ArF Excimer Research Articles

Evolution of the plumes produced by laser ablation of a carbon target

Abstract The time evolution of plumes produced by laser ablation of a graphite target has been followed by means of intensified CCD imaging. The images were obtained in the same conditions used for the deposition of microcrystalline diamond. An ArF (193 nm, 23 ns) excimer laser beam was focused onto a pyrolytic graphite target with a fluence around 3 J cm−2. The study was performed in high vacuum and under a hydrogen or helium pressure of 1 mbar. Each image was obtained after a single laser pulse and acquired with aperture times from 5 ns to several microseconds depending on the delay time. Spatially resolved optical spectroscopy studies of the plume were also carried out. In vacuum, the images show a free expansion of the plume with a front velocity of 4 × 106 cm s−1. Spectroscopy results indicate the presence of C2. At tens of microseconds, the trails of some particulates emitted from the target can be observed. With a background pressure of 1 mbar, the plume decelerates and a shock wave structure is developed. In the case of H2, spectroscopy reveals CH formation in the expansion front.

Complex index-of-refraction measurements for RP-1 liquid rocket fuel

Complex index-of-refraction values of RP-1 liquid rocket fuel are reported at laser wavelengths of 0.193 μm (ArF excimer), 0.4765 μm (argon ion), 0.488 μm (argon ion), 0.5145 μm (argon ion), 0.532 μm (Nd-YAG, frequency doubled), 0.6328 μm (He-Ne), 1.064 μm (Nd-YAG), and 10.5915 μm (CO₂). The imaginary part of the index of refraction (<i>k</i>) is determined by traditional transmission methods. The real part (<i>n_r</i>) at the specific laser lines is determined using reflectance measurements, critical-angle measurements, Mueller matrix elements, and Michelson interferometric measurements. Reflectance measurements are used to obtain <i>n_r</i> at a wavelength of 0.193 μm. The critical-angle method is used to determine <i>n_r</i> at 0.4765, 0.488, 0.5145, and 0.532 μm: the real part of the refractive index is obtained from Snell's law by measuring the critical angle. The real part of the refractive index at 0.6328 and 1.064 μm is derived from elements of the Mueller matrix, which are obtained using a TMA Technologies scatterometer. A Michelson interferometer is used to obtain phase shifts in a wedge cell, which are then used to calculate <i>n_r</i> at 10.5915 μm. The need for many methods to measure the complex index of refraction is a result of the large changes in <i>k</i> over the wavelengths of interest.

Laser wavelength dependence of YBa 2Cu 3O y laser ablation plumes

The plume produced by laser ablation of an YBa 2Cu 3O y target under irradiation with different laser beam wavelengths has been studied by means of intensified CCD imaging. ArF excimer (193 nm) and Nd:YAG (532 and 1064 nm) laser beams were used. The fluence was about 1 J/cm 2. The investigation was carried out under high vacuum. The plume images show the evolution of different velocity components which depend on the laser wavelength. The fastest one shows a front velocity near 10 4 m/s. It is the dominant feature during many μs in the images obtained for 193 nm and can be also seen for the case of 532 nm. A slower emission, with an estimated velocity ≤ 3 × 10 2 m/s, can also be observed for the case of 193 nm laser irradiation. Two slower velocity components are present in the 532 and 1064 nm laser plumes. One of them has a front velocity around 3 × 10 2 and 7 × 10 2 m/s for 532 and 1064 nm laser wavelength, respectively. The velocity of the other one is estimated as ≤ 10 2 m/s.

High-Efficiency Discharge Excited Rare-Gas Halide Excimer Lasers.

Discharge excited rare-gas halide excimer lasers are useful for material processing such as lithography for next generation LSl, laser ablation of polymers and annealing for Si TAT. Among rare-gas halide excimer lasers, three lasers, XeCl, KrF and ArF lasers, are of practical use.In the present paper, basic parameters, which decide the characteristics of these three lasers, are clarified to be the breakdown voltage Vb, excitation duration ts and excitation power density WDE. A guide line to achieve a high oscillation efficiency for the three lasers using a capacitor-transfer-circuit and UV automatic preionization are presented, by considering the three basic parameters. We have obtained a high efficiency of 2.2% for a XeCl laser, 5% for a KrF laser and 2.3% for an ArF laser.The present study is useful to obtain high performance excimer lasers, bacause high-repetition, long-gas-lifetime and compact excimer lasers have been obtained by achieving a high oscillation efficiency.

Generation of intense 10-ps, 193-nm pulses using simple distributed feedback dye lasers and an ArF* amplifier

A pair of holographic distributed feedback dye lasers is used to generate 10-ps pulses at two selected wavelengths that are mixed in a BBO crystal to produce a pulse ~ 10 ps in duration at 193 nm. This seed pulse is subsequently amplified in an ArF(*) excimer laser to an energy of 10-15 mJ with <40 microJ in amplified spontaneous emission. The pulses are nearly transform limited and diffraction limited.

Preparation of PbTiO3 thin films by laser ablation

Abstract PbTiO3 thin films have been deposited on Si or Pt substrates by laser ablation method using ArF excimer or YAG laser. Species evaporated in the vacuum have been studied by mass analysis, and the measured Pb and Ti are not oxidized. Spacial distributions of the deposition rates on the substrate have been studied as a parameter of laser fluence. The excimer laser gives better films than the YAG. Perovskite films have been obtained at substrate temperature ∼ 400 °C and appropriate ambient O2 gas pressure.

Crystal Growth Modified by Pulsed Laser Irradiation on Growing Surface in Ba-Y-Cu-O Film Preparation by Laser Ablation

ABSTRACTBa2YCu3Ox superconducting films were prepared by Nd:YAG laser ablation, equipped with a second (ArF excimer) laser for irradiation onto the growing film surface. The irradiation onto the film during the deposition were delayed for various delay times against the ablation of Ba2YCu3Ox target. The experiment showed that the second laser irradiation within several tens us around the ablation event induces a change of the crystal orientation. This result suggests that the crystal growth for the laser ablation is determined mainly around this time scale.

Effect of UV Laser Irradiation on Tissue.

Laser-tissue interactions have been investigated through Electron Probe Micro Analysis (EPMA), UV-visible optical absorption and Fourier Transform Infrared Spectroscopy (FTIR). Three excimer lasers, ArF, KrF and XeCl, were used to irradiate tissue; cow thighbone and gelatin thin film. Features of UV laser irradiation are described.

Identification and imaging of hot O2 (v?=2, 3, or 4) in hydrogen flames using 193 nm- and 210 nm-range light

Some simple molecules can be excited by light within the tuning ranges of ArF (193–194 nm) and KrF (247.8–248.8 nm) excimer lasers and their fluorescence has been previously used for imaging. Additional wavelength ranges should become available by Raman shifting. As a demonstration, we present excitation and fluorescence spectra from hot O2 obtained (a) with tunable 193 nm-range light and (b) with that light shifted into the 210 nm range. All measurements are via predissociative upper states. In the 193 nm range, results are compared with those of Andresen's group. In the 210 nm range, the light is tuned to various excitation wavelengths in the (5 ← 3), (8 ← 4), and (7 ← 4) bands of the B–X transition. The (7 ← 4) excitations are well separated and the (7 → v″) fluoresence spectrum is in accord with Franck-Condon calculations. The wavelengths tend to overlap for the (5 ← 3) and (8 ← 4) excitations and the fluorescence is weaker. State-specific two-dimensional fluorescence images of an H2-O2 flame are obtained in both wavelength ranges to illustrate the use of the method.

Simultaneous Fabrication of Insulator and Contact Holes by Excimer Laser

AbstractA SiO2 insulator and contact holes were simultaneously fabricated at room temperature by ArF and KrF excimer lasers. In this method, NF3 and O2 gases were employed for the reaction gas. When the ArF laser beam irradiated the NF3 and O2 gases in the presence of Si, SiFn and NO2 were produced by photo-chemical reaction. The SiFn adsorbed on the Si substrate pulled out O atoms from the NO2 to form a SiO2 layer. At the same time, the patterned KrF laser beam projected on the substrate and ablated the part exposed to fabricate contact holes. As the results, the simultaneous fabrication of SiO2 insulator with the 700 Å film thickness and selective pattern with the 10 μm width was demonstrated.

Effects of dissolved hydrogen on durability of silica glass under excimer laser irradiation.

As an evaluation of durability of synthetic silica glass under irradiation of KrF excimer laser (5.0 eV) or ArF excimer laser (6.4 eV), degradation of transmission was studied for a sample that contained 4×1018 molecules/cm3 H2 but was substantially free of other impurities. First, Khotimchenko’s method of H2 analysis was examined with specimens whose H2 contents were varied by vacuum degassing, covering three orders of magnitude down to H2-free (i.e., less than the instrumental detection limit of 5×1016). It was shown that this method was quite reliable.Then the effects of dissolved H2 were assessed. The hydrogen molecules were decomposed under excimer laser irradiation, and reacted with the E’ center. For KrF excimer laser irradiation, the degradation of transmission was found to be suppressed, when the concentration of hydrogen much increased. Whereas for ArF excimer laser irradiation, there seemed to exist an optimum concentration range.The author proposes a reaction model for the last observation as:≡ Si–O–Si ≡+ H2+hν→≡Si·+·O–Si≡+ H2→≡+Si–H + H–O–Si ≡, where ≡Si· is the E’ center, and ·O–Si≡ , the non-bxsridging oxygen hole center.

Modulated reflectance and Raman scattering studies of metalorganic chemical vapor deposited homolayers of GaAs

Homoepitaxial GaAs films grown by metalorganic chemical vapor deposition (MOCVD) using two different growth conditions were characterized by electrolyte electroreflectance and Raman scattering techniques. We report here the results for two sets of GaAs films deposited on n-type GaAs substrates using MOCVD and trimethyl-gallium. The first set was grown at low temperature by ArF excimer laser-induced MOCVD with the use of arsine, and the second set was grown at about 700 °C by conventional MOCVD with the use of elemental arsenic. Electrolyte electroreflectance studies were used to investigate the energy gaps, structural quality, and topographical carrier concentrations for these homolayers. Raman scattering studies were performed to establish that the crystal orientation was the same as that of the substrate, which was (100) orientation. The spectral results are correlated with the growth parameters for the homolayers of GaAs on GaAs.

ChemInform Abstract: ArF Excimer Laser‐Induced Selective Coupling of Cycloalkanes: Photochemical Reaction at the Absorption Edge.

AbstractIrradiation of the cycloalkanes (I) with an argon fluoride excimer laser in the liquid phase results in the formation of the bicycloalkyls (II).

Dynamics Of MoS2 Photoablation

AbstractSpeed distributions were determined for the ions ejected from MoS2 by excimer laser ablation. It was found that the majority of ionic species were atomic and were ablated with speeds in excess of 6 km/s. The speed distributions were found to be non-Maxwellian and were best described by a supersonic expansion model. The differences in ArF and KrF excimer laser ablation are discussed.

Excimer laser induced deposition of tungsten on silicon

Abstract In this paper a new high vacuum apparatus for laser chemical vapor deposition (LCVD) of tungsten on silicon is presented. It features a fast sample transfer system and a nitrogen window purge to prevent tungsten deposition on the laser entrance and exit windows. Tungsten films grown on silicon in this reactor, using WF 6 and H 2 as reaction gasses and an ArF (193 nm) excimer laser as activation source, are shown to have near bulk resistivity (9.5 μΩ cm at 400°C). The W coverage increases linearly with laser-pulse frequency and growth appears to be thermally activated at fixed pulse frequency. RBS spectra indicate that thickness variations are considerably smaller for films formed by LCVD than for films formed by purely thermal CVD.

Laser photolysis shock tube for combustion kinetics studies

An excimer laser photolysis method has been developed for shock tube kinetics studies of elementary combustion reactions. The excimer laser provides a high intensity source of UV photons well suited to the rapid production of reactive radicals, while shock wave heating provides a convenient means of varying the reaction environment over a wide temperature range. An ArF excimer (193.3 nm) was used to photolyze H 2 O behind reflected shock waves to produce H and OH radicals. The temporal variation of the OH concentration was monitored using a cw, narrow-linewidth laser absorption diagnostic, and the rate coefficient of the dominant reaction after photolysis, H+H 2 O→OH+H 2 , was determined. The measured rate coefficient, k =2.4(±.25)×10 14 exp (−10750 (±500)/T,K) cm 3 mole −1 s −1 , T=1600–2500 K, is in good agreement with other recent studies of this reaction in both the forward and reverse directions.

Pulsed Excimer Laser Deposition of YBaCuO and BisrCaCuO Compounds : Material Distribution and Stoichiometry

AbstractWe investigate, in this study, the laser evaporation processes for the deposition of YBaCuO and BiSrCaCuO compounds, using a pulsed ArF (193 nm) excimer laser. The deposition parameters, especially those which are relevant to the geometrical configuration and optical arrangement of the experimental set-up and laser irradiation conditions are examined in details.

Low temperature photon-controlled growth of thin films and multilayered structures

Abstract Pulsed ArF (193 nm) excimer laser photolysis of disilane, germane, and disilane-ammonia mixtures has been used to deposit amorphous superlattices containing silicon, germanium and silicon nitride layers. Transmission electron microscope cross-section views demonstrate that structures having thin (5–25 nm) layers and sharp interlayer boundaries can be deposited entirely under laser photolytic control, using low reactant gas partial pressures and with the excimer laser beam parallel to the substrate. Growth of epitaxial films and structures under similar conditions is discussed.

Emission spectra of common discharge excimer-laser transitions

Measured broadband laser emission spectra are provided for ArF, KrF, and XeCl excimer lasers along with a list of previous references to these spectra.

Argon fluoride laser activated deposition of nitride films

The nitrides of aluminium, gallium and indium and their ternary alloys exhibit a unique range of dielectric and semiconducting properties. Standard kinetic growth techniques (reactive sputtering for example) produce films of good quality but with the unfortunate concomitant of ion-bombardment damage to fragile substrates during the early stages of nucleation and growth. Provision of reactive species by the photodissociation of the appropriate metallorganic and ammonia gas permit the growth of the nitrides in a non-substrate-invasive way. We describe here the construction and operation of an excimer ArF laser powered system designed for the deposition of insulating nitride layers on GaAs substrates.