Pulling from the Melt

Purified polycrystalline CVD siUcon from this reaction is then melted and a single-crystal boule weighing as much or more than 50 kg, and having a diameter up to 20 cm, is pulled from the melt by C2ochralski growth (8). Metallurgical-grade siUcon is not sufficientiy pure for appHcations in electronics... 

The Czochralski Technique. Pulling from the melt is known as the Czochralski technique. Purified material is held just above the melting point in a cmcible, usually of Pt or Ir, most often powered by radio-frequency induction heating coupled into the wall of the crucible. The temperature is controlled by a thermocouple or a radiation pyrometer. A rotating seed crystal is touched to the melt surface and is slowly withdrawn as the molten material solidifies onto the seed. Temperature control is used to widen the crystal to the desired diameter. A typical rotation rate is 30 rpm and a typical withdrawal rate, 1—3 cm/h. Very large, eg, kilogram-sized crystals can be grown. 

T.4BLE 1. Materials Grown by Pulling from the Melt... 

Figure 2. Crystals of lithium niobate up to 10 cm in diameter grown by pulling from the melt. (Courtesy P. Bordui, Crystal Technology.)...

Hurle, D.T.J. Crystal Pulling from the Melt Springer-Verlag Berlin, 1993. 

The results for another copolymer series Is presented In a different way In Figure 2. The partial plots show melting points based on DTA determinations and the temperature at which fibers could be pulled from the melt. The horizontal scale Is the proportion of Y-component. In this series all of the polymers were prepared In a melt system by reaction of the diamines with a blsazomethlne. There was some variation In Inherent viscosity which appears not to have affected the regularity of the data. 

The single crystal grown onto a rotating seed is pulled from the melt in the Czochralski-Kryopoulos method, Fig. 3.30. The flux is formed by the... 

Crude glass rods were originally drawn directly from melts by simply dipping the end of a metal rod into the melt and pulling upward. These rods were of poor quality, with variable diameters and cross-sectional shapes. The rods were often reworked by hand to improve their quality and stretched to form the desired diameter. Tubing was formed by using a blowpipe and forcing a bubble to travel down the rod as it was pulled from the melt. 

Cubic BaTiOs can, however, be grown from a melt composition containing 35 mol% BaO and 65 mol% Ti02, which solidifies below 1460°C, the temperature below which the cubic form is stable. The melt is held just above its solidification temperature, a seed crystal is dipped into its surface, and the crystal is pulled from the melt at a rate of 0.5-1.0 mm/h. The seed crystal is rotated during growth... 

Producing Junction Transistors. Junction transistors can be produced during the original crystal growing process for the silicon (or germanium) crystal by adding known n-type and petype impurities to the molten semiconductor as the solid crystal is slowly pulled from the melt. 

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