泡生法生长大尺寸蓝宝石单晶的等径控制方法

在泡生法生长大尺寸蓝宝石单晶的过程中,为了获得高质量的晶体,精确等径控制至关重要.本文根据晶体的重量变化率来控制热场,实现晶体等径生长.设计了应用在线整定多项式权值的广义最小方差(OAPW_GMV)控制方法,并建立了系统模型.该方法的主要思想是根据在线估计的被控对象参数及OAPW_GMV的输出,调整多项式的权值,实现炉内的热场控制.仿真和实验结果表明该控制方法实现了蓝宝石单晶的精确等径控制,有效地提高了蓝宝石单晶的质量.     

计算机控制CVD金刚石生长系统的研究

在CVD金刚石生长系统的基础上设计开发了计算机控制系统,对金刚石生长过程中各物理信号进行监测与控制,实现了无人值守下金刚石的生长.详细介绍了计算机控制的结构和软件实现方法.最后介绍了在计算机控制之下金刚石厚膜,纳米金刚石薄膜以及复合膜的生长.结果表明该系统运行稳定、可靠,控制效果明显优于人工控制,具有非常广泛的应用价值.     

基于改进BP神经网络算法的激光晶体生长控制研究

针对激光晶体生长后期晶体生长炉温度上漂导致晶体不能维持等径生长的问题,采用一种基于自适应学习率优化算法改进BP神经网络与经典PID控制技术相结合的方法应用到晶体生长控制过程中,通过改进的BP神经网络的自学习以及调整加权系数,实现一种由BP神经网络整定的最佳PID控制.通过MATLAB/Simulink仿真对比表明,改进的BP神经网络PID控制算法较传统PID控制方法具有较好的控制性能和鲁棒性,能够有效克服晶体生长炉的温漂问题,更好地保持晶体等径生长,提高了控制精度.     

12英寸硅单晶生长过程中熔液面位置控制方法研究

集成电路用12英寸硅单晶生长过程中,为满足晶体生长界面附近温度梯度的要求,需要测量并控制晶体生长过程中硅熔体液面位置.传统的设定坩埚上升速度和激光测距的方法有时不能适应直拉硅单晶生长技术的发展.本文提出并实现了一种采用CCD图像捕捉和测量液面位置的方法,结合调节坩埚上升速度来控制液面高度,最终可以满足生长集成电路用12英寸硅单晶的需要.     

提拉法生长晶体的自等径控制

采用JPG技术有限公司所开发的自等径控制程序,利用上称重法实现了晶体生长的自等径控制(ADC).通过对生长曲线PID的具体分析及其他晶体生长相关参数的设置,以铌酸锂晶体为对象,成功实现了按预设程序进行的晶体生长自等径控制.     

KDP晶体(101)面生长动力学研究

晶体法向生长速度是晶体生长动力学研究的-个重要参数.用激光偏振干涉法实现了KDP晶体锥面生长速度的实时测量,发现KDP晶体锥面生长过程中存在与柱面类似的死区,对传统降温法生长大尺寸KDP晶体和点籽晶快速生长技术中过饱和度的控制有重要指导意义.用螺旋位错模型讨论了锥面生长的动力学规律.计算了锥面台阶自由能和动力学系数.     

MOCVD生长InxGa1-Xn薄膜的表征

本文利用MOCVD方法在(0001)取向的蓝宝石衬底上实现了不同生工艺条件下的InxGa-xN薄膜的制备,并通过XRD、SEM、AFM等测量分析方法系统研究了生长工艺参数对InxGa1-xN薄膜的组分和性质的影响.InxGa1-xN薄膜的制备包括蓝宝石衬底表面上GaN缓冲层的生长以及缓冲层上InxGa1-xN薄膜的沉积两个过程.通过对所制备InxGa1-xN薄膜的XRD、SEM、AFM分析发现,调节生长温度和TMGa的流量可以有效控制InxGa1-xN薄膜中In的组分,并且随着生长温度的升高,InxGa1-xN薄膜的表面缺陷减少.     

硅基上Si1-xGex合金的外延生长及性能研究

硅基上高质量的异质外延生长是实现高性能微电子器件的基础,本文通过低温分子束外延技术在Si衬底上实现了全组分的Si1-x Gex(0相似文献   

化学气相沉积(CVD)工艺对ZnS力学性能影响的研究

介绍了化学气相沉积法(CVD)制备ZnS过程中,CVD工艺对材料相关力学性能的影响和控制方法.通过X射线衍射分析、扫描电镜和金相显微镜等手段研究了不同工艺下制备的ZnS样品材料的内部结构和缺陷,提出了ZnS生长过程中晶粒尺寸和材料缺陷的控制方法.研究结果表明,设计合理的喷嘴结构,营造稳定的CVD生长环境,提高CVD ZnS毛坯一致性,抑制材料缺陷形成,有助于提升ZnS材料力学相关性能.     

具有大尺寸(001)晶面的有机DAST晶体生长与THz波产生

具有大尺寸(001)晶面的有机晶体DAST(4-(4-二甲基氨基苯乙烯基)甲基吡啶对甲苯磺酸盐)的生长对构建高强度宽带THz辐射源具有重要意义,但也极具挑战性.本论文采用斜板法结合缓慢冷却技术,研究了生长液浓度对晶体长宽比的影响.通过对生长条件的精确控制,生长出了具有大面积(001)晶面的DAST晶体.经检测,晶体具有良好的表面质量.晶体在无需表面抛光的条件下,实现了单周期太赫兹脉冲输出,光-太赫兹转换效率达到0.66;.     

Process design for the shape control of crystals grown by Kyropoulos or SAPMAC method

A mathematical model has been proposed to design the process for growing a shaped crystals by Kyropoulos method or SAPMAC method. Crystal shape evolution behaviours under various processes were analysed. The results show that the crystal would go through a transitory shoulder‐expanding stage after which the crystal diameter rapidly decreases under a constant pulling rate and a constant heater temperature. Reducing pulling rate and heater temperature could depress the decrease of crystal diameter after the shoulder‐expanding stage so that enhance the length of crystal. However, the crystal diameter is more sensitive to pulling rate than to heater temperature, and an equal‐diameter crystal can not be grown in non‐undercooled melt by soley reducing the heater temperature. That means that adjusting the pulling rate is the most effective and convenient approach for controlling crystal diameter evolution and simultaneously decreasing both the pulling rate and the heater temperature is the optimal process for growing an equal‐diameter crystal. Moreover, a numerical approach for quantifactional designing crystal shape and corresponding growth processes was proposed according to the model, an example of crystal shape design was given out. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Automated growing of large single crystals controlled by melt level sensor

The process of single crystal pulling is considered with simultaneous starting material make-up into the melt and heater temperature control in response to a signal generated by the electronic contact melt level sensor, viz.: (i) conditions ensuring the radial broadening steadiness; (ii) effect of melt level displacement, melt temperature changes, changes of solid/liquid interface shape, melt evaporation on the growing crystal diameter; (iii) conditions of crystal purification from impurities and uniform distribution of dopant.     

Unidirectional seeded single crystal growth from solution of benzophenone

A novel crystal growth method has been established for the growth of single crystal with selective orientation at room temperature. Using volatile solvent, the saturated solution containing the material to be crystallized was taken in an ampoule and allowed to crystallize by slow solvent evaporation assisted with a ring heater. The orientation of the growing crystal was imposed by means of a seed fixed at the bottom of the ampoule. By selecting a suitable ring heater voltage and by controlling the ring heater voltage, nucleation and the growth rate of the crystal were controlled more effectively. By employing this novel method, benzophenone single crystal ingots of diameters 10 and 20 mm and length more than 50 mm were successfully grown using xylene as solvent. The ease in scaling up of diameter from 10 to 20 mm shows the vital advantage of this technique. It was possible to achieve solute–crystal conversion efficiency of 100 percent. The grown benzophenone crystal was characterized by FTIR, TG and DTA, powder X-ray diffraction, X-ray rocking curve, optical transmission study and powder SHG measurement. The results show that the crystal quality is at least as good as the quality of the crystal grown by other known methods. Also, microbial growth was naturally avoided in this method, as the fresh solution is constantly made available for the growing crystal.     

大尺寸电阻加热式碳化硅晶体生长热场设计与优化

大尺寸低缺陷碳化硅(SiC)单晶体是功率器件和射频(RF)器件的重要基础材料,物理气相传输(physical vapor transport, PVT)法是目前生长大尺寸SiC单晶体的主要方法。获得大尺寸高品质晶体的核心是通过调节组分、温度、压力实现气相组分在晶体生长界面均匀定向结晶,同时尽可能减小晶体的热应力。本文对电阻加热式8英寸(1英寸=2.54 cm)碳化硅大尺寸晶体生长系统展开热场设计研究。首先建立描述碳化硅原料受热分解热质输运及其多孔结构演变、系统热输运的物理和数学模型,进而使用数值模拟方法研究加热器位置、加热器功率和辐射孔径对温度分布的影响及其规律,并优化热场结构。数值模拟结果显示,通过优化散热孔形状、保温棉的结构等设计参数,电阻加热式大尺寸晶体生长系统在晶锭厚度变化、多孔介质原料消耗的情况下均能达到较低的晶体横向温度梯度和较高的纵向温度梯度。     

基于贝叶斯参数优化的无模型自适应硅单晶直径控制

直拉硅单晶的生长过程涉及多场多相耦合与复杂的物理化学变化,其中工艺参数的波动是导致晶体直径不均匀的重要原因,如何实现工艺参数的控制以获得理想的、均匀的晶体直径具有重要的研究意义。本文分析现有控制方法存在不稳定以及控制效果不佳的问题后,提出基于贝叶斯参数优化的无模型自适应控制模型来控制硅单晶生长过程中的晶体直径。首先以坩埚上升速度与加热器的功率作为控制输入参数,晶体直径作为输出,搭建无模型自适应控制模型,并分析算法的稳定性。其次将控制模型进行仿真实验,发现硅单晶直径控制模型中不同的超参数设定会影响控制过程的迭代次数以及控制效果。最后,利用贝叶斯优化超参数的取值范围,并进行最终的仿真实验,结果表明,经贝叶斯参数优化后的控制模型计算快、迭代次数少,输出的晶体直径稳定,同时将生长工艺参数控制在实际生产要求范围内。因此,基于贝叶斯参数优化的无模型自适应控制实现了硅单晶直径均匀稳定的有效控制,具有结合工程背景的实际应用前景。     

Analysis of the Diametral Response of a Czochralski Crystal (III) Solution of the Equation Set. Transfer Functions

The paper is the third in a series which presents results on the small-signal diametral response of a Czochralski crystal grown in a resistively heated furnace to variations in heater temperature and pull rate. For typical growth conditions and a wide range of materials it has been shown that this response is obtained by solving a set of linear differential equations. Conditions for normal response, i.e. the diameter increasing on heater temperature and/or pull rate decrease, have been established and shown to hold for most practical cases. The transfer function obtained is consistent with previous results for an inductively heated growth apparatus.     

Influence of Gravitation on the Processes of Heat and Mass Transfer in Solution Crystal Growth by the Travelling Heater Method (THM) (I)

In axially symmetric and planar cases the formulation is given of a two-dimensional hydrodynamic thermodiffusive problem on the crystal PbTe growth from solution by the travelling heater method. The analysis of the one-dimensional thermo-diffusive problem solution is presented. The dependences were obtained of the growing and dissolving interface positions relative to the heater on the heater travel rate for different lengths of solvent zone.     

A modified heater system for RF-Czochralski equipments

The temperature gradients in a Czochralski-type crystal growth equipment with induction heating can be advantageously influenced by additionally heating the growing crystal and the crucible bottom during the pulling procedure. An experimental solution is presented for both afterheater and bottom heater coupled to the same induction coil as the crucible.     

Influence of Gravitation on the Processes of Heat and Mass Transfer in Solution Crystal Growth by the Travelling Heater Method (THM) (II)

The two-dimensional quasi-stationary thermodiffusive hydrodynamic problem of the crystal PbTe growth from solution by the travelling heater method has been solved. Computation is given for the temperature field distribution in crystal and solution. The picture of fluxes in solution was obtained under free convection for different lengths of solvent zone. It is shown that in the absence of absence of gravitation at the growing interface in solution there occurs a constitutional supercooling, whereas the free convection removes it, which leads to greater morphological stability of a growing crystal face.     

Investigations of the process of crystal growth from a liquid zone by Seebeck measurements

An arrangement for measuring the thermoelectric voltage (Seebeck signal) during the crystal growth from a liquid zone is described. Using the example of growing PbTe single crystals by THM it is shown that different equilibrium temperatures at both phase boundaries provide a differential Seekeck voltage depending on the crystal growth rate. Relaxation times which are needed to reach steady-state conditions with respect to the concentration difference between the growing and solving interface in the case of a start or sudden stop of the heater motion can be obtained.