Melt Technique Czochralski

TABLE 29.4 Materials Grown by the Cz Technique (for Crystals 2cm in Diameter)  

Material rc) Crucible Atmosphere Pulling rate (mm/h) Rotation rate (rpm) 

To determine the factors that affect the growth rate of the crystal we need to consider the heat flow in the system. The heat input, gi , to the crystal across the crystal/melt interface is given by the sum of the heat associated with crystallization, l, and the heat flow from the melt, q.  

According to Eq. 29.6 the maximum growth rate possible occurs when dT/dx approaches 0 (if dT/dxi becomes negative the liquid would be supercooled and the interface would advance rapidly and dendritic growth would occur). The maximum growth rate, (dx/dt), is then given by 

FIGURE 29.5 Growth rings on crystal surface top section of Si crystal after removing seed. 

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The most common methods of growing crystals involve solidification from the melt (in the case of one-component systems) or crystallization from solution. Some of the methods for growing crystals from melt are described schematically in Fig. 3.6. In the Czochralski method, commonly known as the pulling technique, the material is melted by induction or resistance heating in a suitable nonreactive crucible. The melt temperature is adjusted to slightly above the melting point and a seed crystal is dipped into the melt. After thermal equilibration is attained, the seed is slowly lifted from the... 

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 A rotating seed crystal is touched to the melt surface and is slowly withdrawn as the molten material solidifies onto the seed.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. 

Overview of Unit Operations. To maximize the electron or hole (carrier) mobility and thus device speed, ICs are built in single-crystal substrates. Methods of bulk crystal growth are therefore needed. The most common of these methods are the Czochralski and float-zone techniques. The Czochralski technique is a crystal-pulling or melt-growth method, whereas the float-zone technique involves localized melting of a sintered bar of the material, followed by cooling and, thus, crystallization. 

For our investigations we use a single crystal of sbn doped with 0.66 mol% Cerium. It was grown by the Czochralski technique from the congruently melting composition by... 

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