微重力双向温度梯度下Cz液池内热毛细-Marangoni-旋转对流基本特性的研究

发布时间：2018-04-12 10:28

本文选题：微重力 + 双向温度梯度　；参考：《重庆大学》2016年硕士论文

【摘要】：Czochralski(Cz)法是最重要的人工晶体制备方法之一,广泛应用于硅单晶的生长。晶体生长过程中的熔体流动对晶体材料的质量有很大的影响。在Cz法晶体生长过程中驱动熔体流动的力主要为热毛细力、旋转离心力、Coriolis力以及浮力等,各力的相互耦合使得熔体流动十分复杂。在太空微重力环境下生长晶体时,浮力对流消失。此时由熔体的自由表面水平温度梯度和内部垂直温度梯度以及坩埚旋转所诱发的热毛细-Marangoni-旋转对流为熔体的主要流动形式,这对晶体的质量产生了极大的影响。目前关于这些流动已有的研究主要针对单向温差存在下的流动,对Cz液池中双向温差下的热毛细-Marangoni对流以及双向温差下坩埚旋转的热毛细-Marangoni-旋转对流研究较少,然而在工业上以及自然界中,双向温差往往同时存在。因此,本课题采用三维数值模拟的方法对微重力双向温差下Cz液池中的热毛细-Marangoni对流以及热毛细-Marangoni-旋转对流的流动特征进行了详细的研究。重点分析了不同驱动力耦合情况下各力对流动的驱动作用,研究了不同驱动力耦合下熔体对流的基本形态,得到了热毛细-Marangoni对流转变的临界条件,获取了流动失稳后各种流型之间的转变规律,讨论了流动不稳定的原因。所得结论丰富了热毛细-Marangoni对流以及旋转热对流理论,对微重力下的晶体生长以及工业上的晶体生长提供了理论指导。主要研究内容如下:首先,通过数值模拟研究了Cz液池内仅有双向温度梯度驱动的熔体基本流的特征,得到了水平温度梯度(Ma数)和垂直温度梯度(Q)在驱动熔体流动中各自发挥的作用:随着Ma数的升高和Q的降低,熔体内部流动由双胞流向三胞流转变。晶体侧逆时针流胞由双向温度梯度共同驱动,坩埚壁侧逆时针流胞和顺时针流胞分别由Ma数和Q驱动,其流动强弱相互抑制。熔体内部流胞的流动强弱决定了熔体的流动形式。随着水平温度梯度不断增大,流动转变为三维时相关振荡流动,增大Q会使得转变的临界水平温差(Mac数)急剧下降。然后,研究了三维振荡时的流动特征,得到了Ma数和Q对振荡流的影响:随着Ma数的增大,流动不稳定性增强。自由表面上的温度波动形式随着流动不稳定性的增强发生改变,开始由双层花瓣状振荡波转变为热流体波,随后转变为外层三维稳态、内层三维振荡的双层振荡结构,最后转变为振幅随时间变化的振荡波。这种转变规律主要是因为熔体流动由Q主导转变为由Ma数主导所致。当Ma数不变增大Q时,自由表面温度波动形态几乎不发生改变,流动不稳定性强。在流动失稳后,熔体开始周向旋转,其自由表面周向速度的波动幅度大于径向速度波动并随流动不稳定性的增加不断增大,而径向速度的大小远大于周向速度。因此提出了用自由表面周向速度波动来表征熔体的失稳程度,用自由表面径向速度波动来表征熔体的流动强度。最后通过数值模拟分析了热毛细-Marangoni-旋转对流中,Ma数和旋转雷诺数(Rec)对熔体流动的影响:流动为稳态时,增大Ma数后熔体流动和无旋转时的变化规律一致,但其改变的幅度较无旋转时小。增大Rec会减小自由表面熔体的径向外流并增大自由表面在坩埚壁附近的径向内流和熔体的周向流动。当流动失稳后,增大Ma数使得自由表面温度波动幅度出现先增大后减小后又增大的规律,因为Ma数驱动的熔体流动经历了最开始扰动基本流使之失稳,然后和各力驱动的流动平衡,最后主导熔体流动的过程。增大Rec则会使得自由表面温度波动出现先增大后减小后又增大最后又减小的复杂规律,这是因为Rec驱动的流动首先和Ma数驱动的流动经历了一样的过程,但在由Rec驱动的流动和各力驱动的流动相互平衡过渡到最后由Rec主导熔体流动的过程中,熔体内各流胞相互挤压导致流动不稳定性增强。随着Rec主导作用增强,自由表面温度波动幅度下降直至流动转变为稳态,说明Rec主导流动之后可以增强流动的稳定性。
[Abstract]:Czochralski (Cz) method is the most important one of the preparation methods of artificial crystal, widely used in silicon single crystal growth. Have a great impact on the quality of melt flow during crystal growth of crystal materials. The Cz method in the process of crystal growth driven melt flow force is mainly thermal capillary force, centrifugal force, Coriolis force and buoyancy, the coupling force makes the melt flow is very complicated. Crystal growth in space microgravity environment, the buoyancy convection disappeared. The melt free surface of the horizontal temperature gradient and the vertical temperature gradient and internal crucible rotation induced by thermocapillary convection is the main form of -Marangoni- rotary flow produced melt. A great impact on the quality of the crystal. The current research on the existing flow mainly for the presence of the temperature difference between one-way flow of two-way temperature difference Cz liquid pool under thermal capillary -Ma Rangoni convection and two-way temperature of crucible rotation thermocapillary convection rotation of -Marangoni- less, but in industry and nature, the two-way temperature difference often exist. Therefore, this thesis adopts the method of numerical simulation of thermocapillary convection -Marangoni Cz liquid pool temperature in microgravity and bidirectional flow characteristics of thermocapillary convection in rotating -Marangoni- are studied in detail. The key point is the analysis of different driving force under the condition of coupling the force driving effect on the flow of different driving, the basic form of melt convection force coupling under the transition conditions, thermocapillary convection -Marangoni, obtained the change rule between the flow instability after various flow patterns, flow instability the conclusion is discussed. The thermocapillary convection and rich -Marangoni rotating heat convection theory, the crystal growth in microgravity And the industrial crystal growth provides a theoretical guidance. The main contents are as follows: firstly, through the numerical simulation research on characteristics of Cz melt pool only two-way temperature gradient driven flow, the horizontal temperature gradient (Ma) and the vertical temperature gradient (Q) dynamic melt flow in each play a role in drive: with the decreasing number of Ma and Q increased, the melt flow by twin flow sanpower flow transition. The crystal side counter clockwise flow cell is driven by a two-way temperature gradient, the crucible wall side counter clockwise flow cell and clockwise flow cell respectively by the Ma number and the Q drive, the flow intensity inside the melt flow inhibit each other. Cell flow determines the strength of the melt flow form. With the increase of the horizontal temperature gradient, flow into three-dimensional oscillatory flow related, Q will increase the critical level temperature change (Mac number) dropped sharply. Then, on the three Flow feature dimension oscillation, the number of Ma and Q on the effect of oscillatory flow: with the increase of Ma number, enhance the flow instability. The form of temperature fluctuations on the free surface with the increase of flow instability change, starting from the double petal shaped oscillating wave into hot fluid wave, then changes to the outer 3D steady, double inner three-dimensional oscillation oscillation structure, finally transformed into amplitude oscillatory wave changes with time. This is mainly because the transition of melt flow led by Q into a Ma number of dominant. When the Ma number increases due to constant Q, free surface temperature fluctuation almost does not change, the flow instability in strong. The melt flow instability after the start of circumferential rotation, the free surface fluctuation of circumferential speed is greater than the radial velocity fluctuations and increasing with increase of flow instability, and the radial velocity is much bigger than the size of The circumferential velocity. Therefore proposed to characterize the melt to the free surface velocity fluctuation with week instability degree, intensity of flow with free surface radial velocity fluctuations to characterize the melt. Finally, through the analysis of numerical simulation of thermal convection in rotating capillary -Marangoni-, Ma number and Reynolds number (Rec) effect on the melt flow: a flow for the steady state, the melt flow Ma number is increased after consistent with and without rotation changes, but the amplitude of the change is small. The increase of Rec rotation will reduce the free surface of the melt and increase the radial outflow of free surface in the crucible wall near the radial inward flow and melt the circumferential flow when the flow instability. The Ma number increases, which make the surface temperature fluctuations increase first and then decrease and then increase the law, because the melt flow Ma number driven through the basic flow to start disturbance instability, and then the force driven flow Dynamic balance, finally leading the process of melt flow. The increase of Rec will make the surface temperature fluctuation law complex increases first and then decreases and increases and finally decreases, this is because the Rec flow driven by the first Ma number and the driven flow through a similar process, but the driver in the Rec driven by the flow and the the flow balance transition to finally led by Rec in the process of melt flow, melt in the flow cell extrusion resulted in enhanced flow instability. With the increase of Rec leading role, the free surface temperature fluctuation of flow into a steady decline until after Rec, the dominant flow can enhance the stability of the flow.

【学位授予单位】：重庆大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：O363.2;TK124

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