The wafer is the substrate where the chips will be built on. Raw wafers are made of silicon, which comes from beach sand. They are created thru a method called Czochralski process, where a seed crystal (a piece of silicon crystal) is mounted on a rod and then dipped into molten silicon. The rod is pulled upwards and rotated at the same time, making a big cylindrical piece of silicon crystal, also known as ingot.
The ingot resulted from this process measures from three to six feet (one to two meters) long and can have up to 12 inches (300 mm) in diameter (this is where terms like 12-inch or 300-mm wafers come from). The ingot is then sliced into wafers. These wafers are polished and sent to the chip manufacturers. As mentioned, these raw (“virgin”) wafers are where the chips will be manufactured on.
click to enlarge Figure 1: The ingot is sliced to create raw wafers.
One common question is why wafers are rounded and not squared. The answer is simple. Since thru the Czochralski process the ingot is created by pulling and rotating the molten silicon, the natural shape for the silicon crystal resulted from this process is rounded, not squared.
