鈮酸鋰單晶區熔提拉法-直徑與溫場改良之研究

Zone-Leveling Czochralski Growth of Lithium Niobate Crystals-Crystal Diameter Control and Hot-Zone Design

夏英庭(Ying-Ting Hsia)

指導教授 ： 戴怡德

國立臺灣大學/工學院/化學工程學研究所/碩士(2004年)

https://doi.org/10.6342/NTU.2004.10290

摘要

在工業上，鈮酸鋰單晶(Lithium niobate，簡稱LN)大多採用柴氏法(Czochralski method，簡稱CZ method)生長。但是柴氏法是一個批次程序，存在著因生長偏析所造成的軸向濃度分佈不均的問題。濃度不均的問題可以採用區熔提拉法(Zone-Leveling Czochralski method，簡稱ZLCZ method)，以連續進料的方式改善。然而，區熔提拉法在泥酸鋰晶體的生長上仍然存在著直徑控制及晶體劈裂問題。理論上，ZLCZ法是一個自穩的系統，在晶體的直徑控制上可以靠著熔湯液面上的溫度梯度來達成，不幸的是，由於熱環境的末端效應，均勻的直徑控制室很難達到的。在本論文中，吾人設計上秤重系統成功的運用在LN晶體等徑的生長上，生長直徑4公分長9公分的晶體其直徑變化在3%以下。另一方面，在生長直徑2公分長速3mm/h的晶體上，因為有20℃/cm的大溫度梯度存在，所以晶體仍有劈裂的情形發生。利用白金套桶及白金遮罩可以有效的解決溫度梯度過大的問題，使得熔湯液面以上9公分內有較小的溫度梯度，因此，可以容易的生長出完美的晶體

關鍵字

溫場設計 ； 晶體劈裂 ； 直徑控制 ； 鈮酸鋰 ； 區熔提拉法

並列摘要

In industry, lithium niobate (LN) single crystals are usually grown by the Czochralski (Cz) method. Because the Cz growth is a batch process, the distribution of dopant concentration in not uniform in the growth direction direction due to segregation. With a continuous solid feeding, this problem can be improved greatly by the zone-leveling Czochralski (ZLCz) method. Nevertheless, the ZLCz LN growth still has problems in diameter control and cracking of the crystal. In principle, the ZLCz method is a self-stabilized system, and the crystal diameter could be controlled by the temperature gradient above the melt level. Unfortunately, due to the end effect of the thermal environment, a constant diameter growth is hard to achieve. In this study, an upper weighting system was designed, and applied successfully to the diameter control of LN growth. The diameter variation of a 4-cm-diameter crystal over 9 cm in length was below 3%. On the other hand, the crystal cracking was found to be the cause of a large thermal gradient of over 20oC/cm for a 2-in-diameter crystal having the growth rate of 3mm/h. By using a heat pipe and a cover made of platinum, the region having smaller thermal gradients was extended to more than 9cm. As a result, a cracking-free single crystal could be easily grown.

並列關鍵字

diameter control ； Zone-Leveling Czochralski ； ZLCZ ； crystal cracking ； Lithium niobate

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