發(fā)布時(shí)間：2018-04-12 10:28

  本文選題：微重力 + 雙向溫度梯度��； 參考：《重慶大學(xué)》2016年碩士論文

【摘要】：Czochralski(Cz)法是最重要的人工晶體制備方法之一,廣泛應(yīng)用于硅單晶的生長(zhǎng)。晶體生長(zhǎng)過(guò)程中的熔體流動(dòng)對(duì)晶體材料的質(zhì)量有很大的影響。在Cz法晶體生長(zhǎng)過(guò)程中驅(qū)動(dòng)熔體流動(dòng)的力主要為熱毛細(xì)力、旋轉(zhuǎn)離心力、Coriolis力以及浮力等,各力的相互耦合使得熔體流動(dòng)十分復(fù)雜。在太空微重力環(huán)境下生長(zhǎng)晶體時(shí),浮力對(duì)流消失。此時(shí)由熔體的自由表面水平溫度梯度和內(nèi)部垂直溫度梯度以及坩堝旋轉(zhuǎn)所誘發(fā)的熱毛細(xì)-Marangoni-旋轉(zhuǎn)對(duì)流為熔體的主要流動(dòng)形式,這對(duì)晶體的質(zhì)量產(chǎn)生了極大的影響。目前關(guān)于這些流動(dòng)已有的研究主要針對(duì)單向溫差存在下的流動(dòng),對(duì)Cz液池中雙向溫差下的熱毛細(xì)-Marangoni對(duì)流以及雙向溫差下坩堝旋轉(zhuǎn)的熱毛細(xì)-Marangoni-旋轉(zhuǎn)對(duì)流研究較少,然而在工業(yè)上以及自然界中,雙向溫差往往同時(shí)存在。因此,本課題采用三維數(shù)值模擬的方法對(duì)微重力雙向溫差下Cz液池中的熱毛細(xì)-Marangoni對(duì)流以及熱毛細(xì)-Marangoni-旋轉(zhuǎn)對(duì)流的流動(dòng)特征進(jìn)行了詳細(xì)的研究。重點(diǎn)分析了不同驅(qū)動(dòng)力耦合情況下各力對(duì)流動(dòng)的驅(qū)動(dòng)作用,研究了不同驅(qū)動(dòng)力耦合下熔體對(duì)流的基本形態(tài),得到了熱毛細(xì)-Marangoni對(duì)流轉(zhuǎn)變的臨界條件,獲取了流動(dòng)失穩(wěn)后各種流型之間的轉(zhuǎn)變規(guī)律,討論了流動(dòng)不穩(wěn)定的原因。所得結(jié)論豐富了熱毛細(xì)-Marangoni對(duì)流以及旋轉(zhuǎn)熱對(duì)流理論,對(duì)微重力下的晶體生長(zhǎng)以及工業(yè)上的晶體生長(zhǎng)提供了理論指導(dǎo)。主要研究?jī)?nèi)容如下:首先,通過(guò)數(shù)值模擬研究了Cz液池內(nèi)僅有雙向溫度梯度驅(qū)動(dòng)的熔體基本流的特征,得到了水平溫度梯度(Ma數(shù))和垂直溫度梯度(Q)在驅(qū)動(dòng)熔體流動(dòng)中各自發(fā)揮的作用:隨著Ma數(shù)的升高和Q的降低,熔體內(nèi)部流動(dòng)由雙胞流向三胞流轉(zhuǎn)變。晶體側(cè)逆時(shí)針流胞由雙向溫度梯度共同驅(qū)動(dòng),坩堝壁側(cè)逆時(shí)針流胞和順時(shí)針流胞分別由Ma數(shù)和Q驅(qū)動(dòng),其流動(dòng)強(qiáng)弱相互抑制。熔體內(nèi)部流胞的流動(dòng)強(qiáng)弱決定了熔體的流動(dòng)形式。隨著水平溫度梯度不斷增大,流動(dòng)轉(zhuǎn)變?yōu)槿S時(shí)相關(guān)振蕩流動(dòng),增大Q會(huì)使得轉(zhuǎn)變的臨界水平溫差(Mac數(shù))急劇下降。然后,研究了三維振蕩時(shí)的流動(dòng)特征,得到了Ma數(shù)和Q對(duì)振蕩流的影響:隨著Ma數(shù)的增大,流動(dòng)不穩(wěn)定性增強(qiáng)。自由表面上的溫度波動(dòng)形式隨著流動(dòng)不穩(wěn)定性的增強(qiáng)發(fā)生改變,開始由雙層花瓣?duì)钫袷幉ㄞD(zhuǎn)變?yōu)闊崃黧w波,隨后轉(zhuǎn)變?yōu)橥鈱尤S穩(wěn)態(tài)、內(nèi)層三維振蕩的雙層振蕩結(jié)構(gòu),最后轉(zhuǎn)變?yōu)檎穹S時(shí)間變化的振蕩波。這種轉(zhuǎn)變規(guī)律主要是因?yàn)槿垠w流動(dòng)由Q主導(dǎo)轉(zhuǎn)變?yōu)橛蒑a數(shù)主導(dǎo)所致。當(dāng)Ma數(shù)不變?cè)龃驫時(shí),自由表面溫度波動(dòng)形態(tài)幾乎不發(fā)生改變,流動(dòng)不穩(wěn)定性強(qiáng)。在流動(dòng)失穩(wěn)后,熔體開始周向旋轉(zhuǎn),其自由表面周向速度的波動(dòng)幅度大于徑向速度波動(dòng)并隨流動(dòng)不穩(wěn)定性的增加不斷增大,而徑向速度的大小遠(yuǎn)大于周向速度。因此提出了用自由表面周向速度波動(dòng)來(lái)表征熔體的失穩(wěn)程度,用自由表面徑向速度波動(dòng)來(lái)表征熔體的流動(dòng)強(qiáng)度。最后通過(guò)數(shù)值模擬分析了熱毛細(xì)-Marangoni-旋轉(zhuǎn)對(duì)流中,Ma數(shù)和旋轉(zhuǎn)雷諾數(shù)(Rec)對(duì)熔體流動(dòng)的影響:流動(dòng)為穩(wěn)態(tài)時(shí),增大Ma數(shù)后熔體流動(dòng)和無(wú)旋轉(zhuǎn)時(shí)的變化規(guī)律一致,但其改變的幅度較無(wú)旋轉(zhuǎn)時(shí)小。增大Rec會(huì)減小自由表面熔體的徑向外流并增大自由表面在坩堝壁附近的徑向內(nèi)流和熔體的周向流動(dòng)。當(dāng)流動(dòng)失穩(wěn)后,增大Ma數(shù)使得自由表面溫度波動(dòng)幅度出現(xiàn)先增大后減小后又增大的規(guī)律,因?yàn)镸a數(shù)驅(qū)動(dòng)的熔體流動(dòng)經(jīng)歷了最開始擾動(dòng)基本流使之失穩(wěn),然后和各力驅(qū)動(dòng)的流動(dòng)平衡,最后主導(dǎo)熔體流動(dòng)的過(guò)程。增大Rec則會(huì)使得自由表面溫度波動(dòng)出現(xiàn)先增大后減小后又增大最后又減小的復(fù)雜規(guī)律,這是因?yàn)镽ec驅(qū)動(dòng)的流動(dòng)首先和Ma數(shù)驅(qū)動(dòng)的流動(dòng)經(jīng)歷了一樣的過(guò)程,但在由Rec驅(qū)動(dòng)的流動(dòng)和各力驅(qū)動(dòng)的流動(dòng)相互平衡過(guò)渡到最后由Rec主導(dǎo)熔體流動(dòng)的過(guò)程中,熔體內(nèi)各流胞相互擠壓導(dǎo)致流動(dòng)不穩(wěn)定性增強(qiáng)。隨著Rec主導(dǎo)作用增強(qiáng),自由表面溫度波動(dòng)幅度下降直至流動(dòng)轉(zhuǎn)變?yōu)榉�(wěn)態(tài),說(shuō)明Rec主導(dǎo)流動(dòng)之后可以增強(qiáng)流動(dòng)的穩(wěn)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.

【學(xué)位授予單位】：重慶大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2016
【分類號(hào)】：O363.2;TK124

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