Excimer Laser Wavelength Research Articles

Electron beam propagation in a space-charge regime

We report on the propagation of electron beams generated by a niobium photocathode illuminated by different wavelength excimer lasers. The cathode used was a polycrystalline disc. Its work function was 4.3 eV while the laser photon energy was 4.02 eV for the XeCl laser and 5.6 eV for the KrCl laser. The anode–cathode distance was variable as well as the saturation output current. At low accelerating voltage the beam was space charge dominated but its peak value was not limited by the Child–Langmuir calculated value. A fast shunt resistance allowed to record the electron beam generated with a fast rise time. The maximum output current was reached with the KrCl laser which provided an electron bunch containing 980 mA and 9 nC.

Experimental investigation of laser induced forward transfer process of metal thin films

Dependence of size accuracy of deposited structure on the film–acceptor substrate distance and fluence, and the factors which influence the dependences were investigated. Au and Ni thin films of several tens to hundreds of nanometer thickness deposited on quartz substrates using ion sputtering deposition were irradiated by single pulse of KrF excimer laser (wavelength: 248 nm, pulse width 30 ns). Changes in the intensity of reflected He–Ne laser from the front and rear sides of the thin films show that film removal finishes during the excimer laser pulse. Plume images and shadowgraphs of transferring materials show that the velocity of both the leading edge of the plume and the transferring materials become faster with increasing fluence, and that the transferring material precedes the plume. At lower fluences, the deposited structure shows bad appearance due to incomplete removal from the support substrate. At higher fluences, the big shock causes the wide range of spread of deposited structure when the transferring particles have a collision with the acceptor substrate. At optimum fluences, high size accuracy of the deposited structure is achieved when the film–substrate distance is made as short as possible.

Spun-on carbon antireflective layer with etch resistance for deep and vacuum ultraviolet lithography processes

Dry etch resistance and antireflective performance were studied for a film containing a high amount of carbon (83.4 wt %), which was named the spun-on carbon film. The film was formed by using a carbon cluster precursor synthesized by reductive coupling of a mixture of carbon tetrabromide and phenylbromide. The refractive indices of the spun-on carbon film at the exposure wavelengths of excimer lasers are n=1.72, k=0.35 (KrF), n=1.46, k=0.67 (ArF), and n=1.37, k=0.14 (F2). A bilayer bottom antireflective coating system composed of upper spun-on glass (SOG) and lower spun-on carbon was evaluated. By optimizing the SOG thickness, the reflectivity is reduced to 0.2% (KrF), 3.3% (ArF), and 0.5% (F2). Remarkable improvement is observed at the KrF and F2 wavelengths. Resist profiles are obtained without any footing, residue, or standing wave using the KrF and ArF scanning steppers. The etch resistance of the spun-on carbon film is 1.34 times greater than that of the thermally oxidized novolak film (i.e., a conventional underlayer for a trilevel resist process).

Emission spectroscopy and size distribution of gas phase nanoparticles generated by laser-based methods

Tungsten and iron/carbon composite nanoparticles were generated via ArF excimer laser-assisted CVD from WF 6/H 2/Ar gas mixture and photolytic decomposition of ferrocene (Fe(C 5H 5) 2), respectively. Time-resolved spectroscopic measurements were performed and the emitted black-body-like radiation from these particles, due to the laser heating, was analyzed determining the temperature of the particles. Dominant cooling processes as evaporation and heat transfer by the ambient gases were identified; thermionic emission and black-body-like radiation were found to be negligible. Melting of tungsten and boiling of iron nanoparticles were observed. The size distributions of the particles were found lognormal and it was explained by the residence time approach model, functioning at the limit with no coagulation of the particles. Amorphous carbon nanoparticles were formed via laser ablation of a highly oriented pyrolytic graphite target at 193 nm excimer laser wavelength in N 2 atmosphere at normal pressure. The size distribution of the particles was in situ monitored by a differential mobility analyzer in the size-window of 7–130 nm. Change of size distributions was monitored as the laser fluence was varied. The observed effects are discussed and related to the ablation dynamics. Compositional and structural examinations of deposited particle-films were performed by Raman spectroscopy, X-ray and electron diffraction techniques.

Preparation of Organic Soluble Polyimides and Their Applications in KrF Excimer Laser LIGA Process

In this study two organic soluble polyimides were successfully synthesized via polycondensation of a hexafluoropropyl group contained dianhydride with two kinds of diamines. These two polyimides (DMDB/6FDA, OT/6FDA) can be dissolved in most aprotic solvents (for example, NMP, DMAc) and many other common solvents (for example, THF, DMSO). The soluble polyimides also show good thermal stability and high absorption at the KrF excimer laser wavelength (λ = 248 nm). (The absorption coefficients of DMDB/6FDA and OT/6FDA were 1.26×105 cm–1 and 1.49×105 cm–1, respectively.) The photoablation properties of the polyimides were studied in detail. Due to incorporating the hexafluoropropyl group into the chemical structure, these two polyimides have higher etching rates than Kapton (a commercial PI film). The effects of exposure parameters on linewidth and taper-angle of polyimides with different chemical structure were also investigated here. Under the proper control of exposure conditions, good precision patterns with near-vertical side wall can be produced. The 300 mm thick comb-shape and Fresnel patterns with 10 mm linewidth have been made. Moreover, the complementary metallic microstructures have also been realized in the following electroforming procedure. The results showed that these two soluble polyimides were very suitable for KrF Laser LIGA process.

The new ultraviolet spectral responsivity scale based on cryogenic radiometry at Synchrotron Ultraviolet Radiation Facility III

The recently completed upgrade of the Synchrotron Ultraviolet Radiation Facility (SURF III) at the National Institute of Standards and Technology (NIST) has improved the accuracy of radiometric measurements over a broad spectral range from the infrared to the soft x ray. The beamline 4 at SURF III is a cryogenic-radiometer based radiometric facility for the ultraviolet (UV) spectral range. The upgrade of SURF III has allowed us to use beamline 4 to improve the detector spectral power responsivity scales in the wavelength range from 125 to 320 nm. The achieved combined relative standard uncertainty is better than 0.5% over most of this spectral range. This is a significant improvement over the more than 6% relative standard uncertainty in this spectral range of the current scales maintained at the Spectral Comparator Facility (SCF) in the Optical Technology Division and the Far UV Calibration Facility in the Electron and Optical Physics Division. The new UV scale of beamline 4 was subsequently intercompared and transferred to the SCF and to the Far UV Calibration Facility to improve their UV scales and ensure consistency within NIST. The new scale established at beamline 4 improves NIST’s calibration capabilities for environmental monitoring, astrophysics, and the UV industry. The new scale also includes wavelengths such as 193 and 157 nm excimer laser wavelengths, which are of particular interest to the semiconductor photolithography industry.

Deep-ultraviolet transparent conductive β-Ga2O3 thin films

Thin films of β-Ga2O3 with an energy band gap of 4.9 eV were prepared on silica glass substrates by a pulsed-laser deposition method. N-type conductivity up to ∼1 S cm−1 was obtained by Sn-ion doping and deposition under low O2 partial pressure (∼10−5 Pa) at substrate temperatures above 800 °C. The resulting internal transmittance at the wavelength (248 nm) of the KrF excimer laser exceeded 50% for the 100-nm-thick film, making this the most ultraviolet-transparent conductive oxide thin film to date and opening up prospects for applications such as ultraviolet transparent antistatic electric films in ultraviolet lithography.

Extension of the ArF Excimer Lithography to Sub-0.10 µm Design Rule Devices Using Bi-layer Silylation Process

The device design rule has been significantly reduced, and a practical pattern fabrication technique for sub-0.10 µm or smaller dimensions is urgently required. The top surface imaging (TSI) process using an ArF excimer laser (wavelength=193 nm) is a promising approach to the realization of this demand. We have been evaluating the positive-tone silylation process as one of the TSI processes in order to extend the limit of ArF optical lithography. We found that for the positive tone silylation process, control of the silylation depth and profile is very important, and the bi-layer silylation process using a thin silylation resist as a top layer is a practical and effective process for fine pattern fabrication. In this report, we describe the high lithographic performances of this bi-layer silylation process and its application to sub-0.10 µm rule device manufacturing.

Excimer Laser Recrystallization of a-Si Employing Aluminum Masking Window

ABSTRACTA new excimer laser recrystallization method of amorphous silicon is proposed to increase the grain size and control the grain boundary locations in polycrystalline silicon films. The proposed method is based on the lateral grain growth which occurs at the interface between molten and unmolten regions. To obtain selectively molten regions, the proposed method employs aluminum patterns on amorphous silicon. The aluminum patterns act as the beam shield during the laser irradiation as well as the lateral heat sink during the solidification period. The high reflectance of aluminum at the wavelength of XeCl excimer laser offers stable beam shielding property, and the high thermal conductivity enhances the lateral heat flow by the quick draining of laterally propagated heat. TEM observation has revealed that the well arranged large grains were successfully obtained.

Trend of Short Wavelength Excimer Laser

Trend of Short Wavelength Excimer Laser

Influence of ion-beam energy and substrate temperature on the synthesis of carbon nitride thin films by nitrogen-ion-assisted pulsed laser deposition

Carbon nitride thin films were deposited on silicon wafers by pulsed KrF excimer laser (wavelength 248 nm, duration 23 ns) ablation of graphite with assistance of nitrogen ion beam bombardment. X-ray photoelectron spectroscopy, Raman spectroscopy, and ellipsometry were used to identify the binding structure, nitrogen content, and optical properties of the deposited thin films. The influence of the nitrogen ion beam energy on the compositional, electronic, and optical properties of the deposited thin films was investigated. The thin films deposited with nitrogen ion bombardment had an N/C ratio of 0.43. Raman spectroscopy measurements indicated the formation of CN triple bonds in the deposited thin films. The optical band gap Eopt was observed to decrease with the nitrogen ion energy. A nitrogen ion energy between 50 and 100 eV was deduced to be the optimal condition for depositing the carbon nitride thin films.

Excimer-laser-induced densification in binary silica glasses

We report that the rate of excimer-laser-induced densification is a strong function of composition in the binary metal-oxide-silica system. The pulsed excimer-laser-induced densification rate is shown to increase with metal-oxide content. A good correlation was found between the densification rate and the relative softness of the glass, as indicated by the annealing temperature. The densification rate for all the glasses was also found to be a strong function of the excimer-laser wavelength in the order 157nm>193nm >248nm .

Submicron laser writing on diamond

A synthesized HPHT IIb diamond plate is irradiated with a KrF excimer laser (wavelength λ =248 nm, pulse duration τ =20 ns). The beam is focused onto the surface with an ultrafluar objective [numerical aperture (NA)=1]. The quality of the optical imaging system is first investigated by performing atomic force microscopy (AFM) measurements on holes ablated into Perspex (PMMA). On diamond, holes are drilled at various pulse energies down to values slightly above the ablation threshold. The hole depth and width are measured by AFM after annealing in air at 600°C during 3 h. Holes with submicrometre diameters are obtained, and suggestions on how to produce even smaller holes are given.

Synthesis of spherical luminescent particulate coatings

In this communication, we show the feasibility of the pulsed laser ablation technique to make very thin, uniform luminescent coatings on particulate systems. To deposit continuous particulate coatings, the laser-induced plume from the target comes in contact with an agitated bed of core particles (size 1 μm). The pressure and nature of the background gas (inert or active) controls the cluster size of the particles in the laser plume. Experiments were conducted for laser deposition of phosphor nanoparticles on SiO2 core particles by pulsed excimer laser (wavelength=248 nm and pulse duration=25 ns) irradiation of a yttria:Eu (Y2O3:Eu3+) sputtering target.

Chlorine atom formation dynamics in the dissociation of CH3CF2Cl(HCFC-142b) after UV laser photoexcitation

The dynamics of chlorine atom formation after UV photoexcitation of CH3CF2Cl(HCFC-142b) in the gas phase was studied by a pulsed laser photolysis/laser-induced fluorescence (LIF) “pump-and-probe” technique at room temperature. The parent molecule was excited at the ArF excimer laser wavelength (193.3 nm) and nascent ground state Cl(2P3/2) and spin-orbit excited Cl*(2P1/2) photofragments were detected under collision-free conditions via laser induced fluorescence in the vacuum ultraviolet spectral region. Narrow-band probe laser radiation, tunable over the wavelength range 133.5–136.4 nm, was generated via resonant third-order sum-difference frequency conversion of dye laser radiation in Krypton. Using HCl photolysis at 193.3 nm as a source of well-defined Cl(2P3/2) and Cl*(2P1/2) concentrations, values for the total Cl atom quantum yield (ΦCl+Cl*=0.90±0.17) and the [Cl*]/[Cl] branching ratio 0.39±0.11 were determined by means of a photolytic calibration method. From the measured Cl and Cl* atom Doppler profiles the average relative translational energy of the fragments could be determined to be 125±25 kJ/mol. The corresponding value fT=0.48±0.10 of the fraction of total available energy channeled into product translational energy was found to be (within experimental uncertainty) in agreement with the result fT=0.39 of a dynamical simulation assuming a repulsive model for single C–Cl bond cleavage. Both the measured total Cl atom quantum yield and the energy disposal indicates that direct C–Cl bond cleavage is a primary fragmentation mechanism for CH3CF2Cl after photoexcitation at 193.3 nm.

LiAr, LiKr and LiXe excimers: Photochemical formation of the $\mathsf3^{2}\Sigma^{+} $ - $\mathsf1^{2}\Sigma ^{+}$ bands

We investigated the photochemical formation of lithium-rare-gas excimers in the 3\(\) state through the reaction of Li2(2(C)\(\)) and the ground-state rare-gas atom. Lithium-rare-gas vapor mixture was prepared in the heat-pipe oven. We populated the 2(C)\(\)state of the Li2 molecule using the XeCl excimer laser wavelength at 308 nm or the PTP dye laser wavelength at about 335 nm. The 3\(\)-1\(\) transitions were observed with peaks at 414, 420 and 435 nm for LiAr, LiKr and LiXe, respectively. We estimated thermally averaged rate constants for these photochemical reactions, which are \(\)cm3s-1 for LiAr, \(\)cm3s-1 for LiKr and \(\)cm3s-1 for LiXe. Ab initio potential-energy curves and transition dipole moments for LiKr were calculated applying the SCF MRDCI method. Available data for the LiAr and LiKr excimers are presented, including potential-energy curves, electronic transition dipole moments, and spectroscopic constants. Possible photochemical formation of these molecules in the excited states is discussed. We performed the quantum-mechanical spectral simulations of the LiAr and LiKr 3\(\)-1\(\) transitions, using ab initio potential-energy curves.

Pulsed-laser deposition of diamond-like carbon: Relations between laser fluence, velocity of carbon ions, and bonding in the films

In the pulsed-laser deposition process, high intensity laser pulses expel material from a solid target and form expanding plasma near the solid surface. The expansion of the plasma produces a forward-directed beam of ionized and neutral species with typical energies of 1–100 eV. In this study, amorphous diamond-like carbon (DLC) thin films were deposited onto silicon substrates at room temperature using an XeCl excimer laser (wavelength 308 nm, pulse length 20 ns) with laser fluences in the range 5–45 J cm−2, on a pyrolytic graphite target. The effect of laser fluence on the velocity and kinetic energy distribution of carbon ions was measured by time-of-flight (TOF) spectrometry using a system based on a Faraday cup with biased grids, and a multichannel plate based particle detector. We have found high kinetic energies, up to 500 eV, for expelled atomic species. In order to study the effect of the energy of the arriving ions on the structure of DLC, the bonding of carbon atoms in films, deposited under similar conditions as in the TOF measurements, was studied by x-ray absorption near-edge structure.

Synthesis and properties of nanofunctionalized particulate materials

A wide range of advanced technology for existing and emerging products based on high temperature metal-ceramic composites used in aircrafts, cutting tools, lithium-ion based rechargeable batteries, superconductors, field emission based flat-panel displays, etc. employ micron to submicron sized (0.1–10 microns) particulate precursors in their manufacturing process. Although there has been a significant emphasis given to control of the particle characteristics (shape, size, surface chemistry, adsorption, etc.), relatively little or no attention has been paid to concomitant designing desirable surface and bulk properties at the particulate level, which can ultimately lead to enhanced properties of the product. By attaching atomic to nano-sized inorganic, multi-elemental clusters either in discrete or continuous form onto the surface of the core particles, i.e nano-functionalization of the particulate surface, materials and products with significantly enhanced properties can be obtained. In this paper, we demonstrate the synthesis of artificially structured, nano-functionalized particulate materials with unique optical, cathodoluminescent, superconducting and electrical properties. In this paper, we show the feasibility of the pulsed laser ablation technique to make very thin, uniformly distributed and discrete coatings in particulate systems so that the properties of the core particles can be suitably modified. Experiments were conducted for laser deposition on Al 2O 3, SiO 2, core particles by pulsed excimer laser (wavelength = 248 nm and pulse duration = 25 nanosecond) by irradiation of a Ag and Y 2O 3:Eu 3+ targets.

Nanometric Dry Powder Coatings Using a Novel Process

A wide range of advanced technology for existing and emerging products based on high temperature metal-ceramic composites used in aircrafts, cutting tools, lithium-ion based rechargeable batteries, superconductors, field emission based flat-panel displays, etc. employ micron to submicron sized (0.1-10 microns) particulate precursors in their manufacturing process. Although there has been a significant emphasis given to control of the particle characteristics (shape, size, surface chemistry, adsorption, etc.), relatively little or no attention has been paid to concomitant designing desirable surface and bulk properties at the particulate level, which can ultimately lead to enhanced properties of the product. By attaching atomic to nano-sized inorganic, multi-elemental clusters either in discrete or continuous from onto the surface of the core particles, i.e. nano-functionalization of the particulate surface, materials and products with significantly enhanced properties can be obtained. In this paper, we demonstrate for the first time the synthesis of artificially structured, nano-functionalized particulate materials with unique optical, cathodoluminescent, superconducting and electrical properties. In this paper, we show the feasibility of the pulsed laser ablation technique to make very thin, uniformly distributed and discrete coatings in particulate systems so that the properties of the core particles can be suitably modified. Experiments were conducted for laser deposition of Ag nano particles on Al2O3 and SiO2 core particles by pulsed excimer laser (wavelength =248 nm and pulse duration =25 nanosecond) irradiation of a Ag, Y2O3:Eu3+, and TaSi2 sputtering targets. Analytical techniques using scanning electron microscopy (SEM), wavelength dispersive x-ray mapping (WDX) , transmission electron microscopy (TEM) , scanning transmission electron microscopy with z contrast (STEMZ), and photoluminesence (PL) were utilized to examine the structural, chemical, and morphological characteristics of the nanometric coatings. Qualitative surface uniformity measurements by WDX mapping techniques showed a high degree of coating uniformity on the core particulate. Structural TEM and STEMZ imaging showed both continuous and discrete polycrystalline, multiply twinned nano particle coatings ranging from 5-40 nm in thickness.

Laser-induced surface modifications of poly(ether ether ketone): influence of the excimer laser wavelength

The modifications induced by excimer laser irradiation of poly(ether ether ketone) (PEEK) surfaces have been investigated as a function of the laser process parameters for laser fluences below the material ablation threshold. In the case of 193 nm laser treatment, a significant increase in the adhesion properties of PEEK was obtained due to the formation of new polar and reactive groups on the surface. The extent of these reactive groups has to be controlled since their presence in high concentration may also have a negative effect on the mechanical properties of the treated surface. Laser treatments using 248 nm radiation did not result in a significant increase in the adhesion properties of PEEK. This probably results from thermal degradation of the surface at this laser wavelength.