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.     

西门子反应器中硅棒热电行为数值模拟与分析

改良西门子法制备多晶硅过程中,化学气相沉积所需能量全部由电流加热硅棒提供.本文考虑多晶硅还原炉中辐射和对流热量传递形式,耦合频率控制的焦耳电加热方程,建立了12对棒多晶硅还原炉热场-电磁场耦合模型,并通过工业数据验证了其模拟结果的合理性.分析了硅棒半径、交流电频率以及反应器壁发射率对西门子还原炉内、外硅棒内部温度及电流密度分布的影响.结果表明:当硅棒半径增长到所用交流电频率引起的趋肤深度时,交流电趋肤效应开始显著影响硅棒内部温度梯度;交流电频率的增大,硅棒内部温度梯度逐渐减小;反应器壁发射率增加,低频时硅棒内部温差增大,而高频时发射率对硅棒内部温度分布影响不再显著.     

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.     

Heteroepitaxial growth of GaP on silicon

Epitaxial gallium phosphide layers have been grown on silicon substrates by the metal-organic process. This process involves the reaction between trimethylgallium (CH₃)₃Ga and PH₃ and gives a high density of nucleation sites on the silicon. The influence of the substrate orientation and of the deposition temperature on the crystallinity of the layers has been studied. Best results were obtained on (001) oriented substrate at a deposition temperature of 800°C. X-ray reflection topographs of the layers have revealed the formation of cracks extending along the [110] direction, which are explained by the lattice mismatch and the difference in thermal expansion coefficients. The cracking is asymmetric with the main direction parallel to [110]. The density of cracks can be reduced by a two stage epitaxy. The electrical properties of undoped and n-type doped layers have been assessed by Hall and C(V) measurements. It shows auto-doping with silicon coming from the substrate.     

Polycrystalline silicon carbide film deposition using monomethylsilane and hydrogen chloride gases

A polycrystalline silicon carbide film is formed on a silicon surface by chemical vapor deposition using monomethylsilane gas along with hydrogen chloride gas in ambient hydrogen at atmospheric pressure. The film deposition is performed near 1000 K, at which temperature the monomethylsilane maintains a chemical bond between the silicon and carbon present in the molecular structure. The excess amount of silicon on the film surface is reduced using the hydrogen chloride gas. Although the film deposition stops within 1 min after beginning the supply of the monomethylsilane gas and hydrogen chloride gas, annealing at 1273 K in ambient hydrogen after the film deposition allows further deposition so that a thick silicon carbide film can be obtained.     

On the Chemical Reaction Mode of Polysilicon Deposition from Silane

Silane decomposition and silicon layer growth will be described by way of theory taking into account heterogeneous as well as homogeneous reaction mode and 1st as well as 0.5th order of the chemical reaction. Comparing axial layer growth rate distribution and total substrate surface area effect on the latter with respect to theoretical and experimental results (for the process conditions investigated), it will be shown that the deposition of undoped poly silicon is characterized by a heterogeneous reaction mode, whereas chemical reaction is of first reaction order in the temperature range above 973 K and of 0.5th reaction order below 973 K. The deposition kinetics of strongly in-situ phosphorus doped poly silicon is shown to be in agreement with a homogeneous reaction mode of 0.56^th reaction order.     

用快速光热退火制备多晶硅薄膜的研究

用等离子体增强型化学气相沉积先得到非晶硅(a-Si:H)薄膜,再用卤钨灯照射的方法对其进行快速光热退火(RPTA),得到了多晶硅薄膜.然后,进行XRD衍射谱、暗电导率和拉曼光谱等的测量.结果发现,a-Si:H薄膜在RPTA退火中,退火温度在750℃以上,晶化时间需要2min,退火温度在650℃以下,晶化时间则需要2.5h;晶化后,晶粒的优先取向是(111)晶向;退火温度850℃时,得到的晶粒最大,暗电导率也最大;退火温度越高,晶化程度越好;退火时间越长,晶粒尺寸越大;光子激励在RPTA退火中起着重要作用.     

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。     

Cracking assisted nucleation in chemical vapor deposition of silicon nanoparticles on silicon dioxide

Deposition of sub-monolayer silicon on SiO₂/Si(1 0 0) greatly facilitates nucleation in subsequent thermal chemical vapor deposition (CVD) of silicon nanoparticles. Sub-monolayer seeding is accomplished using silicon atoms generated via disilane decomposition over a hot tungsten filament. The hot-wire process is nonselective towards deposition on silicon and SiO₂, is insensitive to surface temperature below 825 K, and gives controlled coverages well below 1 ML. Thermal CVD of nanoparticles at 1×10⁻⁴ Torr disilane and temperatures ranging from 825 to 925 K was studied over SiO₂/Si(1 0 0) surfaces that had been subjected to predeposition of Si or were bare. Seeding of the SiO₂ surface with as little as 0.01 ML is shown to double the nanoparticle density at 825 K, and densities are increased twenty fold at 875 K after seeding the surface with 30% of a monolayer.     

Effect of oxygen content on barrier properties of silicon oxide thin film deposited by dual ion-beam sputtering

A silicon oxide thin film barrier was prepared with various oxygen contents and its chemical composition, surface morphology and optical and barrier properties were related to the deposition conditions used. Our study showed that under Ar and O₂ assisted process conditions, a stoichiometric silicon oxide thin film formed at a critical oxygen content during deposition of 40-50%. The thin films deposited at the critical condition showed the lowest surface roughness giving similar or higher optical transmittance than that of the bare polycarbonate (PC) substrate. The boiling and tensile strength test performed on the thin film deposited with assisted ions before the deposition process showed improvement in the adhesion between the oxide layer and the polymer substrate. In addition, interface modification to improve for improving the barrier layer properties of the silicon oxide thin film was achieved through the introduction of dual ion beam sputtering without pre-treatment.     

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.     

Deposition Efficiency Reducing Reactions in Silicon Deposition from Silane at Low Pressure

Silane pyrolysis at polysilicon low-pressure-deposition conditions is analyzed along the reactor-tube axis with respect to the existence of competing decomposition reactions leading to the formation of silicon-containing gaseous byproducts. The presence of such a parallel reaction is indicated by a difference between silane decomposition efficiency η_SiH4 and silicon deposition efficiency η_si. The rate of such a competing parallel reaction is influenced by the variation of deposition temperature and/or substrate area of silicon deposition. It is drastically accellerated by the presence of phosphine in the gas phase. For the latter case the competing parallel reaction is shown to occur as a homogeneous reaction.     

Preparation of microcrystalline silicon solar cells on microcrystalline silicon carbide window layers grown with HWCVD at low temperature

N-type microcrystalline silicon carbide layers prepared by hot-wire chemical vapor deposition were used as window layers for microcrystalline silicon n–i–p solar cells. The microcrystalline silicon intrinsic and p-layers of the solar cells were prepared with plasma-enhanced chemical vapor deposition at a very high frequency. Amorphous silicon incubation layers were observed at the initial stages of the growth of the microcrystalline silicon intrinsic layer under conditions close to the transition from microcrystalline to amorphous silicon growth. ‘Seed layers’ were developed to improve the nucleation and growth of microcrystalline silicon on the microcrystalline silicon carbide layers. Raman scattering measurement demonstrates that an incorporation of a ‘seed layer’ can drastically increase the crystalline volume fraction of the total absorber layer. Accordingly, the solar cell performance is improved. The correlation between the cell performance and the structural property of the absorber layer is discussed. By optimizing the deposition process, a high short-circuit current density of 26.7 mA/cm² was achieved with an absorber layer thickness of 1 μm, which led to a cell efficiency of 9.2%.     

On chemical kinetics of silicon deposition from silane (IV). In-situ phosphorus doping of LPCVD poly silicon in the temperature range 900–950 K

Highly in-situ phosphorus-doped LPCVD poly silicon deposition from mixtures consisting of silane and phosphine has been investigated for limited conditions regarding temperature, silane input, phosphine-silane ratio and total pressure. Agreeing with the deposition of undoped poly silicon, growth rate linearly decays along the axis of the wafer cage applied for in-situ doped poly silicon. In consequence layer growth should be controlled by a chemical reaction of 0.5^th order. In contrast to undoped poly silicon the slope of axial growth rate decay increases with the distance between wafers increased. This behaviour is a proof for a homogneous chemical reaction mechanism. The silicon forming reaction is characterized by an activation energy of about 25 kcal/mole for PH₃/SiH₄ = 0.003.     

无电镀沉积于硅衬底上铜纳米晶的场发射性能

采用无电镀沉积技术在经过机械抛光的单晶硅衬底上沉积了铜纳米晶.利用X射线衍射数据,估算出所沉积铜纳米晶的平均粒径大约为40nm.对120s无电镀沉积样品的场发射测试表明,该样品的开启场强为～5.5V/μm,在场强达到9.26V/μm时的场发射电流密度可达到62.5μA/cm2.对相应的沉积过程和场发射机理进行了分析.结果表明,无电镀沉积技术有可能成为制备具有较好场发射性能的金属/硅冷阴极的一种可供选择的方法.     

Generating ordered Si nanocrystals via atomic force microscopy

We describe two successful routes for generating ordered arrays of Si nanocrystals by using atomic force microscopy (AFM) and amorphous silicon thin films (200–400 nm) on Ti/Ni coated glass substrates. First, we show that field-enhanced metal-induced solid phase crystallization at room temperature can be miniaturized to achieve highly spatially localized (below 100 nm) current-induced crystallization of the amorphous silicon films using a sharp tip in AFM. In the second route, resistive nano-pits are formed at controlled positions in the amorphous silicon thin films by adjusting (lowering and/or stabilizing) the exposure currents in the AFM process. Such templated substrates are further used to induce localized growth of Si nanocrystals in plasma-enhanced chemical vapor deposition process. In both cases the crystalline phase is identified in situ as features of enhanced current in current-sensing AFM maps.     

VHF-PECVD制备微晶硅薄膜的微结构研究

用甚高频等离子体化学气相沉积(VHF-PECVD)法在玻璃衬底上低温制备了不同沉积时间微晶硅薄膜.用拉曼散射光谱仪、X射线衍射(XRD)、原子力显微镜(AFM)等表征手段对薄膜的微观结构进行了研究.研究结果表明:随着沉积时间的延长,薄膜呈岛状生长,薄膜晶粒度在微晶核形成后迅速升高并逐渐饱和;其微观结构经历了"非晶相→非晶/微晶混合相→微晶相"的演变过程.本实验制备的微薄膜仍以(111)为优化取向.     

In-situ Raman spectroscopy used to study and control the initial growth phase of microcrystalline absorber layers for thin-film silicon solar cells

The continuous deposition of microcrystalline silicon has been monitored with in-situ Raman spectroscopy. The process and measurement settings were chosen such that one spectrum was taken during approximately 9 nm of layer growth. This allows observing the crystallinity in the initial growth phase of microcrystalline silicon absorber layers. The influence of different p-doped seed layers has been studied. Under constant deposition conditions, an initial decrease in crystallinity was observed over the first tens of nanometers. By profiling the process gas flows during the initial phase it was possible to reduce the amount of amorphous material that was detected during the initial phase of deposition.     

The influence of gas-phase etch removal,deposition temperature and substrate properties on the crystallographic perfection of silicon epitaxial layers

An investigation of the defect structure of silicon homoepitaxial layers, as influenced by gas phase etching, deposition temperature, and substrate properties, is presented. The minimum values of etch removal and deposition temperature necessary for sufficient layer perfection have been determined. The defect and impurity distribution in the substrate, as formed during a preceeding arsenic buried layer processing, have been evaluated and are discussed here with regard to their influence on the epitaxial layer perfection.     

Si/SiGe growth by low-energy plasma-enhanced chemical vapor deposition

Nowadays, microelectronic industry targets (in term of down-scaling and throughput) require some severe reduction of the SiGe epitaxial growth temperature or/and increase of the growth rate. A possible alternative to meet these requirements is low-energy plasma-enhanced chemical vapor deposition (LEPECVD). We have studied the deposition kinetics of silicon, silicon–germanium and germanium using LEPECVD. This new deposition technique offers promising advantages compared to thermally activated CVD such as low deposition temperature and high growth rate. Different regimes are observed depending on the growth temperature. High temperatures can be associated to a mix between thermally and plasma-activated deposition, whereas only plasma-assisted deposition occurs at low temperatures. Crystalline quality of the layers was checked through the mean of photoluminescence, which revealed no defects. A high growth rate (100 nm min⁻¹) that can be achieved very easily with LEPECVD allows to grow quickly very thick layers. We have used this technique to grow step-graded thick SiGe layers which are almost fully relaxed. Those virtual substrates exhibited the well-known cross-hatch pattern, with RMS roughness from 2 to 10 nm for pure Ge layers.