One game that can be played is to use isotopically pure Si-28 in place of natural silicon. The thermal conductivity of Si-28 is 10% higher than natural Si at room temperature (but 8x higher at 26 K).
How difficult is the purification process? Is it as difficult as uranium hexafloride gas?
Yes, gas centrifuge appears to be a leading method.
'The purification starts with “simple” isotopic purification of silicon. The major breakthrough was converting this Si to silane (SiH4), which is then further refined to remove other impurities. The ultra-pure silane can then be fed into a standard epitaxy machine for deposition onto a 300-mm wafer.'
https://www.eejournal.com/article/silicon-purification-for-q...
Doesn’t silane like catching fire when it sees an oxygen molecule? The other day I heard about it being used as rocket fuel for lunar ISRU applications.
A rocket and a sandblaster at the same time.
This is no worse than before. All electronic grade silicon is already produced starting from silane or trichlorosilane, and both are about equally hazardous to handle. See this overview of producing purified silicon:
"Chemistry of the Main Group Elements - 7.10: Semiconductor Grade Silicon"
https://chem.libretexts.org/Bookshelves/Inorganic_Chemistry/...
How much does it costs to manufacture? Are there any other benefits from using isotopically pure Si-28? Are there any other isotopes used in common thermal conductive material that are more conductive?
The point of improving the thermal conductivity of silicon is that silicon is what chips are made of instead of, say, diamond.
Of course cost would have to be acceptable.
I was thinking more about isotopes of copper than carbon but I can't find data about thermal conductivity of isotopically enriched copper.
I don't think there would be much difference because much of the conductivity of copper is from the conduction electrons, not phonons. Isotopic purification increases thermal conductivity in silicon because it decreases phonon scattering.
Isotopically pure diamond, now there's something to look at.
https://en.wikipedia.org/wiki/Isotopically_pure_diamond
"The 12C isotopically pure, (or in practice 15-fold enrichment of isotopic number, 12 over 13 for carbon) diamond gives a 50% higher thermal conductivity than the already high value of 900-2000 W/(m·K) for a normal diamond, which contains the natural isotopic mixture of 98.9% 12C and 1.1% 13C. This is useful for heat sinks for the semiconductor industry."
I understand isotopically pure Si-28 may be preferred for quantum computing devices. The Si-28 has no spin or magnetic moment, reducing the rate of decoherence of certain implementations of qubits.
https://spectrum.ieee.org/silicon-quantum-computing-purified...