Semiconductor Electronics/Discrete Components Manufacture/Making Ingots
Silicon ingots are necessary for the manufacture of IC's. To make an ingot we need nearly 100% silicon which has impurities at a concentration of only few parts per million. To make the mono crystalline silicon ingot, mordern industry employs Czochralski process which is explained below.
Melting Pure Silicon
Nearly 100% pure silicon is taken in a quartz crucible that can handle very high temperatures. The entire operation is carried out in a very clean environment so that almost no contamination takes place. The silicon in the Quartz crucible is subjected heat or in other words heated high enough for the silicon to melt to form a molten mass.
After obtaining silicon melt, dopant's of pentavalent or trivalent atoms may be added to make the silicon N-type or P-type. Once impurities are added, its made sure the mix is homogeneous so that no error arises when the semiconductor is fabricated. The temperature of the molten mass is maintained at a constant preferable temperature so that crystallization can take place easily. A chuck is lowered into the molten mix, the chuck has a piece of mono-crystalline silicon at its grip.
The chuck is maneuvered so that the crystalline silicon touches the molten mix. The molten silicon then solidifies around the crystal making it larger and larger. The chuck is rotated so that the crystal maintains a cylindrical shape.
Controlled Crystal Growth
Slowly and steadily the chuck is rotated at a constant rate and lifted up so that the crystal grows at a steady rate. By this process we can get a mono-crystalline cylindrical silicon ingot thats perfect for making semiconductors.
The final crystal looks as shown above. A cone atop of a cylinder. This is the raw material used to make silicon wafers.