English  |  正體中文  |  简体中文  |  Items with full text/Total items : 72887/72887 (100%)
Visitors : 23142100      Online Users : 547
RC Version 7.0 © Powered By DSPACE, MIT. Enhanced by NTU Library IR team.
Scope Tips:
  • please add "double quotation mark" for query phrases to get precise results
  • please goto advance search for comprehansive author search
  • Adv. Search
    HomeLoginUploadHelpAboutAdminister Goto mobile version

    Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/65966

    Title: CZ法生長大尺寸藍寶石單晶之熱流場與溶質數值模擬研究;Numerical Simulation of the Flow, Temperature, and Solute Fields for Growing the Larger Sapphire Crystal in Czochralski System
    Authors: 陳旻聰;Chen,Ming-tsung
    Contributors: 機械工程學系
    Keywords: 柴式晶體生長;藍寶石單晶;氣泡;數值模擬;Czochralski;crystal growth;sapphire;bubble;numerical simulation
    Date: 2014-07-29
    Issue Date: 2014-10-15 17:19:24 (UTC+8)
    Publisher: 國立中央大學
    Abstract: 對晶體產業而言,柴式提拉法(Czochralski)是一項重要的關鍵技術。在近年工業的發展中,這項技術已經成為應用於生長大尺寸藍寶石晶體的方法之一。為了提升藍寶石單晶的生長品質,我們有必要深入了解長晶爐內部的整體熱傳與熔湯流動行為。然而這種生長較大尺寸晶體方法,受限於爐體內的高溫使我們無法直接去做實驗量測;除此之外,在長晶過程中容易產生化學雜質,使生長出的藍寶石單晶摻雜許多氣泡,進而影響晶體的光學性質與品質。在業界通常以調整長晶參數的方式進行製程優化,但是需花費許多人為控制時間,因此,我們必須用更有效的方式來獲得長晶參數與條件。本文運用有限元素法,且以準穩態的方式模擬藍寶石生長過程的熱場和流場的耦合行為、熔湯內部溶質流動的傳輸機制,進而去推論其與晶體內氣泡間的關係。
    本文模擬結果顯示,當系統內溶質濃度和晶體提拉速度愈大,界面產生溶質組成過冷的機會愈高,並且在中心軸附近的組成過冷程度較大,模擬得到的結果與實驗文獻結果相似。除此之外,長晶爐內部的溫度會影響生成雜質的多寡,故需要非常小心的控制,不宜太高。;The Czochralski method is one of important technologies for the crystal industry. For recently, it had been mainly applied for industrial larger size sapphire crystal growth. The thermal and flow transport play significant roles in CZ crystal growth, and it is hard to directly observed in experiments. Moreover, the grown sapphire single crystal is commonly accompanied by small bubbles which might affect the optical properties. Manual control for the amount and distribution of this kind chemical defects strongly depends on the trial experiences. Therefore, we must use a more efficient way to obtain growth parameters or conditions. This thesis is numerically investigated on both thermal-flow and solute transport phenomenon using the finite element method and quasi-steady approximation.
    The results presented in this study show the effect of different positions of support, heat shield devices, different upper furnace chambers, different support materials, and different crucible bottom shapes. Strong buoyant flow distorts the isotherms in the melt, and the strength decreases when the power supply decreases. The deflection height of the melt-crystal interface increases, as the melt level goes down. The power supply and temperature gradient inside solid crystal increase, when the support is lifted up. This is not good for crystal quality. Besides, the crystal convexity decreases, when the crucible bottom shape is round or the heat shield device made by carbon fiber is adopted. Furthermore, it is more likely grow more flat crystal and no solidified crystal touched at the crucible bottom, as the ZrO2 bubble insulator of support is used.
    Then, we used the solutions of thermal-flow field to discuss its influence on the solute field in CZ system. The results show that the maximum value solute concentration locates at the crucible sidewall and solute distribution strongly depends on the flow motion of molten melt. Besides, solutes are inclined to gather near the melt-crystal interface, and the local-maximum value located at the center sites. The gas bubbles are easily incorporated into solid crystal, as the melt-interface is not stable. The instability of crystallization front is proportional to the solute constitutional supercooling.
    The results show the chance of constitutional supercooling increases, when the solute concentration in molten melt increases or pulling rate of system is larger. In addition, the degree of constitutional supercooling is larger particularly near the center sites. These computational results are consistent with the experimental results done by foreign researchers. The temperature degrees in the furnace also should be controlled carefully and we concluded that the heat shield system is better than the others. Based on these results, the crystal quality of sapphire is expected to be improved.
    Appears in Collections:[機械工程研究所] 博碩士論文

    Files in This Item:

    File Description SizeFormat

    All items in NCUIR are protected by copyright, with all rights reserved.

    社群 sharing

    ::: Copyright National Central University. | 國立中央大學圖書館版權所有 | 收藏本站 | 設為首頁 | 最佳瀏覽畫面: 1024*768 | 建站日期:8-24-2009 :::
    DSpace Software Copyright © 2002-2004  MIT &  Hewlett-Packard  /   Enhanced by   NTU Library IR team Copyright ©   - Feedback  - 隱私權政策聲明