The necessary process stages for producing FZ silicon involves initial preparation of the polysilicon ingot, followed by surface purification to ensure removal of dirt from transport and other contamination.
The polysilicon ingot is subsequently mounted in an FZ processing machine together with a seed crystal. The FZ processing machine is a closed chamber with mechanical movement of the polysilicon ingot and the seed crystal.
In the FZ process, polysilicon is melted through induction heating. Once the silicon has melted, a seed crystal is introduced into the smelter, and the crystal is grown by adjusting heat conditions.
The processing time for growing a crystal is 10–12 hours. The crystal, now a monocrystalline ingot, is cooled down, and samples for quality testing are taken.
An important element in the production of FZ silicon is controlling electrical conductivity of the monocrystals. Conductivity is controlled by adding phosphorus to the crystal, either directly in the FZ process during crystal growth, resulting in FZ-PFZ products, or through neutron irradiation of the crystal in a nuclear
reactor, which is more costly, but results in more precise doping. The latter products are the so-called FZ-NTD products.
Topsil invented the irradiation technique together with Risø National Laboratory in 1976 and the neutron irradiation is now performed by around ten external partners on the basis of long-term contracts. The development of new electrical FZ wafer properties and research into the development of new processes and products based on the FZ technology are essential for identifying future component needs. Topsil is conducting such research at Frederikssund, assisted by knowledge centres and universities all over the world.
