Float-zone silicon

In the vertical configuration molten silicon has sufficient surface tension to keep the charge from separating.

The major advantages is crucibleless growth that prevents contamination of the silicon from the vessel itself and therefore an inherently high-purity alternative to boule crystals grown by the Czochralski method.

Another light impurity, nitrogen (N2), helps to control microdefects and also brings about an improvement in the mechanical strength of the wafers, and is now being intentionally added during the growth stages.

The diameters of float-zone wafers are generally not greater than 200 mm due to the surface tension limitations during growth.

A polycrystalline rod of ultrapure electronic-grade silicon is passed through an RF heating coil, which creates a localized molten zone from which the crystal ingot grows.