I'm hoping to modify a vacuum chamber so that it can be used for the deposition of silicon nitride using ammonia and nitrous oxide. However, I'm having trouble specifying an appropriate material for the CF flange gaskets. I'm pretty sure standard copper or silver-plated gaskets will break down. The deposition is done at temperatures of up to 450 Celsius, with the heater close to the gasket, so aluminum or polymer isn't an option. The only thing that looks promising is nickel or nickel-platted, but I haven't found anything consistent.
Does anyone have any experience with this or ideas on who might be suitable to ask?
EDIT (Sep 21): Thanks for the replies so far!
It's an existing PECVD system for a-Si:H (using silane gas and hydrogen) with a stainless steel chamber, so that's not going to change. The gaskets are currently copper, as that's appropriate for silane.
A large number of components are being changed over, as ammonia is so corrosive. It's just the gaskets on the CF flanges that I haven't been able to find a definitive solution for.
The problem you are trying to resolve remembers me my first paper (M. Bianchetti, G. Herrren, G.E. Lascalea and N.E. Walsöe de Reca. "Cointercalation in a ternary chalcogenide", Solid state ionics. Ed. Elsevier Science BV 50 (1992) 115. ISSN 0167-2738). The whole experiment was made in a sealed quartz cell and everything ran fine. Try quartz then, it possibly works... Greets. Gustavo.
What is the problem at all? Vacuum chamber with CF flanges supposedly run under low to medium vacuum(if UHV then even better), internal surface of gasket is in contact with corrosive atmosphere indeed, but actually sealing part is not(by design). Use standard copper gasket and inspect them after experiment. I bet you will not see corrosion within gasket-to-flange contact area. To be in safe side for 150% just change gasket after each run.
This might help:
https://www.munacosealing.com/upload/Thermiculite-Ammonia-Whitepaper-Low-Res.PDF
Thank you for your responses Nagesh Sharma, Gustavo E. Lascalea, Oleg A Nerushev, and Debarati Bhattacharya!
The chamber is relatively large and part of a cluster tool. There are 15 CF flanges ranging in size from 2.75" to 13.25", so doing routine swaps is not really an option. It will probably be a hundred depositions between openings for maintenance.
You're probably right in that I'm overthinking the need to replace the copper with something more stable, given it will be usually be operating under high vacuum.
That said, I did a more detailed check of the flange temperatures when the heater is at 540 ℃ and at a hydrogen gas pressure of 0.3 Torr. None of the flanges appear to reach above 100 ℃. The heater is much more thermally separated from the gaskets than I thought it would be. From consultation of some specs and colleagues/suppliers, aluminum gaskets should work for temperatures below 200 ℃. There's sufficient factor of safety (even given the limitations of my temperature measurement), so that's now my plan going forwards.
Thanks again for all your replies!
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