Krypton Fluoride Excimer Laser Research Articles

Capillary electrochromatography with thermo-optical absorbance detection for the analysis of phenylthiohydantoin-amino acids

Capillary columns were packed with 3 μm C18 stationary phase, interfaced with an ultraviolet-laser based thermo-optical absorbance detector, and evaluated for separation of a mixture of phenylthiohydantoin–amino acids. These columns demonstrated consistent performance with a relative standard deviation (RSD) for migration time of less than 1.5% and a separation efficiency of 216 000 plates/m for the electroosmotic flow marker, thiourea. The thermo-optical absorbance detector was based on a 248 nm krypton–fluoride excimer laser. Detection limits (3σ) ranged from 1.6 to 4.8×10−7M phenylthiohydantoin (PTH)–amino acid injected onto the column, which is a factor of three superior to those obtained in micellar electrokinetic chromatographic analysis of these compounds. A mixture of 17 PTH amino acids was injected onto the capillary; 13 components were nearly baseline resolved in 14 min.

Laser surface cleaning of organic contaminants

Laser surface cleaning process has been a useful and efficient technique for various industrial applications. The removal of photoresist contaminants on silicon wafers was investigated with a krypton fluoride (KrF) excimer laser, and the irradiated area was characterized using a profilometer, a scanning electronic microscopy (SEM), an Auger electron spectroscopy (AES) and a Fourier transition infrared spectroscopy (FT-IR). It was found that there exist an optimal number of pulses to remove the contaminant from the substrate surface without any laser-induced damage, depending on the laser density on the surface. A model to predict the optimal number of pulses, which agrees well with Beer–Lambert's law, is proposed and proved to be operable.

Excimer pulsed laser ablation of polymers in air and liquids for micromachining applications

Micromachining of polymers is an important field that has both immediate and future applications in diverse fields such as medicine, microelectromechanical systems, and photonics. In this work, ultraviolet pulsed laser ablation of polymethyl methacrylate (PMMA), polypropylene (PP), and polyethylene (PE) was performed using a KrF (krypton-fluoride) excimer laser in air, methanol, and ethyl alcohol. The size of the hole and etch depth were marginally increased in PMMA but were markedly reduced in PP and PE by the organics. There are other beneficial and detrimental effects of the organics in regard to the taper of the hole, contamination, thermal damage, and cracking that are explained based on laser-liquid-polymer interactions, which include self-focusing, chemical reactions, pressure-wave generation, and thermal quenching. Existing polymer ablation models were used to describe the observed etch depth versus incident laser energy fluence.

Excimer Pulsed Laser Ablation of Polymers in Air and Liquids for Micromachining Applications

Micromachining of polymers is an important field that has both immediate and future applications in diverse fields such as medicine, microelectromechanical systems, and photonics. In this work, ultraviolet pulsed laser ablation of polymethyl methacrylate (PMMA), polypropylene (PP), and polyethylene, (PE) was performed using a KrF (krypton-fluoride) excimer laser in air, methanol, and ethyl alcohol. The size of the hole and etch depth were marginally increased in PMMA but were markedly reduced in PP and PE by the organics. There are other beneficial and detrimental effects of the organics in regard to the taper of the hole, contamination, thermal damage, and cracking that are explained based on laser-liquid-polymer interactions, which include self-focusing, chemical reactions, pressure-wave generation, and thermal quenching. Existing polymer ablation models were used to describe the observed etch depth versus incident laser energy fluence.

Possible Mechanisms of Vascular Relaxation Induced by Pulsed‐UV Laser

This study was designed to examine the mechanism of vasorelaxation induced by pulsed-UV laser. Luminal diameters of rat femoral arteries were measured prior to and following krypton-fluoride excimer laser irradiation of 248 nm in wavelength. The diameter was enlarged to 1.3 times the preirradiated size at 1 or 10 Hz irradiation when the fluence was over 2.0 mJ/pulse/mm2, while the diameter reached 1.8 times at 100 Hz with a fluence of 0.8 mJ/pulse/mm2. Vasorelaxation by the 100 Hz irradiation was inhibited when the artery was pretreated with methylene blue but was enhanced with superoxide dismutase. Pathological analysis revealed an ablation crater and vacuole formation in the vessel at 1 or 10 Hz irradiation, but these changes were not remarkable in the 100 Hz-exposed sample. These findings suggest that vasorelaxation induced by the pulsed UV irradiation at 1 or 10 Hz results from structural alteration of vascular smooth muscle by the ablation crater or vacuolization. On the other hand, a possible mechanism of vasorelaxation at the 100 Hz irradiation is partially related to nitric oxide.

Extension of krypton fluoride excimer laser lithography to the fabrication of 0.18 μm devices

This article presents the extension of krypton fluoride (KrF) excimer laser lithography. An 0.18 μm device can be fabricated by KrF excimer laser lithography when weak off-axis illumination is combined with an attenuated phase-shifting mask, a high-performance antireflective layer, and a high-numeral-aperture exposure tool. A 1.0 μm depth-of-focus can be achieved for 0.18 μm rule logic patterns. The weak off-axis illumination can reduce the influences of the secondary peak in the high-duty periodic patterns, and retain the depth-of-focus for isolated patterns when it is used in combination with an attenuated phase-shifting mask. A high-performance antireflective layer can increase the depth-of-focus because a uniformly exposed area in the photoresist can be formed when the light reflected from the substrate is eliminated.

Hydrogenated Silicon-Oxynitride Film Antireflective Layer for Optical Lithography

We present a theoretical method for antireflective layer (ARL) optimization in optical lithography and report the performance of hydrogenated silicon oxynitride ( SiOx Ny :H) film used as an ARL for krypton fluoride (KrF) excimer laser lithography. The optimum optical conditions of an ARL for tungsten silicide (W–Si) and aluminum silicon (Al–Si) substrates, which minimize the fluctuation of energy absorption in photoresists for photoresist thickness variations, are investigated. There are two types of optimum optical conditions, which give zero reflectance with the first and second cycle in thin film interference effects in an ARL, respectively. A type of SiOx Ny :H, which can satisfy the optimum optical conditions of an ARL for W–Si and Al–Si substrates, was found from the standpoints of its spectroscopic characteristics. Refractive indices of SiOx Ny :H film at the wavelength of 248 nm can be controlled by varying the deposition conditions in a plasma-enhanced chemical vapor deposition system. The variations in critical dimension caused by the thin-film interference effects in the photoresist for W–Si and Al–Si substrates are drastically reduced to within 0.02 µ m for 0.30 µ m patterns using this SiOx Ny :H film. Moreover, these SiOx Ny :H films can be left in the device structure without any influence on the electronic characteristics.

Excimer laser cleaning of mold-contaminated paper: Sterilization and air quality considerations

The Excimer laser can be used to remove biological debris from underlying substrates. The ability of the krypton fluoride (KrF) Excimer laser to removeAspergillus niger mold, which had been grown on filter paper, was evaluated in the present study. The air in the immediate vicinity of the laser cleaning apparatus was sampled to determine if viable mold fragments were released into the air during treatment. It was found that filter paper could be sterilized with the Excimer laser wavelength with the proper selection of parameters. During this process, viable spores and mold fragments are released into the atmosphere, and pose a relative risk unless proper measures to prevent contamination of the work area are taken.

Advantages of a SiOxNy:H Anti-Reflective Layer for ArF Excimer Laser Lithography

This paper presents the advantages of using hydrogenated silicon oxynitride ( SiOx Ny :H) film as an anti-reflective layer (ARL) for argon fluoride (ArF) excimer laser lithography. This material has already been used as an ARL in both i-line and krypton fluoride (KrF) excimer laser lithography, because its refractive indices can be controlled by varying the deposition conditions. We describe the results of measuring the optical constants for the various materials at the wavelength of 193 nm using a spectroscopic ellipsometer to clarify the importance of the anti-reflective process. The influence of the thin-film interference effects in the photoresist of the 193 nm wavelength are almost same as that of the 248 nm. Then we describe the possibility of using the SiOx Ny :H film as an ARL at the wavelength of 193 nm, from the standpoint of the spectroscopic characteristics in the optical constants. The SiOx Ny :H film is desirable for use as an ARL. Finally, we propose that SiOx Ny :H film has great potential as a high-performance ARL for ArF excimer laser lithography.

Excimer laser assisted chemical machining of SiC ceramic

A highly effective method of machining ceramic has been newly developed using a krypton fluoride (KrF) excimer laser with a 248 nm wavelength. The laser was irradiated on SiC in water to form a soft hydrous oxide layer by photochemical reaction. The softened layer was then cut with a diamond tool to form a mirror surface finish. The optimum conditions were found for both high machining rate and better surface integrity of SiC.

Krypton fluoride excimer laser ablation of tooth tissues: precision tissue machining

A variety of lasers using different wavelengths have been used to remove dental hard tissue. The infrared lasers produce their effects photothermally whereas ultraviolet excimer lasers remove tissue in a controlled and precise manner by photoablation. This study investigates the use of 248 nm laser radiation in the precision removal of both enamel and dentine using diffraction limited ultraviolet optics. The data showed that enamel and dentine were machined to a high level of precision (1–2 μm tolerances). The rate of removal was greater in dentine than enamel at a range of energy densities between 1.15 and 2.2 J/cm 2. The method of removal of both tissues appears to be by the preferential ablation of the organic phases of each, exposing the anatomical details of their structure. An explanation of the possible method of ablation is proposed for these tissues. Biomaterials (1994) 15, (12) 1013–1018

Electrical Characteristics of Barium Strontium Titanate-Oxide Composite Films

AbstractIn a previous work. composites of BSTO combined with other nonelectrically active oxide ceramics have been formulated and have demonstrated adjustable electronic properties which can be tailored for use in various electronic devices. One application has been for use in phased array antennas and insertion has been accomplished into several working antenna systems. To further accommodate the frequencies required by these phased array antennas, thin films of the composites have been fabricated using a Krypton Fluoride excimer laser as an ablation source. The electrical properties, including the dielectric constant and the tunability (change in the dielectric constant with applied voltage) have been measured. The results have been compared to those obtained for the bulk, ceramic composites and other BSTO/oxide composite thin film structures.

高繰り返し周波数エキシマレーザーを用いた骨切断

高繰り返し周波数エキシマレーザーを用いた骨切断

Krypton fluoride excimer laser for advanced microlithography

The excimer-laser-based stepper is now expected to play a significant role in the manufacturing of ULSI devices requiring sub-0.4-μm design rule features. They will be used in a mix-and-match strategy along with high NA <i>i</i>-line steppers for critical layers in the production of 64-Mbit dynamic random access memory (DRAM) generation of IC devices. This is supported by the present availability of a number of production worthy high-NA, wide-field excimer stepper models, along with the recent introduction of several process worthy and moderate cost, positive tone deep-UV photoresists. The excimer laser for the stepper, since its introduction in 1987, has evolved from a laboratory instrument to fully production worthy fab-line equipment. The status of such a laser is discussed. We will discuss the operating theory and the design features of an excimer laser; in particular, the discharge chamber, spectral narrowing module, and the wavemeter. Some of the latest technical innovations incorporated into the laser that reduce maintenance intervals and increase reliability are also presented. Finally we will present and discuss the performance specifications of a current production lithography excimer laser.

Laser micromanipulation in the mouse embryo: a novel approach to zona drilling

To introduce the use of excimer lasers for penetration of the zona pellucida for micromanipulation purposes. Cryopreserved two-cell mouse embryos were thawed and exposed to the 248-nm line of a krypton fluoride excimer laser (Lambda Physik EMG 202, Goettingen, Germany) creating a 2 to 4-micron opening in the zona pellucida. The Laser Ablation Laboratory at DuPont and the in Vitro Fertilization Laboratory at The Medical Center. The embryos were exposed in either phosphate-buffered solution (PBS) or modified human tubal fluid (HTF) with the laser power varying from 1 to 2 J/cm2 and cultured in Ham's F-10 medium (GIBCO, Grand Island, NY) with 0.4% bovine serum albumin. The outcome of each experiment was measured by blastocyst formation of laser-exposed embryos as compared with a set of unexposed control embryos handled in a similar fashion. Successful laser penetration of the zona pellucida was achieved using the 248-nm line of a krypton fluoride excimer laser. A higher blastocyst formation was found for embryos exposed in PBS. The higher optical absorption of the modified HTF partially inhibited embryo development. The blastocyst statistics increased 2.5-fold times by reducing the exposure of the embryos to ablation by-products. The use of a krypton fluoride excimer laser was introduced as a new method to open the zona pellucida of two-cell mouse embryos without interrupting blastocyst formation.

Optical Lithography at 248 nm

The krypton fluoride excimer laser has provided a means of exploiting the deep‐ultraviolet for optical lithography. The use of this new light source requires the development of new photoresists and opens up a new set of concerns for the lithographer. Durability of lenses, coatings, and photomask materials are potential problems because of the very high peak power emitted by the pulsed laser. Optical interference effects, caused by the coherence of the laser light, could also cause trouble. Finally, the laser itself has high requirements for reliability and safety.

Performance improvements with advanced design foils in high-current electron beam diodes

A design for the vacuum/pressure barrier of an electron-beam diode ready to be fielded on a large krypton-fluoride excimer laser is described. The barrier is a composite foil, fabricated from carbon fibers, Kapton-membrane, epoxy, and copper foil. This composite foil has advantages over more traditional metal foils, exhibiting particularly high tensile strength and a high modulus of elasticity. Other important properties of these composites for use in KrF excimer laser applications include: high electron transmission with low loss to scattering, chemical compatibility with fluorine, low porosity, and low reflectivity in the ultraviolet. The mechanical properties of the composite foil allow the design of support structures (hibachis) which incorporate larger openings than are possible with metal foils with similar electron transmission characteristics.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Photochemical etching of copper thin films of circuit board in chlorine and trichloroethylene ambients with a KrF excimer laser.

Photochemical etching of copper thin films of circuit boards in chlorine and trichloroethylene (TCE) ambients by line-focused krypton fluoride excimer laser irradiation are described. It isdemonstrated for the first time that trichloroethylene is successfully used as an etching agent. Theaspect ratio of trichloroethylene is improved by a factor of two compared with chlorine.

Photochemical aerosol formation from organic gases

It is found that many kinds of organic gases, which belong to aromatics, terpenes, and cycloalkanes, produce aerosols when irradiated by a deuterium lamp with spectrum ranging from 180 to 400 nm in wavelength, and by a krypton-fluoride excimer laser operated at 249 nm. Two initial processes are important, direct excitation of organic molecule by the ultraviolet light, and reaction of organic molecule with ozone produced photochemically by the ultraviolet light. It depends on compounds which process is dominant. For some compounds, both are possible.

Photolysis of phosphodiester bonds in plasmid DNA by high intensity UV laser irradiation.

Abstract— The cleavage of phosphodiester bonds in DNA exposed to high intensity UV laser pulses in aerated aqueous solution has been investigated using a krypton fluoride excimer laser (248 nm) and bacterial plasmid DNA. The dependence of strand breakage on fluence and intensity has been studied in detail and shows that the process is non‐linear with respect to intensity. The relationship between the quantum yield for strand breakage and intensity shows that the strand breakage reaction involves two‐photon excitation of DNA bases. The quantum yield rises with intensity from a lower value of 7 times 10‐5 until a maximum value of 4.5 times 10‐4 is attained at intensities of 1011 W m‐2 and above. This value is approximately fifty‐fold higher than the quantum yield for strand breakage induced by exposure to low density UV irradiation (254 nm, 12 W m‐2). DNA sequencing experiments have shown that strand breakage occurs by the specific cleavage of the phosphodiester bond which lies immediately 3′ to guanine residues in the DNA, leaving some alkali‐labile remnant attached to the terminal phosphate. A mechanism for DNA strand breakage which involves the generation of guanine radical cations is proposed.