Shaped crystal growth refers to the growth of single crystals with a predetermined cross sectional configuration designed for a specific application. The quest to develop such techniques has been driven by the need to minimize costs associated with device fabrication such as cutting or polishing, the loss of expensive materials during these fabrication processes, and the damage created by machining processes.Perhaps the first intentionally shaped crystals were the metal filaments grown by Von Gomperz [1] in Germany in 1922 through a hole in a mica plate positioned on the melt surface. In 1938, Stepanov [2] in the USSR, began studies on the growth of shaped crystals using mechanical means to control the forces of surface tension. In his approach, the melt column was crystallized outside of the container by inserting wettable or nonwettable dies of different shapes into the melt.In the United States, work on growing sapphire filaments and single crystal superalloy jet engine turbine blades began in the late 1960's [3,4]. The former led several years later to the development of the EdgeDefined Film Growth Process (EFG) [5] for the production of sapphire tubes, filaments, ribbons and other shapes for special purposes. The EFG process (which is similar to the Stepanov method) and the unidirectional casting method for single crystal turbine blades were the first shaped crystal growth methods to find practical commercial applications.Aside from these two applications, shaped crystal growth technology would probably have remained a laboratory curiosity were it not for the energy crisis in the mid-seventies and the emergence of an urgent need to produce high quality silicon for solar cell applications. The cost of producing silicon single crystals had to be reduced dramatically to make these devices competitive with other energy sources. Increased growth rates compared with conventional methods and reduction in machining costs and material losses were necessary. Development of production methods for the preparation of high quality single crystal silicon ribbon at very high growth velocities was therefore a highly desirable approach to minimize fabrication costs. As a result, existing methods such as the Stepanov, EFG, and Dendritic Web Processes were studied for this application, and
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H. Arend et al. (eds.), Crystal Growth in Science and Technology
