Czochralski Method and Crystal Growth Furnace

Czochralski method is abbreviated as CZ method. This method is mainly used to pull crystals from the solution. In the crystal growth furnace, molybdenum crucible is mainly used as a carrier. In 1964, this method was first applied to the growth of sapphire single crystals, successfully growing the sapphire crystals with higher quality.

The steps of Czochralski method are listed as below:

1.0 To heat the raw material to the melting point. Owing to difference in temperature, it forms the super-cooling. Therefore, the melt then begins to solidify on the surface of the seed crystal and grow the single crystals which own the same crystal structure with the seed crystal. Meanwhile, the seed crystal is pulled up at a slow speed, and the molten metal gradually solidifies on the solidification interface of the seed crystal, thereby forming an axisym metric single crystal ingot.

By controlling the speed of pulling, it grows the crystal neck, head, body and tail. 

2.0 When the crystal neck has been formed, the speed of pulling needs to slow down in order to make the diameter of crystal increase to the needed length. This step is the growth of crystal head. 

3.0 When the diameter of crystal increases to the needed length, the pulling speed should be uniform. The diameter of the crystal at this step is fixed. This is the part of crystal body.

4.0 After the growth of crystal body, the crystal ingot should be removed from the molten metal. At this time, the pulling speed begins to accelerate. The diameter of the ingot will decrease until the ingot turns into a point and is separated from the molten metal. This step is the growth of tail. The purpose is to prevent from generating the thermal stress during the quick separation between the ingot and the melt. The thermal stress which is generated during the separation will leads to the defects of the ingot, such as dislocation, slip line and so on.

It is convenient for us to observe the growth of crystal if we adopt CZ method. The crystal grows on the liquid surface without the influence of Mo crucible. In addition, this method can decrease of the stress of crystals and make people use the seed crystal orientation more conveniently. It helps grow crystals with higher quality at a faster rate.

• < Prev
• Next >