| 题名 | 固体激光晶化制备多晶硅薄膜 |
| 作者 | 袁志军 |
| 学位类别 | 博士 |
| 答辩日期 | 2010 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 楼祺洪 ; 王之江 |
| 关键词 | 激光晶化，非晶硅薄膜，多晶硅薄膜，太阳能电池，液晶显示 |
| 其他题名 | Study on solid-sate laser crystallization of amorphous silicon thin films |
| 中文摘要 | 激光晶化技术是目前多晶硅薄膜的主要制备方法之一。与激光晶化传统的准分子激光相比，固体激光器具有运行成本低、维护简便、稳定性高等优点。而且可以提供更大的晶化加工窗口，因此被认为是能够代替准分子激光器的理想晶化光源。本论文将从理论和实验两方面对固体激光晶化技术进行研究，重点研究脉冲倍频Nd:YAG激光对非晶硅薄膜的晶化作用。主要内容如下： 第一章介绍了多晶硅薄膜在液晶显示和光伏领域的应用和主要制备方法，以及激光晶化技术与其他技术相比较的优势。综述了目前不同波长(紫外－可见－红外波段) 激光对非晶硅薄膜晶化的进展。 第二章以热传导方程为基础，用有限差分方法对激光与非晶硅薄膜作用的熔融、再结晶过程进行了计算模拟。得出了薄膜不同深度处温度随时间的变化关系。分析了此过程中薄膜初始温度、激光脉宽以及波长等因素对薄膜内温度场的影响。全面考虑了从紫外到红外激光波长对非晶硅薄膜的晶化作用，并对其熔融深度进行了分析比较，这对长波长激光晶化在光伏领域的应用有一定指导意义。 第三章研究倍频Nd:YAG激光对非晶硅薄膜的诱导晶化作用。首先对倍频Nd:YAG进行光束整形和均匀化，实验了包括蝇眼、波导板和传能光纤等多种整形方案。结果表明，蝇眼整形系统的损耗小且能提供较好的整形效果。扫描晶化后非晶硅薄膜的表面形貌粗糙度有所增加，拉曼光谱表明其完成由非晶到多晶的相变。在400~1000mJ/cm2范围内薄膜呈多晶与非晶相共存的网络结构。根据拉曼峰红移和窄化特性，确定了532nm激光晶化所需最佳能量密度出现在850mJ/cm2左右。这一数值与理论计算结果吻合的比较好。 激光晶化技术在液晶显示领域已经有很成熟的应用，但在光伏领域则鲜有报导。这是由于非晶硅对传统的准分子激光吸收太强，晶化深度只有几十个纳米。相比之下，倍频Nd:YAG绿光可以达到更深的熔融深度。第四章将介绍绿光晶化技术应用于太阳能电池领域的探索。 第五章介绍国产氧化镧钇透明激光陶瓷的激光光谱测试结果。氧化镧钇是我国拥有完全自主知识产权的激光透明陶瓷体系，该材料具有类玻璃结构，这种结构导致Nd3+离子在氧化镧钇中的吸收带展宽，以及荧光寿命增长。我们与上海大学材料学院合作，首次实现Nd3+: (Y1–x Lax)2O3 透明陶瓷激光输出。 |
| 英文摘要 | Laser induced crystallization of amorphous silicon (a-Si) is a well-established technology for producing polycrystalline silicon (Poly-Si) thin films in the TFT-LCD industry. However, only very thin layers can be crystallized by the traditional excimer lasers. Solid state lasers, comparing with the excimer lasers can provide higher stability of output power and wider processing window. Furthermore, they are low cost and easy to maintain. Therefore, the Solid state laser, especially the frequency-doubled Nd: YAG is regarded as one kind of the promising laser for crystallization of a-Si films thicker than 100nm. In this thesis, the dynamics of crystallization of amorphous silicon by a frequency-doubled pulsed Nd: YAG laser has been studied both theoretically and experimentally. Firstly, the applications and preparation methods of Poly-Si thin films are introduced. The advantage and drawbacks of laser crystallization technology comparing with others are also analyzed. The recent progresses on crystallization with lasers of different wavelengths are reviewed. Secondly, an effective numerical model based on the heat transfer equation is set up simulate the laser crystallization process. Finite difference method is used to solve the equation. Temperature distribution with time and depth during the crystallization are analyzed. The melting threshold and the optimized laser fluence for crystallization of s-Si of specified thickness are predicted. The influence of laser parameters, such as wavelengths and pulse duration, and substrate temperature on temperature of films are discussed in detail. The simulation results show that, the crystallization with excimer lasers requires the lowest threshold energy densities. However, it does not create the deepest melt depth, compared with green or red lasers. This conclusion can be instructive for the application of laser crystallization on solar cells. Besides the simulation, we also studied the green laser crystallization technique experimentally. Before the crystallization process, the laser beam of frequency-doubled Nd: YAG must be homogenized because of the severely interference effect. Two schemes of beam shaping are developed and contrasted, and the fly-eye lens optical system is chose for the crystallization because it can provide better homogenization. Raman spectra of thin films treated with different fluences are measured to confirm the phase transition and to determine the optimized fluence. The surface morphology of Poly-Si thin films was analyzed basing on the measurement results of Atomic Force Microscopy (AFM). Both of the estimated grain size and crystallinity evaluated from the data of Raman spectrums are found to increase almost linearly with the laser fluence. However, the Raman signal for poly-Si disappeared when the laser power exceeds 1000mJ /cm2.There exist the optimized value for laser fluence from 400 to 1000mJ/cm2 in the crystallization. In this experiment, it is about 850mJ/cm2 to produce the best crystallization, which accords well with the calculated value. Laser crystallization technology is being used widely in the TFT-LCD industry, but been seldom reported in the photovoltaic field due to the strong absorbance of a-Si to ultra-violet wavelength. Are there any potential applications of the green laser crystallization technology in the fabrication or upgrading of solar cells? Subsequently, we presented some research results on this field in the forth chapter. The last chapter presents the lasing characteristics on two kinds of home-made yttrium lanthanum oxide transparent ceramic with independent property right. The absorption band of Nd doped yttrium lanthanum broadens due to its glass-like inner-structure. And the Fluorescent lifetimes also remarkably enhanced with the doping of La3+ ion. Recently, We achieved laser output from Nd3+: (Y1–x Lax)2O3 transparent ceramic for the first time by cooperation with the school of material science & engineering of Shanghai University. |
| 语种 | 中文 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15291]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 袁志军. 固体激光晶化制备多晶硅薄膜[D]. 中国科学院上海光学精密机械研究所. 2010. |
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