Surface aspects of crystal growth from the melt

Abstract

A three-phase boundary between crystal, melt and an ambient phase must be present in all configurations used in the growth of crystals from the melt. Techniques for which the ambient phase is gaseous are briefly reviewed and the role of surface tension effects in determining the statistic and dynamic characteristics of the major growth techniques (Czochralski, floating-zone melting and ribbon growth techniques) are considered. The equilibrium conditions which apply at the three-phase boundary are shown to depend on whether or not the crystal is completely wetted by its own melt. Theoretical descriptions of the shape of the meniscus encountered in the above named growth techniques are reviewed. The dynamic stability of the shape of the growing crystal against perturbations in the parameters which determine the shape of the meniscus are examined. It is shown that, whilst the floating ??? process is inherently self-stabilising, the Czochralski technique requires careful control of the thermal geometry for it to be stable. Finally, the occurence and form of surface tension-driven convection (Marangoni flow) in floating-zone melting and in Czochralski growth is briefly reviewed.