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基于CFD的流态化多晶硅CVD过程研究

发布时间:2018-06-19 10:31

  本文选题:多晶硅 + CVD ; 参考:《青岛科技大学》2015年硕士论文


【摘要】:本文基于CFD分析手段,针对流化床反应器内复杂的多晶硅CVD气-固反应过程编写Mfix代码,扩充了硅氢化合物热力学数据库,建立了耦合化学反应、热量、动量、质量传递的数值模型,对流化床内的反应过程和温度、压力、气速、颗粒分布等情况进行了分析,并对无定形硅粉成核机理进行了探索性研究。具体工作如下:1、根据量子化学计算结果,确定了102个硅氢化合物(Si1-Si10)的分子结构式;采用基团因子贡献法确定了各硅氢化合物的标准生成焓、标准摩尔熵以及七个温度(300K、400K、500K、600K、800K、1000K、1500K)下的比热容;利用Matlab软件编程计算了104种硅氢化合物的热力学物性多项式系数a1-a7、a15,借助化学分子量计算器计算了上述所有物质的分子量;将NIST数据库、商业软件(Fluent、Chemkin、Mfix等)、实验和模拟方面的文献数据与本文计算结果进行了对比,校正了H2、SiH4等Mfix已有2种物性,扩充了SiH2、Si2H6等Mfix缺乏的102种硅氢化合物的热力学数据,建立了硅氢化合物热力学数据库。该数据库可准确计算各物质的比热、熵、焓等热力学物性,为本文数值模拟反应源项的计算和无定形硅粉成核机理的研究打下了基础。2、确定了多晶硅CVD表面化学反应、气相反应共222个反应的动力学参数;通过在控制方程中加入反应速率源项、化学反应热、辐射传热、相间传热系数、颗粒碰撞耗散项等实现了化学反应和质量、动量、热量传递过程的耦合;采用卡迪尔网格划分方法划分网格,提高了计算速度和准确性;采用二阶迎风格式对控制微分方程进行离散,SIMPLE算法求解压力耦合方程,进而完成对流态化多晶硅CVD过程的数值模拟计算。3、采用Caussat和Hsu的实验条件模拟流态化多晶硅CVD过程,多晶硅CVD速率误差分别为0.8%-30%、19%-28%,表明本文建立的数学模型能确切描述流态化多晶硅的CVD过程。综合多晶硅CVD反应速率、抑制无定形硅粉形成两方面因素,选择氢气为流化气体,基于CFD分析了多晶硅CVD速率随硅烷进口浓度、进口操作气速、操作温度、操作压力变化情况,确定硅烷与氢气最佳操作进气比为3/17(即硅烷进口浓度15%),最佳操作气速为最小流化速度的5.5倍,最佳操作温度为963.15 K,最佳操作压力为0.2 MPa。4、对反应器出口处气相质量、速度、温度分布,反应器内轴向、径向气相分布,反应器轴向固含率分布进行了分析,对无定形硅粉成核机理进行了初步探索,结果表明:反应器内以甲硅烷和硅烯的非均相热裂解反应为主,气相反应为辅;气相质量分布与速度分布、温度分布直接相关,轴向速度对气相分布的影响高于径向速度分布;无定形硅粉在反应器稀相区质量分率较大,低温利于抑制无定形硅粉的形成。本文建立的热力学数据库可准确表达各硅氢化合物在不同压力、温度下的比热、熵、焓等热力学物性,为本文计算结果的可靠性奠定了基础;本文建立的综合气固流体力学、动力学且耦合化学反应的数学模型能确切描述流态化多晶硅CVD过程,给出不同工艺条件对反应过程的影响,实时分析流化床内温度、气速、反应速率、硅氢化合物质量等分布情况。本文研究结果可对多晶硅CVD流化床反应器内构件的设计提供指导,对高纯度多晶硅实际生产工艺的设计提供理论支持。
[Abstract]:In this paper, based on CFD analysis, the Mfix code is written for the complex polysilicon CVD gas solid reaction process in a fluidized bed reactor, and the thermodynamic database of the silicon hydrogen compound is expanded. The numerical model of the coupling chemical reaction, heat, momentum, mass transfer, the reaction process in the fluidized bed and the temperature, pressure, gas velocity, particle distribution and so on are established. The analysis is carried out and the nucleation mechanism of amorphous silicon powder is explored. The specific work is as follows: 1, according to the results of quantum chemical calculation, the molecular structure of 102 silicon hydrogen compounds (Si1-Si10) is determined, and the standard formation enthalpy, standard molar entropy and seven temperatures of each silicon hydrogen compound are determined by the group factor contribution method (the group factor contribution method). The specific heat capacity of 300K, 400K, 500K, 600K, 800K, 1000K, 1500K) was programmed by Matlab software to calculate the thermodynamic property polynomial coefficient A1-A7, A15, and the molecular weight of all the above substances was calculated with the chemical molecular weight calculator. Compared with the results of this paper, 2 kinds of physical properties of H2, SiH4 and other Mfix have been corrected. The thermodynamic data of 102 kinds of silicon hydrogen compounds, such as SiH2 and Si2H6, are expanded, and the thermodynamic database of the silicon and hydrogen compounds is established. This database can accurately calculate the thermodynamic properties of the specific heat, entropy and enthalpy of each substance, which is the value of this paper. The calculation of the simulated reaction source term and the study of the mechanism of amorphous silicon powder nucleation have laid the foundation.2, determined the surface chemical reaction of the polysilicon CVD, and the kinetic parameters of 222 reactions in the gas phase reaction; by adding the reaction rate source term in the control equation, the chemical reaction heat, the radiation heat transfer, the interphase heat transfer coefficient, the particle collision dissipation term and so on. The coupling of the chemical reaction and the mass, momentum and heat transfer process is used. The computational speed and accuracy are improved by using the Kadeer grid division method. The two order upwind scheme is used to discretize the control differential equations. The SIMPLE algorithm is used to solve the pressure coupling equation, and then the numerical simulation of the CVD process of the convective state polysilicon is completed. .3, using the experimental conditions of Caussat and Hsu to simulate the flow of fluidization polysilicon CVD process, the CVD rate error of polysilicon is 0.8%-30%, 19%-28% respectively. It shows that the mathematical model established in this paper can describe the CVD process of the fluidization polysilicon. It combines the CVD reaction rate of polysilicon, inhibits the formation of amorphous silicon powder in two aspects, and chooses hydrogen as the fluidization Gas, based on the CFD analysis, the CVD rate of polysilicon with the concentration of silane inlet, inlet operating gas speed, operating temperature, and operation pressure change, the optimum operation intake ratio of silane and hydrogen is 3/17 (i. e. 15% of silane inlet concentration), the optimum operating gas velocity is 5.5 times of the minimum flow rate, the optimum operating temperature is 963.15 K, and the optimum operating pressure is 0. .2 MPa.4, the gas phase mass, velocity, temperature distribution at the outlet of the reactor, axial, radial gas distribution and axial solid content distribution in the reactor were analyzed. The nucleation mechanism of amorphous silicon powder was preliminarily explored. The results showed that the non homogeneous thermal cracking reaction of methylene silane and Silene was the main reaction in the reactor and the gas phase reaction was supplemented in the reactor. The gas phase mass distribution is directly related to the velocity distribution and the temperature distribution. The effect of the axial velocity on the gas phase distribution is higher than the radial velocity distribution; the mass fraction of the amorphous silicon powder in the dilute phase region of the reactor is larger, and the low temperature is beneficial to the formation of the amorphous silicon powder. The thermodynamic database established in this paper can accurately express the different silicon hydrogen compounds in different types. The thermodynamic properties such as pressure, specific heat, entropy and enthalpy at temperature have laid the foundation for the reliability of the results of this paper. The mathematical model of integrated gas-solid fluid mechanics, dynamics and coupling chemical reaction can describe the CVD process of fluidization polysilicon accurately, and the effect of different process conditions on the reaction process is given, and the real-time analysis of fluidization is given. The distribution of temperature in bed, gas velocity, reaction rate, and the quality of silicon and hydrogen compounds. The results of this paper can provide guidance for the design of the internal components of the polysilicon CVD fluidized bed reactor, and provide theoretical support for the design of the actual production process of high purity polysilicon.
【学位授予单位】:青岛科技大学
【学位级别】:硕士
【学位授予年份】:2015
【分类号】:TQ127.2

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