| Summary: | 博士 === 國立成功大學 === 工程科學系碩博士班 === 96 === In the fabrication of a poly-Si film, an amorphous silicon (a-Si) thin layer on glass substrate is melted by the irradiation of a excimer laser with nanosecond duration, and then is cooled down to form the poly-Si one. In this thesis, the excimer-laser-induced crystallization of a-Si films was investigated numerically and experimentally. The basic structure is an a-Si film on a glass substrate. The control parameters are the laser intensity (200~500 mJ/cm2), the pulse number (1~2 shots) and delay time between two shots (one nanosecond). The effects of SiO2 and SiNx layers which are utilized as heat buffer zones located between the Si film and glass substrate were also studied. In this paper, a double-splitting-laser method is proposed. In the method, a laser pulse from an excimer laser is divided into two pulses by a beam splitter. The cyclic optical path is used to control the delay time of the second pulse. Optical mirrors and optical attenuators are utilized to adjust the energy density of these two laser pulses. The delay time between these two pulses is changeable and controlled in the order of nanosecond. The second pulse is applied when the Si film is solidifying after the irradiation of the first one. This could enhance the solidification time and enlarge the grain size of the poly-Si film. In the microstructure analysis of the laser-irradiated area, the critical fluences (full-melt threshold, FMT) between the partial melting and complete melting regimes can be found by applying scanning electron microscopy. The corresponding efficient two-dimensional numerical model is built to predict the critical fluences (FMT) and the transient temperature distribution during the laser processing, based on the finite element method and the efficient specific heat and the specific heat/enthalpy method used to handle the release or absorption of latent heat. The FMT’s obtained from the simulation results of the proposed model agree fairly well with those from the experimental data reported in the literature and acquired in this research. The results of this paper are expected to be helpful to the processing designers or researchers.
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