【作者】 陆利新；

【导师】 方明伦；

【作者基本信息】 上海大学 ， 机械制造及自动化， 2010， 博士

【摘要】 开发新能源和可再生清洁能源是21世纪最具决定影响的技术领域之一,太阳能光伏技术是近年来发展最快、最有活力的可再生能源利用技术。薄膜太阳能电池是第二代太阳能电池,是降低太阳电池成本的主要手段和发展趋势,而非晶硅薄膜是高效廉价光伏太阳电池的理想材料,开展对PECVD设备和非晶硅薄膜生长的关键工艺进行研究,对制备高效薄膜电池材料、对新能源的高效利用具有重要的指导意义。薄膜的结构和性质与制备工艺的关系非常密切,目前认为以辉光放电法制备的非晶硅薄膜质量最好。国内外关于薄膜生长的研究较多从实验方面研究薄膜的工艺特性,优化工艺和结构参数。然而计算机数字模拟在模型建立和计算分析方面具有较大优势,可以帮助设计师和工艺师发现设计中的问题,为优化结构设计和工艺参数提供指导依据。本论文采用计算机数字模拟的方法,研究PECVD(Plasma-Enhanced Chemical Vapor Deposition,等离子增强化学气相沉积)设备非晶硅薄膜材料的生长,研究了布气系统和结构参数对a-Si:H薄膜的影响;研究进气流量、硅氢比和温度对薄膜沉积速率的影响;研究工艺参数、功率与电极间距对薄膜沉积速率及电场分布的影响,并对模拟结果进行试验与测试验证。本论文主要研究内容和成果如下:1.分析了气流分布对薄膜生长过程的影响,利用计算流体力学(CFD)方法对等离子增强化学气相沉积反应室流场进行了数值模拟研究,通过改变匀流板布孔方式、进气管与匀流板距离、进气管出口形状和角度、压强等条件,研究反应器内气体流动的相应变化,给出了获得薄膜生长所需的最佳输运过程的条件,以形成稳定均匀的流场,从而保证薄膜的生长质量。通过模拟验证了匀流板采用渐变直径孔方式的气流流动均匀性更好,并根据模拟结果可知,进气管入口距离为4.5mm时气体流动效果较好;进气管喇叭口结构只适合进气速率较大时的情况;压强133 pa时气流波动较小。根据本文优化后的匀流装置已实际加工应用,取得良好效果。2.根据实际沉积非晶硅薄膜的反应腔室结构建立几何模型,根据反应室中表面化学反应建立三维热流场模型。通过对非晶硅沉积过程进行分析和仿真模拟,得到镀膜过程中的化学组分的分布情况以及薄膜的平均沉积速率,沉积速率的得出为进一步进行实验、验证模型的准确性提供数据基础。并运用正交实验法对PECVD薄膜生长的工艺参数进行了数值仿真,对结果进行了极差分析和方差分析,得出了影响沉积速率的工艺参数的主次顺序。仿真结果揭示了进气流量、硅氢比和温度对薄膜沉积速率的影响规律,为合理确定PECVD工艺参数提供理论基础。通过模拟分析得出结论:对于不同的气流速度,气流越大,温度场越不均匀,所以为了得到较均匀的薄膜,应尽量采用小气流进气;通过模拟正交实验得出结论:对沉积速率影响最大的是温度,其次是进气流量,最后是H2和SiH4的比值。3.分析了等离子体的基本特征及其对薄膜生长的影响,并在此基础上对射频电场的分布进行模拟。主要研究薄膜沉积速率与沉积过程中RF电源功率关系,给出靶台与衬底间距不同情况下的电磁场分布;采用电场-等离子-电化学反应耦合求解方法,对加工工艺过程和设备进行仿真,掌握设备内的各种物理参数分布,从而优化工艺,改善设备的工作状态。结果显示极板变化对电场强度和电势产生影响,极板距离越近,电场强度越大,电势标量值也越大。不同极板接地方式也对电场强度和电势产生影响。进气流量、功率、温度、压力、硅氢比等参数变化只对沉积速率有影响,对电场和电势没有影响。进气流量越大,沉积速率越高,但是进气速率进一步增大,沉积速率反而下降。功率选择40W,电极间距25mm时,薄膜的均匀性较好,沉积速率也较高。4.采用平板式PECVD沉积设备进行非晶硅薄膜生长试验,并采用变角度光谱椭圆偏振仪测试薄膜厚度,计算得出薄膜沉积速率,与仿真结果进行对比,通过试验验证得出结论:沉积速率的试验值与计算值之间的误差低于±7.5%,与多物理场模拟数值之间的误差低于±15%,验证模型的准确性和仿真结果的有效性。通过本文的研究,获得在一定条件下高质量薄膜材料的结构和工艺参数,为PECVD设备制造和镀膜工艺提供一定的理论指导依据,对提高太阳电池的效率和质量、实现制造过程的性能优化和提升装备技术水平具有重要的意义。更多还原

【Abstract】 In 21 century, developing new energy and renewable clean energy is one of the most decisive influence technology. Solar photovoltaic technology is the fastest developing and the most dynamic renewable energy technology in recent years. Film solar cell is the second generation solar cell, it is the main way to cut costs of solar cells and development trends, and Amorphous-Silicon Thin Film is ideal for high efficiency low-cost materials of photovoltaic solar cells.There is very close relationship between the structures and properties of the film and it’s preparation process. Present the view that the Amorphous-Silicon thin film prepared by glow discharge gets the best quality. At home and abroad the researching on thin film growth is mainly based on the experiments of the film’s technical characteristics, optimization of process and structure parameters. However,there’re great advantages in computer digital simulation in modeling and calculation, that can help designers and technologist find design problems by providing a basis for optimum structural design and processing parameter. This paper studies the growth of amorphous silicon thin film in the PECVD (Plasma-Enhanced Chemical Vapor Deposition) equipment by using computer simulation methods. The main contents are as follows:1. The flow field in Plasma Enhanced Chemical Vapor Deposition reactor is simulated by Computational Fluid Dynamics (CFD) theory. By varying the way pore distributed through gas distributor, distance between inlet and gas distributor panel, form and angle of inlet, and gas pressure, the corresponding gas velocity, flow filed in the rector is calculated. The geometric structure and inflow pattern of a PECVD reactor is improved in order to provide steady and uniform flow field and improve the quality of thin films. The results show that the gas distributor panel with gradual diameter pore make the airflow more uniform, and the simulation results indicated that the distance between inlet and panel is 4.5 showed very goodeffects; The inlet trumpet-shaped structure only suits the situation that airflow speed is big; The airflow fluctuations are small when pressure is 133pa. The gas distributor is manufactured and improved the gas distribution in the real equipment.2. A three-dimensional numerical model, account for the description of fluid, thermal and chemical phenomena, has been developed for the hydrogenated amorphous silicon deposition from SiH4-H2 in a PECVD reactor. This model provides the capability to predict the main composition and deposition rates across the substrate surface. And orthogonal experimental method was applied to numerical simulation experiment for processing parameters of thin film grown by PECVD. The priority order of processing parameters affecting deposition rate is found. By means of the experimental verification, the simulation results well coincide with experimental results. All those provide theoretical basis for reasonably determining processing parameters of PECVD, deeper understanding and the optimizations of processing parameters of thin film deposition by PECVD. The results abtained through the simulation indicate: regarding the different stream velocity, the air current is bigger, the temperature field is more non-uniform, therefore to obtain the even thin film, the small inlet airflow should be used as far as possible; the conclusion through the simulation orthogonal experiment shows that the temperatur have the greatest effect on the depositon rate, next is the inlet airflow capacity, finally is H2 and the SiH4 ratio.3. This thesis analyzes the basic character of plasma and the influence of thin film growth, and simulates the distribution of RF electric field on this basis. The main research object is the relationship between deposition rate of the thin film and the RF power in deposition, showing electromagnetic field distribution under different circumstances of the space between the electrodes. By using electric field - Plasma - electrochemical reaction coupled solution method, the simulation machining technology process and equipment is carried out, in control of physical parameters in the equipment to optimizate the process and improve the performance of the equipment. The result showed that the space between the electrodes has influence on the electric-field strength and the electric potential, the distance between the electrodes is nearer, the electric-field intensity is bigger, the scalar value of electric potential is also bigger. The grounding method of electrodes also has the influence on the electric-field intensity and the electric potential. The paramaters of airflow rate, power, temperature, pressure, the silicon hydrogen variations is only have influential on the deposition rate, have not affected to the electric field and the electric potential. The airflow rate is bigger, the deposition rate is higher, but the airflow rate further increases, the deposition rate decreased. When the power is 40W, electrode spacing 25mm, the thin film uniformity is good, the deposition rate is also high.4. Flat-type of PECVD deposition equipment used to conduct tests of amorphous silicon thin film growth, then tests the thickness of the thin films by using the variable angle spectral ellipsometry and calculated deposition rate, compared with the simulation results verify the simulation model accuracy and validity of the simulation results. The result comparison between the numerical simulation and experiment shows that: the error of deposition rate between experimental value and the simulation value is lower than±7.5%, and is lower than±15% with the multi-physical field simulation value’s. It is known that the two results coincide with each other well, which certifies the feasibility and validity of the model, and the model meets the needs of engineering practicesBy the study of this paper, the processing parameters of high-quality thin film material are acquired under a certain conditions. The study is of important meaning for improving the efficiency and quality of solar cell.更多还原