Method and apparatus for single crystal pulling downwardly from the lower surface of a floating melt

摘要

An elemental or compound melt is floated on a denser encapsulent. The melt has two horizontal free surfaces (i.e., surfaces not in contact with a solid). A shaft including a seed crystal extends upwardly through the encapsulent to contact the lower free surface of the melt and then is withdrawn downwardly through the encapsulent to grow the crystal. During solidification mechanical stresses are not imposed on the crystal. The melt is heated from above so that the lower melt surface is colder than the upper melt surface which provides a strong stabilizing temperature gradient within the melt. Unsteady natural convective flows in the melt are eliminated. Steady natural convection is substantially decreased compared to the Czochralski process (CZ) and Liquid Encapsulated Czochralski process (LEC). The stoichiometric ratio in the melt is maintained by controlling the pressure of the volatile element over the upper free surface of the melt.