KrF Excimer Laser Irradiation Research Articles

Laser-Induced Removal of Fingerprints from Glass and Quartz Surfaces

Laser removal of fingerprints from glass and quartz surfaces was studied using laser irradiation in air. The KrF excimer laser, continuous wave (CW) CO2 laser and pulsed CO2 laser were used in the investigation. Electron probe microanalysis (EPMA) was performed to characterize the substrate surfaces before and after laser cleaning. It is found that short wavelength and pulse width are necessary for fingerprint removal. EPMA measurements show that KrF excimer laser irradiation can effectively remove fingerprints from glass and quartz surfaces with a few pulses if the pulse energy density is sufficiently high. In the laser removal of fingerprints from quartz surfaces, it is found that the irradiation direction of the incident laser pulse can cause significant differences in the cleaning effect for laser irradiations from the front or back. CO2 laser irradiation, either in CW or pulse form, cannot effectively remove fingerprints.

The Observations of Paramagnetic Centers in Tellurite Glasses

AbstractThis is the first report of ESR observations of three distinct paramagnetic centers in TeO29 glasses. One center is intrinsic to the glass and the other two are induced by KrFexcimer-laser radiation. The intrinsic center with a broad ESR spectrum is tentatively identified as an oxygen-associated hole center. One radiation-induced center fades slowly at room temperature; its proposed structure is that of an electron trapped in a diffuse orbital associated with a modifier ion. The other radiation-induced center is stable at room temperature and corresponds to the Vo· center observed in crystalline paratellurite.

TEM study of laser induced phase transition in iron thin films

Laser induced phase transition from b.c.c.(α) to f.c.c.(γ) iron thin films is studied by high resolution TEM. The iron film has been covered on both sides with carbon layers to protect it against oxidation. Single pulse, τ FWHM = 20ns KrF ( λ = 248nm) excimer laser irradiation was performed in air with the film on the substrate. The laser pulse acts like a heat pulse followed by a rapid quenching revealing sequential aspects of the phase transition process. The presence of a fine mixture of the α + γ phases between the α and γ regions of the film has been interpreted as an incomplet transformation. The results are explained by assuming that the transformation took place via a phonon drag mechanism.

EELS of laser-irradiated kapton polymide

It has recently been demonstrated that the electrical resistivity of a high temperature polymer, polyimide, can be changed permanently from 1017 Ωcm to 10-1 Ωcm by KrF (248 nm) excimer laser irradiation. Further, using a holographic technique, an array of 500-nm-wide electrically conducting wires has been produced on polyimide by direct laser ablation. There is obvious interest in exploiting this phenomenon to create integrated microelectronic devices with conventional polymers as both dielectrics and conductors. The imaging of such patterned nanostructures by scanning and transmission electron microscopy (SEM and TEM) is reported elsewhere. Knowledge of compositional changes that accompany the structural changes is necessary for understanding formation mechanisms, but analytical electron microscopy (AEM) of polymers is usually severely limited by electron beam damage effects, especially when high spatial resolution microanalysis is attempted with focussed probes. However, parallel-detection electron energy-loss spectrometry (PEELS) has been successfully used to investigate laser-induced compositional changes in polyimide (Kapton™, E.I. Dupont) with no apparent signs of beam damage.

Modification of electrical conductivity and surface structure in polymers using ultraviolet laser radiation

Irradiation of most polymers with ultraviolet lasers results in permanent changes in their surface morphology and electrical conductivity. Using KrF (248 nm) excimer laser radiation, the electrical conductivity of polyimide (Kapton) and polybenzimidazole (PBI) has been increased by as much as sixteen orders of magnitude, obtaining values on the order of 10 Ω-1 cm-1. This laser-induced conductivity exhibits a threshold both in fluence and in the number of laser shots and has a saturation conductivity which is slightly fluence dependent. Periodic line structures with a period of 167 nm and linewidths varying from 30 to 100 nm have been produced in polyimide by direct ablation with a KrF laser using an interferometric technique. This experiment establishes the optics- and materials-dependent spatial resolution limits for laser ablation and for the modification of the electrical conductivity in polymers. An array of sub-micron wires has been produced in polyimide, demonstrating the ability to modify electrical conductivity in polymers with high spatial resolution.

Pulsed ultraviolet laser ablation

The radiation transport involved in pulsed ultraviolet laser ablation of organic materials has been studied both theoretically and experimentally. A mathematical description of the absorption process that includes nonlinear effects such as chromophore saturation and multiphoton absorption is presented. This theoretical model accurately describes the observed polymer etch depth versus incident laser fluence relationship for various target materials, laser wavelengths, and pulse durations varying from nanoseconds to subpicoseconds. The theoretical analysis can also be used to explain observed nonlinearities in the transmission characteristics of polyimide subjected to intense KrF excimer laser irradiation.

ＫｒＦエキシマレーザーの気管チューブへの安全性に関する実験的検討

Recently, lasers operating at shorter and shorter wavelengths have become available. The excimer laser emits pulses of ultraviolet irradiation. The KrF excimer laser has high incision efficiency, and can cut hard tissue without thermal damage.Use of a laser in the oral region is dangerous due to the close proximity between the operative field and the tracheal tube. Evaluation of the influence of laser irradiation on tracheal tubes is therefore necessary.The authors assessed the effects of KrF excimer laser irradiation on Portex®, Spiral tube® and Diffencer® tracheal tubes under ordinary atmospheric conditions, and gas flow rates of 3l/min for both O2 and N2O. The laser was used at energy densities of 40 and 60 J/cm2, frequencies of 20 and 40Hz, a beam spot of 0.015 cm2, a pulse width of 15 ns, and a peak power of 2.7 MW.The tubes was perforated by laser irradiation under ordinary atmospheric conditions, but they did not ignite. The time required for perforation of the tubes became shorter as the energy density and frequency increased. The perforation time under the flow of O2 3l/min and N2 O 3l/min was comparable to that under ordinaly atmospheric conditions. Spiral tube® ignited almost simultaneously to the time of perforation at energy densities of 40 and 60J/cm2 and a frequency of 40Hz.

The long-term Biological Effects of KrF Excimer Laser Irradiation

This study investigated the long-term biological effects of the Excimer Laser. The surface of the skin and buccal mucosa in the rat were irradiated with a KrF Excimer Laser at a wave length of 248nm (skin for 15 seconds; buccal mucosa for 2 seconds) at a pulse repetition rate of 20Hz and a pulse width of 15nsec. The peak power was 6MW and average power was 1.8W; spot size was 4.0×1.0mm.The irradiated skin tissue and buccal mucosa, heart, lung, kidney, liver, and spleen were removed two years after irradiation and stained with H-E stain for pathological examina tion.KrF Excimer Laser irradiation at 248nm did not cause carcinogenesis and there were noremarkable observations in the skin, buccal mucosa, or other organs (heart, lung, kidney, liver, and spleen), except for two benign tumors one arising from the alar part and the other from the axillary region.

Characterization of laser vaporization plasmas generated for the deposition of diamond-like carbon

Pulsed laser vaporization of graphite is rapidly emerging as an effective technique for the preparation of high quality diamond-like carbon films. However, the dynamics of the process and mechanisms by which diamond-like properties are obtained have not been well understood. The characteristics of the vapor plume generated by 248 nm KrF excimer laser irradiation of a graphite target are investigated using laser induced fluorescence and a Langmuir probe. It is found that the kinetic energy of the C2 molecule increases with laser fluence, reaching a value in excess of 12 eV in the moderate fluence range (3–5 J/cm2) employed for deposition. The Cn+ ions are 5–10 times more energetic and comprise ∼10% of the vapor flux. A notable finding is that irradiation of the surface at an angle of 70° with respect to the target normal increases the ion velocity when compared with 0° laser incidence at the same surface fluence. Analysis of the films prepared under such conditions supports the theory that diamond-like film character is directly related to the kinetic energy of the depositing species.

Vacuum ultraviolet generation by anti-Stokes Raman scattering of KrF laser radiation in H2

The eleventh anti-Stokes order at 116 nm of the KrF excimer laser radiation was obtained in H2 gas at room temperature. The effects of the depletion of the first Stokes order by the S1-S2 Raman conversion on the efficient vacuum ultraviolet anti-Stokes generation was studied, and it determined the optimal Raman gain coefficient in this experiment. Ne gas was added into hydrogen gas to suppress the S1-S2 conversion, and the significant increase in the conversion efficiency for the lower anti-Stokes orders was observed in certain circumstances.

KrF-laser irradiation induced defects in all silica optical fibers

High power UV laser irradiation of synthetic fused silica material induces transient absorption bands centered at 215 and 265 nm. The temporal behaviour of the 215 and the 265 nm absorption bands and also of the 248 nm laser transmission were measured with a transient absorption spectrometer during KrF excimer laser irradiation. Fiber samples made from stoichiometric and non-stoichiometric fused silica core material were irradiated at room temperature. The absorption at 215 nm correlates with the laser absorption in stoichiometric materials, whereas in the sample with oxygen rich core material a linear correlation is observed for 265 and 248 nm. The experimental data give evidence that the laser induced decrease in transmission at the laser wavelength can be reduced by using stoichiometric material.

Excimer laser cleaning and processing of Si(100) substrates in ultrahigh vacuum and reactive gases

We have examined the effect of KrF excimer laser irradiation (248 nm, 20–25 ns) on Si(100) substrates under ultrahigh vacuum conditions and in controlled partial pressures of reactive gases. Surface compositions were determined before and after irradiation using in situ angle resolved x-ray photoelectron spectroscopy. We varied peak power, pulse energy, and halocarbon (CF4) or carbon monoxide (CO) pressures to investigate their effects on oxygen and carbon removal. Energy densities near 500 mJ/cm2 were sufficient to eliminate the carbon contamination; higher energies, which depended on the silicon preparation conditions, were required for oxygen removal. Samples were irradiated by pulses at 480–740 mJ/cm2 in molecular oxygen (O2) environment after cleaning to determine pulse energy and gas pressure requirements for oxide regrowth.

Modification of the optical properties and dynamics of laser ultraviolet ablation of polyimide

An experimental investigation was made of the ablative photoetching of thin polyimide films by KrF excimer laser radiation. Reversible modification of the optical properties of the polymer was observed when the energy densities of the laser beam were below the ablation threshold. The proposed model was used to analyze possible heat release regimes in the film under conditions of below-threshold laser irradiation. The dynamics of the motion of the ablation front during the laser pulse was calculated numerically.

Liquid film enhanced laser cleaning

‘Liquid Film Enhanced Laser Cleaning” is a technique to remove particulate contamination from surfaces. A thin liquid film deposited onto the contaminated surface is flood irradiated with a short laser pulse. The resulting sudden evaporation of the liquid film leads to high transient explosive forces, large enough to expel even submicron particles from the surface. For instance 0.1μm alumina particles could efficiently be removed from a silicon surface with KrF excimer laser irradiation of 16 ns pulse length and 120 mJ/cm 2 energy density.

A KrF excimer laser induced dehydrochlorination of a chlorinated poly(vinyl chloride): Preparation of conjugated polyene and polyyne

AbstractThe photochemical dehydrochlorination of a chlorinated poly(vinyl chloride) film was investigated with respect to the preparation of a π‐electron‐conjugated polymer. The dehydrocholorination proceeds more effectively upon irradiation with a KrF excimer laser than with a low‐pressure mercury lamp, showing the formation of new absorption bands in the range 300–800 nm. The most effective condition provided KrF excimer laser irradiation of 25− 30 mJ/cm2 at 1 Hz in a vacuum chamber of 10−6 Torr at 90°C. The surface of the irradiated film was analyzed by IR (attenuated total reflection method), X‐ray photoelectron and Raman spectroscopy. The characteristic peaks (1 112, 1 488 and 2 188 cm−1) in the Raman spectrum were ascribed to a structure having eight conjugated CC bonds and twenty conjugated CC bonds.

Suitable precursor/solvent systems for laser-induced surface prenucleation

Thin palladium acetate films, generated by spin coating from a solution of palladium acetate in ethyl acetate, were locally prenucleated by KrF excimer laser irradiation. Copper was selectively deposited on the palladium nuclei using electroless plating. Deposition of copper nuclei from copper formate using KrF excimer laser irradiation was investigated. It is shown that these copper nuclei can also be used for the electroless plating process.

生体組織とエキシマーレーザー

Laser-tissue interactions have been investigated through UV-Visible optical absorption, Fourier Transform Infrared Spectroscopy (FTIR) and Electron Micro Probe Analysis (EPMA). Gelatin thin films and cow thighbone were irradiated by KrF excimer and CO2 lasers and 3 excimer lasers (ArF, KrF and XeCl), respectively.In the case of gelatin, a broad absorption band was observed at around 280 nm by KrF excimer laser irradiation, although no absorption band was observed by CO2laser irradiation. From the result of FTIR measurements, it was clear that this band arised from cutting of C-N and C=0 bonds in polypeptide chain.The result of EPMA showed that P atoms were more spattered than Ca atoms from the surface of cow thighbone by only ArF laser irradiation.

Fundamental Study of KrF Excimer Laser

The KrF excimer laser is a high power pulsed laser oscillating in the ultraviolet field and able to destroy or amputate molecules of tissue without thermal damage.In order to evaluate the effects of KrF excimer laser irradiation on human mandibular bone, we examined by visual, pathological and SEM observation.The laser irradiation on human mandibular bone resected by oral and maxillofacial surgery had a pulse energy: 65mJ, spot size: 0.80×0.50mm2, energy density: 16J/cm2, water volume: 6.5ml, assist gas (N2): 301/min, frequency: 80Hz, incision speed: 5, 10, 15mm/min.Visual observation: the incisions were sharp without thermal damage, and the depth of the inicions ranged from 0.68 to 2.53mm according to the incision speed.Pathological observation: the inicisions were almost sharp and there was almost no thermal damage layer.SEM observation: the incision section was slightly wavy, but the incision surface was almost clear at 20 magnification. Crystals formed at the incision surface at all incision speeds, and there was no melting of bone tissue at 5000 magnification.

Laser ablation of dyes

High density 50 μs pulses of the UV dyes PPF, POPOP and BBO and of two dyes in the visible region, Xanthen N92 and Fluorol 7GA were generated by laser ablation. Dye powders were pressed with 7800 kp/cm 2 in round pellets which were ablated by exposure to KrF excimer laser radiation (248 nm) at a fluence of 100 mJ/cm 2. The ablation cloud was optically activated with a XeCl excimer laser. Its fluorescence spectrum was measured and was identified as a dye vapour fluorescence spectrum by comparison to conventional dye solution and dye vapour spectra. The dye cloud is not deflected in an electric field (10 6 V/m). By changing the delay time between the ablation laser and the focused activation laser, the velocity distribution of the ablated dye was measured. Its maximum is at 600 m/s for PPF. Knowing the thickness of the ablated dye layer per shot (300 Å) and the size of the ablation cloud (pictures of a video camera), one can estimate the maximum density of the dye in the gas pulse to be 10 -5 mol/ l in the range of concentration of lasing dyes. However, no lasing was observed up to now.

Chemical amplification & dissolution inhibition: a novel high performance positive tone deep UV resist.

The chemistry and some performance aspects of a novel chemically amplified positive tone photoresist system sensitive to KrF excimer laser radiation is described. The material consists of three components: an α, α-bisarylsulfonyl diazomethane as the photoacid generator (PAG), an oligomeric N, O-acetal as the acid sensitive dissolution inhibitor (DI), and a poly(vinylphenol) as the hydrophilic matrix resin (MR). The material combines high photospeed through the chemical amplification mechanism with some properties of the conventional dissolution inhibition resist systems, such as standard processing and development conditions, excellent resolution, good contrast, favorable plasma etch stability, and easy stripping. Problems arising from the concept of chemical amplification, viz., delay time stability, formation of T-tops, and linewidth variation upon extended storage intervals are discussed, and first measures to their suppression will be presented. Some micrographs demonstrate the outstanding pattern quality of this newly developed resist material.