流态化多晶硅化学气相沉积过程的数值模拟

利用基于欧拉-欧拉两相流模型,建立硅烷热分解的均相和非均相反应模型,模拟了二维流态化的多晶硅化学气相沉积过程,以及硅烷、硅烯和硅沉积速率在反应器中的分布规律.模拟结果表明多晶硅的沉积主要发生在流化床中的密相区及气泡的周围,浓度相对较小的硅烯非均相反应对多晶硅沉积的贡献约为硅烷的10;.分析了硅烷入口浓度和反应温度对硅沉积速率及转化率的影响,模拟的硅沉积速率与文献中的实验数据做了比较.     

三氯氢硅和氢气系统的气相沉积三维模拟

建立了氢气和三氯氢硅系统的多晶硅气相沉积反应模型,通过Chemkin4.0耦合气相反应、表面反应机理,利用流体力学软件Fluent 6.3.26数值求解.根据模拟结果绘制了进气温度、进气组成、沉积表面温度以及反应压力与硅沉积速率的关系曲线,阐述了这些条件对于硅沉积速率的影响,同时把模拟结果与文献中的实验数据和计算结果进行对比.结果表明,硅沉积速率随反应温度和反应压力的提高而提高,随进气温度的提高而提高,当氢气摩尔组成低于0.8时,与氢气物质的量组成成正比,氢气物质的量组成大于0.8时,与氢气摩尔组成成反比.     

硅烷热分解生产多晶硅的三维模拟

本文建立了硅烷和氢气体系中气体动量、热量和质量同时传递,并且耦合硅烷热分解反应的多晶硅气相沉积模型,选择适宜的物理模型和边界条件通过流体力学软件Fluent 6.3.26进行数值模拟.之后模拟了进气组成、反应温度、反应压力及进口速度等因素对沉积特性的影响,得到结论:当进气组成、反应温度和反应压力增大时,硅的沉积速率增大、单位能耗降低;当进气速度增大时,硅的沉积速率和单位能耗均呈增大趋势;在进口区域硅沉积速率随着硅棒延伸增大,在离进口较远的区域,硅沉积速率随着硅棒延伸而减小.     

多晶硅化学气相沉积过程气相与表面反应模拟验证

针对SiHCl3-H2体系下硅的化学气相沉积过程,采用边界层反应模型和Chemkin模拟软件,耦合不同气相与表面化学反应机理,对不同条件下硅的沉积速率,高温下HCl气体对硅表面的侵蚀速率进行了模拟计算.与文献报道的三组实验数据进行对比,验证现有反应机理的模拟精度,确定一套修正化学反应机理可以较为准确地预测工业级西门子多晶硅还原炉条件下多晶硅的沉积速率.     

多晶硅化学气相沉积反应的三维数值模拟

建立了多晶硅化学气相沉积反应的三维模型,同时考虑质量、能量和动量传递,利用CFD软件对炉内的流动、传热和化学反应过程进行了数值模拟,并分析了硅沉积速率、SiHC13转化率、硅产率以及单位能耗随H2摩尔分数的变化规律.结果表明:计算结果与文献数据吻合较好;随着硅棒高度的增加,硅沉积速率不断增大;最佳的进气H2摩尔分数范围为0.8 ～0.85.     

钟罩式硅烷反应器内流动与传热的数值模拟

针对硅烷热分解生产多晶硅的过程,建立了基于动量、质量、能量同时传递并耦合硅烷热分解反应的硅烷-氢气化学气相沉积模型,采用计算流体力学方法分析了传统钟罩式硅烷反应器内的流场、温度场和浓度场.针对普通反应器内存在的死区以及沉积速率不均匀的问题,提出了新型的带出气筒的反应器结构,并对结构进行了数值模拟.计算结果表明,与普通钟罩式硅烷反应器相比,新型反应器的流场、温度场以及硅烷浓度分布更加合理,有效减小了反应器内的漩涡,缓解了气体在进出口间的“短路”现象,使硅棒表面的沉积速率更加均匀.     

三氯氢硅和氢气系统中多晶硅化学气相沉积的数值模拟

本文建立了三氯氢硅和氢气系统中混合气体动量、热量和质量同时传递,并且耦合气相反应、表面反应的多晶硅气相沉积模型,利用流体力学计算软件(Computational Fluid Mechanics, CFD)Fluent6.2数值分析了气体进口速率、反应压力、表面温度和气体组成对硅化学气相沉积特性的影响,数值结果表明计算结果与相关实验数据吻合较好.分析表明在一定的条件下,硅沉积速率随温度、压力的升高而增加,在氢气浓度较高的情况下,硅沉积速率随氢气浓度增加而线性地降低.     

PECVD法制备不同衬底微晶硅薄膜的研究

采用等离子体增强化学气相沉积(PECVD)法分别在玻璃衬底和p型薄膜硅衬底上制备了微晶硅薄膜。使用拉曼谱仪、紫外-可见分光光度计、傅里叶红外光谱仪等对微晶硅薄膜进行检测,重点研究了硅烷浓度、衬底温度对薄膜沉积速率和晶化率的影响。实验结果表明:两种衬底上薄膜的沉积速率均随硅烷浓度的增大、衬底温度的升高而变大。硅烷浓度对两种衬底的薄膜晶化率影响规律相同,即均随其升高而降低;但两种衬底的衬底温度影响规律存在差别:对玻璃衬底而言,温度升高,样品晶化率减小;而p型薄膜硅衬底则在温度升高时,样品晶化率先增大后减小。此外还发现,晶化率与薄膜光学性能及含氧量存在较密切关联。     

衬底温度对微晶硅薄膜微结构的影响

采用等离子体化学气相沉积(RF-PECVD)技术,在不同衬底温度Ts下沉积了氢化微晶硅(μc-Si:H)薄膜,并深入研究了衬底温度对微晶硅薄膜微结构的影响.研究结果表明随着衬底温度的升高,表征μc-Si:H 薄膜微结构的晶化率和平均晶粒尺寸均呈现了相似的变化规律,其临界温度点随着硅烷浓度的增加向高温方向移动.该实验结果可通过"表面扩散模型"得到合理解释.     

垂直式MOCVD反应器中热泳力对浓度分布的影响分析

从分子动力学理论出发,推导出垂直式MOCVD反应器中热泳力和热泳速度与温度、温度梯度、压强、粒子直径的关系式,以及热泳速度与扩散速度、动量速度平衡时的关系式.在典型的生长条件下,计算得到在温度T=605K时,热泳速度与扩散速度、动量速度动量平衡,TMGa浓度达到最大.然后在不考虑化学反应和考虑化学反应两种情况下,针对垂直式MOCVD反应器内的热泳力对粒子浓度分布和沉积的影响进行数值模拟,模拟给出反应粒子在反应器不同进口温度、衬底温度时的温度分布、浓度分布和反应速率.并与文献中的实验值进行对比,模拟结果与实验值有很好的吻合.     

Computational modeling of SiC epitaxial growth in a hot wall reactor

A computational model for chemical vapor deposition (CVD) of silicon carbide (SiC) in a hot-wall reactor is developed, where the susceptor is tapered with a rectangular cross-section. The present work focuses on the advection–diffusion-reaction process in the susceptor. The precursors are propane and silane, and the carrier gas is hydrogen with mass fraction higher than 99%. Computed growth rates under different system pressures and precursor concentrations are compared to the experimental data measured on samples grown in the Linköping CVD reactor. The gas composition distribution in the susceptor and the growth rate profile on the susceptor floor are shown and analyzed. Dependence of the growth rate on precursor concentrations is investigated. It is demonstrated that the growth rate of SiC may either be carbon transport limited or silicon controlled, depending on the input carbon-to-silicon ratio.     

On chemical kinetics of silicon deposition from silane (I). The first order chemical reaction

Theoretical expressions for silicon layer deposition in consequence of silane decomposition within an open isothermal reaction tube has been derived for the case of homogeneous as well as heterogeneous gas reaction. Layer growth distribution along reaction tube axis has been taken into consideration as well as average layer growth rate related to silane consumption during its passage through the tube on the one hand and to growth rate distribution along the tube on the other. Comparing the theoretical results with experimentally based data homogeneous rather than heterogeneous reaction mode might be preferred. In consequence, however, layer growth rate should be linearly effected by the ratio of reactor gas volume to total substrate surface area. In a practical sense average growth rate, and so axial growth homogeneity, should be expected the higher the lower silane consumption efficiency would be adjusted.     

On chemical kinetics of silicon deposition from silane (III). LPCVD poly silicon formation in the temperature range 900–950 K

LPCVD poly Silicon deposition form silane has been investigated for limited conditions regarding temperature, silane input and pumping speed. It has been found that layer growth is controlled by a chemical reaction of 0.5^th-order in consequence of which growth rate linearly decays along the axis of an open isothermal reactor tube. The slope of that decay is determined not only by the reaction rate constant but also by linear gas velocity within the tube and that part of total substrate surface area that is effectively exposed to silane at each wafer position. In conseqence growth rate decay is the steeper not only the higher temperature will be chosen but also the slower gas velocity is adjusted and the smaller wafers are separated to each other. The kind of how axial layer growth rate distribution is effected by changing wafer spacing is a proof for the heterogeneous reaction mechanism. The silicon forming reaction is characterised by an activation energy of about 52 kcal/mole.     

Low-temperature growth of epitaxial (1 0 0) silicon based on silane and disilane in a 300 mm UHV/CVD cold-wall reactor

Epitaxial (1 0 0) silicon layers were grown at temperatures ranging from 500 to 800 °C in a commercial cold-wall type UHV/CVD reactor at pressures less than 7×10⁻⁵ Torr. The substrates were 300 mm SIMOX SOI wafers and spectroscopic ellipsometry was used to assess growth rates and deposition uniformities. High-resolution atomic force microscopy (AFM) was employed to verify the atomic terrace configuration that resulted from epitaxial step-flow growth. Deposition from disilane exhibited a nearly perfect reaction limit for low temperatures and high precursor flow rates (partial pressures) with measured activation energies of ≈2.0 eV, while a linear dependence of growth rate on precursor gas flow was found for the massflow-controlled regime. A similar behavior was observed in the case of silane with substantially reduced deposition rates in the massflow-limited regime and nearly a factor of 2 reduced growth rates deep in the reaction limited regime. High growth rates of up to 50 μm/h and non-uniformities as low as 1σ=1.45% were obtained in the massflow-limited deposition regime. Silicon layers as thin as 0.6 nm (4.5 atomic layers ) were deposited continuously as determined using a unique wet chemical etching technique as well as cross-sectional high-resolution transmission electron microscopy (HRTEM). In contrast, epitaxial silicon deposited in RPCVD at 10 Torr using disilane within the same temperature range showed imperfect reaction limitation. While activation energies similar to that of UHV/CVD were found, no partial pressure limitation could be observed. Furthermore, layers deposited using disilane in RPCVD exhibited a large number of defects that appeared to form randomly during growth. We attribute this effect to gas phase reactions that create precursor fragments and radicals—an effect that is negligible in UHV/CVD.     

Numerical analysis for the growth of GaN layer in MOCVD reactor

The axi-symmetric vertical reactor is a classical reactor configuration for the growth of compound semiconductors by MOCVD. In the present study, the modified reactor is developed to produce uniform and large-volume epitaxial deposition of gallium nitride (GaN). A comprehensive knowledge of the flow, thermal and concentration fields, as well as gas surface reaction, is necessary to develop a CVD reactor. The full elliptic governing equations for continuity, momentum, energy and chemical species are solved numerically. It is investigated how thermal characteristics, reactor geometry, and the operating parameters affect flow fields, mass fraction of each reactant, and deposition rate uniformity. As results, inlet flow rate, inclination angle of wall and inlet design are proposed for optimum operational conditions.     

On chemically vapour-deposited Si/Ge growth in a multi-wafer deposition process at atmospheric pressure

In multi-wafer deposition of Si/Ge thin films from silane, germane mixtures at low-temperature epitaxy conditions not only the depletion of the silicon source but also of the germanium source along the reactor tube axis has to be counteracted in order to get homogeneous layer thickness as well as composition. Carrier gas throughput must be minimized to have a sufficient effective chemical reaction rate at low temperature. Thus it cannot be used to flatten layer growth along the susceptor. Yet the addition of a chemically reactive gas, as for instance hydrogen chloride, is suitable to ensure a nearly constant content of the layer forming source gases along the reactor tube. On the other hand hydrogen chloride may infiltrate additional contaminants leading for instance to high oxygen concentration in the deposited layer. However, oxygen soluted or precipitated changes particular features of Si/Ge behaviour for instance during the thin film growth, the following technological stress of the wafer, or the running electronic structures of microelectronic devices.     

Transport phenomena analysis for boron CVD in a horizontal cold-wall reactor

The transport phenomena in a horizontal cold-walled semicircular reactor are analyzed for the CVD of boron from BCl₃ and H₂. The mixed problem of energy, momentum, and mass conservations is solved by a simple finite difference method. The concentration of the B-reactant on the deposition surface is substituted by the sum of equilibrium mole fractions of the B-containing gas species. The profiles of temperature, velocity, and reactant concentrations in the CVD reactor are illustrated, and the boron deposition rate profile along the substrate is predicted. The effect of the reactant input composition on the deposition rate is calculated, and compared with the experimental data.     

Residence-time dependent kinetics of CVD growth of SiC in the MTS/H2 system

In most chemical vapor deposition (CVD) experiments in flow reactors carried out until now, growth conditions were chosen which yield growth rates independent or linearly dependent on the total gas flow rate, so that the residence time (t) of the gases in the hot zone of the reactor should not play any role in the growth rate. We have performed CVD experiments in the system MTS/H₂, under conditions of low decomposition of MTS. We have found a region, where the growth rate and its derivatives depend strongly on the operating conditions, in particular, where the growth rate of SiC increases strongly with an increase of t. For lower or higher (but yet incomplete) decomposition of MTS, the growth rate becomes again independent of t, and its apparent energy of activation becomes 200 kJ/mol.