Excimer Laser Light Research Articles

New system for fast submicron optical direct writing

We report on a new system for submicron lithography by fast laser direct writing, where a programmable phase modulating spatial light modulator (SLM) is imaged onto the water using flash on the fly exposure with an excimer laser light source. A SLM with 512×464 pixels has been developed and fabricated using a CMOS active matrix and a reflective, deformable viscoelastic layer on top. Using this light modulator for image generation a demonstrator exposure tool for 0.6μm minimum feature size has been set up and tested including all the components necessary for the exposure of a complete lithographic layer from CAD layout data. The demonstrator is shown to give good quality 0.6μm photoresist pattern at a throughput of roughly one 4″-wafer per hour. Based on the demonstrator results we are designing and setting up a prototype of a production tool with an increased throughput of up to nine 6″-wafers per hour including an automatic alignment system and an automatic wafer handler.

Photorefractive waveguides produced by ion-implantation of fused silica

The implantation of 5 MeV silicon and germanium ions into silica forms a 4 μm thick optical waveguide near the substrate's surface with a refractive index change related to that of the delivered damage. These waveguides are photosensitive due to the presence of color centres created during implantation which can be bleached by laser light illumination. We measure the optical absorption, the compaction and the refractive index of implanted samples as a function of dose. We compare the absorption bleaching efficiency of ArF and KrF excimer laser light on two similar samples and observe an overall efficiency two orders of magnitude higher in the ArF case.

Excimer-Laser Annealing Technology for Hydrogenated Amorphous-Silicon Devices

Dehydrogenation characteristics have been investigated in detail for excimer-laser annealing of hydrogenated amorphous silicon (a-Si:H) films. Only the XeF excimer-laser light has a negligibly small photonic-dissociation rate of the Si-H bonds, and thus hydrogen atoms remain in the annealed film, resulting in highly conductive poly-Si film. The XeF excimer-laser annealing has been confirmed to be useful for fabricating high-performance a-Si:H thin-film transistors.

Mechanistic studies of laser-induced breakdown spectroscopy of model environmental samples

We examine a number of factors which influence the use of laser-induced breakdown spectroscopy (LIBS) to detect the cation content of physical mixtures of Eu 2O 3 and K 2Cr 2O 7 with granular, crystalline SiO 2. Excitation of the powdered specimens is by focused KrF excimer laser light (248 nm, 30 ns pulse width, fluence/pulse 0.3–30 J cm −2, irradiance 10–1000 Mw cm −2) in 1 atm air. We discuss the resulting time resolved UV/vis spectra of the plasma, the parameters and physical effects which influence the detection of impurities and examine the consequences of the presence of water in the samples together with variations in the sample morphology. We also present preliminary results on spectra from mixtures of these compounds with a basaltic soil.

Simulation of the optical effects of particles residing on top antireflective coatings for KrF positive photoresist films

The reflection effects of particles on developed cross-sectional photoresist patterns are simulated by using a two-dimensional waveguide model. The particles were assumed to reside on top antireflective coatings used for chemically amplified positive photoresist films. In order to improve the accuracy of the analysis, the exposure dose of KrF excimer laser light and focus position in the resist were optimized. The top antireflective coating film thickness was also adjusted to the optimum thickness for obtaining the critical dimension of 0.25 μm. Under these conditions, the light intensity distributions in the resist depth and in the lateral direction on the focal plane are discussed, and it is revealed that the influence of the particles is enhanced for the case of weaker light intensity. Finally, it is described that the antireflective coating gives a wider process margin on the smallest critical sizes of particles capable of causing pattern shorts. In conclusion, the light intensity obtained from three-dimensional Fresnel approximation is also taken into account.

Sputtering of tin and gallium-tin clusters

Tin and gallium-tin clusters have been produced by 4 keV Ar + ion bombardment of polycrystalline tin and the gallium-tin eutectic alloy and analyzed by time-of-flight mass spectrometry. The sputtered neutral species were photoionized with 193 nm (6.4 eV) excimer laser light. Neutral tin clusters containing up to 10 atoms and mixed gallium-tin clusters Ga ( n− m) Sn m with n ≤ 4 for the neutrals and n ≤ 3 for the sputtered ionic species have been detected. The measured distributions of mixed clusters with equal nuclearity have been found to be nonstatistical most likely due to significant differences in the ionization efficiencies of clusters with equal nuclearity but different tin content.

Enhanced photosensitivity in lightly doped standardtelecommunication fibreexposed to high fluence ArF excimer laser light

The core refractive index of Corning SMF-28 optical fibre exposed to ArF laser pulses increases with the square of the fluence per pulse. Bragg gratings with a refractive index modulation amplitude higher than 10/sup -3/ have been obtained. This is an order of magnitude improvement over previously reported values for this type of fibre in the absence of treatment to enhance the photosensitivity.

Effects of Light Pulse Duration on Excimer-Laser Crystallization Characteristics of Silicon Thin Films

The waveform of an excimer-laser light pulse has been varied using two laser systems with a delayed trigger. The effects of the pulse duration on the physical properties of crystallized silicon thin films were studied. From the results that threshold energies for crystallization, amorphization and ablation increased in proportion to the square root of light pulse duration, their critical temperatures were estimated to be 1000°C, 1800°C and 2700°C, respectively. It was found that the critical temperature for µ-crystallzation is changed from about 2600°C for a thin film under short pulse duration conditions to 1800°C for a thick film under long pulse duration conditions. The long pulse is effective, but not drastic, in improving the poly-crystallized silicon film quality.

Mechanisms of Excimer Laser induced Positive Ion Emission From Ionic Crystals

AbstractThe energy distributions of positive ions produced by exposing single-crystal MgO to pulsed 248 nm excimer laser light at fluences of 200-1200 mJ/cm2 were determined by combined quadrupole mass spectrometry and time-of-flight techniques. the dominant ionic species is Mg+, although small amounts of Mg2+, MgO+, and Mg2O+ are also observed. IN particular, theMg+ and Mg2+ energy distributions each show two broad peaks, with the energies of the Mg2+ peaks at significantly higher energies. Ion trajectory simulations (accounting for Coulomb forces only and assuming no surface relaxation) suggest that Mg2+ adsorbed at sites directly atop surface F-centers (oxygen vacancies with two trapped electrons) would be ejected upon photo-ionization of the F-center. the experimentally observed Mg2+ kinetic energies agree well with the energies predicted by the simulation.

Photochemical surface modification of polypropylene for adhesion enhancement by using an excimer laser

Polypropylene (PP) surface in water was photochemically modified to render it hydrophilic using ArF excimer laser radiation. The chemical stability of PP is attributed to the C-H and C-H3 bonds present. Thus, it is considered that H atoms are selectively pulled out from the area irradiated with ArF excimer laser light and are replaced with OH functional groups in the presence of water. In this treatment, the irradiated sample becomes hydrophilic with enhanced adhesion properties. The experimental conditions for this surface treatment were ArF laser fluence of 12.5 mJ/cm2 and a shot number of 10000. The treated PP and stainless steel were bonded with epoxy adhesive and the tensile shear strength was 46 kg/cm2.

Treatment of temporomandibular joint structures by 308-nm excimer laser — An in vitro investigation

Arthroscopy of the temporomandibular joint (TMJ) has become a clinically important and increasingly accepted method for diagnosis and treatment of TMJ alteration. This minimally invasive method is clearly limited by the anatomic dimensions of the TMJ. The 308-nm excimer laser has already found clinical applications in angioplasty, ophthalmology, and dentistry. This study aimed to find out whether it is possible to ablate TMJ-related structures under arthroscopic conditions. It also aimed to determine the energy threshold for ablation and the maximum rate of ablation. By histologic investigation of the irradiated tissues, the amount of tissue alteration was determined. TMJ structures of freshly slaughtered pigs served as tissue samples. The 308-nm excimer laser light was guided through optical fibers. The tissue was irradiated under continuous flow of saline solution. The energy threshold for ablation of TMJ structures was found at about 1 J/cm 2. The maximum rate of ablation was found at 3–5 μm/pulse, depending on the type of tissue. The amount of tissue alteration varied between 1 and 150 μm. The types of tissue alteration were vacuolization and hyalinization. The results of the investigations described indicate that the 308-nm excimer laser is an ideal tool for TMJ arthroscopic surgery. Unlike other laser systems, it offers a unique combination of minimal tissue alteration, precise tissue ablation, guidability through optical fibers, and good transmission through water. This makes possible endoscopic removal of free bodies, adhesions, exostoses, and appositions in a minimally invasive surgical procedure.

Multi-photon induced atomic nitrogen production in a low-temperature nitrogen crystal

The emission from the 2D excited state of nitrogen atoms was observed when a low-temperature nitrogen crystal was irradiated by a focused excimer laser light at 248 nm. The emission intensity was found to increase linearly with the laser irradiation time. The increase rate of the emission was dependent on about the third power of the excitation laser intensity. It is concluded that nitrogen atoms and nitrogen molecules in A 3∑+u state are produced through multi-photon processes. Nitrogen atoms accumulate and are excited repeatedly by energy transfer from the excited nitrogen molecules.

Reactions of velocity-aligned atoms probed by Doppler profiles: H+O2→OH+O

Final state resolved vector properties of the reaction H (2S)+O2(3Σ−g)→OH(2Π)+O(3P) have been measured using Doppler spectroscopy. Velocity-aligned H atoms were generated by photodissociation of H2S with linearly polarized ArF excimer laser light. The correlated velocity and angular momentum distribution of nascent OH reaction products was probed by laser induced fluorescence. Techniques are described for analyzing the line shapes, modeling the bipolar moments of the OH velocity and angular momentum distribution as parametric functions of the scattering angle. Distinctive Doppler-broadened lineshapes indicate scattering angle distributions with a strong forward and a weaker backward maximum. A qualitatively different angular momentum polarization for the two lambda doublet components of the OH product is required to explain the Doppler profiles.

Electroless copper deposition on excimer-laser pretreated alumina

Irradiation of ceramic alumina (Al2O3) with 248 nm and 308 nm excimer-laser light results in an activation of the surface for subsequent electroless copper deposition. The dependence of this activity on laser parameters, ambient atmosphere during irradiation, and pattern size is described. The results are tentatively explained by changes in the chemical and electrochemical properties of irradiated areas.

Rotational dependence of the quenching of electronically excited CH(A 2Δ) and CH (B 2Σ −) produced by laser photolysis of acetone at 193 nm

Electronic relaxation rate constants for specific rotational levels of CH(A 2Δ and B 2Σ −) have been measured. In contrast to similar measurements made earlier for other hydrides, the results obtained in the present work show an increase in the quenching efficiency upon rotational excitation. The electronically excited CH states are produced by multiphoton excitation and fragmentation of acetone upon photolysis at 193 nm by means of an ArF excimer laser light. The CG fragments are produced rotationally hot and the time evolution of rotational levels with N′⩽21 for CH(A 2Δ, v′=0) and N′⩽15 for CH(B 2Σ −, v′=0) can be measured.

Photo-excited effects and the growth mechanism on epitaxially grown Al 2O 3(100) on Si(100)

Photo-excited effects on epitaxially grown Al 2O 3(100) on Si(100) were studied using both ArF(193nm) or KrF(248 nm) excimer laser light, and a radical-oxygen source by a RF-remote plasma. These methods can clarify the important photo-excited process by separating the reaction processes, which consist of vapor-phase, surface, and substrate excitation. In the case of KrF irradiation with TMA and O 2, the epitaxial temperature and the growth rate did not change drastically. On the other hand, epitaxial temperature reductions of 140°C and 100°C were observed in the cases of ArF with TMA and O 2, and of a RF-remote O radical source, respectively. Direct photo-excitation of TMA and O 2 is a very important process to reduce the epitaxial temperature of Al 2O 3 on Si. However, the substrate-excited effect was not so useful in this growth because after the initial growth stage an Al 2O 3 barrier layer prevented the carriers from reaching the growth surface.

Excimer laser ablation of soft tissue: a study of the content of rapidly expanding and collapsing bubbles

Both holmium (/spl lambda/=2.09 /spl mu/m) and excimer (/spl lambda/=308 nm) lasers are used for ablation of tissue. In a previous study, excimer laser ablation of aorta produced rapidly expanding and collapsing vapor bubbles. To investigate whether the excimer-induced bubble is caused by vaporization of (tissue) water, the threshold fluence for bubble formation at a bare fiber tip in water and on tissue was compared between the excimer laser (pulse length 115 ns) and the Q-switched and free-running holmium lasers (pulse length 1 /spl mu/s and 250 /spl mu/s, respectively). To induce bubble formation by excimer laser light in water, the absorber Oxybuprocaine-hydrochloride (OBP-HCl) was added to the water. Fast flash photography was used to measure the threshold fluence as a function of the water temperature (6-90/spl deg/C) at ambient pressure and as a function of the boiling temperature of water (100-184/spl deg/C) at augmented environmental pressures (1-11 bar). For both the holmium and excimer laser, the threshold fluence for bubble formation decreased proportionally with increasing water temperature (correlation coefficient r=0.95-0.99). Correspondingly, the threshold fluence for bubble formation increased with increasing boiling temperature of water. A similar correlation was found for the excimer laser-induced bubble formation on tissue. Furthermore, for both the holmium and the excimer laser, the threshold fluence for water vaporization was much lower than theoretically predicted values. It is concluded that the principal content of the large (up to 3 mm), short lived ( >

Graphitization of synthetic diamond by 193 nm laser light: Comparison of 12C-enriched diamonds with those of natural isotopic composition

Polished surfaces of diamonds of natural isotopic composition are transformed to graphite upon irradiation by ArF excimer laser light. The surface of a similar diamond made of enriched 12C is not. A possible explanation involves a competition between graphitization and ablation in which the former is more strongly affected by the recently determined higher thermal diffusivity of 12C diamond.

Ion Extraction Characteristics on a Barium Plasma Produced between Alternately Biased Parallel Plate Electrodes.

The ion extraction characteristics were investigated when a barium plasma was suddenly produced between alternately biased parallel plate electrodes by simultaneously illuminating a tuned dye laser and an excimer laser light. Time evolution of the ion density profile measured by means of laser-induced fluorescence indicated that the ions in the plasma are alternately extracted to both sides following voltage switching, and then, the plasma diffusion has little effect on the density change. As a result, the ion extraction time, which was measured by ion current detection, is reduced by about 0.71 times that for parallel plate electrodes when a constant voltage was applied. This curtailment rate can be deduced by applying the scaling relation established for constantly biased parallel plate electrodes.

Photochemical modification of polyethylene surface with excimer laser irradiation.

Polyethylene surface in water(H2O) ambience was photochemically modified to be hydrophilic using an ArF excimer laser light. The hydrogen atoms of the surface, were pulled out by the hydrogen atoms which were photodissociated from H2O and replaced with the OH radicals which were also photodissociated. The substitution of OH radicals was confirmed by the XPS and the contact angle measurement. Also, chemical bonding of the surface with epoxy adhesive was performed to obtain a shearing tensile strength of 9.5kgf/cm2.