| Abstract: | 物理氣相傳輸法(Physical vapor transport, PVT)為對長晶爐內的坩堝進行加熱，使熱傳導至坩堝內的碳化矽粉末，並在高溫低壓的情況下分解成不同的反應氣體(Si, SiC, Si2C, SiC2等)，因溫度梯度與濃度差的關係，反應氣體由較高溫的碳化矽粉末傳輸至上方較低溫的晶種表面，當到達飽和濃度時晶種表面開始凝固結晶，並生成碳化矽單晶之生長過程。
本研究針對生長6吋單晶碳化矽，開發一物理氣相傳輸法準穩態(Quasi-steady state)熱流場的數值方法，使用其數值方法分析長晶過程中熱流場隨著晶體厚度增加而產生的變化，進一步探討其對晶體長率與表面形狀的影響，並考量不同線圈數量、改變上觀測孔的形狀以及改變絕緣層結構，對晶體表面的長晶速率曲線進行優化，來避免長晶速率過快造成晶體內部的錯位(Stacking fault)發生，以及當徑向溫度梯度太大時，晶體內部熱應力破壞或缺陷形成。
模擬結果表示當晶體厚度增加時，晶體與粉末間的距離會縮小，影響軸向溫度梯度，因此當軸向溫度梯度越小，晶體表面的長率隨之下降。而本研究在PVT製程上的改善建議為(1)增加線圈個數，使生長室內溫度分佈更均勻;(2)改善上觀測孔形狀，使得長率趨於平穩，並探討不同上觀測孔溫度對長率的影響，可以發現當上觀測孔溫度增加時，長率也隨之上升;(3)在絕緣層頂部加入一個方形缺口，隨著距離增加，熱源從缺口散失的量增加，使得傳導到生長室內的溫度降低，使得熱應力值也會隨之降低。;The physical vapor transport method (PVT) is to heat the crucible in the crystal growth furnace, so that the heat is transferred to the silicon carbide powder in the crucible, and decomposed into different reaction gases (SiC, Si2C, SiC2, etc.) under high temperature and low pressure.However, the relationship between the temperature gradient and the concentration difference, the reaction gas is transported from the higher temperature silicon carbide powder to the upper lower temperature seed crystal surface. When the saturation concentration is reached, the seed crystal surface begins to solidify and crystallize, and the growth process of silicon carbide single crystal is formed.
In this study, a numerical method for the quasi-steady-state heat flow field of the physical vapor transport method was developed for the growth of 6-inch single-crystal silicon carbide. Its numerical method is used to analyze the change of thermal flow field with the increase of crystal thickness during the crystal growth process. Further explore its influence on the crystal length and surface shape, and consider different number of coils, changing the shape of the upper observation hole and changing the structure of the insulating layer. Optimize the crystal growth rate curve on the crystal surface to avoid Stacking fault inside the crystal when the crystal growth rate is too fast, and thermal stress damage inside the crystal when the radial temperature gradient is too large.
The simulation results show that when the crystal thickness increases, the distance between the crystal and the powder will shrink, which will affect the axial temperature gradient. Therefore, when the axial temperature gradient is smaller, the elongation rate of the crystal surface will decrease. The improvement suggestions of this study on the PVT process are as follows: (1) Increasing the number of coils to make the temperature distribution in the growth chamber more uniform. (2) Improve the shape of the upper observation hole so that the elongation rate tends to be stable, and discuss the influence of different upper observation hole temperatures on the elongation rate. It can be found that when the upper observation hole temperature increases, the elongation rate also increases. (3) A square gap is added to the top of the insulating layer. As the distance increases, the amount of heat lost from the gap increases, so that the temperature transferred to the growth chamber decreases, and the stress value also decreases. |
