Kayex Silicon Crystal Growing Process

Czochralski Crystal Growth Process

A semi-metal such as silicon is melted in a crucible with an appropriate amount of dopant, either donor or acceptor. The melting occurs and is maintained in a partial pressure atmosphere of inert gas, usually argon, at slightly above the melting point. The heat source is a graphite resistance heater that surrounds the crucible and is contained within an insulation layer inside of the furnace.

A seed crystal of the desired orientation is lowered into the liquid and the temperature is reduced slightly until the liquid begins to crystallize onto the seed. The seed crystal is then drawn up, slowly at first and then more quickly, until a long, thin crystal has formed on the end. This is known as the "neck".

Once the neck has been grown at a sufficient poll rate and diameter to assure that it is free of dislocations (imperfections of the crystal structure), the temperature is reduced further and the growth rate is reduced to allow the crystal to become larger in diameter. This is known as the "crown".

As the diameter of the crystal approaches the desired body diameter, the growth rate is again increased and temperature is adjusted to create a smooth rounded transition between the crown and body. This is known as the "shoulder".

The crystal diameter is controlled during body growth by varying the lift rate of the seed and the temperature of the melt. During this period the crucible is also raised at a rate required to maintain the position of the liquid surface in relation to the heated area of the chamber. The seed and crucible are rotated in opposite directions and at various rates to control the properties of the crystal. The growth rate is dependent on crystal type, diameter, hot zone configuration and various other factors. For silicon, typical body diameters now range from 100 to 300 mm and typical growth rates vary from 40 to 85 mm/hr.

After the melt has been depleted the crystal diameter is again reduced in a gradual cone shaped taper known as the "tail". The crystal diameter must be reduced to a very small point to reduce the thermal shock when the solid loses contact with the liquid.