The edge-defined film-fed growth of controlled shape crystals

The growth of shaped crystals is examined in the various meniscus-controlled growth processes such as Czochralski, floating zone, Stepanov, and edge-defined film-fed growth (EFG). The basic physical processes which shape the crystal are the same in these techniques; they involve the interaction of the three interfaces at the crystal–liquid–vapor junction. Specifically, for a crystal of constant dimensions, the angle ø between the meniscus and the growth axis must be ø_o (a constant; for silicon, ø_o 11°). The degree of crystal shape control and the range of cross-sectional shapes which can be grown in a stable manner by the different techniques are shown to depend on the details of the meniscus shape and of the heat flow in the systems. The use of a die shaper which constrains the meniscus distinguishes the EFG and Stepnov processes from the other methods. The use of a wetted die in EFG versus a non-wetted die in Stepnov growth is shown to have an additional effect on the ability to control the crystal shape and dimensions. The role of the die shaper is examined in detail from the points of view of die material selection (e.g., wettability and chemical compatibility) and die design. The advantages and disadvantages of using wetted and non-wetted dies in the shaping process are discussed from both the theoretical and practical points of view. Specific numerical examples in the paper deal with the growth of silicon ribbons.