Optimization of heat transfer during the directional solidification process of 1600 kg silicon feedstock

• Published in: Journal of crystal growth Vol. 484; pp. 70 - 77
• Main Authors: Hu, Chieh, Chen, Jyh Chen, Nguyen, Thi Hoai Thu, Hou, Zhi Zhong, Chen, Chun Hung, Huang, Yen Hao, Yang, Michael
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.02.2018; Elsevier BV
• Subjects: A1. Computer simulation; A1. Directional solidification; B2. Semiconducting silicon; B3. Solar cells; Convexity; Crystals; Directional solidification; Dislocation density; Heat transfer; Ingots; Insulation; Photovoltaic cells; Reduction; Silicon; Solidification; Thermal stress; A1. Computer simulation; A1. Directional solidification; B3. Solar cells; B2. Semiconducting silicon
• ISSN: 0022-0248; 1873-5002
• DOI: 10.1016/j.jcrysgro.2017.12.042

•A directional solidification furnace is used to grow an 1600 kg multi-crystalline silicon ingot.•Power ratio and gap between the side and bottom insulation are modified.•The c-m interface remains slightly convex to the melt throughout the whole process.•Thermal stress and dislocation density in the ingot are significantly reduced for modified case. In this study, the power ratio between the top and side heaters and the moving velocity of the side insulation are designed to control the shape of the crystal-melt interface during the growth process of a 1600 kg multi-crystalline silicon ingot. The power ratio and insulation gap are adjusted to ensure solidification of the melt. To ensure that the crystal-melt interface is slightly convex in relation to the melt during the entire solidification process, the power ratio should be augmented gradually in the initial stages while being held to a constant value in the middle stages. Initially the gap between the side and the bottom insulation is kept small to reduce thermal stress inside the seed crystals. However, the growth rate will be slow in the early stages of the solidification process. Therefore, the movement of the side insulation is fast in the initial stages but slower in the middle stages. In the later stages, the side insulation gap is fixed. With these modifications, the convexity of the crystal-melt interface in relation to the melt can be maintained during the growth process with an approximately 41% reduction in the thermal stress inside the growing ingot and an 80% reduction in dislocation density along the center line of the ingot compared with the original case.