High-power Excimer Research Articles

Histological evaluation of vascular changes after excimer laser angioplasty for neointimal formation after bare-metal stent implantation in rabbit iliac arteries.

Excimer laser is used to treat coronary artery disease, especially in case of lesions with thrombus and in-stent restenosis (ISR). However, there are no in vivo preclinical studies that have evaluated the pathological reactions of the vessel wall after excimer laser ablation. Bare-metal stents were placed in the external iliac arteries of six healthy rabbits. Twenty-eight days later, excimer laser ablation was performed with low-power (45 (fluency)/25 (rate)) in one side, and high-power (60/40) in the opposite side, followed by optical coherence tomography (OCT) evaluation. Rabbits were sacrificed 15min after the procedure, and histological assessment was performed. Morphometry analysis of OCT showed similar stent and lumen size between low-power and high-power group. Histological evaluation suggested endothelial cell loss, fibrin deposition, and tissue loss. The low-power group showed significantly less pathological changes compared with the high-power group: angle of endothelial cell loss, 32.4° vs. 191.7° (interquartile range, 8.8°-131.7° vs. 125.7°-279.5°; p < 0.01); fibrin deposition, 1.1° vs. 59.6° (0.0°-70.4° vs. 31.4°-178.4°; p = 0.03); and tissue loss 0.0° vs. 18.2° (0.0°-8.7° vs. 0.0°-42.7°; p = 0.03). The pathological changes in neointima were more prominent after high-power excimer laser ablation than after low-power excimer laser. To improve safety in clinical practice, understanding the pathological changes of tissues after excimer laser in lesions with ISR is essential.

Numerical Analysis of Corona Pre-Ionization for High-Power Discharge-Pumped XeCl* Excimer Lasers

The working gas of discharge-pumped excimer lasers is generally a mixture of rare gases and monohalide. Typically, the working gas is preconized to generate reproducible uniform glow discharge. In high-power (more than 100 W) excimer lasers, this pre-ionization is achieved through spark discharge in the discharge chamber. In this study, a high-power discharge-pumped XeCl* excimer laser with corona preionisation was designed to investigate the feasibility of applying corona preionisation in high-power excimer lasers as well as analyse the correlation of corona discharges characteristics with laser discharge properties. The electron avalanche triggered by ultraviolet preionisation in the laser was numerically studied by creating 2D models. The simulation results revealed that the additional ionisation induced by the secondary electron emission of the cathode together with the dielectric constant of the corona bars significantly affect the discharge current of the principal electrodes. Under the condition of the design values, the peak preionisation electron density between electrodes was approximately 108 cm−3, and the laser discharge was quite uniform, which theoretically proved the feasibility of using corona preionisation instead of spark discharge preionisation in high-power practical devices.

Numerical Analysis of Gas Flow Field of High-Power Excimer Laser

Numerical Analysis of Gas Flow Field of High-Power Excimer Laser

Influence of UV Radiation on the Spectral Properties of 2-METYL-4-Chlorophenoxy Propionic Acids

The influence of UV radiation on the spectral properties of 2-methyl-4-chlorophenoxy propionic acid (mecoprop) is studied. An effective high-power excimer barrier-discharge lamp based on working mixtures of krypton with low-aggressive halogen molecules (λ ~ 222 nm) is used as a source of UV radiation. It has been found that under stationary conditions, the use of a flow-through photoreactor for photodegradation of mecoprop is more efficient than the use of an excilamp. The degree of photodegradation depends on the exposure time.

Fine Line Routing and Micro via Patterning in ABF Enabled by Excimer Laser Ablation

Abstract Fan-Out technologies continue to be the main driver for advanced packaging, be it on wafer level (FOWLP) or panel level (FOPLP). There is a continuing need for higher density routing and heterogeneous integration of different devices, but also for continuous cost reduction. While traditional organic flip-chip substrates using semi-additive processes (SAP) have not been able to scale to ultra-fine RDL pitches and via opening below 10um, photo-sensitive spin-on dielectrics and RDL processes used for wafer level packaging do not sufficiently address the cost reduction need, and also face serious technical challenges. This paper presents the latest results from an innovative package RDL and micro via processes using excimer laser ablation in an especially developed non-photo sensitive material, to meet the market's most stringent requirements. To enable panel and wafer based interposers to reduce RDL cost and scale interconnect pitch to 40um and below, excimer laser ablation is introduced as a direct patterning process that uses proven industrialized excimer laser sources to emit high-energy pulses at short wavelengths to remove polymer materials with high precision and high throughput. The combination of a high-power excimer laser source, large-field laser mask and precision projection optics enables the accurate replication and placement of fine resolution circuit patterns without the need for any wet-processing. With excimer laser patterning technology the industry gains a much wider choice of dielectric materials (photo and non-photo) to help achieve further reductions in manufacturing costs as well as enhancements in interposer and package performance. In this paper, we propose a novel patterning process that uses excimer laser ablation to integrate via and RDL traces in one patterning step, followed by seed layer deposition, plating and planarization. The capability of this excimer laser patterning process in non-photo materials Ajinomoto Build-up Film, which is abbreviated to “ABF” in this paper, will be discussed, and its technical robustness and commercial advantages are demonstrated. We will present electrical and reliability data of Via and RDL traces patterned by excimer laser in ABF material.

High-power gas-discharge excimer ArF, KrCl, KrF, and XeCl lasers on buffer-gas free gas mixtures

Results of experimental studies of the gas mixture (laser active medium) effect on the lasing energy and overall efficiency of excimer discharge ArF (193 nm), KrCl (222 nm) KrF (248 nm), and XeCl (308 nm) lasers operating in buffer-free gas mixtures are presented. The optimal (in terms of maximum radiation energy) ratios of the gas components of the excimer laser active media are found, at which efficient operation is achieved with a sufficiently high power of the laser radiation. It is confirmed experimentally that for the rare gas halide discharge pumped excimer lasers the presence of a buffer gas in the active medium is not required for efficient laser operation. For example, in two-component excimer laser gas mixtures, containing working rare and halogen-containing gases, laser pulse energy of up to 170 mJ and high pulsed power of laser radiation of up to 24 MW have been attained for the first time for pulsed gas-discharge excimer lasers operating on electronic transitions at excimer ArF*, KrCl*, KrF*, and XeCl* molecules pumped by a transverse electric volume discharge of a low-pressure buffer-free gas mixture. A overall efficiency maximum of up to 0.8% was experimentally attained for binary gas mixture of KrF and XeCl lasers.

Embedded RDL formation in Non-Photo Polymers using Excimer Laser Ablation

Abstract The continuous trend towards miniaturization, increasing performance and mobility of electronic devices drives interconnect density and integration, not only at the chip level, but also at interposer and package level. Silicon interposers coming from wafer foundries using back end of line (BEOL) redistribution layer (RDL) processes have been introduced successfully. However, there is a continuing need for low cost interposers based on large organic or glass panels. While traditional organic flip-chip substrates using semi-additive processes (SAP) have not been able to scale to ultra-fine RDL pitches, photo-sensitive spin-on dielectrics and RDL processes used for wafer level packaging do not sufficiently address the cost reduction need, This paper presents the latest results from cost effective and innovative package RDL processes using excimer laser ablation, to meet the market's most stringent requirements. To enable panel and wafer based interposers to reduce RDL cost and scale interconnect pitch to 40um and below, excimer laser ablation is introduced as a direct patterning process that uses proven industrialized excimer laser sources to emit high-energy pulses at short wavelengths to remove polymer materials with high precision and high throughput. The combination of a high-power excimer laser source, large-field laser mask and precision projection optics enables the accurate replication and placement of fine resolution circuit patterns without the need for any wet-processing. In addition, with excimer laser patterning technology the industry gains a much wider choice of dielectric materials (photo and non-photo) to help achieve further reductions in manufacturing costs as well as enhancements in interposer and package performance. In this paper, we propose new process that uses excimer laser ablation to integrate via and RDL traces in one patterning process step, followed by seed layer deposition, plating and planarization steps. A new integration process flow is proposed, and its technical robustness and commercial advantages have been demonstrated. The capability of this excimer laser process to extend the current material portfolio to non-photo materials will be discussed, and its commercial benefits as compared to the current process of record (POR) will be highlighted.

High-power gas-discharge excimer ArF, KrCl, KrF and XeCl lasers utilising two-component gas mixtures without a buffer gas∗∗Reported at the Fifth Russian-Chinese Workshop and School for Young Scientists on Laser Physics and Photonics (RCWLP&P, Novosibirsk, August 26 – 30, 2015).

Results of an experimental study of the influence of a gas mixture (laser active medium) composition on an output energy and total efficiency of gas-discharge excimer lasers on and molecules operating without a buffer gas are presented. The optimal ratios of gas components (from the viewpoint of a maximum output energy) of an active medium are found, which provide an efficient operation of laser sources. It is experimentally confirmed that for gas-discharge excimer lasers on halogenides of inert gases the presence of a buffer gas in an active medium is not a necessary condition for efficient operation. For the first time, in two-component gas mixtures of repetitively pulsed gas-discharge excimer lasers on electron transitions of excimer molecules and , the pulsed energy of laser radiation obtained under pumping by a transverse volume electric discharge in a low-pressure gas mixture without a buffer gas reached up to and a high pulsed output power (of up to ) was obtained at a FWHM duration of the KrF-laser pulse of . The maximal total efficiency obtained in the experiment with two-component gas mixtures of KrF and XeCl lasers was 0.8 %.

Selective Fabrication of SiC/Si Diodes by Excimer Laser Under Ambient Conditions

This letter presents SiC/Si diodes fabricated by the selective growth of SiC on Si substrate under ambient (atmospheric) conditions. The selective growth of $\beta $ -SiC was obtained by irradiating a high-power KrF excimer laser beam on a polymethyl methacrylate (PMMA)-coated Si wafer. The laser decomposed carbon atoms from the PMMA, which dissolve into molten Si to form SiC. The Raman spectrum of the grown samples shows a dominant band in the range of 930–990 cm $^{-1}$ , i.e., the spectral region characteristic for $\beta $ -SiC. The quality of SiC can be optimized by changing the induced power. The best performing SiC/Si diode shows a good rectification ratio of $\sim 3 \times 10^{4}$ (±1 V), a low leakage current density of $\sim 1~\mu \text{A}$ /cm2 (−1 V), and high breakdown (>200 V), which confirms the high quality of the SiC/Si interface. The doping of SiC was calculated from 1/ $C ^{2}$ versus $V$ plot and found to be $\sim 5 \times 10^{15}$ cm $^{-3}$ . In addition, the measured photoelectric response shows a short circuit current density of 17 mA/cm2, an open circuit voltage of 0.33 V, and a fill factor of 62%.

About Losses in Pumping Generators of High-Power Electrodischarge Excimer Lasers

Energy losses in pumping systems of discharge high-power lasers are investigated. To estimate the losses, the discharge circuit operation was modeled, and its calculation was performed using the program PSpice. Results of measurements and calculations demonstrate that the resistance of a rail gap with electric field distortion exceeds several times the resistance of a single-channel gap without field distortion. A difference in the resistances is explained by different mechanisms of discharge burning: in the first case diffusion mechanism and in the second case the spark mechanism. The low efficiency of the high-power excimer lasers (~1%) is explained by high energy losses in the rail gap that reach more than 50% of the initially stored energy.

Prototype of a high-power, high-energy industrial XeCl laser

We discuss the results of fabrication and experimental study of a high-power excimer XeCl laser for industrial applications. Compactness of the laser is achieved by the employment of a laser chamber based on a ceramic tube made of . High laser output energy is obtained using a wide-aperture (up to ) volume discharge with pre-ionisation by a creeping discharge. The pre-ionisation is realised through a semi-transparent electrode by the UV radiation of a creeping discharge in the form of uniform plasma sheet on a surface of a plane sapphire plate. The operating lifetime of the gas mixture amounts to at a stabilised average laser power of . The results obtained demonstrate real prospects for developing a new class of excimer XeCl lasers with an average power of .

10.1007/s11455-008-3002-6

We have studied the action of nanosecond-pulsed high-power KrF excimer laser radiation on the composite layer of a soda-lime-silicate glass containing ion-synthesized silver nanoparticles, with the purpose of modifying the material properties by changing the size of metal particles. It is established that, as the number of laser pulses increases, the treatment leads to a decrease in the average size of silver nanoparticles in the ionimplanted layer. However, after the almost complete disintegration of silver particles, a further increase in the number of pulses leads to new growth and a coarsening of the metal particles. The observed phenomena are interpreted in terms of heating of the surface layer of glass and silver particles by nanosecond laser pulses and the related increase in the diffusion mobility of silver atoms in the glass matrix.

Improvement of green cathodoluminescence of zinc oxide stacked films prepared by high-power excimer laser irradiation of sol–gel-derived precursors

Zinc oxide (ZnO) stacked films were prepared by repeating a procedure involving KrF excimer laser irradiation at various energy fluences ( E f) of sol–gel-derived precursors. All the stacked films are wurtzite-type and highly c-axis oriented on glass substrates. The green cathodoluminescence (CL) efficiency of the films is strongly influenced by the preparation conditions. Especially, laser E f and stacking number are important control factors. The stacked film prepared under optimized preparation conditions consists of large grains and indicate low electric resistivity. The green CL efficiency of the stacked film is 0.0139 lm/W, which is higher than those of ZnO thin films prepared by a single stacking.

Fabrication of crystalline Si spheres with atomic-scale surface smoothness using homogenized KrF excimer laser reformation system

A technique applying the homogenized KrF excimer laser reformation to fabricate Si spheres on the silicon on insulator platform is presented. High-power excimer laser was used to illuminate the Si rods which were fabricated using typical procedures. The Si rods were then melted and reshaped to spheres due to surface tension. This method is capable of fabricating submicrometer Si spheres with extremely smooth surface. Atomic force microscopy was used to reveal the atomic-scale surface smoothness of the fabricated Si spheres. It shows that root-mean-square roughness is smaller than 0.1nm. In addition, tunneling electron microscopy was used to investigate crystalline property of the Si spheres, showing that single-crystalline Si with lattice plane spacing of about 0.24nm was formed after the transformation of the Si rod into the sphere.

Photochemical Removal of N2O in N2 or Air Using 172 nm Excimer Lamps

N2O removal was investigated in N2 or air using 172 nm Xe2 excimer lamps (50 or 300 mW/cm2) without using any expensive catalysts. The residual amount of N2O and the formation ratios of products were measured as functions of photoirradiation time, N2O concentration, and O2 concentration. N2O (100 ppm) was completely converted to N2 and O2 without NOx emission in N2 at atmospheric pressure after 30 min photoirradiation using a high-power Xe2 excimer lamp (300 mW/cm2). 76% of N2O (100 ppm) was also converted to N2, O2, and HNO3 in air (20% O2) after 30 min photoirradiation using the high-power lamp. We concluded that N2O is dominantly decomposed by 172 nm photolysis in N2 and by the O(1D) + N2O reaction in air, where O(1D) atoms dominantly arise from the 172 nm photolysis of O2. The conversion of N2O in air increased more than twofold by decreasing the total pressure from atmospheric pressure to 20 kPa by suppressing the collisional quenching of O(1D) by N2 and O2 buffer gases. In a flow experiment, the conversion of N2O in N2 was only 6–18% in the total flow rate range of 0.1–1 L/min owing to the short residence time of N2O in the photolysis chamber.

Proton conducting BaZr 0.8Y 0.2O 3−x thin films by pulsed laser deposition technique

Here we report the synthesis of high-quality single-phase thin films of BaZr 0.8Y 0.2O 3− x (BZY20) by pulsed laser deposition (PLD) technique. BZY20 films were deposited on various substrates including single-crystal sapphire (0 0 0 1), LaAlO 3 (0 0 1), LaAlO 3/LaNiO 3 (0 0 1), and polycrystalline Cu and Fe foils. Depositions were performed using a high-power pulsed KrF excimer laser (wavelength 248 nm, 25 ns pulse duration) under controlled oxygen ambience. Substrate temperature and laser energy density during the depositions were maintained in the range 500–600 °C and 2–3 J/cm 2, respectively. The microstructural, electrical, and gas-sensing properties of BZY20 films were studied, with the goal of understanding growth characteristics and optimizing their sensory response. X-ray diffraction (XRD) and orientation imaging microscopy (OIM) results showed that for BZY20 films grown on a sapphire (0 0 0 1) substrate, films tend to orient in the 〈1 1 1〉 and 〈2 1 1〉 directions, while for those grown on LaAlO 3 (0 0 1) and LaAlO 3/LaNiO 3(0 0 1) substrates, films tend to orient preferably in the 〈2 1 1〉 direction. Possible atomic positions of the constituent atoms at the film/substrate interface were determined to understand the growth characteristics and to estimate the epitaxial strains at the film–substrate interface. Typical conductivity of BZY20 thin films grown on single-crystal substrates was ∼1×10 −3 and ∼10×10 −3 S/cm at 500 and 800 °C, respectively. BZY20 films grown on single-crystal substrates were found to be very sensitive to H 2O vapor pressures with film resistance changing by >18% at temperatures of 400 °C when water vapor partial pressure changed from 2 to 50 kPa.

Modification of ion-synthesized silver nanoparticles in glass by high-power excimer laser pulses

We have studied the action of nanosecond-pulsed high-power KrF excimer laser radiation on the composite layer of a soda-lime-silicate glass containing ion-synthesized silver nanoparticles, with the purpose of modifying the material properties by changing the size of metal particles. It is established that, as the number of laser pulses increases, the treatment leads to a decrease in the average size of silver nanoparticles in the ionimplanted layer. However, after the almost complete disintegration of silver particles, a further increase in the number of pulses leads to new growth and a coarsening of the metal particles. The observed phenomena are interpreted in terms of heating of the surface layer of glass and silver particles by nanosecond laser pulses and the related increase in the diffusion mobility of silver atoms in the glass matrix.

Luminescence of intrinsic and extrinsic defects in hafnium oxide films

Both intrinsic and extrinsic defects of hafnium oxide films are investigated based on photoluminescence (PL) and cathodoluminescence (CL) measurements. Instead of using the high-power synchrotron radiation or ArF excimer laser sources, a hydrogen-deuterium lamp (HDL) was used for the PL measurements to avoid the possible generation of active oxygen and hydroxyl ions. Results show that the HDL PL spectra generally agree with those registered using the conventional high-power excitation sources. CL spectra also agree with the PL ones. Narrow emission band at peak energy of $4.0\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, which is ascribed to the vibronic transition of excited $\mathrm{O}{\mathrm{H}}^{\mathbf{∙}*}$ radical, was found using photoluminescence excitation and at energy of $4.25\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$.

UV detection for excimer lamps using CVD diamond in various gaseous atmospheres

The recently emerged high-power vacuum ultraviolet excimer lamps operating at 222, 172 and 126 nm will require robust photodetectors to ensure efficient operation for the photo-processing of materials which is often carried out in various ambient atmospheres. Conventional silicon detectors could not meet the stringent requirements, particularly for the 172 and 126 nm lamps. In this paper, we report an initial study on the use of the thin film CVD diamond device for the excimer VUV detection in air, oxygen or nitrogen. The device in the 3 atmospheres exhibits a low similar dark current around 0.3 nA. Working in air leads to significantly prolonged “turn-off” time due to the increased surface conductivity of the device, caused mainly by moisture penetrating into the surface layer. The moisture penetration is enhanced by the increased surface porosity of diamond due to the strongly oxidizing ozone and active oxygen species formed during 172 nm illumination reacting with non-diamond carbon and amorphous materials within the film. However, the UV detection in different environments can still give similar outputs from the same lamp source, probably due to several counteracting effects. Preliminary results on the UV detection for more energetic 126 nm excimer photons using this diamond device have also been reported.

High-power excimer laser systems

Two-high power excimer laser systems with square (25 × 25 cm) and circular (with a diameter of 40 cm) cross sections of the output laser beam are described. The first (second) system consists of four (five) excimer lasers. The experimental results on the generation of the high-quality high-power laser pulses are presented. Laser beams with a pulse duration of 1–250 ns, a divergence of 0.01 mrad, a spectral line width of 0.01 cm−1, and a pulse energy of up to 330 J are obtained.