Tri-arc furnace for Czochralski growth with a cold crucible

Abstract

A crystal puller using the arc-melting technique has been developed for the Czochralski growth of single crystals. The circumference of the melt is heated by three arcs, and the crystal is pulled from the center of the melt with a water-cooled seed rod. The charge is contained in a hollow water-cooled copper hearth fitted with a piston so that the melt can be continuously fed. Use of this apparatus eliminates the difficulty of finding crucible materials suitable for high-temperature growth, since the melt is contained by a solid shell of the same substance in contact with the hearth. The furnace is economical, convenient to use, and requires a relatively small mass of material. Boules of Sn, Ge, Si, Cu 2O, V, VO, Ti 2O 3, Ni, Nb, NbO, and TiC, with melting points between 232 and 3150°C, have been grown. A number of good quality crystals of NbO with various stoichiometries were grown for measurement of the electrical properties. Mass spectrographic analysis of grown crystals usually shows no copper or tungsten above 10 ppm, the limit of detection. Silicon crystals grown on a graphite hearth have a resistivity of about 10 ohm-cm. This suggests that the concentration of electrically active impurities introduced from the arc or hearth does not exceed 0.1 ppm. The tri-arc modification also has advantages for other uses such as ordinary arc melting, freeze purification, arc casting, “splat cooling”, arc-Verneuil crystal growth and zone refining.