A physical model for electromagnetic control of local temperature gradients in a Czochralski system.

A. Cramer - M. Röder - J. Pal - G. Gerbeth

Forschungszentrum Dresden--Rossendorf, Institute of Safety Research, P.O. Box 510119, 01314 Dresden, Germany

Abstract
The shape of the solidification front and the related mono-crystalline growth in the Czochralski crystal growth process is thought of being strongly influenced by the ratio of the horizontal and the vertical temperature gradient r^∗ = ∆T_h / ∆T_v at the triple point liquid-solid-atmosphere, which ratio desirably should be in the order of unity. A liquid metal model experiment was therefore built that allowed studying r^∗ under the influence of magnetic fields. The cylindrical liquid metal column was homogeneously heated from below, whereas on top the heat was extracted in a centrical region covering only one third of the surface in order to simulate the growing crystal. Without flow control, r^∗ ≈ 3 is far removed from unity. It was then possible to reach the target value r^∗=1 for any temperature difference between the bottom and the top at a moderate field strength while applying a rotating magnetic field. Figs 9, Refs 6.