The BBC article is referring to high purity quartz, not silicon. It is used to make a quartz crucible - a large cup - of that high purity quartz. It’s essential that the crucible not contaminate the polysilicon.
(A note in passing: the semi industry doesn’t use hyperpure silicon. They use a lesser grade and add epitaxial layers.)
The crucible can stand the high temperature of molten silicon. The purified polycrystalline silicon is melted in the crucible. Then a single crystal ‘seed’ is dipped in the molten silicon and slowly withdrawn, while rotating. That’s how you make a high purity single crystal silicon ingot.
Before it’s zone refined, the poly is synthesized by reducing high purity silane gas (SiH4), which was in turn produced from quartz sand.
It would be interesting to know if the industry is still using natural quartz crucibles - the latest wafer size is now 450 mm - nearly 18 inches. Maybe someone else here can comment whether the traditional pulling process will be used at 450 mm.
