That's not clear actually. It's been awhile since I watched the video on the ASML EUV system for etching wafers, but from my recollection, the UV light ablates away layers of wafers and so particles of silicon presumably contaminate the noble gas that's flowing over it. I don't think a closed loop is possible in the existing setups.
High thermal conductivity, inertness, and low absorption of the EUV wavelength used are the primary characteristics needed, and purity is needed to eliminate contamination of numerous ultrasensitive stages. AI summarized it as follows:
EUV tools require ultra‑high‑purity helium, typically grade 9N (99.9999999%) or better, with strict ppb‑level limits on: Nitrogen, Oxygen, Moisture, Hydrocarbons, Refractory compounds, Particulates.
How helium is used:
- Cooling the EUV plasma source
- Purging and protecting optics
- Maintaining inert, ultra‑clean environments
- Leak detection
