The most common technique for silicon crystal growth is the Czochralski 
Process. It involves bringing into contact a dislocation-free seed crystal and 
a melt. Single-crystal silicon is obtained by precise and strict control of the 
rotating rate and pulling rate of a rotational mechanism that suspends the seed 
crystal over the melt. Since silicon expands about 10% in volume after it 
solidified from its melt to its solid state, it cannot be grown in some kind 
of crucible. Even if the crucible can withstand the expansion, excess stresses 
exerted on the Silicon will cause undesirable dislocation effects on the crystal. 

The Czochralski Process as shown in Figure 1, is included in a cooled 
silica enclosure. The crucible is made of graphite or quartz. The silicon 
is kept in molten condition. As mentioned before, a seed crystal is suspended 
over the melt. Once it is inserted into the melt, the tip of the seed crystal 
will begin to melt. After it reaches a molten state, the rotational mechanism 
is slowly pulling away from the melt at a rate of about 10 um/sec. The 
resulting crystal is a single-crystal grew by the progressive freezing at the 
liquid-solid interface. It can measure up to 2 m in length with a diameter of 
12cm. 

Figure 1: Czochralski process

For growing doped crystal, impurities can be added to the melt. Some of the 
most common impurities are P, As, Sb, B, and Al. One problem encountered in 
growing doped crystal is the difference in impurity concentration of dopant 
in the solid and the liquid state. The ratio of impurity concentration in 
solid, Cs, to the concentration in liquid, Cl, is called the segregation 
coefficient. The pulling rate of the seed crystal is limited to the 
concentration gradient of the growing crystal. Care must be taken that the 
dopant concentration does not fluctuate too much along the direction of 
crystal growth. 

The presence of oxygen in silicon also poses another problem. The oxygen usually 
comes from the erosion of the quartz crucible. The concentration of oxygen found 
in silicon depends on the rotating rate. Fast rotations tend to produce higher 
concentration of oxygen atoms. Although fast growth rate (faster rotation of the 
seed crystal out of melt) helps dislocations propagate out of crystal, it also 
introduces large amount of unwanted oxygen atoms. Most of the oxygen ends up as 
SiO2. They tend to segregate along dislocations. Circuits built on that part of 
the crystal are therefore defective. Hence controlling the rotational rate and 
keeping oxygen concentration level low are crucial to crystal growth.