外加水平式磁場柴氏法生長單晶矽之熱流場及氧雜質傳輸數值分析; Numerical simulation of flow, thermal and oxygen distributions for a Czochralski silicon growth with in a transverse magnetic field

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Title:	外加水平式磁場柴氏法生長單晶矽之熱流場及氧雜質傳輸數值分析;Numerical simulation of flow, thermal and oxygen distributions for a Czochralski silicon growth with in a transverse magnetic field
Authors:	江姵儀;Chiang,Pei-yi
Contributors:	機械工程學系
Keywords:	三維數值模擬;水平式磁場;柴氏晶體生長;氧雜質;3D Numerical simulation;Transverse magnetic field;Czochralski crystal growth;Oxygen concentration
Date:	2014-01-24
Issue Date:	2014-04-02 15:51:15 (UTC+8)
Publisher:	國立中央大學
Abstract:	柴氏長晶法是目前最常用來生長矽晶體的方法，但其長晶過程中容易產生氧雜質，影響晶體品質，過去多以調整長晶參數的方式，進行製程優化，但目前該方法已無法解決，需尋求其它方法突破瓶頸。而外加水平式磁場方式可以有效降低傳統柴氏長晶法之晶體中氧雜質濃度，並提高晶體徑向氧雜質濃度分佈之均勻性，但在水平式磁場作用下，熔湯受羅倫茲力影響，呈現三維型態，將增加晶體生長及模擬的困難度。因此，本研究利用三維數值模擬方法，於柴氏晶體生長過程外加水平式磁場，探討水平磁場的影響並深入瞭解其作用機制，再藉此分析生長參數對熔湯流場、溫場與氧雜質分佈之影響，以生成低含氧量單晶矽。在長晶參數部分，低坩堝轉速不僅可以降低堝壁溫度，並會造成自由液面的徑向流速變慢，使過多的氧雜質可在自由液面蒸發為氧化矽，模擬結果顯示坩堝轉速若小於1rpm時可大幅的降低氧雜質濃度；而當降低晶體轉速時，雖然可以降低氧雜質的濃度，但是卻使得晶體徑向氧雜質分佈開始變得不均勻，破壞晶體品質。因此坩堝轉速為水平磁場下控制晶體氧含量多寡的一重要因素。在氬氣流量方面，流量增加時，雖然更容易將自由液面處的氧化矽雜質帶走，但卻使得熔湯中原本逼近靜止的流動受到擾動，進而加快氧雜質進入晶體，因此，晶體中氧雜質濃度隨著氬氣流量增加呈現上升的趨勢。另外，對於不同晶體大小而言，生長大尺寸晶體影響氧雜質蒸發量，使得更多氧雜質進入晶體，因此欲生長大尺寸晶體，勢必得面臨雜質過多的問題。除了生長參數影響外，不同的長晶階段氧雜質濃度亦會有所差異，本研究模擬結果顯示晶體頭部和尾部為氧雜質濃度最高的地方，晶體軸向氧雜質濃度呈現不均勻曲線，該現象與中美公司實驗結果趨勢一致。藉由模擬結果可知長晶過程中，坩堝內熔湯的深度、流動型態、堝壁溫度及氬氣流速的快慢，是導致不均勻軸向氧雜質分佈的原因。為了提高軸向均勻性，本研究調整加熱器位置和坩堝轉速，透過此方法，軸向不均勻性可以分別改善約6.6％及24.7％。; A three-dimensional numerical simulation has been performed to understand the motion of the melt flow, thermal field and oxygen distributions during the Czochralski silicon single crystal growth process under the influence of a transverse magnetic field. With the application of a transverse magnetic, the velocity, temperature and oxygen concentration fields in the melt become three-dimensional and asymmetric. There were two different flow patterns on the plane parallel and crossing transverse magnetic field, separately. Therefore, the presence of a transverse magnetic field decreases the oxygen concentration level along the melt-crystal interface. The uniformity of oxygen concentration at the melt-crystal interface is also improved when the magnetic field is applied. However, the two flow motion will cause the different temperature distributions form distorted in the whole melt. It is hard to simulation and crystal growth. In this study, the numerical simulation has been performed to clear the mechanism of oxygen transportation, such as the distribution of oxygen concentration in the melt is related to the crystal rotation rate and crucible rate. The lower temperature at the crucible wall and the free surface velocity decrease as the crucible rotation rate decrease. When the crucible rotation rate reaches below 1 rpm, the oxygen concentration value along the melt-crystal interface decrease enlarges. The uniformity of oxygen concentration is better for higher crystal diameters. The crystal rotation rate has negligible influence on the oxygen concentration. But the radial distribution of oxygen uniformity is improved at higher crystal rotation rates. In the case of transverse field, the crucible rotation rate is a key parameter in the control of oxygen concentration in the crystal. The quantity of the oxygen transportation and silica concentration on the free surface can be increased by increasing the gas flow rate. Because the argon gas velocity affect the radial velocity and interfere the free surface flow motion. However, the crystal oxygen concentration was increased with an increase in the flow velocity of argon gas in the TMCZ. This thesis analysis silicon crystal growth process under magnetic Czochralski method, this trend is in consistence with the experimental one. The variation of the axial oxygen concentration with the growth length of the silicon crystal is related to the melt depth of the crucible, the flow structure inside the melt, the crucible temperature, and the argon flow speed along the free surface. In order to improve the axial non-uniform of oxygen concentration, the heater position and crucible rates are adjusted. The axial non-uniform of oxygen concentration can be improved approximately 24.7% and 6.6% by revising the crucible rates and modifying the heater position.
Appears in Collections:	[Graduate Institute of Mechanical Engineering] Electronic Thesis & Dissertation

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