NUMERICAL SIMULATION OF CHEMICAL VAPOR DEPOSITION PROCESSES UNDER VARIABLE AND CONSTANT PROPERTY APPROXIMATIONS

The chemical vapor deposition (CVD) process for silicon, using silane (SiH₄) with hydrogen (H₂) as the carrier gas, is modeled numerically using constant properties evaluated at various reference temperatures T _{r e f}. Results are compared with those from a numerical model based on variable transport properties. When the susceptor is isothermally heated, deposition rates predicted by the simplified model agree very well (5% error) with the variable property solution. A susceptor heated by means of a uniform heat flux input has a large temperature variation across the susceptor surface, yielding considerable error from the constant property model. However, a carefully chosen T _{r e f} for cases with large heat flux input, which gives rise to diffusion-controlled deposition (surface Damkohler number Da^s >> 1), is able to capture property variation effects and predict the deposition rate with reasonable accuracy. A variable property model is necessary at low heating rates, since reaction-controlled deposition (Da^s << 1) has a strong dependence arising from exponential temperature dependence of the chemical reactions and the properties. The study shows that the constant property model may be used to obtain solutions with satisfactory accuracy for a variety of operating conditions. The results and observations may be used as guidelines for future CVD reactor design and choice of appropriate operating conditions.     

三维还原炉内多晶硅化学气相沉积的数值模拟

建立描述SiHCl3—H2系统中混合气体的动量、热量和质量同时传递,且耦合气体反应、表面反应的模型,研究利用计算流体力学CFD(Computational Fluid Mechanics)软件Fluent6.2结合物质传递和反应模型,数值模拟三维还原炉内物质分布规律、热传递现象和多晶硅的沉积特性。计算结果表明,随气体流量、硅棒表面温度和操作压力的增加,硅沉积速率增长。理论研究结果对优化现有12对棒还原炉工艺参数和设计新型、大直径还原炉具有理论指导意义。     

等离子体引入热丝CVD对沉积过程的影响

将等离子体引入热丝化学气相沉积(HWCVD)过程,并采用该技术制备了多晶硅和微晶硅薄膜,通过Raman散射、红外吸收谱等手段研究了薄膜结构性质,讨论了等离子体引入热丝CVD对沉积过程的影响.结果表明,与单纯的HWCVD技术相比,等离子体的加入在一定条件下有助于薄膜晶化、增加薄膜致密度、提高薄膜均匀性并阻止硅化物在高温热丝表面的形成.     

CHARACTERISTICS OF THREE-DIMENSIONAL FLOW,HEAT, AND MASS TRANSFER IN A CHEMICAL VAPOR DEPOSITION REACTOR

The three-dimensional flow, heat, and mass transfer characteristics in a horizontal chemical vapor deposition (CVD) reactor with a tilted susceptor are analyzed numerically. As the physical domain for the CVD reactor has an irregular region, the Cartesian coordinates are transformed into a general curvilinear coordinate system. For calculating the governing equations, the finite volume method (FVM) is adopted and the SIMPLE algorithm is extended and modified to employ the curvilinear system. The effects of flow rate and tilted angle of the susceptor on the transport phenomena (i.e., heat transfer rate, uniformity and growth rate of reactant gas, etc.) at the susceptor are investigated. The results show that the existence of return flows leads locally to improvement of the heat transfer, but it is not good for the uniformity of the deposition. As the tilted angle of the susceptor is increased (from 0^o to 9^o), the amount of heat transfer and growth rate in the main flow direction are improved irrespective of the Reynolds number. The growth rate and uniformity are less sensitive to the inclined angle of the susceptor than that of the Reynolds number.     

以SiF4+H2为气源PECVD法低温制备多晶硅薄膜

采用常规的PECVD法在低温(≤400℃)条件下制得大颗粒(直径＞100nm)、高迁移率(～20cm2/vs),择优取向(220)明显的多晶硅薄膜.选用的反应气体为SiH4和H2混合气体.加入少量的SiH4后,沉积速率提高了将近10倍.通过本实验,我们认为在低温时促使多晶硅结构形成的反应基元应是SiFmHn(m+n≤3),而不可能是SiHn(n≤3)基团.     

TEMPERATURE DISTRIBUTION OF AN OPTICAL FIBER TRAVERSING THROUGH A CHEMICAL VAPOR DEPOSITION REACTOR

A fundamental understanding of how reactor parameters influence the fiber surface temperature is essential to manufacturing high-quality optical fiber coatings by chemical vapor deposition (CVD). In an attempt to understand this process better, a finite-volume model has been developed to study the gas flow and heat transfer of an optical fiber as it travels through a CVD reactor. This study showed that draw speed significantly affects fiber temperature inside the reactor, with temperature changes over 50% observed under the conditions studied. Other parameters affecting fiber temperature include fiber radius, fiber coating emissivity, and gas flow velocity at inlet. Multiple heat transfer modes contribute to these phenomena, with convection and radiation heat transfer dominating the process. The numerical model is validated against analytical cases.     

PECVD—MgO超导缓冲层的制备及其性质

超导技术是开发新能源的重要技术之一。超导缓冲层是超导薄膜的重要组成部分。以有机镁[Mg(thd)2]为起始物，采用等离子强化化学气相沉积(PECVD)工艺，在玻璃、石英、不锈钢和镍衬底上制备了超导缓冲层MgO薄膜，当衬底温度≥400℃时，MgO薄膜为单一(100)晶向，具有理想的表面织构．研究了实验参数，包括射频功率和自偏压对沉积速率和薄膜性能的影响。     

NUMERICAL MODELING OF INTERIOR BOUNDARIES

The numerical modeling of interior boundaries of finite and infinitesimal volume (area) is described for finite volume numerical methods. The treatment of passive structures such as solid obstacles and infinitesimally thin porous and nonporous walls, as well as hydro-dynamically active structures such as pumps and fans, are discussed. Properties peculiar to the pressure-velocity coupling are stressed, while more generally applicable techniques for other dependencies are shown. Heal transfer and turbulence effects complementary to the hydrodynamics are discussed. An example is presented showing application of the techniques to the flow of air about a very large directly air-cooled heat exchanger.     

MODELING OF RADIATIVE TRANSFER IN OPTICAL FIBER DRAWING PROCESSES WITH FRESNEL INTERFACES

ABSTRACT

This article presents a comparison of the discrete gradient, the discretized continuous gradient, and the intermediate gradients when dealing with inverse problems coupled with nonlinear parabolic direct problems. The article shows that the best strategy resides in differentiating the direct model after all are performed, but before the linearization procedure.     

MODELING OF INTERFACIAL TRANSPORT PROCESSES IN A DIRECT-CONTACT CONDENSER FOR METAL RECOVERY

A three-dimensional computational fluid dynamic model has been developed to investigate the efficiency of a direct-contact metal recovery condenser as a function of the operating conditions ( droplet diameters, droplet injection rate) and overall condenser dimensions. The Eulerian-Lagrangian approach is used to model the condenser, where liquid zinc droplets are injected into a zinc vapor laden gas stream so that zinc vapor can directly condense on the droplets. The results show that there exists an optimum droplet injection rate that maximizes condenser efficiency     

NUMERICAL MODELING OF INTERNAL RADIATION AND SOLIDIFICATION IN SEMITRANSPARENT MELTS IN MAGNETIC FIELDS

This article presents a numerical study on the effects of magnetic fields and internal radiation on the melt flow and solidification morphology during solidification processing of semitransparent oxide melts. The numerical solution of the integral differential equation characterizing the internal radiation and the magnetohydrodynamic equations describing the magnetic and transport phenomena is obtained by applying the combined discontinuous and continuous finite-element method. Deforming finite elements based on an arbitrary Eulerian-Lagrangian formulation are used to track the moving boundaries resulting from solidification. Computed results show that both internal radiation and external magnetic fields can have strong effects on the melt flow, temperature distribution, and solidification behavior during the melt processing of oxide materials.     

ION- AND PHOTON-ASSISTED p-TYPE DOPING OF CdTe DURING PHYSICAL VAPOR DEPOSITION

“Art jumps ahead – science plods ponderously on behind to consider, describe, and finally document what “;actually” happened in the chaos of the leap” (ALF)

This paper reviews our recent research on ion- and photon-assisted doping and growth of homoepitaxial CdTe thin films. Our earlier work demonstrated doping to 2 × 10¹⁷ cm^?3 with 60 eVP ions during growth by vacuum deposition, but gave low values of minority-carrier diffusion length L_d. To increase Ld, we (a) explored photon-assisted doping, (b) varied the Cd/Te ratio, and (c) used lower ion energies. Although illumination (≈512 nm, ≈100 mW-cm^?2) during growth enhanced crystalline quality, there was no evidence for any increase in doping over that of the non-illuminated films. Increasing the Cd/Te ratio (1.00 < Cd/Te < 2.2), both with and without ions and/or light during deposition, had strong effects on the In/p-CdTe junction transport, but gave little useful alteration of the doping behavior. Decreasing the P ion energy to 20 eV and adding an electron flux has thus far yielded substantially larger L_d with controlled doping up to 6 × 10¹⁶cm^?3.     

NUMERICAL MODELING OF HELICAL FLOW OF PSEUDOPLASTIC FLUIDS

The laminar helical flow of non-Newtonian pseudoplastic fluids in concentric and eccentric annuli with a rotating inner cylinder has been investigated numerically. A finite volume algorithm with a nonstaggered grid system is used to analyze the problem. A nonorthogonal curvilinear coordinate system is employed to handle the irregular geometry of aneccentric annulus. The power-law constitutive equation is used to model the shear rate dependent viscosity of a pseudoplastic fluid. The computer code is validated against an available analytical solution for helical flow in a concentric annulus. It is observed that for a certain axial pressure gradient the axial flow rate increases within creasing rotational speed of the inner cylinder. The torque needed to rotate the inner cylinder decreases with increasing axial pressure gradient. These are explained in terms of the shear-thinning effect of a pseudoplastic fluid. The discharge as well as torque are found to increase with increasing eccentricity. The flow field in an eccentric annulus is complex in nature since vigorous secondary flow is produced in addition to the primary axial helical flow. The location and extent of the secondary flow is studied and theresults are presented for various eccentricities. The results will be useful in planning oil and gas well drilling operations.     

低成本衬底上快热CVD法制备晶体硅薄膜电池

以RTCVD方法在低成本衬底--颗粒硅带(SSP)上制备了外延晶体硅薄膜电池.在20×20mm2上得到的最高转换效率为7.4%,开路电压488mV,短路电流21.91mA/cm2,填充因子0.697.外延晶体硅薄膜电池暗特性表明晶体硅薄膜电池具有较高的饱和暗电流I02和片并联阻Rp.外部量子效率(EQE)和内部量子效率(IQE)表明载流子收集率在长波方向比较低,量子效率最大值的波长范围大约在500nm.     

NUMERICAL MODELING OF A NUCLEATE BOILING SURFACE

ABSTRACT

A computer program developed to analyze nucleate boiling over a heated surface is described. The model solves the three-dimensional transient conduction equation within the heater. The conduction solution is coupled with closure relationships to mimic the bubble dynamics and the associated heat transfer coefficients. Sample problems are run using a copper surface subject to partial nucleate boiling in saturated water at atmospheric pressure. The results are shown to be in good qualitative agreement with the pertinent experimental observations.     

NUMERICAL PREDICTION OF LAMINAR FORCED CONVECTION IN TRIANGULAR DUCTS WITH UNSTRUCTURED TRIANGULAR GRID METHOD

The flow and heat transfer characteristics of smooth triangular ducts with different apex angles of 15, 30, 60, and 90 under the fully developed laminar flow condition were predicted numerically using a finite volume method. The SIMPLE-like algorithm was employed together with an unstructured triangular grid method, where the grid was generated by a Delaunay method. The triangular grid was adopted instead of the traditional rectangular grid to fit better into the triangular cross section of the duct. Two kinds of boundary condition (uniform wall temperature and uniform wall heat flux) were considered. Comparison of the predictions with previous computational results indicated a very good agreement. Both the friction factor and Nusselt number (Nu) showed a strong dependence on apex angle of the triangular duct. When the apex angle was 60, the duct provided the highest steady-state forced convection from its inner surface to the airflow under the laminar flow condition.     

NUMERICAL ALGORITHM USING MULTIZONE ADAPTIVE GRID GENERATION FOR MULTIPHASE TRANSPORT PROCESSES WITH MOVING AND FREE BOUNDARIES

Abstract

The primary objective of this study is to develop a numerical scheme far accurate and efficient simulation of phase-change and transport processes of industrial importance. These processes may include a variety of heat transfer and flaw mechanisms in irregularly shaped domains with moving and / or free boundaries. Based on the muttizone adaptive grid generation ( MAGG) technique ( IJ, a curvilinear finite-volume scheme has been developed to discretize the governing equations. The combination of these two techniques provides a powerful tool for numerical modeling of complex transport processes. Several problems are considered to demonstrate the applicability and accuracy of the proposed method. They are ( 1) natural convection in a differentially heated eccentric annuli, ( 2) solidification of a pure material in a rectangular enclosure, ( 3) solidification in an open cavity with shrinkage due to volume change, and ( 4) Czochralski crystal growth of silicon. The predictions show good agreement with experimental data, much better than the previously reported numerical solutions.     

化学水浴法制备CuxS薄膜

CuInS2薄膜是最有前途的多晶薄膜太阳电池材料.为了用化学水浴法制备CuIn岛薄膜,该文研究了化学水浴法制备CuxS薄膜,用SEM、XRD、EDX分别研究了薄膜的形貌、结构和组分,并且对薄膜的光学性质进行了讨论.     

HIGH-PRECISION NUMERICAL SIMULATION WITH AUTOADAPTATIVE GRID TECHNIQUE IN NONLINEAR THERMAL DIFFUSION

Many engineering problems concern the determination of a steady state solution in the case with strong thermal gradients, and results obtained using the finite-element technique are sometimes inaccurate, particularly for nonlinear problems with unadapted meshes. Building on previous results in linear problems, we propose an autoadaptative technique for nonlinear cases that uses quasi-Newtonian iterations to reevaluate an interpolation error estimation. We perfected an automatic refinement technique to solve the nonlinear thermal problem of temperature calculus in a cast-iron cylinder head of a diesel engine.     

NUMERICAL MODELING OF ELECTROHYDRODYNAMIC (EHD) EFFECT ON NATURAL CONVECTION IN AN ENCLOSURE

Mathematical and numerical modeling of electrohydrodynamic (EHD) enhancement of natural convection in enclosures is carried out. An electric current in dielectric liquid is modeled as a directed motion of electrically charged particles injected into a neutral fluid; the electric body force and Joule heat are added to the momentum and energy equations, respectively. Based on this, numerical studies are carried out for EHD effects on natural convection in enclosures. It is found that, at the same electric field intensity, the EHD enhancement of heat transfer is different for different electric density injections; applying a nonuniform electric field offers better EHD enhancement of heat transfer than applying a uniform electric field.