Wafer (electronics) - Formation

Formation

See also: Ingot

Wafers are formed of highly pure (99.9999999% purity), nearly defect-free single crystalline material. One process for forming crystalline wafers is known as Czochralski growth invented by the Polish chemist Jan Czochralski. In this process, a cylindrical ingot of high purity monocrystalline semiconductor, such as silicon or germanium, is formed by pulling a seed crystal from a 'melt'. Donor impurity atoms, such as boron or phosphorus in the case of silicon, can be added to the molten intrinsic material in precise amounts in order to dope the crystal, thus changing it into n-type or p-type extrinsic semiconductor.

The ingot is then sliced with a wafer saw (wire saw) and polished to form wafers. The size of wafers for photovoltaics is 100–200 mm square and the thickness is 200–300 μm. In the future, 160 μm will be the standard. Electronics use wafer sizes from 100–300 mm diameter. (The largest wafer made has a diameter of 450 mm but is not yet in production.)

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