Numerical Investigation on the Effect of Thermal Gate Moving Rate on Directional Solidification Process

Abstract

The temperature field distribution during the growth of crystalline silicon by the directional solidification (DS) method is an important factor affecting the growth rate, the shape of the melt-crystal (m-c) interface, and thermal stress. To solve the problem of m-c interface convexity at the early stage of crystal growth caused by supercooling at the bottom center of silicon ingot during DS. In this paper, a two dimensional (2D) global transient numerical model based on a large-size ALD-G7 (G7) crystalline silicon ingot furnace is established and experimentally verified. Based on the model, the influence of different bottom thermal gate moving process curves on the convexity of the m-c interface at the early stage was studied, with emphasis on the changes in temperature field, m-c interface, and thermal stress at the early stage of crystal growth. We have designed three cases, case 1 uses the original moving process curve of bottom thermal gate, case 2 and case 3 adjust the process curve to 0.95 and 0.9 of the original ratio, respectively. The numerical simulation results show that compared with case 1, the average heat dissipation at the bottom of the silicon ingot in case 2 and case 3 is reduced by 2.7 kW·m−2 and 4 kW·m−2, and the maximum thermal stress is also reduced by 3 MPa and 4 MPa, separately. The maximum convexity of the interface is reduced by 25 mm and 20 mm, and the convexity is reduced by 55% and 44% on average, respectively.