  Silicon-based quantum bits with electron spins in quantum dots or nuclear
spins on dopants are serious contenders in the race for quantum computation.
Added to process integration maturity, the lack of nuclear spins in the most
abundant $^{28}$silicon isotope host crystal for qubits is a major asset for
this silicon quantum technology. We have grown $^{28}$silicon epitaxial layers
(epilayers) with an isotopic purity greater than 99.992 % on 300mm natural
abundance silicon crystals. The quality of the mono-crystalline isotopically
purified epilayer conforms to the same drastic quality requirements as the
natural epilayers used in our pre-industrial CMOS facility. The isotopically
purified substrates are now ready for the fabrication of silicon qubits using a
state-of-the-art 300 mm Si CMOS-foundries equipment and processes
