Buoyancy-Driven Flows in Crystal-Growth Melts

Abstract

In most of methods for synthetic production of single crystals, crystal grows slowly from a fluid nutrient. Several different mechanisms can drive motions in this fluid, and these motions are of concern to crystal grower because they influence transport of dopant, impurities, and heat to growth interface. The seriousness of this concern is reflected by commissioning of at least seven review articles on subject during past decade (Carruthers 1975, 1979, Hurle 1977, Langlois 1981a, Pimputkar & Ostrach 1981, Kobayashi 1981, Jones 1984). The nutrient fluid may be a vapor or a supersaturated solution, but we focus here upon systems in which a crystal is grown from its melt. Actually, . we deal mostly with one specific method of growing crystals, viz. Czochralski process. There are several reasons for this. The first is its importance. Four of references cited in this review are from a single issue of PhysicoChemical Hydrodynamics, which was devoted to role of convection and fluid flow in solidification and crystal growth. In introductory article of that issue (HurIe & Jakeman 1981), Czochralski process was described as the most important and widely used technique. Indeed, Czochralski growth is ideally suited for producing large quantities of pure crystal required by present technology. For example, single crystals of elemental silicon tens of kilograms in mass, and with diameters exceeding 100 mm, are now routinely produced. The second reason for dwelling on Czochralski growth follows from first: Because of its importance, it has attracted far more attention from hydrodynamicists than have other melt growth systems. Finally, flow in Czochralski melts is possessed of a rich structure with regard to both driving mechanisms and streaming patterns. The results obtained for this system provide at least a qualitative understanding of other systems as well.