Si multilayer-coated mirror were used for an ablation of organic polymers and silicon. Various materials were irradiated with ellipsoidal-mirror-focused XUV radiation (λ = 86 nm, τ = 30-100 fs) generated by the free-electron laser (FEL) operated at the TESLA Test Facility (TTF1 FEL) in Hamburg. The beam of the Ne-like Zn XUV laser (λ = 21.2 nm, τ < 100 ps) driven by the Prague Asterix Laser System (PALS) was also successfully focused by a spherical Si/Mo multilayer-coated mirror to ablate various materials. Based on the results of the experiments, the etch rates for three different pulse durations are compared using the XUV-ABLATOR code to compensate for the wavelength difference. Comparing the values of etch rates calculated for short pulses with those measured for ultrashort pulses, we can study the influence of pulse duration on XUV ablation efficiency. Ablation efficiencies measured with short pulses at various wavelengths (i.e. 86/46.9/21.2 nm from the above-mentioned lasers and ~ 1 nm from the double stream gas-puff Xe plasma source driven by PALS) show that the wavelength influences the etch rate mainly through the different attenuation lengths.
In the paper a newly developed compact laser plasma EUV source is presented. The source is based on the double-stream gas puff target approach. The targets are formed by pulsed injection of high-Z gas (xenon) into a hollow stream of low-Z gas (helium) using the valve system composed of two electromagnetic valves and equipped with the double-nozzle setup. The outer stream of gas confines the inner stream improving the gas puff target characteristics (higher density of high-Z gas at longer distance from the nozzle output). It causes efficient absorption of laser energy in a plasma and strong EUV production. The source has been developed in the frame of the EUV sources development project under the MEDEA+ program.
Spectral measurements of a laser-produced soft x-ray and EUV source based on a double-stream gas puff target are described. The target was irradiated with a Nd:glass laser producing 1 ns pulses with energy up to 10 J. Production in the wavelength range up to 20 nm (x-ray and EUV emissions) have been measured from xenon, krypton, argon, and nitrogen targets using the transmission grating spectrometer with the back-illuminated CCD. Spectral characteristics of x-ray and EUV emissions are presented.
In this paper laser plasma radiation sources for x-ray and EUV lithography technologies are proposed. The sources are based on a recently developed double-stream gas puff target formed by pulsed injection of high-Z gas into a hollow stream of low-Z gas by using the double-nozzle setup. Strong x-ray and EUV production from the laser-irradiated double- stream gas puff target has been demonstrated. Characterization measurements of the source performed using a Nd:glass laser are presented and discussed.
In this work we demonstrate a soft x-ray laser with neon- like argon ions using a gas puff target irradiated with a combination of long 600 ps and short 6 ps high-power laser pulses with a total of 10 J energy. The gas puff target was formed by pulsed injection of gas from a high-pressure solenoid valve through a nozzle in the form of a narrow slit. The target was irradiated in a traveling-wave excitation geometry. Lasing was observed on the 3p 1S0 implies 3s 1P1 transition at 46.9 nm and the 3d 1P1 implies 3p 1P1 transition at 45.1 nm. Gain of 11 cm-1 was measured on these transitions for targets up to 0.9 cm long.
Characterization measurements of a laser-produced x-ray source based on a double-stream ga puff target are presented. The target was irradiated with a Nd:glass laser producing 1 ns pulses with energy up to 10 J. Production in the wavelength range up to 200 nm have been measured form xenon, krypton, argon, and nitrogen targets using the transmission grating spectrometer with the back-illuminated CCD and the absolutely calibrated silicon photodiodes. Spectral characteristics of x-ray and EUV emissions are presented.
Generation of x-ray and extreme ultraviolet (EUV) radiation from laser-produced source with a new double-stream gas puff target has been investigated. The target was formed by pulsed injection of heavy gas (argon, or xenon) into a hollow gas stream from helium by using a double-nozzle setup. This new approach allows to form a high-density gaseous target at a relatively large distance from the nozzle output. X-ray emission was produced by irradiation of the argon/helium target with pulses of 1 ns time duration with energy up to 20 J from a Nd:glass laser. Strong x-ray emission at the wavelength near 0.4 nm from the argon target, similar to the emission from the solid sulphur target irradiated in the same conditions, have been observed. These new results may be useful to develop a laser-produced radiation source for x-ray lithography. To generate EUV radiation the xenon/helium target was irradiated using a Nd:YAG laser producing pulses of 10 ns and 0.7 J or energy. Efficient production near 11 nm from the xenon target exceeding emissions from solid targets was observed that should be useful for EUV lithography.
In this work a double stream ga puff target was applied in experiments connected with a laser plasma soft x-ray source. The results of the gas puff target density measurements was presented. The experimental results of x-ray measurements concern two experiments. The first one was performed in the Institute of Optoelectronics using 1 ns Nd:glass laser. In this experiment soft x-ray radiation around 1 keV and 3 keV was investigated. The measurements were performed using an x-ray pinhole camera, a flat crystal spectrograph and a soft x-ray photodiode. The second experiment was performed in the Institute for Plasma Physics using a 27 ns KrF laser. In this experiment EUV radiation of the wavelength around 13 nm from the gas puff plasma was measured using a multilayer mirror combined with an x-ray detector. In both experiments it was shown that the emission from the plasma created in the double stream gas puff target was even an order of magnitude higher than in a case of using the ordinary gas puff target.
Soft x-ray emission from plasmas produced using a laser- irradiated gas puff target have been investigated. The use of the gas puff targets, created by pulsed injection of high- density gas from a solenoid valve through a nozzle, eliminates the production of debris associated with solid targets. To improve the gas puff target two approaches have been used: (1) cooling of the valve with liquid nitrogen to increase condensation of gas and (2) formation of the target by injection of gas in gas surrounding the nozzle output using the double nozzle setup. The gas puff targets created with these two approaches were characterized with x-ray backlighting method using laser-produced x-ray source. Laser pulses of 1 ns time duration with energy up to 10 J from a Nd:glass laser and of either 0.9 ns or 10 ns time duration with energies up to 0.7 J from a Nd:YAG laser were used to produce plasmas. Emissions in the soft x-ray range from laser- produced gas puff plasmas were studied for various gases. Significant improvement of x-ray production from the double stream gas puff target has been observed.
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