物理氣相傳輸法生長8吋碳化矽單晶之熱場、流場與熱應力數值模擬分析;Numerical Simulation Analysis of Thermal Field、Flow Field and Thermal Stress of 8-inch Silicon Carbide Single Crystal Growth by Physical Vapor Transport Method

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Title:	物理氣相傳輸法生長8吋碳化矽單晶之熱場、流場與熱應力數值模擬分析;Numerical Simulation Analysis of Thermal Field、Flow Field and Thermal Stress of 8-inch Silicon Carbide Single Crystal Growth by Physical Vapor Transport Method
Authors:	艾信甫;Ai, Hsin-Fu
Contributors:	機械工程學系
Keywords:	物理氣相傳輸法;碳化矽;數值模擬;熱應力;physical vapor transport method;silicon carbide single crystal;numerical simulation;thermal stress
Date:	2024-07-11
Issue Date:	2024-10-09 17:19:33 (UTC+8)
Publisher:	國立中央大學
Abstract:	物理氣相傳輸法(Physical vapor transport, PVT)是目前生長碳化矽單晶的主流製程，製程時坩堝內須處於低壓狀態並利用高溫將碳化矽粉末昇華為反應氣體，反應氣體會因腔室內的溫度梯度和濃度差的關係傳輸至上方較低溫的晶種表面，當晶種表面濃度處於飽和時，便會凝固生成晶體，為了維持晶體生長環境，爐體採密閉狀態，難以透過實驗測量獲得數值資料。本研究優化前人開發之PVT法利用感應加熱生長6吋碳化矽單晶熱流場模型，將感應加熱系統變更為電阻加熱系統，使溫度分佈更為均勻，減少熱應力的產生，並依據業界的主流產品尺寸，將尺寸增至8吋，因此本研究針對8吋碳化矽單晶，改進前人開發之物理氣相傳輸法準穩態(Quasi-steady state)熱流場模型，並依據文獻在坩堝上絕緣層結構做變化，形成一形狀相異之絕緣層結構，減小徑向溫差的同時，亦提升晶體品質，進而分析晶體隨時間變化下對於坩堝內部熱流場和濃度的影響，探討其對晶體在不同時間下的長速、表面形貌與熱應力分佈，並分析不同孔隙率、不同輸入功率及改變絕緣層結構形狀下優化晶體品質及表面長速曲線的方法，藉此導入製程可降低晶體缺陷提高長速。模擬結果顯示晶體厚度增加時，晶體與粉末間距離會減少，造成腔體內軸向溫度梯度降低，造成長速下降。而PVT製程上的改善建議為(1)減少碳化矽粉末之間的孔隙率，可增加傳導至粉末中心之熱能，以增加晶體的長速。(2)調整加熱器輸入功率來改善晶種表面徑向溫度差，並且能發現製程溫度上升，晶體的長速也隨之提高。(3)改變坩堝上絕緣層結構形狀，減少晶種邊緣處的軸向溫度差，降低晶體邊緣處多晶的生長的可能，使整體長率差減少，並有利於提升晶種邊緣區域長率。;The Physical Vapor Transport (PVT) method is currently the mainstream process for growing silicon carbide single crystals. During the process, the crucible must be under low pressure and high temperature to sublimate the silicon carbide powder into reactive gases. These reactive gases are transported due to the temperature gradient and concentration difference within the chamber, moving to the cooler seed crystal surface above. When the concentration on the seed crystal surface reaches saturation, the gases solidify and form crystals. To maintain the crystal growth environment, the furnace is kept in a sealed state, making it difficult to obtain numerical data through experimental measurements. This study optimizes the PVT method developed by predecessors and uses induction heating to grow a 6-inch silicon carbide single crystal thermal flow field model. The induction heating system is changed to a resistance heating system to make the temperature distribution more uniform and reduce the generation of thermal stress. According to industry standards, the size of the mainstream product has increased to 8 inches. Therefore, this study focuses on the 8-inch silicon carbide single crystal, improving the physical vapor transport method quasi-steady-state thermal flow field model developed previously anthors. Based on the literatures, the structure of the insulating layer on the crucible is changed to form an insulating layer structure with a different shape, which not only reduces the radial temperature difference but also improves the quality of the crystal. Then, the impact of the change of the crystal over time on the heat flow field andconcentration inside the crucible is analyzed and discussed. The study analyzes the growth rate, surface morphology, and thermal stress distribution of crystals at different times and examines methods for optimizing crystal quality and surface growth rate curves under different porosity, different input power, and changes in the structure and shape of the insulating layer to introduce them into the manufacturing process. This can reduce crystal defects and increase the growth rate. The simulation results indicate that as the thickness of the crystal increases, the distance between the crystal and the powder decreases, resulting in a reduction of the axial temperature gradient within the cavity and causing a decrease in growth rate. Improvement suggestions for the PVT process are as follows: (1) reducing the porosity between silicon carbide powders can enhance the conduction of thermal energy to the center of the powder, thereby increasing the growth rate of the crystal; (2) adjusting the input power of the heater to improve the radial temperature difference on the crystal seed surface, which also leads to an increase in growth rate as the process temperature rises; (3) modifying the insulation layer structure on the crucible to reduce the axial temperature difference at the edge of the crystal seed, thus lowering the likelihood of polycrystalline growth at the crystal edges, reducing overall growth rate disparity, and facilitating the enhancement of growth rate in the edge region of the crystal seed.
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