Axis symmetry of silicon molten zone interface shape under a mirror-shifting-type infrared convergent-heating floating-zone method. Issue 48 (23rd November 2015) - Hossain, Md. Mukter
Abstract : Axis symmetry of the silicon molten zone shape, which is dependent on the position of the mirror-lamp (M-L) system, is related to the shape of the grown crystal. Abstract : The shape of the silicon crystal, whether spiral or cylindrical, was grown using the infrared convergent-heating floating-zone method, and the stability of the molten zone depended on the position of the mirror-lamp (M-L) system with respect to the grown crystal and molten zone. Through experiment, we studied the changes in the molten zone shape: the melt/feed, melt/gas, and melt/crystal interface shapes of the silicon molten zone under different positions of the M-L system. Although conventional parameters such as convexities ( h / r ) of the interface toward the melt were found to be independent of the position of the M-L system, the asymmetry of the zone length, L, was found to be inversely proportional to the distance of the M-L system from the center of the molten zone. A spiral crystal would be grown in this case. We introduce some parameters such as growth interface angle ( δ ), triple point angle (TPA), meniscus angle (MA), and altitude of the interface curvature ( a C ) to characterize the axis symmetry of the melt/gas and melt/crystal interfaces. The variations in TPA, MA, and a C were significantly reduced when the M-L system was shifted to a distant position from the center of the molten zone. On the other hand, the variations in δ were independent of the position of the M-L system. Thus, a symmetric molten zone was observed when the M-L system was at a distant rather than a close position. These behaviors were validated through observations of the molten zone stability and the crystal shape.