| As the ever increasing prices of oil and natural gas, the renewable energy resources, especially solar energy, have been attracting more and more attention internationally. With the further research into the third generation solar cells - thin film solar cells, to fabricate high quality polycrystalline silicon (poly-Si) thin films is a most straight approach to improve the photovoltaic conversion efficiency.In this thesis, the fabrication of high quality poly-Si thin films is investigated. The silicon thin films deposited either by plasma enhanced chemical vapor deposition (PECVD) or electron-beam evaporation (EBE) are characterized by Raman spectroscopy and X-ray diffraction (XRD) before and after thermal annealing.To begin with, PECVD is employed as the deposition technique for the silicon thin films, and the main results are as follows:The design for the variation of the six influential parameters during the fabrication processes is to change one parameter at a time. Among the six parameters, five of them can be changed to three corresponding values: hydrogen vs. silane flow ratio can be varied to 100 sccm/1 sccm, 100 sccm/5 sccm and 50 sccm/5 sccm; RF power, 50 W, 30 W and 10 W; substrate temperature, 350 ℃, 200 ℃ and room temperature; working pressure, 24 Pa, 48 Pa and 72 Pa; and deposition time, 30 min, 60 min and 90 min. And the electrode spacing can be changed to 5.5 cm, 5.0 cm, 3.0 cm and 1.5 cm. It was found that all of the deposited silicon thin films were amorphous. However, the deposition system was out of work after any variation of the electrode spacing. And it is strongly suggested that the electrode spacing and the dilution gas Ar in silane are probably the two key influential factors.In order to fabricate poly-Si thin films, the as-deposited hydrogenated amorphous silicon (a-Si:H) thin films are thermally annealed. It was found that rapid thermal processing (RTP) at 800 ℃ for 60 s resulted in slightly larger average grain size and higher crystallinity than those without the RTP pretreatment after solid phase crystallization (SPC) at 800 ℃ for 5, 10 and 22 h. The results suggest that the low temperature short-time RTP pretreatment can promote the crystallization process of the as-deposited a-Si:H thin films during the following SPC and then improve their crystallinity.After analyzing the crystallinity and the residual stress results of the a-Si:H thin films, it was found that, with the same RTP conditions, the silicon-based thin filmshad higher crystallinity than the quartz-based ones, and the dehydrogenation process decreased the crystallinity of the quartz-based thin films. Furthermore, the residual stress level of the silicon-based thin film with dehydrogenation was lower than that of the quartz-based one, and the dehydrogenation process increased the residual stress levels of the quartz-based thin films. The results suggest that the natures of the substrates and the dehydrogenation process have a great impact on the crystallization of the a-Si:H thin films.Besides, EBE is also applied as the deposition technique for the silicon thin films. The silicon thin films are fabricated in a high vacuum system with substrate temperatures at 150 °C, 200 °C, 400 °C, 600 °C, and 650 °C, respectively. And the thin films are further annealed by RTP at 900 °C, 1000 °C, 1100 °C, and 1200 °C, respectively. And each of the annealing temperature has three dwell times: 10 s, 30 s, and 50s. It was found that all of the evaporated thin films were amorphous and the crystallinity of the annealed thin films increased with the annealing temperature and changed not much with the variation of the dwell time. Furthermore, with the same RTP conditions, the crystallinity of the annealed thin films increased with the substrate temperature. And the crystallinity increased rapidly as the substrate temperature was heightened for the low annealing temperatures while the effect of the substrate temperature on the crystallinity was weakened for the high annealing temperatures.
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