| Summary: | 碩士 === 國防大學中正理工學院 === 兵器系統工程研究所 === 93 === Recently, the poly-silicon thin film on cheap and low temperature substrate has gained great attraction for being applied on the production of TFT-LCD panels, used on various high performance electronics devices, instead of amorphous-silicon thin film due to its higher electron mobility, which is considered to be strongly dependent on the film’s surface morphology, grain size, microstructure and defect density. Among various poly-silicon thin film fabrication techniques, the pulsed excimer laser annealing has shown to be promising for manufacturing low temperature poly-silicon thin films with better crystallinity, larger super lateral grown (SLG) grains leading to higher electrical conductivity without damaging the glass substrate.
This thesis aims to develop the optimum processing parameters for producing poly-silicon films by laser annealing of amorphous silicon films (100nm thick), deposited on glass substrate using plasma enhance chemical vapor deposition technique, using 193 nm excimer laser. The influence of laser fluence, shot number and repetition rate on the recrystallization mechanisms involved during annealing of amorphous silicon film and the obtained poly-silicon film’s surface morphology and grain size are investigated. The surface morphology and grain size of the silicon films after laser irradiation are examined using secco-etching, SEM, AFM and TEM techniques.
The experimental results showed the surface morphology of laser irradiated amorphous silicon films were observed to become bumps, ridges, hillocks, networked craters, pillars and molten silicon islands depending on the total energy. After secco-etching of irradiated si films, it is noted that the microstructure with required grains of poly-silicon film was able to be produced using the adequate laser fluence leading to the formation of ridges and hillocks. The multi-shot effect, controlled by repetition rate and shot number, in increasing the grain size has been observed in this research. The largest grains were obtained using the laser fluence near the threshold amount of energy densities [repetition rate 1Hz(250~300mJ/cm2),5Hz(~230mJ/cm2), 10Hz(180~230mJ/cm2), 15Hz(45~135mJ/cm2)] for producing the SLG grained poly-silicon films with the shot number controlled ranged from 25 to 100shots. The repetition rate of pulsed laser is proved to have effect in lowering the threshold energy density involved in laser irradiation of amorphous silicon films for producing larger and uniform SLG grains due to the increasing the irradiation energy and the melting duration per minute leading to the reduction of vertical solidification velocity involved in the melt/regrowth laser irradiation process. The pulse repetition rate controlled at the ranges from 5Hz to 10Hz were shown to be able to produce larger grained poly-si films with average grain size of 1000nm using the energy density and shot number set at 230 mJ/cm2 and 100shots respectively.
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