發(fā)布時(shí)間：2018-09-08 08:55

【摘要】：單晶硅廣泛用于光伏發(fā)電系統(tǒng)和微電子領(lǐng)域,隨著行業(yè)的快速發(fā)展,單晶硅朝著大直徑、高品質(zhì)、低成本的方向發(fā)展。對(duì)于生產(chǎn)大直徑單晶硅,坩堝的直徑和投料量勢(shì)必加大,熔體內(nèi)對(duì)流變得更加劇烈復(fù)雜而難以控制,而磁場(chǎng)拉晶技術(shù)對(duì)控制劇烈復(fù)雜的對(duì)流更具有優(yōu)勢(shì)。為此本文首先研究了勾型磁場(chǎng)的結(jié)構(gòu),確定最佳磁場(chǎng)結(jié)構(gòu)。在最佳磁場(chǎng)的基礎(chǔ)上,繼續(xù)研究晶轉(zhuǎn)、堝轉(zhuǎn)、拉速等工藝參數(shù)對(duì)晶體品質(zhì)的影響。另外對(duì)于提高晶體的品質(zhì),晶體內(nèi)氧含量是重要參量之一,而氧雜質(zhì)主要來(lái)源于坩堝壁的受熱分解,隨后被輸運(yùn)至固液界面處再分凝至晶體內(nèi),而邊界層是氧分凝的重要場(chǎng)所。為此本文進(jìn)一步求解出邊界層厚度的解析解,以邊界層厚度在固液界面的分布形勢(shì)研究氧的摻入機(jī)理,同時(shí)這也是本論文的創(chuàng)新點(diǎn)。本文模擬實(shí)驗(yàn)所得結(jié)果如下:(1)隨著上下線圈間距(H)增大,晶體下方強(qiáng)迫對(duì)流強(qiáng)度增加,固液界面的中心撓度逐漸變大。當(dāng)H較大時(shí)氧邊界層厚度在固液界面分布較為均勻,利于氧在固液界面的均勻分布。隨著磁場(chǎng)比(MR)的減小,洛倫茲力對(duì)熔體抑制作用變強(qiáng),熔體內(nèi)對(duì)流強(qiáng)度逐漸減小;當(dāng)磁場(chǎng)比在1附近時(shí),氧邊界層厚度在固液界面分布較為均勻。(2)隨著晶轉(zhuǎn)數(shù)的增大,熔體內(nèi)對(duì)流強(qiáng)度逐漸增大,固液界面中心撓度逐漸增大;當(dāng)晶轉(zhuǎn)數(shù)為6rpm、8rpm、12rpm時(shí),氧邊界層厚度在固液界面分布較為均勻。隨著堝轉(zhuǎn)值增大,坩堝壁溫度逐漸升高;固液界面中心處撓度值逐漸降低,氧邊界層厚度與堝轉(zhuǎn)數(shù)成正比例關(guān)系。(3)隨著拉速值增大,坩堝壁的溫度逐漸降低,固液界面形狀由凸型轉(zhuǎn)變成凹型。氧邊界層厚度與拉速值成反比例關(guān)系,當(dāng)拉速為65mm/h時(shí)氧邊界層在固液界面較為平緩。
[Abstract]:Monocrystalline silicon is widely used in photovoltaic power generation systems and microelectronics. With the rapid development of the industry, monocrystalline silicon is developing towards the direction of large diameter, high quality and low cost. For the production of large diameter monocrystalline silicon, the diameter and feeding amount of crucible will increase, and the convection in melt becomes more complex and difficult to control. In this paper, the structure of the hook magnetic field is studied, and the optimum magnetic field structure is determined. On the basis of the optimum magnetic field, the effects of the process parameters such as crystal transformation, pot rotation and drawing speed on the crystal quality are studied. In addition, the oxygen content in the crystal is one of the important parameters to improve the quality of the crystal. The oxygen impurity is mainly derived from the decomposition of the crucible wall, and then transported to the solid-liquid interface and then condensed into the crystal, and the boundary layer is the important place for the oxygen segregation. In this paper, the analytical solution of the boundary layer thickness is obtained, and the mechanism of oxygen doping is studied by the distribution of the boundary layer thickness at the solid-liquid interface, which is also the innovation of this paper. The results of the simulation experiments are as follows: (1) with the increase of the (H) distance between the upper and lower coils, the forced convection intensity under the crystal increases, and the central deflection of the solid-liquid interface gradually increases. When H is larger, the thickness of the oxygen boundary layer is more uniform at the solid-liquid interface, which is favorable to the uniform distribution of oxygen at the solid-liquid interface. With the decrease of magnetic field ratio (MR), the effect of Lorentz force on the melt becomes stronger and the convection intensity decreases gradually, and when the magnetic field ratio is near 1, the thickness of the oxygen boundary layer distributes more evenly at the solid-liquid interface. (2) with the increase of crystal number, The convection intensity in the melt increases gradually, and the central deflection of the solid-liquid interface increases gradually, and the thickness of the oxygen boundary layer distributes uniformly at the solid-liquid interface when the crystal number is 6rpmM ~ 8rpm ~ (-1) at 12rpm. With the increase of the value of crucible rotation, the temperature of crucible wall increases gradually, the deflection value at the center of solid-liquid interface decreases gradually, and the thickness of oxygen boundary layer is proportional to the number of crucible rotation. (3) with the increase of drawing speed, the temperature of crucible wall decreases gradually. The shape of solid-liquid interface changed from convex to concave. The thickness of oxygen boundary layer is inversely proportional to the drawing velocity. When the drawing speed is 65mm/h, the oxygen boundary layer is relatively flat at the solid-liquid interface.
【學(xué)位授予單位】：寧夏大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類(lèi)號(hào)】：TN304.12

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