Papers by Keyword: Excimer Laser

Abstract: As the higher and higher demand for image definition of flat-panel display (FPD), the minimum linewidth of pixel electrode, which is based on the Indium-Tin-Oxide (ITO) glass, has become narrower and narrower. The feature size of sub-pixel electrode has been narrowed from about 60~100 µm to below 20 µm in recent years. Hence the lithography technology has played a more and more important role in the fabrication of FPD. The laser projection imaging (LPI) technology can solve the problems obviously. In this paper, by using of the 351nm XeF excimer laser projection imaging system we can obtain developed pictures at the resolution between 10 and 20 µm on the ITO glass. In addition, the relation graphs between 10~20 µm linewidth and the modulation transfer function（MTF）of the projection system are simulated and analyzed by the ZEMAX and MATLAB software. Consequently, our system can satisfy the linewidth of the sub-pixel electrode at the resolution between 10 and 20 µm in the production of FPD.

Abstract: The La1-xAxMnO3 (A=Sr, Ca, Ba) film was prepared by excimaer laser-assisted metal organic deposition (ELAMOD). To understand the important controlling factor of the epitaxial growth using ELAMOD, the effects of the substrate temperature, substrate type, wavelength, and film thickness on the epitaxial growth were investigated. When the film thickness was 200nm with heating at 250°C, a polycrystalline LSMO film was formed on the LAO substrate. On the other hand, at 80nm, an epitaxial LSMO film was formed on the LAO substrate at 500°C. The epitaxial growth of the LSMO film was found to be dependent on the substrate materials and the laser wavelength. The formation of the epitaxial and polycrystalline LSMO films was discussed

Abstract: Laser treatment is a promising technique for dental applications such as caries prevention, dental hypersensitivity reduction and improvement of bond strength of restoration materials. In this study the morphological, structural and chemical changes of enamel surface due to treatment with KrF excimer laser radiation were evaluated using scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. For radiation fluences near 1 J/cm², laser processing originates a relatively porous surface due to preferential removal of material in the enamel prism sheaths. Increasing the fluence leads to a relatively flat surface with clear evidence of surface melting. The X-ray diffractograms of both treated and untreated enamel are similar and correspond to hydroxyapatite. The only modification due to the laser treatment is a slight shift of the peaks, probably, due to a loss of the structural water of hydroxyapatite. X-ray photoelectron spectroscopy confirmed that organic matter is removed from the irradiated surface but no significant changes in the mineral phase occur.

Abstract: Excimer lasers have been utilized for the crystallization of hydrogenated amorphous silicon for electronic applications. These lasers typically operate in the ultraviolet and hence photons are absorbed by the silicon thin films within a few nanometres of the surface, melting and solidifying the silicon on a nanosecond timescale, often without affecting the underlying substrate. This technique enables the use of inexpensive substrates, such as glass, which are highly preferable for low cost, large-area electronic devices. The depth of crystallization becomes important for applications such as photovoltaics, which depends on a number of factors; with laser beam shape one of the most significant. A Gaussian beam profile has been reported to be best suited for controlled evolution of hydrogen during crystallization with minimum surface damage. Previous reports show the typical energy densities of crystallization, comparing the crystalline volume and surface roughness of the resultant films for different film thicknesses. We report significant reductions of laser energy densities for crystallization by modifying the Gaussian pulse profile, while retaining the controlled evolution of hydrogen from hydrogenated amorphous silicon films. An asymmetrical, shorter pulse profile retains the desirable gradual leading edge of the Gaussian pulse for controlled evaporation of hydrogen, while increasing the peak energy. The resultant films show increased surface roughness along with higher crystalline volumes, which may be beneficial for photovoltaics.

Abstract: Low temperature polycrystalline silicon (LTPS) thin film transistors (TFTs) are demanded to fabricate high performance liquid crystal displays (LCD) and organic light-emitting diode displays (OLED). The mobility of poly-Si TFT can be two orders of magnitude higher than that of amorphous Si (a-Si) TFT. Excimer laser annealing has been studied to be the most promising technology to meet the stringent requirement in high speed operation. The process parameters were identified as a-Si thickness, laser energy density, overlap ratio, annealing atmosphere and pre-clean condition. The a-Si layer of 40-50 nm was deposited by plasma enhanced chemical vapor deposition (PECVD). The XeCl excimer laser was irradiated on the a-Si film at room temperature under N2 or N2/O2 environment. The energy density ranged 250-400 mJ/cm2, and the overlap ratio was 95-99%. The highly aligned poly-Si array thin film could be obtained. The grain size has been about 0.31x0.33 μm2, and the regular arrangement in poly-Si grains was discussed. In addition, the PMOS TFT has been fabricated from the aligned poly-Si array. The mobility was as high as 100 cm2/Vs and the sub-threshold swing was around 0.24 V/dec. The threshold voltage was -1.25 V and the on/off current ratio was about 106.

Abstract: Pulsed UV laser beams, which are widely used in the processing of polymers, offer many advantages in the field of polymer production, primarily because their photon energy is higher than the binding energy of the polymer. In particular, the fabrication of polymers with an excimer laser process is faster and more convenient than with other processes. Nevertheless, some problems occur in the precision microprocessing of polymers, including the formation and deposition of surface debris, which is produced from the breakdown of either polymer chains or radical bonds. In the present work, a process for eliminating carbonized surface debris contamination generated by the laser ablation of a polymer was developed. The proposed approach for removing surface debris utilizes an erasable ink pasted on the polymer. The surface debris ejected from the polymer is then combined with the ink layer on the polymer. Finally, both the surface debris and the ink layer can be removed using adhesive tape.

Abstract: Biocompatibility has long been associated with surface microtopography, microtexture and microchemistry. The surface topography ultimately affects the nature and the strength of the interactions that occur at biomaterial-biological environment (cell adhesion, mobility, spreading and proliferation). Thus, it is necessary to produce and work with controlled microtopographical surfaces that present reproducible microdomains of a dimension similar to that of the biological elements of interest (for instance, cells). [1] There are a number of substrates that already have been studied (such as silicone, polystyrene, poly-L-lactic acid and titanium coated polystyrene) in terms of surface topography. [2] However, few studies are related to hydroxyapatite substrates. As it is well established, hydroxyapatite is a well known ceramic that is extremely used in medical applications, namely implants and coatings. In this work, the surface topography of dense hydroxyapatite substrates was altered by using KFr excimer laser. Excimer lasers produce high-intensity, pulsed ultraviolet radiation and are especially well suited for materials processing due to their large beam cross-section area, which permits using mask projection technologies to process relatively large areas in a single step.[3]

Abstract: In the present paper, the influence of tubule orientation and areal density on the development of surface textures by excimer laser processing of dentin is analysed. Disks of dentin 2 mm thick were extracted from caries-free human teeth by cross-sectional cutting above the pulp cavity, polished and fixed using standard procedures. The samples were laser-processed using 100 laser pulses of 248 nm wavelength radiation at a fluence of 1 J/cm2, pulse duration of 30 ns and pulse frequency of 5 Hz. The surface texture after processing depends on the angle between the tubules and the laser beam. In inner dentin, where tubules are parallel to the laser beam, cone-like artefacts form, considerably increasing surface roughness. The cones are constituted by partially melted peritubular dentin and develop because the ablation rate of peritubular dentin is lower than the ablation rate of surrounding intertubular dentin. The areal density of cones is roughly identical to the areal density of tubules except when the tubule density is high enough to allow adjacent cones to coalesce. In outer dentin, where tubules are tilted with respect to the laser beam, the surface remains flat. The reason for this orientation dependence is that, when tubules are tilted towards the laser beam, preferential removal of intertubular dentin will expose an increased area of underlying peritubular dentin to laser radiation preventing cone development.

Abstract: Nano-imprinting Lithography (NIL) has been considered as the most promising technique for nano-scaled fabrication and patterning. Recently, a new approach known as Laser-Assisted Direct Imprinting(LADI) has been proposed and demonstrated as an even more efficient way for direct nanofabrication and nanopatterning. In this study, we focused on silicon materials and utilized a single KrF excimer laser pulse (248 nm wavelength and 30 ns pulse duration) as the heating source. Molds of micro-scaled size have been prepared using conventional photolithography techniques. A working platform based on an Excimer Laser Micro-Machining system is constructed for LADI process. The influence of laser fluence and the imprinted pressure on the resulting structures was verifying by varying the laser fluence (1.0 ~ 1.2 J/cm2) and the imprinted load (3 ~ 9kg). The results have shown that the morphology and the imprinted depth were directly related to the laser fluence and the imprinted pressure. Quantitative data are obtained and will be addressed.

Abstract: This paper is to investigate the effects on grain size of different working conditions for making poly Si films by using the excimer laser annealing method. In this research, a KrF excimer laser of 248 nm in wavelength is used to irradiate a-Si films of 0.1 μm in thickness on glass substrate to produce poly-Si ones. The control parameters are laser intensity (200~500 mJ/cm2), pulse number (1~10 shots) and coverage fraction (0~100%). Besides, the effect of a SiO2 layer is also studied, which is utilized as a heat-isolated zone located between the Si film and glass substrate. Average grain sizes from SEM photos are used to analyze the effects of these parameters. Purely from the heat transfer view, the Si film obtains more energy would have the slower cooling or solidification rate, which results in the larger grain. From the experimental results, if the melt pool is within the range of Si film or does not contact its neighboring layer (SiO2 layer or glass substrate), the more absorbed energy from the higher energy intensity, the larger pulse number or the bigger coverage fraction can have the larger average grain size. However, with large enough energy, the melt pool could go through the Si film and touch the lower layer. This would induce much more nuclei due to the homogeneous nucleation in the pool and the heterogeneous nucleation near the interface between the film and the neighboring layer. The resulting grain size is much smaller than that of the former one. The transition points of these two cases for different control parameters can be obtained from the experimental results in this study. When the energy from the laser is small, the SiO2 layer acts like a heat absorber and makes the grain size smaller than that of not having the SiO2 layer. On the other hand, when the energy is large, the SiO2 layer becomes a heat insulator and makes the grain size larger.