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.     

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 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.     

In-situ doping of and trench-refill with LPCVD-poly-silicon (I). (PH3/SiH4) ratio as a process-controlling parameter

The ratio of phosphine- to silane concentration in the reaction gas mixture is a processcontrolling parameter in LPCVD-polysilicon deposition not only with respect to doping level of the layer and layer growth rate on planar wafer surface, but also with respect to the degree of growth rate depression occurring by change-over from wafer surface to sidewall area within trenches in the region of the upper rim of a trench. Trench refill behaviour deteriorates in consequence of growth rate depression within trench the more the higher the doping level of poly-silicon will be chosen. Yet below a lower limit of doping poly-silicon growth rate equals that of undoped poly-silicon, and, as for trench-refill, there is no difference in layer growth within trench and beyond.     

In-situ doping of LPCVD poly silicon (II). Temperature influence

Poly silicon deposition by pyrolysis of silane under low pressure conditions has been investigated with respect to the influence of temperature when simultaneously in-situ doping of the deposited layer takes place. The growth rate of poly silicon is retarded in the presence of phosphine provided that a certain lower PH₃/SiH₄-ratio has been exceeded. It has been shown how that lower ratio depends on temperature. Increasing PH₃/SiH₄-ratio not only slows down layer growth rate but also the apparent activation energy of the layer forming reaction. An empirical equation describing the temperature dependence of that activation energy has been derived. Phosphine adsorption has been discussed as a cause of both layer growth rate and activation energy reduction. Additionally, incorporation of phosphorus during layer growth has been investigated with respect to the total amount and the electrically active concentration, the latter measured after a postdeposition anneal at 1000 °C.     

On Chemical Kinetics of Silicon Deposition from Silane (VI). The Effect of Wafer Diameter

Changing substrate diameter, when depositing poly silicon by decomposition of silane in a hot-wall tube reactor under LPCVD-conditions, alters total substrate surface area as well as the distance between wafer periphery and tube wall. From a theoretical point of view both quantities are expected to take an influence on the steepness of axial layer growth decay. Relovant experimental results confirm the theoretical considerations, if an additional effect of flow resistance will be taken into account.     

On Chemical Kinetics of Silicon Deposition from Silane (V) The Effect of Hydrogen Formation

In consequence of hydrogen formation during silane pyrolysis total gas volume increases, when the reaction proceeds at constant total pressure. Any mole of silane decomposed produces two moles of hydrogen. In the present paper expressions are derived for 1^st and 0.5^th reaction order describing axial growth rate distribution of the isothermally proceeding reaction for the condition of constant total pressure. Those theoretically expected distributions are compared with results obtained by way of experiment on the one hand and those theoretically expected for the condition of constant gas volume on the other. It is concluded that the experimental results discussed rather agree with constant gas volume than with constant total pressure conditions. So, a compensating increase of total pressure along the tube axis might be supposed.     

The current understanding of epitaxial CVD silicon layer doping in the light of modeling and theory development (VIII)

Lateral autodoping along the susceptor in downstream gas direction is described to be the result of a parasitic dopant partial pressure in the gas. Parasitic dopant species are distributed from buried layer surface into the gas during the predeposition period of the epitaxy process. They are diluted as well as gathered by the gas stream along the susceptor. The parasitic dopant pressure profile along the susceptor that exists when layer deposition begins, has been modelled by deriving an exponential expression taking into account a tilted flat susceptor having constant temperature, an increase of gas temperature along the susceptor, total gas throughput, total pressure, buried layer doping level, and the ratio of buried layer area per wafer to the susceptor area related to a wafer.     

Mechanisms of chemical vapor deposition of silicon

The distribution in the silicon epitaxial growth from SiCl₄ and hydrogen are observed in situ by IR absorption spectroscopy. Two methods are used complementarily, one is IR spectroscopy of reactants extracted from the reactor by a fine quartz tube which is not disturbing the reactions, and gives knowledge about the local distribution, the other is direct IR spectroscopy of hot reactants in the reactor which is useful to ascertain the results at the real high temperature situation. The intermediate species are SiHCl₃, SiH₂Cl₂ which is estimated from the induced emission bands at 500 and 570 cm^-1. HCl is a dominant waste product and contributes to reverse reactions. To investigate the reaction, HCl is intentionally injected into the reacting gas. This kind of injection method may also be very effective to analyze the reactions using other reactants such as SiCl₄, SiHCl₃ and SiH₂Cl₂.     

Study of structural characteristics of ferromagnetic silicon implanted with manganese

The structure of manganese-implanted (dose 2 × 10¹⁶ cm^?2) n-type and p-type silicon, ferromagnetic at room temperature, has been studied. During implantation, an amorphized layer is formed in the silicon wafer. Subsequent vacuum annealing improves the structural quality of the implanted material and leads to the formation of a vacancy solid solution of manganese in silicon. A difference in the degree of structural quality of silicon implanted by different impurities has been experimentally established.     

The kinetics of parasitic growth in GaAs MOVPE

Gallium arsenide (GaAs) deposition was carried out in a horizontal quartz reactor tube with trimethylgallium (TMGa) and arsine (AsH₃) as precursors, using a hydrogen (H₂) carrier gas. Temperatures were in the range 400–500 °C, where surface reactions limit deposition rate. Nucleation time and deposition rate were monitored using laser interferometry, optimum reflectance was gained by aligning a quartz wafer to back reflect the incident beam. The 980 nm infrared laser beam was sufficiently long in wavelength to be able to penetrate the wall deposit. Results showing the effect of temperature and V/III ratio on the nucleation time and deposition rate are presented, where with temperature the nucleation delay was observed to reduce and the growth rate to increase. The nucleation delay is consistent with a thermally activated surface nucleation for the parasitic GaAs. A theoretical growth rate model, based on a restricted set of reaction steps was used to compare with the experimental growth rates. Without any free parameters, the growth rates from theoretical calculation and experiment agreed within a factor of two and showed the same trends with V/III ratio and temperature. The non-linearity of the theoretical growth rates on an Arrhenius plot indicates that there is more than one dominant reaction step over the temperature range investigated. The range of experimental activation energies, calculated from Arrhenius plots, was 17.56–23.59 kJ mol⁻¹. A comparison of these activation energies and minimum deposition temperature with the literature indicates that the wall temperature measurement on an Aixtron reactor is over 100 °C higher than previously reported.     

硅烷热解多晶硅气相沉积反应模型分析与验证

在综述现有硅烷热解反应机理的基础上,针对Ho等人提出的气相和表面反应机理,采用二维边界层反应模型和CHEMKIN软件,对水平单基片CVD反应器进行模拟分析,计算结果与文献报道的实验数据拟合良好;通过改变硅烷进气浓度和进气温度,分析沉积速率的变化和各表面反应的贡献率,得到硅微粉再沉积过程随浓度和温度的变化规律;使用上述机理模型,计算了硅烷流化床对应的操作温度和硅烷浓度条件下的沉积速率,与文献报道测量结果比较,误差在合理范围,表明该机理适用于硅烷流化床化学气相沉积过程的CFD耦合模拟.     

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.     

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.     

Transport properties and defects in silicon nanoparticles and effect of embedding in amorphous silicon layers

We study the properties of silicon nanoparticles produced by CO₂ laser pyrolysis of silane in a gas flow reactor, and the effect of sandwiching a thin layer of such particles between two a-Si:H layers. Contrary to the case of hydrogenated polymorphous silicon for which it is known that the electronic and stability properties can be enhanced compared to conventional hydrogenated amorphous silicon, the electronic properties of such a sandwich structure are degraded and the number of deep defects is increased.     

Substrate temperature dependence of microcrystalline silicon growth by PECVD technique

Undoped hydrogenated silicon films have been prepared from a gas mixture of silane and hydrogen, varying substrate temperature from 180–380 °C in an ultrahigh vacuum system using RFPECVD technique. XRD and Raman measurements enable us to know that the films are microcrystalline throughout the substrate temperature range. Bond formation of the SiH films at different substrate temperature is studied through different characterisation techniques like Fourier transform infrared spectroscopy and hydrogen evolution study. The infrared absorption spectroscopy and hydrogen evolution study reveal two types of growth: the formation of a void rich material at low T_s (∼180 °C) and a compact material at comparatively higher T_s.     

Vapour-phase epitaxial growth of ZnS on GaP

Single crystal layers of ZnS about 100 μm thick were grown epitaxially on GaP substrates in an open tube system using source ZnS powder and a flowing hydrogen atmosphere. The growth rate for different substrate temperatures increases with increasing hydrogen flow rate, but the growth rate profiles resemble each other in shape. The profile shifts towards the low temperature side as the source temperature is decreased. The (111)B substrate orientation is found to be preferable to the (111)A or the (100) with respect to surface morphology and crystal quality. X-ray diffraction investigations and luminescent properties show that the (111)B grown layers are of high quality. All ZnS layers grown on GaP substrates are craked on cooling, which may be due to the thermal expansion mismatch between the layer and the substrate. Heat-treatment of the grown layer does not reduce the resistivity, but increases the photoluminescence intensity markedly. Selective vapour-phase epitaxial growth has been successfully applied resulting in crack-free ZnS layers on GaP substrates.     

Vapour phase growth of epitaxial silicon carbide layers

After a brief overview of different epitaxial layer growth techniques, the homoepitaxial chemical vapour deposition (CVD) of SiC with a focus on hot-wall CVD is reviewed. Step-controlled epitaxy and site competition epitaxy have been utilized to grow polytype stable layers more than 50 μm in thickness and of high purity and crystalline perfection for power devices. The influence of growth parameters including gas flow, C/Si ratio, growth temperature and pressure on growth rate and layer uniformity in thickness and doping are discussed. Background doping levels as low as 10¹⁴ cm⁻³ have been achieved as well as layers doped over a wide n-type (nitrogen) and p-type (aluminium) range.

Furthermore the status of numerical process simulation is mentioned and SiC substrate preparation is described. In order to get flat and damage free epi-ready surfaces, they are prepared by different methods and characterised by atomic force microscopy and by scanning electron microscope using channelling patterns. For the investigation of defects in SiC high purity CVD layers are grown. The improvement of the quality of bulk crystal substrates by micropipe healing and so-called dislocation stop layers can further decrease the defect density and thus increase the yield and performance of devices. Due to its high growth rate functionality and scope for the use of multi-wafer equipment hot-wall CVD has become a well-established method in SiC-technology and has therefore great industrial potential.     

Effect of the Temperature Fluctuation of the Melt on β‐BaB2O4 (BBO) Crystal Growth

In this paper the effect of the growth temperature fluctuation, for instance, the transient furnace temperature variation due to a short‐term electric power supply interruption on BBO crystal growth was investigated based on the theory of temperature wave transmitting in melt and the boundary layer theory of melt. It was found that the critical width of the temperature pulse to avoid the temperature wave penetrating through the boundary layer and reaching to the growth interface at a constant rotation speed (9∼4 r/min) is 69∼150 s and the corresponding amplitude of the temperature pulse is high more than 60 °C due to the large thickness of the velocity boundary layer of the melt. This result indicates that a small transient temperature fluctuation has no significant effect on the crystal quality, and therefore implies that not only transport processes but interface growth kinetics, a two‐dimensional nucleation growth mode at the interface may also dominate the crystal growth.     

Optimisation of low-temperature silicon epitaxy on seeded glass substrates by ion-assisted deposition

Using single crystalline Si wafer substrates, ion-assisted deposition (IAD) has recently been shown [J. Crystal Growth 268 (2004) 41] to be capable of high-quality high-rate epitaxial Si growth in a non-ultra-high vacuum (non-UHV) environment at low temperatures of about 600 °C. In the present work the non-UHV IAD method is applied to planar borosilicate glass substrates featuring a polycrystalline silicon seed layer and carefully optimised. Using thin-film solar cells as test vehicle, the best trade-off between various contamination-related processes (seed layer surface as well as bulk contamination) is determined. In the optimised IAD process, the temperature of the glass substrate remains below 600 °C. The as-grown Si material is found to respond well to post-growth treatments (rapid thermal annealing, hydrogenation), enabling respectable open-circuit voltages of up to 420 mV under 1-Sun illumination. This proves that the non-UHV IAD method is capable of achieving device-grade polycrystalline silicon material on seeded borosilicate glass substrates.