一种新型多晶硅还原炉流动与传热的数值模拟

在传统多晶硅还原炉结构基础上,提出了一种内部流场为平推式流动的新型多晶硅还原炉,并采用计算流体力学方法研究了该还原炉内的速度场和温度场。流场模拟结果表明,新型多晶硅还原炉内混合气的流动基本上实现了平推式流动;温度场模拟结果发现,通过改变操作参数,采用平推式流动可实现炉内温度场的控制,解决了传统还原炉局部温度过高的问题,可避免硅粉的产生,长期保持还原炉内壁面的抛光效果,降低还原炉辐射电耗;计算结果表明,在相同的条件下,采用新型多晶硅还原炉的还原电耗较传统还原炉可降低8.5%。     

基于温度场均匀化分析的还原炉底盘结构研究

主要研究多晶硅还原炉的底盘结构,通过改进底盘冷却液流道形式,以提高在该底盘结构形式下温度场分布的均匀性及底盘结构的安全性。本文研究的底盘结构采用了限制射流直喷喇叭口式冷却流道,在底盘上滑板下表面不易形成气膜隔层,大大降低了底盘滑板的温差应力,提高了底盘结构的安全性。结合大型多晶硅还原炉的研制要求,应用Fluent对多晶硅还原炉底盘的辐射、导热和对流的传热过程进行了传热分析,得出了底盘内部温度场的分布云图,并在此基础上通过ANSYS对多晶硅还原炉底盘进行了热-结构耦合分析,得到了满足强度、刚度条件下结构的最优化。     

多晶硅还原炉底盘温度场均匀性分析

针对一种24对棒多晶硅还原炉底盘的冷却模式,应用Fluent对多晶硅还原炉底盘内流体进行模拟分析,得出底盘的上花板温度分布图,并引入平均算数温度和均匀系数的概念分析底盘温度场的均匀性。总结概括出温度场均匀性分布随冷却液进口流量的变化趋势,提出判别温度场均匀化的判据,提供合适的流量参考。     

新型多晶硅还原炉底盘流动与传热的数值模拟

多晶硅还原炉的底盘取热结构对降低能耗有很大影响,提出了一种新型的多晶硅还原炉底盘均匀取热结构,并就其温度均匀性、冷却效果与传统底盘结构进行比较。该新型底盘结构由中间隔板分为2层,并在隔板上安装电极位置的孔周围焊接竖直环隙。冷却水由隔板下层的冷却水进口进入底盘并流经各电极周围的环隙进入隔板上层的还原炉底盘上底板实现均匀取热。与传统多晶硅还原炉底盘结构相比,该结构克服了传统结构下底盘取热不均匀的问题。就新型底盘取热结构中的单棒环隙结构进行模拟优化。重点考察环隙上焊接挡板的厚度、宽度及数量对冷却效果的影响。300 K的冷却水做工作介质,底盘材料用不锈钢。模拟后得到的单棒环隙结构的最适宜结果为竖直环隙挡板厚度1 mm,挡板宽度1 mm,挡板间距10 mm;水平环面挡板厚度1 mm,挡板宽度1 mm,挡板间距10 mm;换热效果较传统底盘提高32%,温度均匀性提高54%。     

新型还原炉流场温度场的模拟研究

为适应太阳能产业的发展需求,提出了一种结构新型的多晶硅还原炉,新型还原炉在传统西门子还原炉的基础上进行了多处的改进：1）增设了外壁面高度刨光的热管;2）在炉膛内部中央出气口处增设了套筒;3）增加了3个内插进气口。并采用计算流体力学方法研究了该型还原炉内的速度场和温度场。速度场模拟结果发现增设的套筒结构起到了收集还原炉顶部气体的作用使气体更好的通过底盘的中央出气口散出;温度场模拟结果发现内插进气口促进了还原炉顶部气体的及时更新,高度刨光的热管表面成功反射硅棒所辐射的热量,降低了还原炉环境温度,有效的防止了粉末硅的生成更加,更加有利于硅棒的生长。     

不同圆球复合无序堆积床内流动传热数值分析

圆球堆积床内孔隙分布影响其内部流场及温度场分布, 且小管径-球径比堆积床由于壁面限制, 内部孔隙率变化剧烈, 其内部流动和传热不均匀现象明显。针对D/d_p为3的圆球无序堆积床构建了3种非等直径圆球复合堆积结构:径向分层复合堆积、轴向分层复合堆积以及随机复合堆积结构, 并采用DEM-CFD方法建模计算, 从径向及整体角度分析比较不同复合堆积床内流动换热特性及其流场和温度场分布的均匀性。结果表明:孔隙率及孔隙大小分布共同影响堆积床内流场和温度场分布;相对于单一等直径圆球堆积, 采用复合堆积结构能使堆积床内部孔隙率分布更均匀, 其内部流场和温度场分布也更为均匀;对于D/d_p为3的堆积通道, 径向分层堆积结构对于提高整体流动换热性能及改善内部流动换热均匀性都有显著效果。     

径向流脱硝反应器的设计与流体力学模拟

设计了一种新型的径向流脱硝反应器,该脱硝反应器中内部催化剂床层采取倾斜安装方式,能够有效减小床层中对反应无贡献的空间区域,较大地提高了反应器内部的空间利用率用.气体的均匀流动对脱硝反应效率至关重要,采用调整内部催化剂床层倾角并在适当位置添加挡板以保证反应气体的均匀流动.采用Fluent 6.3模拟软件对内部催化剂床层进行模拟,模拟结果表明,倾角较小且在特定区域加入档板能有效提高反应气体流动的均匀性.     

影响化学气相沉积多晶硅致密料比例的因素

改良西门子法生产多晶硅还原工艺是高纯的三氯氢硅和氢气在还原炉内发生化学气相沉积反应,得到固态多晶硅,多晶硅根据表观质量,分为致密料、玉米料、珊瑚料。目前,国内多晶硅生产以大型还原炉为主,对成本控制具有明显优势,但存在的问题是多晶硅致密料比例较低。本文通过对还原炉反应温度控制、进料喷嘴布置、反应配比等因素的分析研究,得出了提高还原炉化学气相沉积多晶硅致密料比例的方法、思路。     

CVD法制备C/C复合材料沉积炉流场数值模拟北大核心

化学气相沉积(CVD)法是目前制备C/C复合材料的首选方法,沉积炉内流场的均匀性直接影响目标产物的质量及产量。本文建立了CVD法制备C/C复合材料的沉积炉内气体流动仿真模型,采用计算流体力学方法对沉积炉内流场进行模拟,并研究主要工艺参数对沉积炉内流场分布的影响规律。结果表明,产品区域气体呈现低速均匀的流动特征,真空度增大会导致沉积炉内气体流速显著增加,但对流场均匀性几乎无影响;采用各路相同的送气方式时沉积炉内流场分布比中心增大的送气方式更均匀;较小进气量可以使沉积炉内流场更均匀。     

列管反应器改进结构环形分布器内变质量流动的数值分析

环形分布器是实现载热体在列管式固定床反应器壳程均匀流动的重要部件。采用计算流体力学方法对丙烯氧化反应器壳程熔盐在改进结构型式(即椭圆扩张型进口,进口处两侧分别设置呈45°的导流挡板,挡板上均匀分布小孔,不均匀的开孔方式)的环形分布器内的变质量流动进行了模拟研究,分析了环形分布器内的速度及静压分布规律,并与传统型式环形分布器进行对比,并考察了出口分布孔数目及进口熔盐流量对均布效果的影响。通过计算发现,改进结构的分布器均布特性优于传统结构;优选24个分布孔能够满足流体均布的要求,且分布孔达到36,流体均布情况基本稳定;减小进口熔盐流速,进口区域速度及静压波动较小,减小了进口能量损耗,有利于流体均布。     

A new CVD reactor for semiconductor film deposition

The concept and design of a new chemical vapor deposition (CVD) reactor is presented for both epitaxial and nonepitaxial film deposition in semiconductor processing. The reactor is designed in such a way that a stagnant semiconductor source fluid of uniform concentration is provided for the film deposition without causing free or forced convection. The supply of the source gas for the deposition is by diffusion through a porous material such as quartz or graphite. Compared to the low pressure CVD (LPCVD) reactor with mounted wafer configuration, the new reactor should give a better film thickness uniformity and about an order of magnitude reduction in the amount of the source gas required. Further, at least for polycrystalline silicon deposition, the deposition rate can be much higher than is currently practiced with the LPCVD reactor. Design equations for the reactor are given. Details on the design for the polycrystalline silicon deposition are also given.     

多晶硅气相沉积反应器的研发与应用

基于多晶硅的化学气相沉积技术与工艺,运用计算流体力学（cFD）的气体运动的组分运输和表面反应动力学模型,NAnsys—F1uent对多晶硅的生长过程进行模拟计算,运用有限元应力分析（FEA）方法,对复杂设备结构进行热应力计算和强度安全性校核,研发并设计一系列大型高产能、低能耗的多晶硅反应器。该系列的反应器广泛应用于国内外多晶硅生产线,产能达500t／a,能耗低至45kW／kg。     

Multiwalled carbon nanotube deposition profiles within a CVD reactor: An experimental study

A number of proposed applications of carbon nanotube (CNT) arrays require that uniform deposition of well-aligned CNTs is achieved. The CNT deposition profiles inside a chemical vapor deposition (CVD) reactor are strongly dependant on the reaction temperatures, feed gas flow rates, carrier gas flow rates and reactor geometry. In addition, objects placed in the path of the flow of feed material could affect the deposition patterns. In this paper, an experimental study aimed at achieving better control of the deposition patterns of CNTs is presented. Multiwalled CNTs were grown on a long substrate by the catalytic CVD of a xylene/ferrocene solution. The deposition patterns on the substrate were examined for different furnace temperatures, xylene/ferrocene feed rates and carrier gas flow rates. Small objects representative of electronic devices were placed at different locations on the substrate and their effect on the deposition patterns was explored. The effect of changing the height and the gap distance between these objects was also studied.     

Jet Assisted Aerosol Chemical Vapor Deposition for Optical Fiber Synthesis

Various kinds of high quality optical fibers are routinely fabricated by the modified chemical vapor deposition (MCVD), in which fine particles are generated through the oxidation of chemical precursor and deposited in a silica tube reactor. Efficiency, rate, and uniformity of particle deposition determine the quality and cost of optical fibers; therefore efforts to enhance aerosol deposition performance should be important for further improving both quality and cost. Here we propose a jet assisted aerosol chemical vapor deposition method utilizing gas jets in the conventional MCVD silica tube reactor for the purpose of enhancing the efficiency, rate, and uniformity of particle deposition. High temperature helium gas is injected radially through an electrically heated thin tube inserted inside the silica tube. High temperature gas jets push particles generated in a tube toward the tube wall and therefore shorten the axial length of particle trajectories before deposition and cause particles to experience higher thermophoretic force. As a result, deposition efficiency (and rate) was found to considerably increase compared to the conventional method, and the uniformity was also significantly improved.     

Transient solution of chemical vapor infiltration/deposition in a reactor

A chemical vapor infiltration/deposition (CVI/CVD) reactor used to manufacture carbon/carbon (C/C) composites aircraft brakes has been simulated numerically. This simulation accounts for a homogeneous gas reaction mechanism as well as a heterogeneous surface reaction mechanism that is coupled with hydrogen inhibition effect and a pore model. Non-Boussinesq (low Mach number) equations are used to predict fluid flow, heat transfer, and species concentrations inside the reactor and within the porous brakes. In addition, we use an efficient quasi-steady state integration procedure to predict porosity distribution at different infiltration times. Results showing the flow, temperature and concentration fields, as well as the deposition rate of the pyrolytic carbon and porosity change with time, are presented. Optimized operating conditions for pressure and temperature are obtained through a parametric study that consists of 16 different cases. Recommendations are presented for improving performance.     

Expansion transport regime in pulsed-pressure chemical vapor deposition

Control of transport processes is of critical importance in chemical vapor deposition (CVD), yet conventional steady carrier-gas flow presents challenges in scalability, deposition uniformity and process control. This paper describes the precursor delivery dynamics of pulsed-pressure CVD (PP-CVD) and proposes a mass transport regime in which expansion effects dominate over continuum effects. A modified continuum breakdown parameter for unsteady expansion is presented. Using this parameter an expansion mass transport regime is identified in which unsteady expansion effects become significant compared to continuum flow effects. Experiments using the naphthalene sublimation technique demonstrate the relationship between processing parameters and the viscous-expansion regime transition in a simple PP-CVD reactor. Expansion mass transport is described as a means to achieve 3-D deposition uniformity.     

Experimental and numerical investigation of the position-dependent growth of carbon nanotube–alumina microparticle hybrid structures in a horizontal CVD reactor

The hybrid structures of carbon nanotubes (CNTs) and alumina microparticles were produced in a horizontal chemical vapor deposition (CVD) reactor using ferrocene/xylene/acetylene mixture as the catalyst–carbon source. At a given temperature and hydrogen ratio, the CNT diameter, number density, growth rate and their hybrid structures varied greatly along the axial direction of the reactor. This non-uniform growth is attributed to the position-dependent chemical reaction kinetics inside the reactor, mainly along the gas flow direction. Mass spectrometry was used to identify and quantify the chemical species of the exhaust gas. A numerical simulation of the reacting gas flow in the reactor was conducted in parallel by taking into account the space-dependent pyrolysis kinetics of the catalyst and carbon sources, the reactor temperature gradient and the fluid dynamics. A good agreement existed between the modeling and the experimental results. A double-end-injection method was proposed based on the above results, and the uniform hybrid structures were synthesized in a larger zone inside the CVD reactor. A new kind of CNT structure containing iron crystal particles at their two extremities was obtained under certain conditions, which can be very useful for various CNT junction applications.     

Mathematical modeling for chemical vapor deposition in a single-wafer reactor: Application to low-pressure deposition of Tungsten

A mathematical model for low pressure chemical vapor deposition in a single-wafer reactor in stagnation point flow has been developed to investigate the reactor performance. The transient transport equations for a simulated reactor include continuity, momentum, energy, and gaseous species balances. The model equations are simultaneously solved by using a numerical technique of orthogonal collocation on finite element method. Simulation studies have been performed to gain an understanding of tungsten low pressure chemical vapor deposition process. The model is then used to optimize the deposition rate and uniformity on a wafer, and the effects of operating conditions on deposition rate are studied to examine how system responses are affected by changes in process parameters. Deposition rate and uniformity calculated at the steady state are observed to be very sensitive to both temperature and total pressure. In addition, the model predictions for tungsten deposition from hydrogen reduction of tungsten hexafluoride have been compared with available experimental data in order to demonstrate the validity of the model.     

A combined CFD modeling and experimental study of pyrolytic carbon deposition

Understanding the chemical reaction mechanism and deposition kinetics is of great importance to guide the production of pyrolytic carbon (PC). A practical approach to mimic the commercial chemical vapor deposition (CVD) process and eventually predict the PC deposition rate is highly desired. In this work, a simplified two-step reaction mechanism was proposed for the CVD of PC, with the first step in the gas phase and the second step on the substrate surface. The kinetic parameters were determined by trial and error using a computational fluid dynamics simulation. The velocity, temperature, and concentration profiles in a cold-wall, forced-flow reactor were modeled based on the geometry and experimentally determined boundary conditions. The computed PC deposition rates for substrate temperatures between 700 and 3000 °C were in good accordance with experimental results. Rate limiting steps were observed for both the deposition experiments and simulations. Mass-transport-limited and reaction-limited regimes were identified in wide temperature and flow rate ranges. A higher deposition rate was found in a cold-wall reactor compared with those in an insulated reactor or a hot-wall reactor. Finally, the PC microstructure was characterized using optical microscopy, scanning electron microscopy, Raman spectroscopy, and X-ray diffraction, demonstrating progressive development of graphitization with increasing deposition temperature.     

Deposition uniformities on a wafer and in a trench for tungsten silicide LPCVD in a single-wafer reactor

A transient model of a single-wafer reactor in axisymmetric, stagnation point flow is used to study the effects of operating conditions on film thickness uniformity and composition uniformity across the wafer during low pressure chemical vapor deposition of tungsten silicide. Orthogonal collocation on finite elements is used to solve the transient model equations; continuity, momentum, energy and chemical species balances. A feature scale model for simultaneous Knudsen transport and heterogeneous reactions is used to predict film thickness in infinite trenches. Boundary conditions for the feature scale model are established using the reactor scale model. The use of a combined reactor scale and feature scale model is demonstrated to select deposition conditions which provide both good interwafer uniformity and good intrafeature uniformity. Film thickness and composition uniformity on a wafer are predicted using a model for a single-wafer reactor. Significant differences in step coverage predicted using partial pressures in the feed stream and partial pressures at the wafer surface were observed. Step coverage differences between the wafer center and the wafer edge were also significant under the operating conditions used in this study. Uniformities of interwafer and intrafeature step coverages inceased as either the wafer temperature or the partial pressure ratio of dichlorosilane to tungsten silicide in the feed was decreased.