Apparatus and method for growing long single crystals in a liquid

Abstract

Apparatus and method are provided for growing improved quality long and large single crystals in a liquid encapsulated Czochralski (LEC) process, in which a separate cooling circuit is provided for the upper portion of a vessel which cools that portion independently of any cooling means for the lower portion of the vessel, and in which the gas flow pattern can desirably be controlled such that the gas flow is predominantly downward adjacent the vessel wall, and predominantly upward near the center of the vessel, where the crystal is being pulled from the melt. The apparatus is also provided with a thermal shielding device having an inner and an outer shield tube, connected in fixed positions to a flange member which extends radially from the inner shield tube to a point immediately adjacent the vessel side wall, with the inner shield being disposed to prevent direct radiative heat transfer from the wall of a crucible holding a melt of the material to be pulled into the crystal, to the crystal being pulled from the melt in the crucible. The outer shield tube, the flange member, a lower barrier, and the vessel wall define the boundaries of a convective cell which desirably regulates, to make uniform, the thermal environment to which the crucible is exposed when raised from the region in which it is surrounded by a heater.