Papers by Keyword: Excimer Laser

Abstract: Al doping into 4H-SiC performed by irradiating pulse-width-expanded excimer laser to an Al film deposited on the 4H-SiC surface is investigated. An optical pulse stretcher was constructed to produce the laser pulse whose peak intensity was reduced as half as that of the original pulse and pulse width was expanded from 55 ns to 100 ns. The irradiation of the expanded pulses is found to reduce the ablation of the materials from the surface and enable irradiation of multiple shots. As the result, doping depth of Al is significantly increased. The multiple shots of the expanded pulses is also fund to decrease the sensitivity to spatial non-uniformity of laser intensity and increase the uniformity of doped region.

Abstract: We have demonstrated the possibility for epitaxial regrowth of crystalline SiC by laser melt annealing. The quality of the recrystallization is analyzed by XTEM, EELS, electron diffraction and XRD. The annealing guarantees a uniform activation achieved both in melting and solid phase. Carbon graphitization on the top surface and a crystallized silicon layer below is observed as an effect of the high temperature and the melting phase.

Abstract: Excimer laser micromachining enables us to overcome the conventional lithography-based microfabrication limitations and simplify the process of creating three dimensional (3D) microstructures.The objective of this study is to investigate the relation between the number of laser pulses, number of laser passes through the channel of ablation site and their etch performance. Parameters such as frequency, fluence and velocity were retained as constants. In this paper, we present a parametric characterization study on silicon using KrF excimer laser micromachining. From the result, the etch rate change were recorded as the two major laser parameters (Number of laser pulses and number of laser passes) were varied. Both parameters were showing declination profile however from comparing both graphs, it showed that etch rate dropped more steeply when varied number of laser passes rather than number of pulses.

Abstract: We report nitrogen (N) doping of 4H-SiC by KrF excimer laser irradiation in liquid N₂. In comparison to phosphorus (P) doping performed using phosphoric acid solution, the liquid-N₂ immersion-laser doping can introduce N atoms deeper (~ 1 μm depth) into the 4H-SiC, which results in reduction of doped layer resistance by approximately 3 orders of magnitude. Doping is shown to proceed by the thermal diffusion of species, while loss of the host material from the surface by ablation takes place at the same time. Chemical analysis shows that high density carbon (C) vacancies are generated in the N doped region, which suggests enhanced diffusion of N assisted by the presence of C vacancies. pn junction diodes are formed by using the N doping technique. Turn-on voltage is ~ -3V, which is reasonable for a pn junction diode of 4H-SiC.

Abstract: Amorphous silicon films with and without spin-coating aluminum-salt-solution are treated by 193nm ArF excimer laser with different laser energies. It is observed that the crystalline fraction increases along with the laser energy. By comparation, with the help of Al, higher crystalline volume fraction and lower in-plane stress can be achieved at the same laser energy (2.9mJ). Large grain size of 200~300nm and maximum crystalline fraction of 82.3% are obtained in Al-salt-solution spin-coated sample, which is treated with laser energy of 3.2mJ,and its carrier mobility is 56.3cm²/Vs.

Abstract: Silicon carbide (SiC) is a promising semiconductor for high-power devices due to its superior material properties; high breakdown field, high electron saturation velocity, and high thermal conductivity. To implement SiC power devices, pn junction must be formed in the SiC. However, ion implantation for impurity doping has several issues for the SiC. For example, while a high-temperature (~1700 °C) post-implantation annealing is required to electrically activate implanted species [, it induces generation of crystallographic defects in the SiC, such as segregation of carbon atoms at the surface from the SiC bulk [. Therefore, development of new technology for local doping of SiC is highly demanded.

Abstract: Selected area laser-annealed polycrystalline silicon (p-Si) thin films were prepared by a 248 nm excimer laser. 1 μm thick p-Si films with grain size less than 100 nm were deposited on SiO₂ substrate by chemical vapor deposition using atmospheric pressure (APCVD). Grain sizes before and after annealing was examined by scanning electron microscopy (SEM) and the mechanism of grain growth was discussed in detail. The maximum grain size of a selected area laser-annealed p-Si film can be increased from 100 nm up to 2.9 μm on SiO₂ substrate by using appropriate laser energy densities. It indicated that silicon grains in laser-annealed regions had grown up competitively with three stages.

Abstract: This paper proposed a design of algorithm of an excimer laser coaxial observation processing system which can automatically track preset line. With using of the Visual C + + image processing technology and the least square method, the XY axis in both directions of processing platform can obtain accurate processing displacement, and stability control platform for real-time tracking a straight line center. Processing system can acquire the coordinate of processing place where can get the distance from the centre of image in order to achieve real-time tracking.

Abstract: It is known that UV-C radiation kills fungus by radiating their DNA. We wanted to verify, if we could use radiation produced by excimer laser as an alternative method for the treatment of onychomycosis – nail fungus. Medical procedure like this should meet certain conditions such as perfectly and reliably destroying the fungi and to make no harm to the patient (in this case overheating of the under-nail tissue). The main part of the first stage of this work was to determine the coefficients for transmission, reflection and absorption of nails to determine the quantity of energy going through and absorbed by the nail – that means quantity of energy which could harm the healthy tissue. In the following stage we focused on the irradiation of the fungi. Our final task was to assess whether is it possible to determine the parameters of the radiation (total dose, dose per pulse frequency, repetition rate and number of pulses) for which the elimination of the fungi would be most effective without damaging the nail and the soft tissue underneath it. The results so far have proven that UV-C radiation does not pass through a fingernail to such extent that it could damage the soft tissue beneath it. We've measured the absorption and transmission spectrum for the nail tissue at the first time and we've determined the value of absorption coefficient is α = 1.7 mm-1 at the wavelength of 700 nm (transmission max.). Fungi are destroyed by the application of small doses of radiation using the excimer laser. The goal of the last phase of our work was to determine the modulation parameters of the excimer laser radiation for the treatment of onychomycosis. Refining the parameters and finding out the optimal values for different ranges and types of illnesses will require additional measurements.

Abstract: In this research, machining characteristics of excimer laser ablation for three-dimensional machining of PMMA (Polymethyl methacrylate) is examined. In general, excimer laser ablation of polymeric material has features such as high precision and fine surface quality resulting from a less thermally-affected process, but in an earlier study, a thermal like effect on ablated surface was observed. Therefore, in this research the best machining condition of excimer laser ablation for PMMA by both numerical and experimental approaches was revealed.