單方向凝固多晶矽鑄錠之溫度場與製程參數關係之研究

Abstract

太陽能電池的需求隨著能源短缺越來越高，但要將太陽能電池普遍運用於大眾，必須提升太陽能電池的光電轉換效率。若要使多晶矽的製程更有效率，得到高品質與高效能的多晶矽太陽能電池，研究其真空感應熔煉爐之溫度場與製程參數之關係，將可推動產業科技創新，加速技術發展。 本研究主要目的是探討多晶矽鑄錠的單向凝固用真空感應熔煉爐內溫度場的分佈與製程參數的關係，共分為兩大部份。第一使用COMSOL有限元素分析軟體，模擬多晶矽真空感應爐熔煉製程，建立電磁場與熱傳現象耦合模型，模型和實際使用光學測溫槍所測到的溫度有2%的誤差，依此模型探討的坩堝配置情況對溫度場的影響。 第二部份為實驗驗證，以真空感應電爐熔煉矽鑄錠，除了對實際熔煉的溫度做量測對照模擬的溫度場外，並對熔煉過後之鑄錠的巨觀或微觀金相與成份做分析，間接定性證明模擬的溫度場分佈。並研究拉晶製程中的重要參數，得知本研究中最慢的拉晶速度(2mm/min)可以幫助多晶矽鑄錠的柱狀晶成長至較大的尺寸。

The photovoltaic industry has been generated electric power more than 150 MW. To know well about polycrystalline silicon growth method would lead us to pioneer. Hence, many scientists and corporations are interested in studying of polycrystalline silicon (poly-Si) ingot growth, crystal structure, orientation, growth rate, and grain size. For achieving a high efficiency of poly-Si solar cell, it is necessary to optimize the structural properties of poly-Si. Therefore, it is important to simulate the temperature distribution and reaction field of vacuum induction furnace for the industrial advancement. The main goal of this paper is to simulate the temperature distribution of the vacuum induction furnace during unidirectional solidification process. There are two main parts in this paper. First, we develop a COMSOL finite element model of polycrystalline silicon melting between a harmonic electromagnetic and transient thermal phenomena analysis, factors such as the setting of crucibles and the conditions of crucibles. Second part is the experiment verification of poly-silicon ingot. This paper compares the results of the calculated temperature distributions with the measured temperatures and analyzes the quality of the ingot, such as its macrostructure, microstructure, and composition. There is 2% difference between the modeling and measured temperatures. Finally, microstructures using three different pulling speeds were observed by optic microscope. The microstructure of the ingot using slowest pulling speed (2mm/min) has best result for solar cell.