Another reason crystalline silicon is so popular is because it can be "grown".
Silicon does not occur alone in nature, it is always found as part of a
compound. It would be very expensive to separate and purify all the silicon
needed for semiconductor fabrication, and even then, large single crystals
are needed. Once ultra pure polycrystalline silicon is obtained, a small
"seed" crystal is put on a metal rod and dipped into a melt. This method
is known as the Czochralski method and you can read more about it on pages
17 and 18. The end result is a large, cylindrically shaped crystal of silicon
about 200 mm in diameter and 1 to 2 meters in length. The silicon wafers
used in device processing are then made by cutting the crystal cylinder
into the wafers using a diamond-edged saw.
Fabrication